Class 11 Biology

Longitudinal Tracheal Trunk

Longitudinal Tracheal Trunk Definition: The three pairs of air-filled longitudinal tubes present on each side of the abdominal cavity of a cockroach are called longitudinal tracheal trunks.

Longitudinal Tracheal Trunk Number and types: Three pairs of large longitudinal tracheal trunks are present on each side of the body- one pair dorsal, one pair ventral, and one pair lateral in position.

Therefore, a total of six longitudinal tracheal trunks are present in the body of a cockroach.

Longitudinal Tracheal Trunk Position: The dorsal and ventral pairs of longitudinal tracheal trunks are found in the median region of the abdomen. The lateral pair is present along the lateral part of the abdomen.

Longitudinal Tracheal Trunk Structure: The paired tracheal trunks are interconnected by many transverse commissures or commissural tracheae or transverse tracheal connective (a commissure is a bundle of nerve fibers that cross the midline at the point of their entry or origin). Each longitudinal trunk is divided into many branches called tracheoles.

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Longitudinal Tracheal Trunk Function: The longitudinal tracheal trunk transports air (that has entered through the spiracles) throughout the body.

Tracheae Definition: The air-filled, elastic, closed, membranous network of branching tubules that opens through the spiracles to the atmosphere, is called tracheae.

Tracheae Number: From the mesothoracic spiracles, 6 tracheae originate. The rest of the spiracles lead to 3 tracheae at each end, leading to 6 tracheae per segment.

Tracheae Structure:

• The trachea are hollow tubes that are made up of epithelial tissue.
• These tracheae arise from the longitudinal tracheal trunk and their transverse connectives.
• They undergo repeated branching and form a diffused network of finer tracheae.
• A type of cell known as tracheal end cell is found at the terminal of each trachea.
• Several finer tubes arise from these cells. These are known as tracheoles.
• The cytoplasmic appendages remain suspended in the cell sap.
• Along the length of the trachea, some swollen regions known as air sacs can be seen.
• These air-sacs act as the reservoirs of air.
• Each tracheal tube is lined by a thin strip of cuticle that is arranged in a spiral form.
• This chitinous spiral layer of cuticle is called taenidia or intima. It prevents the collapse of the tracheal walls when empty.
• It also provides an elastic nature to the tracheal walls. Smaller tracheae lack taenidia.

Tracheae Function: The network of tracheae helps in the transport of gases to the different cells.

Tracheoles Definition: Tracheoles are finer branches of tracheae that transport air directly to the body cells.

Number, structure, position: Tracheoles are very large in number. They have very thin walls (diameter lp) and are devoid of taenidia. Their inner wall consists of the protein, trachein.

This thin wall enables the tracheoles to come in direct contact with the cells.

Tracheole Function: The opening of each tracheole within the tissues is immersed in the tissue fluid which supplies O₂ to the cells and removes CO2 from the cells.

Tracheolar fluid is present inside the tracheoles. The level of the tracheolar fluid varies with the metabolic activity of the insect. It is more when the insect is inactive (or at rest).

On the other hand, this fluid gets completely reabsorbed into the tissues, and the space gets filled with air when the insect is more active.

Mechanism of breathing: In cockroaches, the mechanism of breathing includes two phases— inspiration and expiration.

The spiracles mediate inspiration and expiration as they facilitate the exchange of gases. Tergo-sternal muscle is a muscle located between the abdominal tergum and sternum of a cockroach. Contraction and relaxation of this muscle induces breathing.

The steps of inspiration and expiration are as follows—

Inspiration:

• Intake of atmospheric air or more specifically O₂ into the tracheal system is called inspiration. It is a passive process (does not require expenditure of energy).
• The 1st and 3rd pairs of spiracles remain open all the time but, the remaining 8 pairs open only during inspiration.
• Relaxation of the tergo-sternal muscles expands the abdominal cavity. As a
  result, the pressure in the abdominal cavity decreases.
• This causes atmospheric air to enter through the spiracles. This air then passes through the trachea and finally reaches the tracheoles which contain tracheolar fluid.
• O2 diffuses into tissues through the tracheolar fluid and reaches the cells or tissues.

Expiration:

• The process of elimination of CO₂ produced during metabolism is known as expiration. Expiration is an active process (requires expenditure of energy).
• Contraction of the tergo-sternal muscles decreases the volume of the abdominal cavity. As a result, the pressure inside the cavity increases.
• This causes air from the tracheoles and tracheae to be released through six abdominal spiracles.
• Opening and closing of spiracles are influenced by CO₂ tension in hemolymph and O₂ tension in the tracheae.

Discontinuous gas exchange cycles

1. Cockroaches exhibit the phenomenon of discontinuous ventilation or discontinuous gas exchange cycles (DGC).
2. In this process, the exchange of gases is interrupted for certain periods during which spiracles remain closed.
3. This discontinuous gas exchange cycle has three phases—closed phase (spiracles close), flutter phase (spiracles open slightly but close rapidly), and open phase (spiracles open completely).
4. In cockroaches, most of the CO₂ is released through the cuticle by diffusion through the cuticle.
5. However, only a small amount of CO₂ is eliminated through the trachea and spiracles.

Control of breathing: Different factors controlling breathing mechanism in cockroaches are—

5 Role of the nervous system: Breathing in cockroaches is coordinated and regulated by nerve centers in the thoracic ganglia. The coordinating centers in the thoracic ganglia are stimulated by variations in O₂ and CO₂ content.

Role of metabolic rate: When the cockroach is active, i.e., metabolic rate is high, the osmotic pressure of tracheal fluid increases. Most of the fluid gets absorbed by the cells.

This results in a better supply of O₂ into tissues. However, when the cockroach is at rest or during low metabolic activity, the osmotic pressure of tracheal fluid reduces and the fluid fills up the terminal part of the tracheoles. A smaller amount of tissue fluid is absorbed by the cells.

This results in a slow rate of diffusion of O₂.

Thermal control: An increase in temperature increases the diameter of spiracles. This, in turn, allows more gaseous exchange.

A fall in the temperature of the brain to 8°C changes the breathing pattern of cockroaches from a continuous to a discontinuous type.

Chemical control: An increase in C07 concentration I increases the rate of breathing.

Nervous system Definition: The system of nerves and ganglia that coordinates and regulates various functions of the body in response to the environment, is called the nervous system.

 

The nervous system of cockroaches has three components namely, the central nervous system, the peripheral nervous system, and the autonomic nervous system.

Central nervous system: The part of the nervous system, mainly comprising the brain, that coordinates the functioning of the body is called the central nervous system.

The components of the central nervous system are the supra-oesophageal ganglion, sub-oesophageal ganglion, circum-oesophageai ganglion, and ventral nerve cord.

Supra-oesophageal ganglia: It is a bilobed structure that acts as the brain.

Position: It lies above the esophagus, almost in between the bases of the antennae, within the head.

Structure: Supra-oesophageal ganglia are formed by the fusion of three pairs of ganglia known as proto-, auto-, and tritocebrum. it is concerned mainly with sensory function.

Sub-oesophageal ganglia: It consists of a pair of ganglia that innervate the mouthparts.

Sub-oesophageal ganglia Position: It is located below the esophagus.

Sub-oesophageal ganglia Structure: It is formed by the fusion of the remaining three pairs of cephalic ganglia.

It is the main motor center, that is concerned with the motor functions. It innervates the muscles of mandibles, maxillae and labium and hypopharynx.

Nervous Tissue

Nervous Tissue Definition: The tissue, derived from the embryonic ectoderm, that is responsible for coordination of the physiological functions with the external as well as internal environment is known as nervous tissue.

Nervous Tissue Origin: Nervous Tissues Have Originated From Ectoderm.

Nervous Tissue Characteristics: Nerve cells or neurons are the structural and functional unit of the nervous system, They form nerves, that serve as the mode of
communication within the body.

These cells have three main properties that enable them to communicate with other cells of a nerve—

Excitability (irritability): Neurons exhibit the property of irritability. Neurons are excitable—i.e., they get excited and respond to environmental changes (stimuli).

Excitability Conductivity: Neurons respond to stimuli by producing electrical signals. These signals are conducted to other distant cells within the body by the nerves.

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Excitability Secretion: When the electrical signal reaches the end of a nerve fiber, the neuron secretes a chemical called neurotransmitter. This neurotransmitter crosses the gap between two neurons.

On reaching the next neuron, it stimulates it, thereby transmitting the impulse.

Excitability Functions

Excitability Coordination: It coordinates and controls various organs of the body.

Excitability Sensations: It perceives various sensations of the body like touch, pain, pressure, heat, cold, vision, hearing, smell, and taste.

Excitability Homeostasis: It maintains the body’s equilibrium with respect to the changes in the external environment.

Response to stimuli: It brings about an appropriate response to various stimuli.

Consciousness: It helps in carrying out conscious activities.

Components: Nervous tissue consists of nerve cells (neurons) and associated supporting cells (neuroglial cells)

A neuron or nerve cell

A neuron or nerve cell Definition: The structural and functional unit of nervous tissue, which transmits nerve impulses, throughout the body, is called a neuron.

Parts of a neuron: A typical neuron consists of two parts—cell body and cellular processes. These have been discussed under separate heads.

Cell body (neurocytoma or soma) Definition: The nucleated cell body of a neuron is known As Neurocyton or Soma.

Cell body (neurocytoma or soma) Structure

Shape and volume: The cell body of a neuron is polymorphic in shape, i.e., it may be star-shaped, pyramidal, oval, round, or flask-shaped.

Some cell bodies are so large that they can be seen through the naked eye. Very small cell bodies are also found in some neurons.

Covering: The outer covering of the cell body is called neurilemma.

Nucleus: Each cell has a single, large, and oval nucleus with a nucleolus.

Cytoplasm: Cytoplasm is granular in nature. It is also called neuroplasm.

Nissl’s granules: The neuroplasm contains numerous, minute basophilic granules called Nissl granules.

They are composed of rough endoplasmic reticulum along with ribosomes. Nissl granules act as the sites of protein synthesis.

On the basis of the structure and function of the neuron, the number of Nissl granules may vary. For example, more Nissl granules are present in motor neurons than in sensory neurons.

Neurofilament: Bundles of fine protein filaments, called the neurofilaments, form neurofibrils.

These are found scattered throughout the neuroplasm. They take part in the transmission of nerve impulses.

Centrosome: Earlier it was believed that neuron lacks centrosome. This was considered to be the reason why the neurons did not undergo cell division.

However, in recent years, centrosome has been observed in a neuron under an electron microscope.

However, the process of cell division is still absent. Hence, it is considered that the centrosome of neurons may be inactive in nature.

Other organelles: In addition, the neuroplasm contains mitochondria, Golgi bodies, and ribosomes.

Liposuction: It is a brown pigment present in the cytoplasm. It contains lipid residues formed result of lysosomal digestion.

Its abnormal accumulation induces degenerative disorders (disorders in which the structure as well as the functions of the tissues degrade).

Functions

Receives impulse: The cell body of a neuron remains associated with other neurons through its short branching processes (dendrites). These dendrites help to receive impulses from the neighboring neurons.

Secretion: Secretes various structural and functional proteins.

Processes of the neuron Definition: The fiber-like protoplasmic elongations arising from the cyton are known as processes of the neuron.

Processes of the neuron include the axon and the dendron. These have been discussed under separate heads.

Axon: A single, long (generally unbranched) cytoplasmic process arising from the cyton is known as an axon.

Structure

Shape and origin: It is a long, thin appendage with a uniform diameter throughout its length. Axon arises from a conical elevation, called axon hillock, on the cell body.

Axoplasm: The cytoplasm within the axon is known as axoplasm. It is comprised of neurofibrils, mitochondria, and smooth endoplasmic reticulum. But Nissl’s granules are absent.

Covering: The cell membrane of the axon is called axolemma. The axon may be surrounded by another covering over the axolemma, called the myelin sheath.

The outermost thin neurilemma consists of tubular cells, called Schwann cells, that are arranged along the length of the axon.

Each of these cells is wrapped around the axon so that it is covered by a number of concentric layers of Schwann cell plasma membrane.

These membranes fuse to produce the myelin sheath, which is composed of a shining, fatty substance called myelin. The outermost layer of the Schwann cell plasma membrane is called the neurilemma.

Nodes of Ranvier: The myelin sheath is not continuous along the entire length of the axon.

It is interrupted at regular intervals to form certain gaps known as the Nodes of Ranvier.

They are points of branching of the axon. They also contain channels that transport ions, required during the conduction of nerve impulses.

Collateral branches: Generally, the axon lacks branches. However, sometimes the axon may show branching. These branches are called collateral branches.

End brush: Axon ends in numerous fine branches known as axon terminals. These axon terminals form a tuft-like structure called end brush.

Synaptic knob: Each axon terminal swells up into a knob-like structure known as synaptic knob. It contains abundant mitochondria and secretory vesicles, called the synaptic vesicles.

Functions: Axons conduct nerve impulses from the cell body to the next neuron. Hence, it is efferent in nature.

Dendron: The shorter branching processes of the i-cell body of a neuron are called dendrons.

Structure: It is of shorter length than the axon. The diameter of the dendron is not uniform throughout its length. The outer covering of a dendron is 4 neurilemma.

• The thin terminal branches of dendrons are known as dendrites.
• The cytoplasm of dendron ( contains Nissl granules, neurofibrils, and mitochondria.

Functions: Dendrons receive stimulations and conduct them towards the cyton. Hence, they are afferent in nature.

Classification of neuron

On the basis of processes arising from the cell body: According to the number of processes arising from the cell body, neurons may be classified into—

Apolar neuron: The neuron without any processes arising from its cell body is known as apolar neuron. Such neurons are found in the CNS of the vertebrates.

Unipolar neuron: A neuron with only one process arising from the cell body is known as a unipolar neuron. Such neurons are found in the early stages of embryonic development.

Bipolar neuron: The neuron with two processes (one axon and one dendron) arising from the cell body is known as bipolar neuron.

Such neurons are found in the rod and cone cells of the retina and in the olfactory epithelium.

Multipolar neuron: A neuron with more than two processes arising from the cell body is known as a multipolar neuron.

One of these processes acts as an axon and the rest as dendrons. Such neurons are found in the central nervous system and in the ganglia of the autonomic nervous system.

Pseudounipolar neuron: The neuron with a single process formed by the union of the dendron and axon known as a pseudounipolar neuron.

It soon bifurcates and separates into dendrons and axons after emerging from the cell body.

Such neurons are found in the dorsal root ganglia of the spinal nerve in adult vertebrates.

On the basis of structure: According to structure, neurons are classified into two types.

Medullated or myelinated neurons: Medullated neurons are the neurons in which the axon is surrounded by an inner thick medullary sheath or myelin sheath and an outer thin neurilemma or neurolemma.

Medullated or myelinated neurons are found in the white matter of the central nervous system (CNS) and in the peripheral nervous system.

Non-medullated or non-my/inated neuron: Non-medullated neurons are the neurons in which the axon lacks myelin sheath i.e., it is covered only by neurilemma. These neurons also lack the Node of Ranvier.

Non-medullated or non-myelinated neurons are found in the grey matter of the central nervous system (CNS) and in the autonomic nervous system.

On the basis of function: According to the function, neurons are of three types—sensory, motor, and relay neurons.

Sensory or afferent neurons: They transmit impulses from sense organs that receive the stimuli to the central nervous system.

Motor or efferent neurons: They transmit electrical signals from the central nervous system to the effector organs in the body.

Relay neurons: They are found within the central nervous system between the sensory and the motor neurons. These neurons transmit the electrical impulses from sensory to motor neurons. They are also called adjuster neurons interneurons or connector neurons.

Neuroglial cells Definition: The specialized, non-neural, accessory cells of the nervous system that provide support to the nerve cells are known as neuroglial cells.

These are essential for the function and survival of nerve cells.

Neuroglial cells Position: These cells are found both in the central nervous system and peripheral nervous system.

Neuroglial cells Types: The different types of neuroglial cells are as follows—

Oligodendrocytes: These are myelin-secreting cells of the CNS. Their main function is to provide support and insulation to the axons within the CNS

Astroglia or Astrocytes: They are star-shaped cells having several processes extending from their cell body into the surrounding network of nerve fibers.

They provide physical support as well as essential nutrients to nerve cells of the brain and spinal cord.

They help in the transport of ions, taking place between the nerve cell and the extracellular fluid. They also help to form the blood-brain barrier (thin, semipermeable membrane that separates the blood from the cerebrospinal fluid in the brain).

Astrocytes differ from oligodendrocytes in having thicker and more number of processes.

Microglia or microglial cells: These cells are small cells that are similar to macrophages (large scavenger cells) present within the immune system, with respect to functions. They are the phagocytes of the central nervous system.

Ependymal cells or ependymocytes: These cells are found in the central nervous system.

They form an extremely thin epithelial-like lining in the ventricles of the brain and central canal of the spinal cord.

This lining is called ependyma. The apical surface is covered by cilia, which keep the cerebrospinal fluid in circulation. They also form cerebrospinal fluid (CSF).

Satellite glial cells and Schwann cells

Besides the above-mentioned cells, there are certain other accessory cells, that help the nerve cells in different ways. They are called satellite glial cells and Schwann cells.

1. Satellite glial cells: They surround cell bodies of neurons in ganglia (ganglion cells). They provide electrical insulation and nutrients to neurons.
2. Schwann cells: They are responsible for the myelination of axons in the peripheral nervous system.

Synapse Structure: Synapse is the junction between the dendrites of one neuron and the axon of another neuron.

Parts: The terminal swollen part of the axon called the synaptic knob, is covered by a membrane called the presynaptic membrane.

The membrane of the dendrite of the other neuron is called the postsynaptic membrane.

The minute space between the presynaptic and postsynaptic membrane is called the synaptic cleft.

Functions of neuroglia: Various functions of neuroglia are—

1. They (oligodendrocytes) synthesize myelin sheaths.
2. They (ependymal cells) coordinate the flow of CSF.
3. They (microglia) have phagocytic properties.
4. They (astrocytes) form the blood-brain barrier.
5. They (astrocytes) maintain an appropriate balance of Ca2+ and K+ ions needed for synaptic transmission.

Nerve or Nerve trunk

A nerve is formed of several bundles of nerve fibers. Such bundles are called the fasciculi. Each nerve fiber in a bundle is covered by a thin sheath of connective tissue, called the endoneurium.

Each fasciculus is enclosed by another sheath of white fibrous tissue, called the perineurium.

All the fasciculi are surrounded by a thick coat of white fibrous tissue, called the epineurium.

Muscular Tissue

Muscular tissue Definition: The tissue, derived from embryonic mesoderm, and involved in movement and locomotion by virtue of its property of contraction and relaxation is known as muscular tissue.

Muscular tissue Position: Some muscular tissues or muscles are associated with bones and so known as skeletal muscles, Some are associated with visceral organs and are called smooth muscles. Some muscles are associated with the heart, hence known as cardiac muscles.

Muscular tissue Origin: Muscular tissues have originated from mesoderm.

Muscular tissue Components: Muscular tissue is made up of muscle cells or fibers. The main components of the cell include 70% water, 20% proteins like actin, myosin, tropomyosin A, tropomyosin B, myogen, myoalbumin, myoglobulin, etc. 10% glycogen, 0.2% lipids like phospholipid and cholesterol, 1.5% inorganic salts like potassium phosphate, salts of calcium, sodium, magnesium, etc.

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Muscular tissue Structure

Muscular tissue Shape: Muscule Tissue Is Made of Bundles Of Narrow, Elongated Contractile Muscle Cell, called my myocytes. Due to their elongated nature, they are also known as muscle fibers.

Muscular tissue Arrangement: They are contractile in nature. The contractile unit is made up of proteins such as mainly myosin, actin, troponin, tropomyosin, etc. The muscle fibers are arranged like a mesh.

Muscular tissue Matrix: Intercellular matrix is absent but muscle fibers are surrounded by connective tissue.

Muscular tissue Covering: Myofibril or muscle fiber is covered with a plasma membrane known as sarcolemma. They also have mitochondria, known as sarcosomes, and endoplasmic reticulum, known as sarcoplasmic reticulum.

Muscular tissue Innervation: Sensory nerves are present in muscles.

Muscular tissue Circulation of blood: Blood vessels are present in the muscular tissue. So, blood circulation takes place within muscle fibers.

Some Special Contractile Cells

Besides muscle cells, some other cells also have the capacity to contract and expand. Some of these cells are described below.

Muscular tissue Myoepithelial cells: The contractile cells which originate from the ectoderm are called myoepithelial cells. Their contraction is slow and involuntary. They are found in the sweat glands, mammary glands, lacrimal glands, and salivary glands.

Muscular tissue Pericytes: These are contractile cells that wrap around the endothelial cells of capillaries and venules throughout the body. They are also known as mural cells.

Myofibroblasts: The contractile cells that contain actin and myosin are called myofibroblasts. They help in wound repair.

Myofibroblasts Functions

Coordination of organs: Muscles (especially involuntary muscles) control coordination between various organs, movement and locomotion, body posture, speech, facial expression, etc.

Coordination of visceral organs: Involuntary muscles present within the visceral organs, help in the movement of the organs.

Some examples of these movements are—the contraction of the muscles of the GL tract during peristalsis, uterine wall contraction during childbirth, urinary bladder contraction during micturition, contraction, and relaxation of the walls of the blood vessels for regulating blood pressure, etc.

Circulation of blood: The circulation of blood throughout the body as well as the beating of the heart, both are coordinated by the contraction and relaxation of cardiac muscle.

Response to stimuli: The contraction of muscles helps us to respond to external stimuli.

Coordination of respiration: Respiration is regulated by the contraction and relaxation of respiratory muscles (skeletal muscles). It is also regulated by the smooth muscles lining the trachea and airways of the lungs.

Generation of heat: The movement of muscles during vigorous physical activities such as exercise etc., helps to generate heat in the body.

Types: There are several types of muscular tissue or muscles based on position, structure, mode of action, etc.

On the basis of structure, location, and function, the types of muscles are—striated or skeletal or voluntary muscles, non-striated or smooth visceral or involuntary muscles, and cardiac muscles. The structure and function of each of these muscular tissues are described below

Skeletal Muscle

Skeletal Muscle Definition: The muscles with alternate light and dark bands, which remain associated with the skeleton and can contract on will, are called striated skeletal or voluntary muscles.

Skeletal Muscle Position: These muscles remain attached to the bones or the skeleton and are controlled by the somatic nerve.

Characteristic features: Skeletal muscle is called striated because of its appearance.

It contains alternate light and dark bands, that are visible through a phase contrast microscope.

Components:

1. The skeletal muscles (e.g. biceps, triceps) are spindle-shaped, i.e., swollen in the middle region and tapering at the ends.
2. The muscles are attached to the bones by means of a hard, collagenous connective tissue, called tendon. One end of the tendon is bound to the perichondrium of bone and the other end is bound to the sarcolemma of the muscle fiber.
3. Each muscle fiber is enclosed by a connective tissue membrane, known as an endomysium.
4. A bundle of muscle fibers is known as a fasciculus (pi. fasciculi). This is enclosed by another connective tissue layer called the perimysium.
5. Bundles of fasciculi are surrounded by another connective tissue layer called the epimysium.
6. The main structural component of striated muscles or skeletal muscles is muscle cells or muscle fiber.
7. The structural features of muscle fibre as seen under an electron microscope are described below.

Shape: Each muscle cell is elongated, cylindrical, unbranched fiber, with blunt ends. Each muscle fiber has a diameter of 10-100 pm and is 1-40 mm long.

Sarcolemma: The muscle fiber is enclosed within a thin transparent membrane called sarcolemma. This membrane is semi-permeable in nature.

Sarcoplasm: The cytoplasm of muscle cells is known as sarcoplasm. The striated muscle fiber is multi-nucleated. During the formation of striated muscle fiber, its nucleus divides a number of times by mitosis.

This division is not followed by the division of cytoplasm. Due to this reason, muscle fibers are multi-nucleated.

Organelles: It contains sarcoplasmic reticulum (ER), sarcosomes (mitochondria), glycogen, and lipid droplets.

The most important organelle among them is

A-band sarcoplasmic reticulum. The terminal end of the sarcoplasmic reticulum is swollen and is called terminal cisternae. This part stores a huge amount of calcium ions.

These Ca2+ ions are used for muscle contraction.

T-tubule: The sarcolemma of muscle fibers invaginates and extends towards the cytoplasm, at some points.

These extended tube-like structures are called T-tubules or transverse tubules. Each T-tubule remains associated with two terminal cisternae of the sarcoplasmic reticulum.

This structure formed by the T-tubule and the two associated terminal cisternae is called a triad.

Myofibril: The sarcoplasm of skeletal muscle fiber consists of numerous longitudinal bundles of protein fibrils.

These fibrils are called myofibrils. Using an electron microscope, it can be seen that the myofibrils are made up of two types of thin, thread-like contractile protein filaments called myofilaments. The two myofilaments are thicker myosin filaments (100A in diameter) and thinner actin filaments (50A in diameter).

Each myofibril contains approximately 1500 myosin and 3000 actin filaments.

The actin filament comprises actin, tropomyosin, and troponin proteins while the myosin filament is made up of myosin protein.

Alternate light and dark bands, called striations, appear throughout a myofibril. The structural details of these striations are as follows-

A Band And I Band: The Light Bands Of Myofilaments Which Are Composed Of Strands Of Only Actin known as l-bands or isotropic bands.

These bands are called ‘isotropic’ as they have the same refractive index in all planes.

The dark bands of myofilaments contain strands of myosin protein along with a few strands of actin protein scattered within. These are known as the A-bands or anisotropic bands.

These bands are called ‘anisotropic1 as they refract light differently in different planes.

Z-line or Z-disc: The thick line present at the center of the l-band is called the Z-line or Krause’s membrane. It is also known as Dobie’s line.

[The letter Z in ‘Z-line’ has been derived from the German word ‘Zwischenschiebe’ which means, Zwischen = between and Scheibe = disc.]

Sarcomere: The segment of the myofibril between two adjacent Z lines is known as sarcomere.

1. It is the contractile unit of the myofibril and hence, that of the muscle.
2. The ends of actin strands in adjacent sarcomeres are connected by the Z-line.
3. Sarcomere = Half of l-band + One complete A-band + Another half of the next l-band

H-zone: Along the midline of each A-band is a lighter zone. This is known as the H-zone or Hensen’s zone.

M-line: A thick line is present vertically in the middle of the H-zone. This is known as the M-line.

[The letter ‘M’ in the M-line has been taken from the German word ‘Mittlescheibe’ which means ‘central disc’]

Function: The movement of the skeleton is under the conscious control of the body, hence controlled by striated muscles.

These include movement of limbs, fingers, toes, neck, etc. Changes during facial expressions Example ability to smile or to frown, are also controlled by voluntary muscles.

Smooth Muscle Definition: The muscles that are non-striated, involuntary in nature, and found in the visceral organs are known as visceral muscles or non-striated or involuntary muscles.

Smooth Muscle Position: These muscles are found in the wall of the alimentary canal, urinary tract, blood vessels, uterus, fallopian tube, the dermis of the skin, iris, and ciliary bodies of the eyes.

Characteristic features:

1. These muscles do not have any cross-striation and so these are known as smooth muscles.
2. Due to their presence in the visceral organs, these are also known as visceral muscles.
3. These muscles are controlled by the autonomic nervous system and hence, are involuntary in nature.
4. The cells are capable of mitosis.
5. These muscles can remain contracted for a long time. These muscles never get fatigued.

Components

Muscle fibers: Each muscle fiber is spindle-shaped. These are generally unbranched but, in some fibers, terminal branches can be seen.

Length and diameter: The average length of a muscle fiber is 20 pm with a maximum width of about 6 pm.

Outer covering: The outer covering of muscle fiber is called sarcolemma. It is indistinct in nature.

Cavioli and sarcoplasmic reticulum: Certain structures formed by sarcolemma within the smooth muscle cells are called cavioli. The inner portion of the ravioli contains the sarcoplasmic reticulum.

Nucleus: Cells are uni-nucleated with a centrally placed oval or elongated nucleus.

Mitochondria: Cells contain fewer mitochondria.

Golgi bodies: Cells contain smaller Golgi bodies.

Contractile protein: The sarcoplasm contains numerous fine contractile myofibrils. Unlike skeletal muscles, the myofibrils are not arranged in a distinct pattern in a smooth muscle cell.

The myofilaments, actin, and myosin, present within the myofibrils, are irregularly arranged.

They are not organized to form sarcomeres (structures formed by two adjacent l-bands with an A-band between), hence striations are not formed

Cellular connections: Adjacent smooth muscle cells are separated by a basal lamina.

However, this basal lamina is not continuous. It is absent in the regions where adjacent muscle cells are connected.

These regions that appear like band-shaped tight junctions are called fascia occludes or nexus.

Cellular connections Types

Single-unit smooth muscle: The muscles formed by the muscle fibers that contract together at the same time are called single-unit smooth muscles.

In such cases, the muscle cells are connected by tight junctions and hence, these muscles form a covering.

These tight junctions are known as cytoplasmic bridges. Due to this property of forming tight junctions, single-unit smooth muscle bundles form a syncytium.

This structure contracts in a coordinated manner, leading to muscle contraction.

Examples are the muscles of the uterus, gastrointestinal tract, and urinary bladder.

Multi-unit smooth muscle: The muscles formed by the muscle fibers that contract separately, each as a single unit are called multi-unit smooth muscles.

Examples are the muscles of walls of blood vessels, ciliary bodies, iris, esophagus, dermis, hair root, etc.

Cellular connections Functions

Peristalsis: The action of smooth muscles helps food to be carried along the gastrointestinal tract.

Regulation of opening and closing of orifice: Smooth muscle forms the structures called sphincters, which are present at the beginning of the orifices.

The sphincters control the opening and closing of a number of orifices in the body. This in turn regulates several physiological processes like the movement of food from the stomach into the intestine or evacuation of the urinary bladder and rectum.

Controlling vasodilation: Vasodilation is controlled by the contraction of smooth muscles, thereby regulating blood pressure.

Contraction of the urinary bladder and uterus: Contraction of the urinary bladder during micturition and forceful contraction of the uterus during childbirth occurs with the help of smooth muscles.

Other functions: The smooth muscles of the stomach also help in the churning of food.

Cardiac Muscle Definition: The striated involuntary muscle present in the myocardium (wall) of the heart is known as cardiac muscle.

Cellular connections Position: These muscles are found in the wall of the heart.

Characteristic features:

1. Cardiac muscles are associated with the heart.
2. They are capable of involuntary and rhythmic movements.
3. Cross striations are observed, hence they are a type of striated muscles.

Components Muscle fibers: Cardiac muscle fibers are striated, and branched. The cells that form the cardiac muscle are called cardiomyocytes or myocardiocytes. They have a single, large, oval, central nucleus.

Sarcolemma: The outer covering of cardiac muscle (sarcolemma) is indistinct.

Syncytium: Cardiomyocytes are connected with one another forming a syncytium.

Intercalated disc: Sarcolemma of the cardiac muscle fiber is thickened at intervals to form plate or disc-like structures called intercalated discs.

They separate the cardiac muscle cells from one another. At each intercalated disc, the cell membranes of two adjacent cells fuse with one another, forming permeable communicating junctions (gap junctions). These junctions help in the transmission of nerve impulses.

Other types of cell junctions formed through intercalated discs include fascia adherens (binding site for actin, connect sarcomeres) and desmosomes (binding site for intermediate filaments, join the cells).

Sarcoplasm: Sarcoplasm is granular in nature. It has several mitochondria, scattered throughout. A small Golgi body, with few lipid droplets and sarcoplasmic reticulum (endoplasmic reticulum), are also present.

Myofilament: Numerous distinct myofibrils with alternate dark and light cross bands, forming prominent sarcomeres, are found within the sarcoplasm.

As stated earlier, myofibrils are made up of myofilaments, that are composed of actin and myosin protein strands. They are present as bundles.

T-tubules: Sarcolemma penetrates inside muscle fibers at specific regions. These structures formed by the sarcolemma are called transverse tubules or T-tubules. Together these tubules are known as T-system.

This network stores calcium ions, required for muscle contraction.

Functions: Pumping of blood through the heart takes place by alternate contraction and relaxation of cardiac muscles.

Besides the above-mentioned types, there are several types of muscular tissue, such as—

Types of muscles on the basis of function and pigments: Details regarding the classification (Locomotion and movement).

Types of muscles based on the nature of their activity: Muscles are classified on the basis of the nature of their activity into two groups.

White muscle or fast muscle: The skeletal or voluntary muscles which appear pale due to less blood vessels and the absence of myoglobin are called white muscles.

Such muscles show prominent striations. They react fast to impulses but cannot hold the contraction for a long time. Example muscles of the lip, tongue, etc.

Red muscle or stow muscle: Skeletal muscles that appear red due to more blood vessels and myoglobin are called red muscles.

Such muscles show fewer striations. They react slowly to impulses but can hold the contraction for a long time. Example muscles controlling body posture.

Few Concepts About Muscular Tissue

Refractory period: The brief period during which the muscle cannot get excited to a second stimulus after receiving the first stimulation is called the refractory period.

Heart muscles have a long refractory period. Hence, they do not fatigue easily.

Tetanus: In terms of physiology, if a series of I stimuli from the external environment are applied successively during a single contraction, then they fuse together leading to sustained contraction.

This phenomenon is called tetanus, Summation: A weak stimulation may fail to produce a contraction in the muscles.

But when this weak stimulation is applied repeatedly, it may produce considerable contraction in the muscles. This phenomenon is called summation.

Rigor mortis: The rigidity of muscles after death is called rigor mortis.

Glandular Epithelial Tissue Function

Synthesis and secretion: The glands, formed by these glandular cells, synthesize and secrete mucus, hormones, enzymes, etc.

Storage: Some chemical substances are stored in these glandular cells, such as—protein in the stomach, lipids in the adrenal and sebaceous glands, and sugar and protein in the salivary gland.

Excretion: When present in sweat glands and sebaceous glands, glandular epithelium helps to excrete sweat and sebum, respectively.

Classification of glands: On the basis of the number of cells present in the epithelium, glands are divided into two types—

1. Unicellular glands and
2. Multicellular glands.

Unicellular gland: Unicellular gland may be defined as an isolated single secretory cell that itself functions as a gland.

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Unicellular gland Position: It is found in the mucous membrane of the stomach, intestine, rectum, and trachea.

Structure They are elongated and flask-shaped. The cell consists of a nucleus, surrounded by cytoplasm containing numerous Golgi bodies.

The apical part of the cell contains granules which contain the glycoprotein mucin. The distal part of the cell becomes swollen and bursts. This causes secretion of mucin.

Unicellular gland Functions: Some of them (goblet cells) secrete mucus which forms a protective layer on the intestinal mucous membrane,

• They neutralize acids and alkalis, thereby maintaining pH balance.
• They provide protection by engulfing bacteria and foreign particles that enter the trachea or alimentary canal.
• They lubricate the alimentary canal and trachea.

Example: Goblet cells, calciform cells.

Multicellular gland: Multicellular glands may be defined as glands comprising aggregates of secretory cells.

On the basis of types of secretion, there are three types of multicellular glands—

Endocrine glands are ductless glands. They pour their secretions (hormones) directly into the blood. Example pituitary, thyroid or adrenal glands etc.

Exocrine glands, these glands are provided with ducts. They pour their secretions (enzymes) through ducts into the target organs. Example salivary, gastric-OPlntestjnal glands,

Mixed glands, glands comprise both endocrine and exocrine parts. Example pancreas— whose exocrine secretory part is called ‘acinus’ and endocrine secretory part is made up of cells called ‘islets of Langerhans’.

On the basis of the mode of secretion, glands are of three types. They are—

Holocrine gland: Secretion is discharged along with the entire cytoplasm of the cell. This leads to the disintegration of the cell. Example sebaceous gland.

Apocrine gland: The apical surface of the secretory cell is discharged along with the accumulated secretions. Examples mammary glands, and apocrine sweat glands.

Merocrine gland: The secretion is released to the external environment through the cell membrane slowly by diffusion. The whole cell remains intact. Examples salivary gland, and pancreatic gland.

Types of multicellular glands on the basis of the nature of ducts

Simple gland: Simple glands are multicellular glands with unbranched ducts. These are two Simple tubular glands, which are unbranched, tube-like simple glands. Example intestinal gland, sweat gland,

Simple saccular or alveolar glands, which are unbranched, sac-like simple glands. Example mucous glands in frog’s skin. It is absent in mammals.

Compound gland: Compound glands are multicellular glands with branched ducts. These are of two types—

Compound tubular gland, the distal end of these glands is branched and tube-like. Example Brunner’s gland of duodenum.

Compound saccular or racemose gland, a distal end of these glands is branched and sac-like.

Examples exocrine pancreas, salivary gland, and sebaceous gland.

Tubulo-saccular/alveolar gland, distal ends of these glands comprise both tubule and sac-like structures. Examples are parts of the salivary gland, mammary gland, and glands of respiratory passage.

Functions of glands

Hormone secretion: The endocrine glands are involved in the secretion of hormones. For example, thyroxine is secreted from the thyroid gland, insulin is secreted from the endocrine part of the pancreas, etc.

Enzyme secretion: The exocrine glands secrete various enzymes. For example, ptyalin is secreted from the salivary gland, pepsin from the gastric gland, etc.

Compound or stratified epithelial tissue

Functions of glands

Hormone secretion: The endocrine glands are involved in the secretion of hormones. For example, thyroxine is secreted from the thyroid gland, insulin is secreted from the endocrine part of the pancreas, etc.

Enzyme secretion: The exocrine glands secrete various enzymes. For example, ptyalin is secreted from the salivary gland, pepsin from the gastric gland, etc. Compound orstratified epithelial tissue.

Transitional epithelial tissue Definition: The epithelial tissue that has multiple (3-4) layers of cells and shows properties of both simple and compound epithelium, is called transitional epithelial tissue.

Transitional epithelial tissue Position: It is found in the renal pelvis, broader parts of the ureter, upper part of the urinary bladder, urethra, and urinary duct.

Transitional epithelial tissue Structure:

1. The cells of the superficial layer are large, flat, irregular-shaped (generally quadrilateral), and may be binucleate.
2. The next layer contains pyriform cells (flame-shaped cells). One end of these cells is round and the other end is narrow.
3. Cells in the third layer are polyhedral. These cells are located in between the narrow ends of pyriform cells.
4. The cells of the basal (bottom) layer are round or cuboidal in shape. © The nuclei are oval or spherical in shape and the cytoplasm is granular.
5. This epithelium forms walls of the organs that undergo continuous expansion and contraction.

Transitional epithelial tissue Function:

• It prevents the reabsorption of ions during excretion.
• It regulates the distension of organs like the urinary bladder.

Stratified squamous epithelial tissue

Stratified squamous epithelial tissue Definition: Epithelial tissue in which the uppermost layer has squamous cells, that may or may not be keratinized, is called stratified squamous epithelial tissue.

Stratified squamous epithelial tissue Position: It is located in the epidermis of the skin, oral cavity, pharynx, esophagus, vag*na, cervix, cornea, etc.

Stratified squamous epithelial tissue Types: It is of two types—stratified keratinized squamous epithelium and non-keratinized stratified squamous epithelium. These are discussed under separate heads.

Stratified keratinized squamous epithelial tissue Definition: The epithelial tissue, consisting of multiple cellular layers, whose uppermost cellular layer contains keratin, is called stratified keratinized squamous epithelial tissue.

Stratified squamous epithelial tissue Position: It is found in the epidermis of the skin (nails, horns, the enamel of teeth, etc).

Stratified squamous epithelial tissue Structure:

• Cells of the superficial layer are dead. However, these cells store keratin and are thus cornified.
• Hence, this layer is called stratum corneum (Latin term, meaning ‘horny layer’).
• Cells of the middle layer are polygonal and squamous in nature.
• The lower layer has columnar cells which are attached to the basement membrane.
• The cells of the superficial layer are constantly sloughed off and replaced by new cells from the inner layers.

Function: Its major role is to protect the underlying soft tissues against mechanical injury and friction. It is water-resistant and hence, prevents water loss from the body.

Non-keratinized stratified squamous epithelial tissue Definition: The epithelial tissue, consisting of multiple cellular layers, in which the uppermost layer does not contain keratin is called non-keratinized stratified squamous epithelial tissue.

Non-keratinized stratified squamous epithelial tissue Position: It is found in the lining of oral and nasal cavities, urethra, cervix, cornea, vag*na, anal canal, etc.

Non-keratinized stratified squamous epithelial tissue Structure:

• This tissue has multiple layers of cells. These cells lack keratin.
• The outer layer consists of living cells and the middle layer contains polyhedral cells.
• Cells attached to the basement membrane are columnar.

Non-keratinized stratified squamous epithelial tissue Function: Its major role is to protect the underlying soft tissues against mechanical injury and friction. It is water-resistant and hence, prevents water loss from the body.

Prickle cell: The cells at the basal surface of stratified keratinized squamous epithelial tissue are connected with each other by intercellular fibers and protoplasmic appendages.

These fibers and appendages are called prickles and the associated cells are called prickle cells due to their thorny appearance. These cells can withstand pressure.

Stratified Cubodial Epithelial Tissue

Stratified Cubodial Epithelial Tissue Definition: The epithelial tissue, consisting of multiple cellular layers, in which the uppermost layer does not contain keratin is called non-keratinised stratified squamous epithelial tissue.

Stratified Cubodial Epithelial Tissue Position: It is found in the larger duct of sweat glands, salivary glands, female urethra, and pancreas.

Structure:

The tissue is usually multi-layered.

Cuboidal cells are present in the uppermost layer and polyhedral cells are found in the middle layer.

Function: It provides strength to the walls of the lumen and also helps in the secretion of sweat, saliva, etc.

Stratified Columnar Epithelial Tissue Definition: The epithelial tissue, made up of multiple layers of cells, whose uppermost cellular layer has columnar cells is called stratified columnar epithelial tissue.

Stratified Columnar Epithelial Tissue Position: It is found in the pharynx, epiglottis, a mucous layer of the anus, and urethra.

Stratified Columnar Epithelial Tissue Structure:

The uppermost layer has columnar cells with an oval nucleus.

The lowermost layer has cuboidal cells.

Function: Its main function is to give protection to the underlying organ.

Endothelium

The squamous epithelial tissue present in the inner wall of blood vessels and lymphatic vessels is called endothelium.

Endocardium: The squamous epithelial tissue present in the inner wall of the heart is called the endocardium.

Endocardium Functions

• Protection: It protects internal organs from mechanical injury and infection.
• Diffusion: It helps in the diffusion of gases and nutrients, for example, lung alveoli and capillary endothelium.
• Filtration: It helps in ultrafiltration in the Bowman’s capsule of nephron, epithelium, and endothelium.

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Cuboidal Epithelial Tissue

Cuboidal Epithelial Tissue Definition: The epithelial tissue that consists of cube-shaped cells that rest on the basement membrane is called cuboidal epithelial tissue.

Cuboidal Epithelial Tissue Position: It is found in the thyroid gland, salivary gland, bronchioles in the lungs, proximal and distal convoluted tubules of the nephron, covering of the ovary (germinal epithelium), etc.

Cuboidal Epithelial Tissue Structure:

1. Cells of this tissue are cuboidal in shape and similar in size i.e., they have almost equal length, breadth, and height.
2. The nucleus is spherical and centrally located.
3. The cytoplasm is granular.
4. The free surfaces of the cells are sometimes lined by microvilli.
5. Such a surface containing microvilli is called a brush border.

Cuboidal Epithelial Tissue Function

Protection: It protects the organs to which it is associated.

Secretion: It secretes various secretory products when present in secretory glands such as the thyroid, pancreas, mucous gland, salivary gland, and sweat gland.

Reabsorption: Under special conditions (within convoluted tubules in nephrons), cuboidal epithelium reabsorbs molecules and ions from the urine. Thus, this tissue takes part in urine formation.

Cuboidal epithelial tissue Function Types: Different types of cuboidal epithelium, their definition, positions, and functions are given in the following table

Columnar epithelial tissue

Columnar epithelial tissue Definition: The epithelial tissue in which cells are column-shaped (i.e., height is more than their breadth), is called columnar epithelial tissue.

Columnar epithelial tissue Position: It is found in the lining of the digestive tract, gall bladder, bile duct, ducts of gastric gland, intestinal gland, sweat, and sebaceous gland, and pancreatic lobules.

Columnar epithelial tissue Structure: Cells of this tissue are tall and elongated.

The nucleus is oval-shaped and is situated near the base of the cell, in case the cell is secretory in nature. Otherwise, the nucleus lies at the center of the cell.

A brush border is seen in the free surface of the epithelium lining the inner cavity of convoluted tubules of the small intestine.

Columnar epithelial tissue Functions

Absorption: It helps in the absorption of digested food into blood by the intestinal epithelium.

Secretion: Columnar epithelium of the gastric and intestinal glands transform into pitcher-shaped cells, known as goblet cells. They secrete mucus.

Protection: The mucus, secreted by the goblet cells, protects the lining of the stomach from the effect of the HCI acid secreted in it. In this way, they protect the organs to which the epithelium is associated.

Types: Types of columnar epithelium, their definition, position, and functions are given in the table below.

Ciliated epithelial tissue Definition: The epithelial tissue that is made up of generally columnar, sometimes cuboidal cells, with fine JiaÿBce processes or cilia on the free surface is known as ciliated epithelial tissue.

Position: It is found in the fallopian tube, most of the uterus, the efferent tubule of testes, the lining of the ventricles of the brain, and the central canal of the spinal cord.

Structure:

1. Cells of this tissue are either columnar or cuboidal.
2. The free surface of the cells has 20-30 cilia.
3. The root of the cilia has a row of particles or corpuscles at its base, called basal granules. These are considered to be the residue of centriole.
4. Thread-like structures extend inward, from each basal granule, into the protoplasm of the cell.

Types of cilia on the free surface of epithelial tissue

Kinocilia: These are motile in nature. These cilia originate from basal granules of the cytoplasm. These are present on the inner walls of the trachea.

Stereocilia: These are non-motile in nature. These cilia are formed by the foldings of the plasma membrane. These are seen in epididymis and vas deferens.

Types of cilia on the free surface of epithelial tissue Function

Protection: Wave-like unidirectional movement of cilia of the columnar epithelial cells helps to sweep out mucus and dust particles in organs such as the trachea, nasal passages, etc.

Transport of ovum: The fallopian tube, helps in the transport of the ovum towards the uterus.

Transport of cerebrospinal fluid (CSF): It helps in the circulation of CSF into cerebrospinal cavities of the central nervous system.

Glandular epithelial tissue Definition: The epithelial tissue that is made up of cells specialized mainly in secretory functions is known as glandular epithelial tissue.

The secretory organs formed by the glandular epithelia are called glands. The secreted substances can be enzymes, hormones, or chemicals. The secretions are transported to their target organs or cells either by duct (in case of enzymes, chemicals, etc.) or without duct (in case of hormones).

Position: It is found in mammary glands, sweat glands, sebaceous glands, salivary glands, part of Intestinal glands, and thyroid gland.

Glandular epithelial tissue Structure:

1. Cells of this tissue are generally cuboidal, columnar, or polygonal in shape.
2. The cells are usually arranged in one layer but in the salivary gland, a second layer may be found.
3. Sometimes, the secretory cells may be present as bundles. These cells are specialized for the synthesis and secretion of enzymes, hormones, or certain chemicals required by the body.
4. The cytoplasm is granular in nature. It contains membrane-bound secretory vesicles.
5. Each cell bears a large nucleus.

Epithelial Tissue

Types of tissues: The bodies of all vertebrates and most of the invertebrates are made of a variety of tissues.

However, all the tissues may be grouped into four main types. These are epithelial tissue, connective tissue, muscular tissue, and nervous tissue.

Epithelial Tissue Location: Epithelial tissue is present mainly in two regions—the external covering of the body (skin) and the walls (both inner and outer) of all internal organs.

Epithelial Tissue Components: Epithelial cells are compactly arranged with minimum intercellular spaces.

The tissue is made up of three major components. They are—the non-cellular basement membrane, epithelial cells, and intercellular cementing material. This cementing material is a mucoprotein complex containing hyaluronic acid and calcium salt.

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Epithelial Tissue Structure: An epithelium consists of one or more layers of cells. The outer layer of cells, when present in the skin, is exposed to the external environment outside the body.

But, this layer is also present on the outer surface of internal organs. Here, it is exposed to a lumen or cavity within the body. The deep inner layer of cells is bound by a basement membrane.

Basement membrane: Basement membrane is not actually a membrane. Rather, it is an extracellular matrix present between the epithelial tissue and the loose connective tissue below it.

It is composed of a network of collagenous fibers which are formed from secretions of the underlying cells of the connective tissue. It consists of two layers—the outer thin basal lamina and the inner thick, fibrous, reticular lamina (also known as lamina reticularis).

The basal lamina is further made up of two layers—lamina lucida and lamina densa. The lamina lucida is closer to the epitheium while the lamina densa is closer to the connective tissue.

The lamina reticularis is attached to the basal lamina with collagen fibrils. This layer is also attached together by microfibrils made of fibrillin protein.

Functions of the basement membrane of epithelium

1. Anchorage: It binds the epithelium to the loose connective tissue underneath and holds the layers -c6
2. Growth: Controls the growth and differentiation of cells within the epithelial tissue.
3. Exchange of molecules: Acts as a filter during an exchange of large molecules between epithelium and the underlying connective tissue.
4. Signaling: Helps in cell-to-cell signaling.

Lamina propria: It is a layer of loose vascular connective tissue, present at the base of the basement membrane. It provides mechanical support to the epithelium.

It also contains several blood vessels and nerves. These blood vessels and nerves provide nutrition and innervation to the epithelium.

Papilla: The hair-like appendages that lie at the junction of epithelium and the underlying connective; tissue are called papillae (sing, papilla). They hold the epithelium in position.

Surface layers of cells: The epithelial cells have three surfaces. These are as follows—

Basal surface: It is the lower surface of the cells, adjacent to the basement membrane.

Apical surface: It is the upper surface of the cells, that remains free. It increases the surface area for absorption.

This property is achieved by modification of the surface into structures like microvilli, stereocilia, etc.

Lateral surfaces: These are surfaces of the cells, on both sides, facing adjacent epithelial cells.

Intercellular junctions: These are specialized regions between the plasma membrane of adjacent cells. These are also known as cell junctions. They provide mechanical support and help in cell-to-cell communication.

However, sometimes they may act as impermeable barriers, preventing the transport of certain molecules between the cells.

Intercellular junctions are of the following types—

Tight junctions: These are specialized regions between adjacent epithelial cells where the cell membranes are fused together by means of sealing strands.

They bind the epithelial cells together and check the passage of molecules and ions between them.

Gap junctions: These are specialized junctions directly connecting the cytoplasm of cells. They allow the passage of ions and small molecules from one cell to the adjacent one.

Adherens junctions: Junctions present in heart muscles and skin epithelium. They join the actin filaments present in the muscles to form a continuous belt.

Desmosomes: Intercellular junctions of epithelia and cardiac muscle. They are of two types—Belt and Spot desmosomes. The belt desmosomes are belt-like and the spot desmosomes are spot-like or circular in appearance.

Cilia and Flagella: These are microtubular structures that arise from the plasma membrane of the epithelial cells. Cilia are found in animal cells whereas flagella are primarily found in prokaryotes and unicellular eukaryotes.

They help in locomotion as well as to propel away harmful, unwanted particles.

Cilia and Flagella Functions: The functions of epithelial tissue are as follows—

Cilia and Flagella Protection: Epithelial tissue forms the skin of animals. It also forms the wall of internal organs, thus protecting them from injuries.

Terrestrial vertebrates have keratin in their skin cells. This makes them resistant to water loss from their skin. Ciliated epithelium, lining the respiratory tract, sweeps away impurities with the help of cilia.

Cilia and Flagella Absorption: The gut is lined with epithelial tissue that absorbs nutrients from food. The lungs are also lined with epithelial tissue which helps them to absorb oxygen.

Cilia and Flagella Secretion: Glandular epithelium forms the exocrine and endocrine glands. Endocrine glands secrete hormones into the circulation. Exocrine glands secrete mucus, saliva, wax, milk, etc., through ducts.

Contractile property: Myoepithelium is the contractile epithelium, present in sweat glands, mammary glands etc. It helps in the flow of secreted fluids from the glands.

Reproduction: Gametes (such as sperm and ova) are produced from the germinal epithelium lining the testis and ovary.

Sensation: It is perceived with the help of sensory epithelium present in the skin, taste buds in the tongue, nasal epithelium, etc.

Excretion: Ultrafiltration by Bowman’s capsule and tubular reabsorption during urine formation is carried out by renal epithelium in the kidney.

Transport: The beating of cilia in ciliated epithelium present in food pipe, respiratory tract, reproductive tract, etc., helps to transport food, mucus, gametes, etc.

Respiration: The epithelium of alveoli in the lungs helps in gaseous exchange.

Classification: Based on the shape of the cells that lie above the basement membrane and on the number of layers of cells, the different types of epithelial tissues are shown in the given flowchart.

Simple epithelial tissue Definition: The epithelium that is made up of a single layer of cells, is called simple epithelial tissue or epithelium.

Based on the structure of the cells, the simple epithelium is classified as—squamous epithelium, cuboidal epithelium, columnar epithelium, ciliated epithelium, and glandular epithelium.

Squamous Epithelial Tissue Definition: The epithelial tissue that consists of a single layer of large, flattened, polygonal cells is called squamous epithelial tissue.

Squamous Epithelial Tissue Position: It is found in the alveoli of lungs, endothelium of capillaries, Bowman’s capsule and Henle’s loop of the nephron, pericardium and the inner lining of the heart, and the peritoneal lining of the coelom.

Squamous Epithelial Tissue Structure:

1. Cells of this tissue are flat, polygonal in shape with irregular margins. Their shapes resemble the scales of fish. It is also known as pavement epithelium as it forms a pavement-like structure.
2. Cells are compactly arranged without any intercellular spaces.
3. The nuclei are oval or disc-shaped and centrally located.
4. Cytoplasm may be clear or granular.

Aestivation

Aestivation Definition: The pattern of arrangement of calyx, corolla or perianth in a flower bud is known as aestivation.

Aestivation Types:

Different types of aestivation are as follows—

Open: The margins of the sepals or petals do not touch or overlap each other. example Magnolia champaca, Allaria sp., etc.

Valvate: The margins of sepals or petals just touch side by side closely, without overlapping each other. example, calyx of Hibiscus rosa-sinensis, both calyx and corolla of Mimosa pudica and Acacia nilotica, etc.

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Twisted or contorted: One margin of each sepal or petal overlaps the margin of the neighboring sepal or petal. example corolla of Hibiscus rosa-sinensis, Nerium odoratum, etc.

Imbricate: One member of the whorl remains completely outside without any overlapping both the edges of another member remain overlapped by the neighboring members and the rest are arranged in a twisted manner. example corolla of Solanum torvum, Nicotiana tabacum, Clerodendrum viscosum, etc.

Quincuncial: Two members of the whorl remain completely external and two remain completely internal. The rest are present in a twisted manner. example petals of Lantana camara, sepals of Holarrhena antidysenterica, etc.

Vexillary: Out of five members the posterior single petal is the largest and outermost (vexillum), which overlaps the two lateral petals (wings). The two wings partially overlap the two smallest and innermost, partially fused petals (keel). example corolla of Pisum sativum, Clitoria ternatea, Crotolaria sp., etc.

Variations Infloral Members

The floral parts, i.e., calyx, corolla, androecium, and gynoecium, show different variations in their shapes, position, arrangement, and association with other floral parts. These variations or forms of different floral members are described below.

Variation in calyx

Different types of sepals are discussed below.

Based on the color of the calyx: According to the color of sepals, calyx are of two types. The green-coloured calyx is known as sepaloid. example, Cocos nucifera. Sometimes the calyx becomes colored like the petals and is known as a petaloid or tepal. example Mussaenda sp.

Based on whether sepals are united or not: According to the union of sepals, calyx are of two types.

Polysepalous: In this type, the sepals remain free and separate. example Brassica nigra.

Gamosepalous: In this type, the sepals remain partially or completely united. example Datura metel, Hibiscus rosa-sinensis.

Based on the duration of attachment of calyx to the flower: According to the duration of attachment of calyx to the flowers, calyx are of two types.

Caducous or fagacious: It sheds off just before the complete blooming of the flower. example Papaver somniferum.

Deciduous: It remains attached to the flower until fertilization. It sheds off with corolla. example Brassica nigra.

Persistent: It remains attached till fruit maturation and never sheds off. It is of two types—

Marcescent: This type of persistent sepals cease further growth after fertilization, get shrunk, and become wrinkled. example Solarium melongena.

Accrescent: This type of persistent sepals continues to grow along the growth of the fruit. example Cocos nucifera, and Dillenia indica.

Based on the structure of calyx: The structure of calyx varies with species. Types of calyx based on their structures have been mentioned.

Variation In Corolla

On the basis of different characters corolla can be of various types. Sometimes the petals can be green in color, known as sepaloid or sepaline. example Annona squamosa, Pergularia daemia, etc.

Based on whether petals are united or not: According to the union of petals, corolla are of two types—

Polypetalous: The petals remain free. example Brassica nigra.

Gamopetalous or sympetalous: The petals are completely or partially united. example Datura metel, Catharanthus roseus, etc.

Appendages of Corolla

Sometimes various types of appendages may develop on the corolla.

These are as follows—

1. Saccate or gibbous: This is a sac-like or pouch-like structure formed by the dilation of the lower region of the corolla tube on one side. example Antirrhinum majus (snapdragon), Calceolaria mexicana.
2. Corona: These are hair-like or scaly outgrowths of various kinds that develop from the inner wall of the corolla tube. example Passiflora suberosa, Nerium indicum, Scoparia dulcis, etc.
3. Spurred or calcarate: These are tubular structures formed by the elongation of a single petal or petals of the corolla tube. example Delphinum majus and Aquilegia sp.

Based on the structure of corolla:

According to the structure, corollas are of the following types—

Polypetalous and regular type:

This type of Corolla is divided into three types—

1. Cruciform: In this type, four clawed free petals are arranged in the form of a cross. example Brassica nigra (mustard) and Raphanus sativa (radish), etc.
2. Caryophyllaceous: In this type, five petals have claws, arranged at right angles to their limbs. example Dianthus chinensis and Saponaria vaccaria, etc.
3. Rosaceous: In this type, five or more almost sessile petals are widely spread outside. example Rosa lucida (wild rose), and Camellia sinensis (tea).

Polypetalous and irregular type: Out of five irregular free petals, the posterior, odd petal is the largest and outermost. This is known as vexillum or standard. The vexillum overlaps two lateral petals, known as wings or alae.

The wings partially overlap the two smallest and innermost petals known as keel or carina. These two interior petals remain more or less united. It is also known as a papilionaceous type of corolla. Examples are Pisum sativum (pea), Sesbania grandriflora, Clitoria ternatea, etc.

Gamopetalous and irregular type:

This type of Corolla is of three types—

1. Ligulate: Five petals unite to form a flat tongue-shaped upper part of the corolla gradually forms the short tubular lower part. example, Ray florets of Helianthus annuus (sunflower).
2. Bilabiate or two-lipped: The upper part of the corolla tube is divided into two lip-like structures to form a wide open mouth above the throat. example Ocimum sanctum, Anisomeles indica, Leucas linifolia.
3. Personate or masked: The flower contains, a bilabiate corolla limb, but here the mouth is closed by a projection (palate) of the lower lip. example Antirrhinum majus (snapdragon), Lindenbergia indica, etc.

Gamopetafous and regular type:

This type of corolla is divided into the following types—

1. Tubular: Here, the petals unite to form a cylindrical corolla tube. example Disc florets of Helianthus annuus (sunflower).
2. Campanulate or bell-shaped: The petals unite to form a bell-shaped structure. example Cucurbita maxima (pumpkin), Thevetia peruviana (yellow oleander), Physalis peruviana, etc.
3. Rotate or wheel-shaped: The short corolla tube spreads its flat limbs at right angles to the tube axis example Scoparia dulcis, Solanum melongena (brinjal), Calotropis procera, etc.
4. Hypocrateriform or salver-shaped: The long and narrow corolla tube spreads its limbs at right angles to the tube axis. The limbs arrange themselves in a wheel-like structure. example. Ixora coccinea, Ipomoea quammoclit,etc.
5. Infundibuliform or funnel-shaped: The lower tubular corolla gradually widens at the top like a funnel. example, Ipomoea pulchella (morning glory), and Datura sp. (thorn apple).
6. Urceolate or urn-shaped: The corolla tube becomes inflated in the middle and comparatively narrower at both ends. example Rhododendron sp., Bryophyllum calycinum.

Variation in androecium

On the basis of the number, location, structure, etc. of stamen, androecium is of different types.

Based on the number of other lobes:

Based on the number of enter lobes, androecia are of the following types—

Monothecous: Anthers have a single lobe. Example Brassica nigra.

Dithecous: Anthers have two lobes. Example Hibiscus rosa-sinensis.

The number of stamens varies from one to many. On the basis of the number of stamens,

The flowers are grouped as—

1. Monandrous: This type of flower contains single or solitary stamen. Example Curcuma longa (turmeric).
2. Diandrous: This type of flower contains two stamens. Example Adhatoda vasica (vasaka).
3. Triandrous: This type of flower contains three stamens. Example Triticum aestivum (wheat).
4. Tetrandrous: This type of flower contains four stamens. Example Ocimum sanctum (tulsi).
5. Pentandrous: This type of flower contains five stamens. Example Solanum nigrum.
6. Hexandrous: This type of flower contains six stamens. Example Oryza sativa.
7. Polyandrous: This type of flower contains numerous stamens. Example Rosa centifolia.

Based on the insertion of stamens:

Based on the insertion of stamens, androecia are of the following types—

Isostemonous: In this type, one whorl of stamens is arranged alternately with the sepals i.e., antisepalous (Example Pisum sativum) or petals i.e., antipetalous (Example Primrose)

Diplostemonous: In this type, the stamens are arranged in two whorls and the number of stamens is double the number of petals. Usually, the inner whorl remains opposite to the petals. Example Cassia’s fistula.

Obdiplostemonous: In this type, the stamens are arranged in two whorls such that the members of the outer whorl are opposite to petals and those in the inner whorl are opposite to sepals. Example Geranium sp.

Polystemonous: In this type, stamens are arranged in more than two whorls. Example Delphinium sp.

Alternipetalous: In this type, the stamens remain opposite to the perianth. Example Diosporous embryopteris.

Based on the length of the stamen:

Based on the length of stamens, androecia are of the following types—

Didynamous: There is a solitary whorl of four stamens, among which two stamens are longer than the other two. Example Leonurus sibiricus.

Tetradynamous: Six stamens are arranged in two whorls. In the outer whorl, two stamens are there which are shorter than the four stamens of the inner whorl. For example, Brassica nigra.

Heterodynamous: In this type, stamens of different lengths occur in one whorl. Example Cassia Tora.

Based on the attachment of anther with the filament:

According to the attachment of anther with filament, stamens are of the following types—

Adnate: The filament remains attached throughout the length of the anther. Example Magnolia sp.

Basifixed or innate: The apex of the filament remains firmly attached to the base of the anther. Example Brassica sp.

Dorsifixed: The tip of the filament remains firmly attached to the dorsal side of the anther. Examples are Sesbania sp., Passiflora sp.

Versatile: The tip of the filament remains attached at a point near the middle of the connective and thus the anthers can move freely. Example Triticum aestivum.

Based on the shape of the anther: Different types of anthers, based on their shapes are given below.

Based on the dehiscence of anthers: The pollen grains inside the mature anther develop and exert some pressure on the outer wall. The anther wall bursts open due to the pressure and the pollen grains are set free in the air.

The dehiscence pattern of anthers can be of the following types—

Longitudinal: The anther lobes burst longitudinally. This occurs along the line of suture from base to apex. Example Datura sp.

Transverse: The anther splits up transversely along the suture. Example Hibiscus rosa-sinensis.

Apical or porous: The pollen grains are discharged through the apical pores of the anther. Example Solarium tuberosum.

Valvular: The walls of the anther open up like valves to discharge the pollens. Examples are Berberis vulgaris, Cinnamomum zeylanicum, etc.

Based on the union of stamens: The stamens may be fused with each other or with the gynoecium or perianth.

The union of stamens found in different flowers is of the following types—

Cohesion of stamen: Stamens may remain fused with each other or with filament or another. This is known as the cohesion of stamen.

This can be of the following types—

1. Adelphous: In this type, the stamens are united by the fusion of their filaments.

The adelphous condition may further be divided into the following types—

1. Monadelphous: In this type, filaments of all the stamens are fused to form a single tubular structure. Example Hibiscus rosa-sinensis.
2. Diadelphous: In this type, the stamens are fused at their filaments and form two bundles. Example Pisum sativum.
3. Polyadelphous: In this type, the stamens are fused by their filaments and form more than two groups. Example Bombax ceiba.

2. Syngenesious: In this type, all the anthers remain fused but the filaments are free. Example Helianthus annuus (sunflower).

3. Synandrous: In this type, the anthers and filaments are fused throughout their length to form a compact structure. Example Cucurbita maxima (pumpkin).

Adhesion of stamens: When the stamens are attached with other floral whorls or perianth, then the condition is known as adhesion of stamen.

it is classified into the following types—

1. Epipetalous stamen: The stamens remain attached to the petals by their filaments. Example Solanum nigram.
2. Epiphyllous stamen: The stamens are attached to the perianth by their filaments. Example Polyanthes tuberosa (tuberose).
3. Gynandrous stamen: The stamens remain attached to the gynoecium, either throughout their length or only by their anthers. Example Calotropis sp.
4. Episepalous stamen: The stamens remain attached to the calyx. Example Quinsqualis sp.

Variation in Gynoecium

Based on the number and position of the thalamus, the gynoecium is of various types.

Based on the number of carpels in the gynoecium:

According number of carpels, gynoecium are of the following types—

Simple or monocarpellary gynoecium: The gynoecium is composed of solitary carpel. Example Pisum sativum.

Bicarpellary: The gynoecium is composed of two carpels. Example Justicia sp.

Tricarpellary: The gynoecium is composed of three carpels. Example Allium cepa.

Tetracarpellary: The gynoecium is composed of four carpels. Example Datura metel.

Pentacarpeliary: The gynoecium is composed of five carpels. Example Melia sp.

Compound or polycarpellary: The gynoecium is composed of more than five carpels. Example Papaver sp. It is of the following two types, on the basis of their union—

Apocarpous: In this type, the carpels remain completely free from one another to form multiple ovaries. Example Michelia Champaca.

Syncarpous: In this type, the carpels are fused with each other to form a single ovary. Example Mangifera indica.

Based on the number of locules in the ovary: According to the number of locules or chambers in the ovary,

Gynoecium can be of the following types—

Based on the position of the ovary on the thalamus: The position of the ovary on the thalamus varies in plants.

Superior: In this type, the ovary is situated on the top of the thalamus and the other floral whorls reside just below the ovary. The flowers which bear this type of ovary are known as hypogynous flowers. Example Hibiscus rosa-sinensis.

Inferior: In this type, the ovary resides at a level that is lower than the other floral whorls on the thalamus. The thalamus becomes cup-shaped due to fusion with the ovary wall. The flowers which bear this type of ovary are known as epigynous flowers. Example Cucurbita maxima.

Semi-inferior: In the type, the ovary is situated in such a position, which is intermediate to that of the superior and inferior types. the flowers that bear this type of ovary are known as perigynous flowers example pisum sotivum.

Phyllotaxy

The leaves remain arranged on the stem in such a manner that they can get the maximum amount of sunlight for their physiological functions.

Phyllotaxy Definition: The arrangement of leaves on stems or branches in a definite manner is known as phyllotaxy.

Phyllotaxy Types:

Phyllotaxy is mainly of three types—

1. Alternate or acrylic or spiral,
2. Opposite and
3. Whorled. The last two types are known as cyclic type.

Alternate or acyclic or spiral: In this type, one leaf develops from each node and remains spirally arranged around the stem. Examples are china rose, and mango. Here, phyllotaxy is determined by passing an imaginary line through the bases of the leaves.

Read and Learn More: WBCHSE Notes for Class 11 Biology

This shows a spiral path is known as a genetic spiral. if this spiral path is placed on a flat surface then it is known as a flat spiral. The distance between the bases of two consecutive leaves is known as divergence.

The angle subtended at the center of the shoot by two consecutive leaves is known as angular divergence. The imaginary vertical line that connects the leaves vertically is known as orthostichies.

On the basis of the number of orthostichies or the number of rows in which the leaves are arranged,

Alternate phyllotaxy is divided into the following types—

1. Distichous or 2-ranked phyllotaxy: Leaves are arranged in two rows, i.e., two orthostichies can be drawn. example, sugarcane, maize
2. Tristichous or 3-ranked phyllotaxy: Leaves are arranged in three rows, i.e., three orthostichies can be drawn. exampleCyperus sp., orange.
3. Pentastichous or 5-ranked phyllotaxy: Leaves are arranged in five rows, i.e., five orthostichies can be drawn. example Hibiscus rosa-sinensis.
4. Octastichous or 8-ranked phyllotaxy: Leaves are arranged in eight rows, i.e., eight orthostichies can be drawn. example papaya.

Opposite: In this type, two leaves develop from each i node opposite to each other.

It may be of two types— Opposite decussate and opposite superposed.

1. Opposite decussate: In this type, consecutive pairs of opposite leaves are arranged at a right angle to each other. example Ocimum sanctum, Calotropis procera, etc.
2. Opposite superposed: In this type, successive pairs of opposite leaves are arranged in one plane. example Quisqualis sp., Hiptage madablota, etc.

Whorled or verticillate phyllotaxy: In this type, more than two leaves develop from each node forming a whorl. example, Alstonia scholars, etc.

Modifications Of Leaves

Other than photosynthesis and transpiration leaves perform other functions. For that purpose, they modify themselves through different adaptations.

Different types of modifications are discussed below—

Leaf tendrils: In weak plants, the lamina becomes modified either partially or wholly into a coiled thread-like structure called a tendril. This tendril helps the plant to climb up support.

These can be of the following types—

Whole leaf tendril: In this type, the entire leaf gets modified into a tendril. example Lathyrus aphasia.

Leaflet tendril: In this type, the terminal leaflets are modified into tendrils. example Pisum sativum.

Petiolar tendril: In this type, the petiole is modified into tendrils. example Clematis gouriana.

Leaf apex tendril: In this type, the leaf apex is modified into a tendril. example Gloriosa Superba.

Stipular tendril: In this type, the stipules are modified into tendrils. example Smilax macrophylla.

Leaf spines: The leaf may be completely or partially modified into a spine. This protects the plants from predators and reduces the rate of transpiration in plants.

These are of the following types-

1. The apex of the lamina can be modified into spine as found in Phoenix sylvestris.
2. The margin of the lamina can be modified into the spine as found in Argemone mexicana.
3. The apex and margin of lamina both can be modified into spines as found in Aloe perfoliata.
4. Leaves can be modified into spines. But the leaves that emerge from axillary buds remain normal, as found in Berberis vulgaris.

Fleshy or succulent leaves: In some plants, the leaves become fleshy due to the storage of water, mucilage, and food. This is mostly found in xerophytes and halophytes. example Bryophyllum sp., Basella rubra, etc.

Leaf or leaflet hooks: In some plants, three-terminal leaflets of a compound leaf get modified into sharp, curved, and anchored on the support for climbing example biononia angiocath.

Root-like structure: In some aquatic plants, the submerged leaves are modified into narrow root-like structures. These adventitious roots absorb water and help to float the plant on water. example Myriophyllum indicum.

Leaf-pitcher: In Nepenthes khasiana, an insectivorous plant, the leaf lamina is modified into a pitcher with a lid developed from the apex. The pitcher helps the plant to fulfill its nitrogen requirement by trapping and digesting insects.

Bladder: A rootless aquatic herb, the bladderwort {utricuiaria stellaris), has segmented leaves. Some of the segments of the leaves are modified to form bladder-like structures. These bladders help them to trap insects and digest them.

Water reservoir leaf: In Dischidia rafflesiana, a non-insectivorous plant, the leaf lamina is modified to form a pitcher-like structure. The main function of this pitcher is to store rainwater for future use.

This plant is an epiphytic climber. Certain adventitious roots develop from the node, from where the stalk of the pitcher develops. These roots absorb water from the pitcher by entering into the cavity of the pitcher.

Scale leaves: These are membranous leaves that mainly provide protection to the plants. example zingiber officinale.

Functions Of Leaf

Leaves serve two types of functions—primary and special functions.

Primary functions: The basic functions of leaves are—

Photosynthesis: Leaves produce carbohydrates through photosynthesis, which is the main source of food.

Gaseous exchange: The gaseous exchange in plants occurs through the stomata present on the leaves.

Transpiration: The stomata also help in transpiration and thus maintain the water balance in the plant body.

Protects bud: Leaves protect the apical and axillary buds during their development.

Transportation: The vascular bundles of the leaves help in the conduction of food and water within the plant body.

Special functions: Leaves of many plants perform some special functions. Those are—

Food and water storage: The fleshy leaves of xerophytes and some other plants store mucilage and food for future use. example Allium cepa, Aloe vera.

Protection: Some leaves are modified into thorns or spines. These structures protect the plants from different external factors. example Argemone spv Cacti sp.

Climbing: In some plants, leaves get wholly or partially modified into tendrils. These tendrils help the weak stem to climb up on supports. example Pisum sativum.

Reproduction: Adventitious roots and vegetative buds emerge from the leaf margin of Bryophyllum sp. These give rise to new plants.

Catching insects: Some plants have specialized leaves through which they can catch insects. Such plants are called insectivorous plants. These plants grow on nitrogen-deficient soil. To overcome this they feed on insects, from which they get nitrogen.

Helps in floating: In aquatic plants, the leaves contain aerenchyma cells, which help the plants to float on water.

The Inflorescence

As the plants mature, flowers grow on the floral axis either singly or in clusters. Flowers are arranged in various ways on the floral axis in different plants.

The Inflorescence Definition: The arrangement of flowers on the floral axis either singly or in clusters, is known as inflorescence.

The stalk of a solitary inflorescence is known as the floral axis or peduncle. Sometimes, it branches out and bears flowers at the branched apices. The stalk of the individual flowers is called pedicel.

A long, simple, or branched peduncle is known as a rachis. The small main axis of a spikelet present in grass-like plants is called rachilla.

The unbranched naked peduncle that develops from the underground stem, is termed as scape. The stalked flowers are called pedicellate flowers, whereas the flowers without stalks are known as sessile flowers.

Some plants bear flattened peduncles. This is known as a receptacle. The part on which the floral parts grow is called the thalamus. The conical receptacle is known as the torus.

Bracts

Sometimes, the flowers grow at axils of expanded leafy structure, known as a bract. The flowers having bract are known as bracteate flowers and those without bract are known as ebracteate flowers.

Sometimes, very small thin bract-like, leafy, or scaly structures develop on the flower stalk in between the flower and bracts. These structures are known as bracteoles or secondary bracts.

Bracts are of various types—

1. Leafy or foliaceous,
2. Scaly,
3. Spathy,
4. Petaloid,
5. Epicalyx,
6. Involucre,
7. Glume, and
8. Cupule.

Types of Inflorescence: Inflorescence is mainly of three types.

They are as follows—

Morphology Of Flowering Plants Introduction

As we look around, we see different kinds of plants. They are of different forms and structures. Each of them has certain structural features that distinguish them from others. The branch of biology dealing with the study of these different forms and structural features of plants is called plant morphology [Greek: morphe = form and logos = discourse].

Importance Of Studying Plant Morphology:

1. The study of morphology is important for understanding phytogeography, phylogeny, and evolution of plants.
2. Plants are usually identified and classified on the basis of their morphological characters.
3. Modification of different parts of a plant can be identified by comparing the morphological characters.
4. It also helps in the study of plant breeding, genetics, crop production, etc. This chapter deals mainly with the morphology of angiosperms or flowering plants.

Read and Learn More: WBCHSE Notes for Class 11 Biology

Different Parts Of An Angiosperm

Angiosperm or flowering plants are the plants in which the seeds are embedded within the fruits. These types of plants appeared on Earth many years ago. These plants are most diverse and are found all over the world.

The body of an angiosperm is divided into two systems—the root system (the underground portion) comprising roots and their branches and the shoot system (the aerial or sub-aerial portion) comprising stem, branches, leaves, flowers, and fruits.

Root system: The root system usually consists of a main axis—the tap root, and its lateral branches—the branch roots. This system helps in water and mineral absorption from the soil. It also anchors the stem to the soil.

Shoot system: The shoot system consists of the main axis of the plant body—the stem. It bears the branches and the leaves. This system helps in reproduction as it bears flowers and fruits. Shoot system also helps in the transportation of water and minerals, food production, gaseous exchange, transpiration, etc.

Stipules

Stipules Definition: The lateral outgrowths from both sides of the leaf base are known as stipules.

Stipules  Location: Present mainly in pairs at the leaf base.

According to their presence or absence, leaves are of the following types—

Stipulate leaves: These leaves bear stipules. example china rose.

Exstipulate leaves: These leaves do not bear any stipule. example mango, Psidium guajava, etc.

Stipules Function:

1. Stipules protect the axillary buds from mechanical injury at the young stage.
2. They protect the leaves as bud scales.
3. Photosynthesis occurs in foliaceous stipule.
4. Spiny stipule provides protection to the plant.
5. Tendrillar stipule helps the plants to climb.

Stipules Types: On the basis of life span, shape, location, and special functions, stipules are of different types. Those are discussed under separate heads.

According to life span

Caducous: The stipules that fall off before leaf maturation, are called caducous stipules. example Ficus benghalensis, Michelia champaca, etc.

Deciduous: The stipules that fall off soon after the maturation of the leaf, are called deciduous stipules. example Dillenia indica.

Persistent: The stipules that persist throughout the life span of a leaf, are called persistent stipules. example, Rose.

According to position

Free-lateral: When two distinct small stipules grow on two sides of the leaf base, it is called the free-lateral type. example china-rose.

Adnate: When the stipules grow and remain attached on both sides of the petiole up to a certain distance, then they are called adnate type. example Rosa centifolia (rose).

Intrapetiolar: When two stipules, occurring on both sides of opposite leaves, unite together by their inner margins and remain at the axils of leaves, then it is known as intrapetiolar stipule. example Paederia foetida and Gardenia jasminoides, etc.

Interpretiolar: Weakhen the stipules, occurring on both sides of opposite leaves, fuse along their outer margins, and remain on both sides of the stem between the petioles of opposite leaves, then it is known as interpetiolar stipule. Examples are Anthocephalus indicus, Ixora coccinia, Strychnos nux-vomica, etc.

Ochreate: In this type, two stipules emerge from a single leaf base and fuse along both of their margins to form a tube-like structure around the lower portion of the internode. Examples are Polygonum orientate, Rumex vesicarius, etc.

Modified Stipule

Sometimes the stipules are modified for various special functions.

Modifications in stipules are as follows—

Foliaceous: These stipules are modified into leaf-like structures that perform the functions of foliage leaves. example wild peas (Lathyrus aphaca) and peas (Pisum sativum).

Tendrillar: These stipules are modified into tendrils and help in climbing. example Smilax macrophylla.

Spiny: These stipules are modified into spines and protect the plants from herbivorous animals. example Ziziphus mauritiana, Acacia arabica, etc.

Convolute or bud scales: These stipules are membranous and remain a protective covering of the buds. They fall off as the bud matures. example Ficus religiosa (peepal) and F. benghalensis (banyan), etc.

Winged: These stipules are modified into an expanded wing-like structure. example Crotalaria aiata.

Venation

Venation Definition: The arrangement of veins in leaves is known as venation.

The arrangement of veins varies with plant species.

Usually, two types of venations are observed in leaves—

1. Reticulate and
2. parallel (striate).

Reticulate venation

In this type of venation, the main vein or midrib of the leaf divides into numerous branches which again branch repeatedly to develop a network throughout the lamina.

Depending on the number of main veins, reticulate venation may be of two types

1. Unicostate and
2. Multicostate.

Unicostate or pinnate: In this type of venation, leaves bear one midrib. This runs centrally to the lamina and develops branches laterally resembling the pattern of a feather. These branches again form veinlets which form a network. example Artocarpus heterophyllus, Mangifera indica, etc.

Multicostate or palmate: in this type of venation, leaves bear many main veins. These develop from the tip of the petiole and run either towards the apex or towards the margin of the lamina.

Venation  is of two types—

1. Convergent and
2. Divergent.

Convergent type: In this type of venation, the main veins initially diverge out in different directions from the base of the lamina, and gradually converge at the apex. example Ziziphus mauritiana, cinnamon, etc.

Divergent type: In this type of venation, the main veins diverge in different directions from the base of the lamina towards the margin. example Cucurbita maxima, Gossypium herbaceum, etc.

Parallel or striate venation

In some leaves, all the veins grow parallel to each other, either vertically or horizontally without forming any network. This type of arrangement of veins is known as parallel venation. Based on the number of mid veins,

It may be of two types—

1. Unicostate and
2. Multicostate,

Unicostate or pinnate: Leaves of some plants only bear a single midrib at the center of the lamina. Several parallel lateral branches arise from the midrib, on both sides. The lateral branches are perpendicular to the midrib. example Zingiber officinale, Canna indica, etc.

Multicostate or palmate: Leaves of some plants bear many major parallel veins. These develop from the base of the lamina and run either towards the margin or towards the apex.

It is further divided into two types—

1. Convergent and
2. Divergent.

Convergent type: In this type of venation, all the major veins run parallel to each other from the base of the lamina and converge at the apex of the lamina. example rice, bamboo, etc.

Divergent type: In this type of venation, all the major veins arise from the base of the lamina and diverge towards the margin in a parallel fashion. example Borassus flabellifer.

Types Of Leaves

Based on the origin, nature and incision of lamina leaves are of different types.

On the basis of nature and origin

Foliage leaves: These are the green, expanded leaves that perform physiological functions such as photosynthesis, respiration transpiration, etc. These are the lateral appendages of the aerial shoot growing at the nodes.

Seed leaves or cotyledons: The embryonic leaf, present within the seed, is known as seed leaf or cotyledon. Dicotyledonous plants contain two seed leaves and monocotyledonous plants contain only one seed leaf.

Usually, cotyledons are swollen and fleshy due to the reserved food stored in them. During germination, they provide food to the growing embryo.

Scale leaves or cataphylls: These leaves are usually achlorophyllous, scaly or membranous and usually brown in color. In some cases, these leaves become fleshy due to food reserved in them. Sometimes they are chlorophyllous, such as, in aerial shoots of young bamboo, Casuarina, Asparagus, etc. The scale leaves are reduced forms of foliage leaves.

Prophylls: The first few leaves of a branch which modify into different structures other than the foliage leaves, are known as prophylls. Generally, prophylls are modified into one (orange) or two (wood apple) spines or tendrils (Cucurbita sp.).

Bract leaves or hypsophylls: These are the reduced form of foliage leaves and bear floral buds at their axils. They can be colored or colorless. They may be leafy (Acalypha indica), petaloid (Bougainvillea spectabilis), spathe (Colocasia antiquorum), glume {Triticum aestivum), epicalyx i.e., present below calyx (Hibiscus rosa-sinensis), involucre or cupule (Quercus spicata, Betula bhojpatra).

Floral leaves: These are the specialised leaves of a typical flower which constitute sepals, petals, stamens, and carpels. They are discussed in detail while discussing the flower.

Homophyllous and heterophyllous plants

On the basis of the shape of leaves, plants are of two types—

Homophyllous plant: When a plant bears leaves of similar shape, then it is known as homophyllous plant. example Hibiscus rosa-sinensis.

Heterophyllous plant: When a plant bears leaves of more than one shape, it is known as a heterophyllous plant. example, Brassica campestris.

Sporophyll: Some leaves of gymnosperms and ferns, which bear spore-producing structures called sporangia, are known as sporophylls. They mainly produce and protect the sporangia.

On the basis incision of the lamina

On the basis of the incision of the lamina,

The leaves may be divided into two groups—

1. Simple leaf and
2. Compound leaf.

Simple Leaf

Simple leaf Definition: When a leaf is formed of a single lamina with usually entire or incised margin, but the incision never touches the mid-rib, the leaf is referred to as a simple leaf.

Simple leaf Characteristics:

1. These leaves have entire or incised margins.
2. The incision does not touch the midrib.
3. They may have axillary bud in their axil and stipules at their base.

Simple leaf Types: On the basis of incision, simple leaves are of two types-

1. Simple pinnate leaf and
2. Simple palmate leaf

Simple pinnate leaf: In this leaf, the direction of the incision is towards the midrib. According to the extent of incision they are of different types.

1. Pinnate: In this type, the leaf blade is entire, i.e., the leaf does not have an incision. example mango leaves.
2. Pinnatifid: In this type, the incision extends halfway towards the midrib. exampleChrysanthemum coronarium.
3. Pinnatipartite: In this type, the incision extends more than halfway towards the midrib. example, Argemone mexicana.
4. Pinnatisect: In this type, the incisions almost touch the midrib but the lamina is not separated into leaflets. Example Tagetes patula.

Simple palmate leaf: In this leaf, the incision is directed towards the petiole from the margins. According to the extent of incision they are of different types.

Palmatifid: In this type, the incision extends halfway towards the petiole from the margins. example Gossypium herbaceum.

Palmatipartite: In this type, the incision extends more than halfway towards the petiole from the margins. Example Ricinus communis.

Palmatisect: In this type, the incision almost touches the tip of the petiole. example Ipomoea paniculata.

Compound Leaf

Compound Leaf Definition: When the lamina of a leaf becomes completely incised and the incision reaches up to the midrib or petiole forming separate leaflets, then the leaf is known as a compound leaf.

Compound Leaf Characteristics:

1. these leaves do not have any apex or apical buds.
2. they have axillary buds in their axil and stipules at their base.
3. leaflets do not have any axillary bud or stipule.

Compound Leaf Types: According to the arrangement of leaflets,

Compound leaves are of two types—

1. Pinnate compound leaf and
2. Palmate compound leaf.

1. Pinnately compound leaf: In this type, the incision of the lamina extends towards the rachis (main midrib), and the leaflets are arranged on both sides of it or on its branches.

On the basis of the arrangement of leaflets on the rachis, leaves are of four types—

1. Unipinnate: In this type, the leaflets are directly attached on both sides of the rachis, as in feathers.
   It is of two types—
   • Paripinnate: In this type, the leaflets are arranged in pairs on opposite sides of the rachis. The terminal end of the rachis contains an even number of leaflets. example, Tamarindus indicus.
   • Imparipinnate: In this type, the leaflets are arranged in pairs on the rachis, and the terminal end of the rachis contains an odd or unpaired leaflet. example Azadirachta indica.
2. Bipinnate: In this type, the rachis gives rise to secondary branches laterally. The leaflets are arranged on both sides of these secondary branches. These leaflets are known as pinnules. example , Mimosa pudica, Caesalpinia pulcherrima.
3. Tripinnate: In this type, the secondary branches of rachis further divide to produce tertiary branches, The leaflets are laterally arranged on these tertiary branches. example Moringa oleifera, Oroxylon sp.
4. Decompound: In this type, the tertiary branches are again branched in an indefinite manner. The J branches become flat and the pinnules become highly suppressed. example, Daucus carota, and Coriandrum sativum.

2. Palmately compound leaf: In this type of leaf, the incision of the leaf lamina extends towards the petiole. As a result, all leaflets seem to be attached to the apex of the petiole.

It does not consist of any rachis and may be of the following five types—

1. Unifoliate: In this type, only one leaflet is attached to the apex of the petiole. example lemon, orange.
2. Bifoliate or bipinnate: In this type, two leaflets are attached to the apex of the petiole. example of Bignonia grandiflora.
3. Trifoliate or ternate: In this type, three leaflets are attached to the apex of the petiole. example Vitex negundo.
4. Quadrifoliate or quadrinate: In this type, four leaflets are attached to the apex of the petiole. example, Marsilea quadrifolia.
5. Multifoliate or digitate: In this type, more than four leaflets are attached to the tip of the petiole. example Bombax ceiba.

 

Racemose (Indefinite Or Ndeterminate) Inflorescence

Racemose Definition: The inflorescence, where the rachis grows indefinitely by producing lateral flowers acropetally or centripetally is known as racemose inflorescence.

Racemose Characteristics:

1. The floral axis increases indefinitely in length.
2. It is terminated by a bud.
3. Sessile or stalked flowers are borne acropetally or centripetally on the floral axis. It means the mature flowers remain at the lower region of the axis and immature flowers at the upper region.
4. Sometimes the rachis is condensed and develops into a round structure known as a receptacle. The flowers open from periphery J to center, centripetally.

Racemose Types:

The racemose inflorescence is divided into the following groups—

Raceme: In this type, the main axis or the rachis grows indefinitely, and bears pedicellate flowers. The flowers grow acropetally on the axis. example Raphanus sativus and Brassica nigra.

Raceme is of two types—

1. Simple raceme and
2. In compound raceme or panicle, compound raceme, the floral axis is branched and each branch appears like a simple raceme.

(Numbers in the figures given indicate the gradual growth of the flowers. For example, the flower which is numbered as 1 grows first followed by 2, and so on.)

Corymb: In this type, the floral pedicels or stalk are unequal in length. (The main floral axis is shorter than the axis of the basal flowers. All flowers grow almost at the same plane.) The flowers grow centripetally. example Prunus cerasus (cherry), Cassia sophera, Iberis amara.

Corymb is of two types—

1. Simple or unbranched and
2. Compound or branched. In compound corymb, the floral axis is branched and each branch appears like a simple corymb.

Spike: In this type, the floral axis grows indefinitely and bears sessile flowers. The flowers grow acropetally on the rachis and are bracteate. example Piper longum, Achyranthes aspera, Adhatoda vasica, etc.

Spike is of two types—

1. Simple or unbranched and
2. Compound or branched or spikelet. In compound spike, the floral axis is branched and each branch appears like a simple spike.

Umbel: In this type, the main floral axis is much reduced and the pedicels of all flowers are of equal length. The flowers grow centripetally.

Flowers are usually bracteate and the bracts unite to form an involucre (covering) at the base of the pedicellate flowers. example Centella Asiatica and Coriandrum sativum of Apiaceae, Prunus cerasus during the young stage.

Umbel is of two types—

1. Simple and
2. Compound In a compound umbel, the floral axis is branched and each branch appears like a simple umbel.

Spikelet or Locusta

It is a small spike with one or more flowers on the rachilla (secondary rachis). Usually, many flowers are borne on each inflorescence as in Triticum aestivum but in Oryza sativa, it has a single flower. In Zea mays, the male inflorescence bears a spikelet of two flowers.

In grasses like Panicum sp., two scaly bracts are present at the base of the entire inflorescence. These are known as glumes or empty glumes. Above them, there are one or more fertile glumes. These are known as the flowering glumes or lemmas.

Each lemma contains a single sessile flower in its axil, opposite to which a small glume is present, known as palea.

Catkin: In this type, the sessile, unisexual flowers grow acropetally on a pendulous peduncle. It is a modified compact spike. Example Acalypha hispida.

Spadix: It isCatkina special type of spikeFig. with fleshy rachis having both male and female flowers. The whole inflorescence is surrounded by a large bract called spathe. The spathe is absent in some cases such as in the Acorus calamus.

The female flowers are always borne towards the base of the rachis whereas the male flowers are towards the apex. This inflorescence also bears sterile flowers which are present in between the male and female flowers.

The terminal region does not bear any flowers and is infertile. This region is termed an appendix. example Coiocasia antiquorum.

Capltulum: In this type, the small sessile flowers grow centripetally on the modified thick, fleshy, and flattened rachis, known as the receptacle.

Mostly two types of flowers are found in the capitulum—

1. Ray florets on the margin of the receptacle and
2. Disc floret in the center. Each floret is covered with green-colored scaly bracteoles. The whole inflorescence is surrounded by a cover of bracts. The disc florets are bisexual whereas the ray florets are sterile. example Helianthus annuus.

Cymose Inflorescence

Cymose Inflorescence Definition: The inflorescence, in which the rachis or peduncle grows up to a definite point and is terminated with a flower, is known as cymose inflorescence.

Cymose Inflorescence Characteristics:

1. The growth of the floral axis is limited.
2. The first flower grows at the tip of the axis, thus pausing the growth of the peduncle.
3. The flowers are borne basipetally or centrifugally on the axis.

Cymose Inflorescence Types: Cymose inflorescence is of four types.

Solitary: In this type, the terminal or apical bud grows into a single flower. E.g. Hibiscus rosa-sinensis.

Uniparous or dichasial cyme: In this type, the main floral axis is terminated by a single flower. The main axis gives rise to a single lateral branch which is also terminated by a single flower.

The other lateral branches grow in the same manner. This type is again divided into the following groups—Scorpioid cyme and helicoid cyme or bostryx.

1. Scorpioid cyme: In this type, the lateral branches bearing flowers grow alternately on both sides of the main axis forming a zigzag structure. example Hamelia patens, and Commelina benghalensis.
2. Helicoid cyme or bostryx: In this type, the lateral branches bearing flowers grow successively on the same side forming a curved structure. example, Heliotropium indicum, and Ranunculus bulbosus.

Biparous or monochasial cyme: In this type, the main floral axis is terminated by the flower. Two lateral branches develop from the same point of the main axis in opposite directions. They are also terminated by flowers. This process continues. example Jasminum sp., Clerodendrum infortunatum.

Multiparous or polycrystal cyme: In this type, the main axis is terminated by a flower and two or more lateral branches develop from the main axis. They are also terminated by flowers.

The lateral branches also behave like the main axis and the branching process continues. Examples are Caiotropis procera, and Carissa carandas.

Special Inflorescence

Special Inflorescence Definition: The highly modified and condensed cymose inflorescence.

Special Inflorescence Types: they are of the following types

Hypanthodium

Hypanthodium Characteristics:

1. In this type, the main axis condensed to form a hollow, fleshy, cup-like receptacle,
2. The receptacle has an apical pore (ostiole) which is guarded by scales.
3. The cup-like cavity of this inflorescence bears three types of flowers—male flowers in the apical region, female flowers in the basal region, and neutral sterile flowers, in between male and female flowers. The flowers grow on the margins of the receptacles. example Ficus benghalensis, Ficus hispida.

Cyathium

Cyathium Characteristics:

1. The floral axis condenses and forms a conical receptacle.
2. There is only one female flower in the central part of the receptacle and it hangs down due to the long pedicel.
3. This flower is represented by a single pistil.
4. Surrounding the female flower, several male flowers grow centrifugally on the receptacle.
5. Male flowers bear a single stamen.
6. A bright-colored involucre surrounds the whole floral arrangement on the receptacle. Thus, it appears as a single flower. example Poinsettia pulcherrima, and Pedilanthus tithymaloides.

Verticillaster

Verticillaster Characteristics:

1. It is a condensed, biparous cymose inflorescence.
2. This inflorescence occurs at the axil of two opposite decussate leaves surrounding the stem.
3. At first, the inflorescence is dichasial cyme and then each branch of dichasium is reduced to scorpioid cyme.
4. Here, the sessile and bilabiate flowers develop in clusters around the stems. example Leonurus sibiricus.

Coenanthium

Coenanthium Characteristics:

1. This is like the hypanthodium but here the floral axis becomes a saucer-shaped receptacle, with slightly curved margins.
2. The small flowers are arranged with cymose inflorescence on the receptacles. For example, found in Dorstenia sp.

The Flower

The flower is the main organ for sexual reproduction in angiosperms. The axillary or apical bud, from which the flower develops is known as the floral bud. Flower is a modified shoot.

Fruits and seeds both develop from flowers. So it is also known as the reproductive shoot. It is mainly composed of four parts—corolla, calyx, androecium and gynoecium.

The Flower Definition: The highly condensed and modified shoot responsible for reproduction is known as a flower.

Morphological characteristics of a flower:

1. The flower has definite growth.
2. This modified shoot is a temporary part of the plant.
3. Flowers grow at the shoot apex or axils of the leaves or bract.
4. A typical flower grows on a stalk called a pedicel.
5. The swollen upper part of the pedicel is known as the thalamus. The thalamus is also differentiated into nodes and internodes. The internodes are highly condensed, thus the nodes are packed closely together.
6. On the thalamus, the floral parts remain arranged in four concentric whorls.
7. The outer two whorls, i.e., calyx and corolla, are the accessory whorls. The inner two whorls, i.e., androecium and gynoecium are the essential or reproductive whorls.

Different Parts Of A Typical Flower And Their Functions

The flower that bears all the floral parts, i.e., pedicel, thalamus, corolla, calyx, androecium, and gynoecium with their proper functions is known as a typical flower. example, Hibiscus rosa-sinensis.

Pedicel: The green-colored stalk below the flowers, which bears the thalamus is known as the pedicel. The flowers with pedicel are known as pedicellate flowers (Example Hibiscus -sp.) and the flowers without pedicel are known as sessile flowers (Example Tube rose).

Pedicel Function: It connects the flower with the stem.

Thalamus: The disc-like, flattened structure above the pedicel, which bears all the floral whorls in concentric rings is known as the thalamus. It is also called the torus axis or receptacle. Usually, it is convex or concave and often it is very short or condensed. Sometimes it becomes elongated (axis) and shows distinct internodes.

Thalamus Function: It bears different floral whorls.

Calyx

Calyx Definition: A generally green-colored lowermost or outermost whorl of the flower, formed of sepals is known as calyx.

Calyx Characteristics:

1. It is the first and outermost floral whorl on the thalamus.
2. The individual member of the calyx is known as a sepal.
3. The sepals may be free i.e., polysepalous, or may be partially or completely united i.e., gamosepalous.
4. Generally, sepals are sessile and green, but sometimes they are of different colors. The number of sepals in the whorl is variable.

Calyx Function:

1. It protects the other whorls in their bud stage.
2. Green calyx takes part in photosynthesis.
3. Colored calyx, helps in reproduction by attracting insects for pollination.

Corolla

Corolla Definition: The white or bright-colored, second whorl of the flower, formed of petals is known as a corolla.

Corolla Characteristic:

1. It is the second whorl from the outside, situated above the calyx.
2. The individual member of this whorl is known as the petal.
3. The petals are mostly bright in color or white and have a sweet smell.

Corolla Function:

1. Either with their bright color or smell, petals attract insects for pollination.
2. They protect the essential reproductive whorls i.e., the androecium and the gynoecium.
3. Usually, the base of the petals contains, nectaries(the nectar-secreting glands).

Androecium

Androecium Definition: Androecium is the essential, male reproductive whorls formed of one or more stamens.

Androecium Characteristic:

1. It is the first essential and third whorl of the flower.
2. The structural unit of the androecium is the stamen. They are placed on the thalamus either in a cyclic or in a spiral fashion.
3. A stamen appears quite different from sepals and petals.
4. Stamen is generally composed of an elongated narrow stalk called a filament. A sac-like structure, called anther, is present at the tip of the filament.
5. Each anther usually consists of two anther lobes connected by connective formed by the extension of the filament.
6. Each anther lobe has two chambers, called pollen sacs or microsporangia.
7. Each stamen, therefore, consists of four microsporangia and each microsporangia contains a large number of pollen grains or microspores.

Androecium Function:

1. Stamens produce pollen grains (male gametophytes) inside the anther lobes.
2. They help in fertilization.

Gynoecium or pistil

Gynoecium or pistil Definition: The essential, female reproductive whorl of flower that lies innermost and terminates the thalamus.

Gynoecium or pistil Characteristic:

1. It is the second essential and fourth whorl of the flower.
2. The gynoecium, also called the pistil, is the most essential reproductive whorl of the flower. The sterile pistil or gynoecium is known as pistillode.
3. The gynoecium consists of one or more carpels, which is the structural unit of the gynoecium.
4. Each carpel consists of three parts—ovary, style, and stigma.

1. Ovary: It is the lowermost swollen, pitcher-like part of the gynoecium. It contains ovules (structures that later form the seeds) inside. It may be made up of single (monocapellary) or many (polycapellary) carpels. It may be of the following types.

2. Style: It is the slender and elongated stalk-like structure formed by gradual tapering of the tip of the ovary. Style development may be apical or terminal (For example Adhatoda vasica), lateral (For example, Mangifera indica), or basal (gynobasic—for example, Ocimum sanctum).

3. Stigma: It is the extreme tip of the style, which receives the pollen grains during pollination. The shape of stigma varies among species.

Stigma Function:

1. Carpels produce female gametophytes.
2. After fertilization embryo is produced the ovary matures to form fruits and seeds.

Perianth

In some flowers, the accessory floral whorls can not be differentiated into calyx and corolla. Such an accessory floral whorl is known as perianth. example Polyanthes tuberosa etc. The individual member of the perianth is known as tepal.

Again in some flowers, only one set of these accessory whorls are present. These members of the perianth can be like sepal (sepaloid), for example, Borassus flabellifer and Cocos nucifera, etc., or like petal (petaloid), for example, Michelia champaca, etc.

The flower that contains only one accessory whorl, i.e., either calyx or corolla or perianth, is called monochlamydeous or haplochlamydeous. example Polyanthes tuberosa. Ordinary flowers with both calyx and corolla are called dichlamydeous. example Pisum sativum etc.

Flower is a modified shoot

The vegetative shoot is composed of an elongated stem differentiated into nodes and internodes with leaves arranged at the nodes. The flower is morphologically similar to the shoot.

It has been modified for similar to the shoot. It has been modified for parts in different flowers proving that, flowers are the modified shoots.

The modifications of various parts are as follows

1. Axis nature of thalamus,
2. The leaf-like nature of the floral members and
3. Homology of floral buds.

Axis nature of thalamus: Each flower bears a condensed axis—thalamus, on which the floral leaves remain arranged in concentric whorls. In some exceptional cases, it gets modified into an elongated axis and shows the stem characters.

1. The floral leaves develop from the nodes. The elongated internodal region between petal and androecium is referred to as androphore, as seen in Passiflora suberosa.

The elongated axis between the androecium and gynoecium is referred to as gynophore as in Capparis septaria. Gynandropsis gynandra contains gynandrophore, i.e., both androphore and gynophore.

Anthophore is produced due to the elongation of the internode between the calyx and corolla and is found in Sielene sp.

2. The growth of the thalamus usually stops and is terminated by the gynoecium. But sometimes the thalamus develops beyond the gynoecium bearing either a leafy vegetative shoot or a flower above the first one. This growth is known as proliferation or monstrous development. example Found in pears, roses, etc.

3. In some plants, after fertilization the thalamus elongates like an ordinary stem and gives rise to an aggregate fruit. example Michelia champaca and Polyalthia longifolia.

Leaf nature of the floral members: The sepals, petals, stamens, and carpels are the modified leaves. They exhibit the same type of ptyxis and aestivation.

These may be proved from various instances, which are as follows

Gradual transition of floral members: The floral leaves are spirally arranged on the thalamus. The outermost sepals are green with distinct venations and they gradually transform into petals.

The petals gradually become narrow bearing anther at the tip and then are transformed into a typical stamen. It is commonly found in water lily, Nymphaea sp.

Modification of sepal into leaf: In Mussaenda frondosa, out of five sepals one remains as the leaf with prominent venation, but instead of being green, it is colored like petals.

In Mussaenda philippica, all five sepals maintain leaf-like structures and have prominent venations but are colored.

Transformation of leaf to petal: In Paeonia officinalis, a gradual transition of leaves to sepals and sepals to petals can be observed, supporting the leafy nature of perianths.

Leafy petals: In some flowers, sepals, and petals appear as foliage leaves, as in green roses.

Petaloid stamen: In Canna indica, the stamens become petaloid staminodes. However, in some cases, a part of the anther lobe becomes petaloid and the other part remains fertile.

Petaloid and sepaloid carpel: In Zinnia sp., the carpels become petaloid or sepaloid.

Leafy nature of carpel: In Pisum sativum, the gynoecium is formed by the folding of a single leaf along its midrib. The leaf develops a single-chambered ovary containing seeds. The upper elongated part of the leaf develops into the style and its apex forms the stigma.

Homology of floral buds: Floral buds are homologous to some organs. In some cases, the floral buds get transformed into vegetative buds or bulbils. example Agave sp., Allium sativum, Globba bulbifera, etc. Floral buds occupy the terminal or axillary positions, like the vegetative buds.

Types Of Flower

Flowers are of different types based on different characteristics of their whorls.

Classification of flowers based on the presence or absence of the floral whorls:

Flowers based on the presence or absence of floral wholes are of the following types.

Complete flower: The flower that bears all the four floral whorls i.e., calyx, corolla, androecium, and gynoecium, is known as a complete flower. example Datura metel.

Incomplete flower: A flower that lacks one or more floral whorls is known as an incomplete flower. example Polianthes tuberosa

Naked or achlamydeous flower: The flowers which bear either androecium or gynoecium, or both but do not have calyx and corolla, are known as naked or achlamydeous flowers. example Beta vulgaris.

Classification of flowers on the basis of the absence or presence of essential whorls: Flowers on the basis of presence or absence of essential wholes are of the following types.

Bisexual (perfect or hermaphrodite or monoclinous) flower: The flower that bears both the essential whorls i.e. androecium and gynoecium, is known as bisexual flower. Common examples of bisexual flowers are china-rose, mustard, etc.

Unisexual (imperfect or diclinous) flower: The flower which bears only one essential whorl i.e. either androecium or gynoecium, is known as an unisexual flower.

Thus they are called—pistillate or female flower and staminate or male flower. In Cucurbita maxima, the flower is incomplete and unisexual due to the absence of either androecium or gynoecium.

Sterile flower: The flower in which both the androecium and gynoecium are either absent or non-functional, is known as a sterile or neutered flower. example Amorphophallus companulatus.

Classification of flowers on the basis of symmetry: Flowers on the basis of symmetry are of the following types.

Actinomorphic or regular flower: The flower that can be divided into two equal and symmetrical halves if cut through any vertical plane passing through the axis, is known as actinomorphic or regular flower. example Vinca rosea, china rose.

Zygomorphic or irregular) flower: The flower that is equally and symmetrically divisible only through a single vertical plane passing through the axis, is known as a zygomorphic or irregular flower. example Pisum sativum, Clitoria ternatea, etc.

Asymmetrical flower: There are some flowers, that can not be divided into two equal halves through any vertical plane are known as asymmetrical flowers. example Canna indica.

Classification of flowers on the basis of arrangement of floral whorls on the thalamus:

Flowers on the basis of the arrangement of floral whorls on the thalamus are of the following types.

Cyclic flower: When the sepals, petals, stamens, and carpels are arranged on the thalamus in separate whorls, then the flower is termed a cyclic flower. Most angiosperms have cyclic flowers. example Hibiscus rosa-chinensis (china rose), Brassica nigra, etc.

Acyclic flower: When all the floral leaves of a flower are spirally arranged on the thalamus but not in distinct whorls, then it is termed an acyclic flower. example Nelumbo nucifera, Michelia champaca, etc.

Spirocyclic (hemicyclic flower: When some floral leaves are arranged in whorls and some are arranged spirally, then the flower is called a spirocyclic or hemicyclic flower. example, Nymphaea stellata, rose, etc.

Classification of flowers on the basis of number of the members in floral whorls: Flowers on the basis of number of the members in floral whorls are of the following types.

Isomerous flower: In this type of flower, the number of sepals, petals, stamens, and carpels are of the same number or present in multiples of the same number. It may be of the following types.

1. Bimerous flower: The number of floral members in each whorl is two or multiple. example Circaea lutetiana.
2. Trimerous flower: The number of floral members in each whorl is three or multiple. example Tulipa clusiana, Annona squamosa, etc. Monocotyledonous flowers are mostly trimerous.
3. Tetramerous flower: The number of floral members in each whorl is four or multiple.example radish and mustard, Gynandropsis gynandra, etc.
4. Pentamerous flower: The number of floral members in each whorl is five or multiple. It is commonly found in dicotyledons. example Hibiscus rosa-sinensis.

Heteromerous flower: The number of floral leaves of different whorls is not the same. example Beilis perennis.

Classification of flowers on the basis of presence or absence of bract: Flowers on the basis of a number of presence or absence of bract are of the following types.

Bracteate flower: The flower which arises from the axil of a bract is known as a bracteate flower. example Clitoria ternatea.

Ebracteate flower: The flower that does not arise from any bract is known as an ebracteate flower.example Mangifera indica.

Classification of flowers on the basis of insertion of floral leaves on the thalamus in respect to the ovary: Flowers on the basis of a number of insertion of floral leaves on the thalamus in respect to the ovary are of the following types.

Hypogynous flower: The ovary (gynoecium) is seated at the uppermost position on the convex or conical thalamus. The other whorls arise below the ovary. Thus, the thalamus is present below the gynoecium. Hence, the ovary is superior and all other floral members are inferior, by position example Hibiscus rosa-sinensis.

Perigynous flower: The thalamus is cup-shaped or concave, and the ovary remains in the center of the cup. The other floral whorls remain attached to the rim of the cup-shaped thalamus.

The ovary is superior by position in this flower. Sometimes the ovary is said to be half inferior instead of inferior. example pea, rose, Portulaca oleracea, etc.

Epigynous flower: The deep concave cup-like thalamus completely encloses the ovary and fuses with the ovary wall. Here, the other floral whorls remain above the ovary. The ovary in such cases is inferior and the rest of the floral members are superior. Common examples are sunflower, pumpkin, etc.

Classification of plants, on the basis of the presence of male and female flowers

Plants on the basis of the presence of male and female flowers are of the following types.

1. Monoecious plant: When both the male (staminate) and female (pistillate) flowers are borne on the same plant, then the plant is known as a monoecious plant. example Trichosanthes dioica and Cucurbita maxima.
2. Dioecious plant: When male and female flowers are borne on different plants, then such plants are known as dioecious plants. example Borassus flabellifer (palm) and Carica papaya.
3. Trioecious plant: If the male, female, and bisexual flowers are borne on different plants, then they are known as trioecious plants. example Silene sp.
4. Polygamous plant: If unisexual, bisexual, and sterile flowers are borne on the same plant, then the plant is known as a polygamous plant. example Mangifera indica.

 

Placentation

The ridge of soft parenchymatous tissue on which the ovules grow by means of funicles (stalk) is known as the placenta.

Placentation Definition: The arrangement of the placenta bearing the ovules inside the ovary is known as placentation.

Types of placentation

Marginal: This type of placentation is found in the monocarpellary, and unilocular ovary. The placenta develops on one side of the ovary. Ovules are present at the margins of the carpel in one or two rows. Example Dolichos lablab.

Axile: This type of placentation is found in polycarpellary, and multilocular ovary. The carpels remain joined together to form an axis. The placenta with ovules develops around this axis. Example Citrus limon.

Parietal: This type of placentation is found in the polycarpellary, and unilocular ovary. Several false partition walls are formed in the ovary due to the fusion of carpels, known as replum. The placenta occurs along the wall of the ovary. Example Brassica nigra.

Free central: This type of placentation is found in polycarpellary, and unilocular ovary. The placenta with ovules develops on the central axis. Example Scoparia dulcis.

Basal: This type of placentation is found in the monocarpellary, and unilocular ovary. The placenta grows at the base of the ovary. Example Helianthus annuus.

Superficial: This type of placentation is found in the polycarpellary, and multilocular ovary. The placenta with ovules is present all around the inner wall of the ovary. Example Nymphaea sp.

The Fruit

After fertilization, the floral parts, except the ovary, dry up and fall off. The ovary enlarges and the ovules get modified into seeds. This enlarged ovary with seeds is the fruit. Besides this, fruits may also develop from a whole inflorescence. Sometimes different parts of a flower may also develop into fruits.

The Fruit Types:

Fruits can be of various types—

Structure Of A True Fruit

A true fruit consists of mainly two parts

1. Seeds and
2. Pericarp.

Pericarp: The pericarp can be thin or thick and fleshy or dry.

A well-developed pericarp is differentiated into three layers—

Epicarp or exocarp: It is the outermost thin layer of the fruit, i.e., the skin of the fruit.

Mesocarp: It is the thick, fibrous, or fleshy middle layer of the fruit. It is present just below the epicarp and forms the pulp. In most of the fruits, this part is edible.

Endocarp: It is the innermost layer of the fruit and encloses seeds or seeds. It may be membranous or hard.

Seed: Fruits contain one or more seeds. After fertilization, the ovules are transformed into seeds. The seed coat may remain attached or separated from the inner wall of the fruit.

Structure of a true Function of fruit: it protects the seeds and helps in seed dispersal.

Classification Of Fruits

Based on origin, texture, and dehiscence, fruits are mainly of three types—

1. Simple fruit,
2. Aggregate fruit and
3. Composite or compound or multiple fruit.

Simple fruits

The fruit, which develops from the ovary of a solitary pistil is known as a simple fruit. Example Pisum sativum (pea), and Oryza sativa (rice).

These types of fruits are further classified into two categories—

1. Dry fruits and
2. Succulent or fleshy fruits.

Dry fruits: The fruit in which the pericarp is simple, dry, and cannot be differentiated into three layers, i.e.,ectocarp, mesocarp, and endocarp, is known as dry fruit.

The dry fruits are further divided into the following three types

1. Dry dehiscent fruit,
2. Dry indehiscent three and
3. Dry schizocarpic fruit.

Dry dehiscent fruits: In this type of fruit, the pericarp ruptures at maturity, and then the seeds are dispersed. These fruits contain numerous seeds. These fruits are further divided into five types.

Dry indehiscent fruits: In this type of fruit, the pericarp does not rupture even after maturity or ripening. The seeds remain inside the fruits. These fruits mostly contain single seed. These fruits can be divided into six types as given in the.

Dry schizocarpic fruits (splitting fruits): In this type, the ripe fruits are divided into two or more indehiscent segments. These segments are called mericarps. Each mericarp contains only one seed. These fruits are divided into four types as given in the.

Succulent or fleshy fruits: These fruits become succulent and juicy after ripening. The pericarp of the fruit is differentiated into three layers—epicarp, mesocarp, and endocarp.

They have thick, fleshy, or fibrous mesocarp. The fruits are indehiscent. Hence, the seeds are released only after the decay of the fleshy tissue enclosing them.

These fruits are of the following types—

Drupe (Stone fruit): The fruits develop from the monocarpellary, superior ovary. They are generally one-seeded. The pericarp is differentiated into an outer exocarp or epicarp, a middle fleshy mesocarp, and an inner hard (stony) endocarp. Examples are mango, peach (Prunus persica), etc.

Pome: The fruits develop from syncarpous, bi- or multicarpellary, inferior ovary. They are mostly false fruits. The edible part of this fruit is the fleshy thalamus which surrounds the true fruit. Seeds are surrounded by a thin ovarian wall. For example pear(Pyrus communis) and apple (Malus sylvestris), etc.

Berry or Bacca: The fruits develop from the multicarpellary, syncarpous, superior, or inferior ovary. The seeds are embedded freely in the massive pulp from by mesocarp and endocarp. The epicarp remains as the outer skin of the fruit. Example brinjal (Solanum melongena), tomato (Lycopersicon esculentum), etc.

Berry or Bacca: The fruits develop from the multicarpellary, syncarpous, superior, or inferior ovary. The seeds are embedded freely in the massive pulp from by mesocarp and endocarp. The epicarp remains as the outer skin of the fruit. Example brinjal (Solanum melongena), tomato (Lycopersicon esculentum), etc.

Date palm—berry or drupe

An example of a one-seeded berry is the date palm, (Phoenix sylvestris). In the case of date palms, the endocarp is thin and paper-like. But, it is also considered as a type of drupe.

Pepo: The fruits developed from tri carpellary, syncarpous, and inferior ovary. The seeds are firmly attached to the placenta. The exocarp is tough and leathery. Example cucumber (Cucumis sativa); pumpkin (Cucurbita maxima), etc.

Hesperidium: The fruits are multi-chambered and developed from the multicarpellary, syncarpous, superior ovary. In these fruits, the epicarp and mesocarp remain fused together and form the skin.

The endocarp projects inwards forming distinct chambers or lobe-like structures. The inner part of the endocarp contains unicellular juicy hairs. Example sweet orange, (Citrus sinensis) lemon (Citrus aurantium), etc.

Balausta: The fruits are many-chambered and develop from the polycarpellary, syncarpous, and inferior ovary. They contain many seeds. The seeds have seed coats known as outer fleshy testa and inner hard tegmen. The fleshy testa is the edible part.

Seeds are irregularly arranged inside the fruit. The pericarp is rough and leathery with persistent calyx. Example pomegranate (Punica granatum).

Amphisarca: The fruits are many-chambered and develop from the polycarpellary, syncarpous, superior ovary. They contain many seeds scattered within the fruit.

They have hard epicarp fleshy mesocarp and endocarp. The mesocarp, endocarp, and swollen placenta are the edible parts. For example wood apple (Aegle marmelos) and Feronia limonia.

Aggregate Fruit

The fruit that develops from a single flower containing polycarpellary, and apocarpous ovary (many carpels and ovary) is known as aggregate fruit. This type of fruit is composed of many small fruits, known as etaerio of fruitlets.

These fruits are divided into the following four types—

Etaerio of follicles: In this type, each free carpel grows into a follicle and remains arranged together on the enlarged thalamus. This scenario may be composed of two follicles as in Calotropis procera or many as in Magnolia grandiflora.

Etaerio of achenes: In this type, the fruits are achenes and remain aggregated on the thalamus. Many such achenes are arranged in different forms. In lotus (Nelumbo nucifera), the thalamus becomes spongy and achenes are embedded inside it. In Naravelia zeylanica, the hairy achenes are aggregated on the thalamus.

Etaerio of drupes: In this type, the fruits are drupes. Many small drupes are aggregated on the fleshy thalamus. Example strawberry (Fragaria vesca) raspberry {Rubus idaeus), etc.

Etaerio of berries: In this type, the fruits are berries. Many such small berries are arranged on the sides of the fleshy thalamus. The apical part is fused with each other forming a common rind. For example Artabotrys odoratissimus and custard apple (Anona squamosa), etc.

Composite or compound or multiple fruit

The fruits that develop from the complete inflorescence are known as composite compounds or multiple fruits. These are also called infructescences or syncarps.

These fruits are of the following two types—

Sorosis: These fruits develop from a spike, spadix, or catkin inflorescence, where the axis and the ovaries are fused together to form a single fruit. Example pineapple (Ananas comosus), and jackfruit (Artocarpus heterophyllus).

Syconus: These fruits develop from entire hypanthium or coenanthium inflorescence, where the receptacle contains many seeds. Example fig (Ficus hispida), banyan (F. benghajensis), etc.

The Seed

The Seed Definition: A seed is a fertilized matured ovule, consisting of an embryo enclosed by protective seed coats.

Generally, all flowering plants bear seeds. It contains a fully developed embryo in it. This embryo develops into a seedling during germination.

Formation of seeds after fertilization: After fertilization, different parts of the ovule modify to form different parts of the seed. Integuments are modified into testa and tegmen. Funiculus is modified into the stalk of the seed.

Micropyle and hilum of ovule become that of the seed. Egg (n) cells are modified into a zygote (2n) while the definitive nucleus (2n) is modified into the endosperm (3n) of the seed.

Different Parts Of A Typical Seed

A typical matured seed of angiosperms consists of the following parts

Types of seeds: Depending on the number of cotyledons and the presence of endosperm, seeds are of various types. Based on the number of cotyledons, seeds are of three types- monocotyledonous, dicotyledonous, and polycotyledonous and polycotyledonous based on the presence of endosperm seeds are of two types endospermic and non-endospermic.

On the basis of the number of cotyledons

1. Monocotyledonous: The seeds with one cotyledon, are known as monocotyledonous seeds. These types of seeds are found in rice (Oryza sativa) wheat (Triticum aestivum), maize (Zeo mays), etc.
2. Dicotyledonous: The seeds with two cotyledons, are known as dicotyledonous seeds. These types of seeds are found in mango (Mangifera indica), gram (Cicer arietinum), pea (Pisum sativum), castor (Ricinus communis), gourd (Cucurbita maxima), etc.
3. Polycotyledonous: The seeds that bear more than two cotyledons are known as polycotyledonous seeds. These types of seeds are found in pine and in most conifers.

On the basis of the presence of endosperm

Exalbuminous (non-endospermic): In these seeds, the food is stored in the cotyledons and the endosperm is inconspicuous. This type of seeds is found in both dicot (Pisum sativum) and monocot (Alisma sp.) plants.

Albuminous (endospermic): In these seeds, the food is stored in a separate tissue, called the endosperm. The cotyledons of these seeds are thin papery structures without reserve food. This type of seed is found in both dicotyledonous (Ricinus communis, Carica papaya) and monocotyledonous (Zea mays, Oryza sativa) plants.

Structure of some important seeds

The structures of some seeds are discussed below.

Structure of non-endospermic dicotyledonous seed:

Gram (Cicer arietinum), mango (Mangifera indica), and pea (Pisum sativum) are examples of dicotyledonous, non-endospermic seeds The structure of a gram seed is discussed below.

The two main parts of this seed are—

1. Seed coat and
2. kernel.

Seed coat: The outer covering of the seed is known as the seed coat. It has two parts—

Testa: It is the brown-colored, thick, leathery outer covering of the seed.

Tegmen: It is present below the testa. It is a thin white-colored membrane that remains attached to the testa. The pointed part of the seed has an oval scar on its surface, known as a hilum. The seed remains attached to the placenta inside the ovary, through this hilum.

A small opening, called micropyle is present near the hilum. The lens-shaped scar present on the middle of the testa is known as strophiole or chalaza.

Kernel: After removal of the seed coat a thick, fleshy, spherical part can be seen within the seed. It is known as the kernel.

It is the embryo. It has two parts—

1. Cotyledons: These are the thick, fleshy, pale yellow-colored hemispherical structures. They store food for the embryo.
2. Tigellum or embryo axis:
   • This is a hook-like structure, present in between the cotyledons.
   • The tigellum remains attached to the cotyledons at a point. This point of attachment is known as the cotyledonary node or nodal zone.
   • The upper growing region of the embryo axis is known as the plumule and the lower growing region is known as the radicle,
   • The region between the plumule and the cotyledonary node is known as epicotyl.
   • The region between the radicle and cotyledonary node is known as hypocotyl.

Structure of the endospermic dicotyledonous seed: Castor (Ricinus communis), cotton (Gossypium herbaceum), and jute (Corchorus olitorius) are examples of endospermic dicotyledonous seeds. The structure of castor seed is described below.

The seed is flat and oval in shape. Its two main parts are—

1. Seed coat and
2. Kernel.

Seed coat: These seeds are composed of thick, hard, and fragile testes. Tegmen is absent in these seeds. Testa has black, brown, and white colored ornamentations. The white-colored fleshy outgrowth on the narrow region of the seed is known as a caruncle.

This structure covers the micropyle and hilum. A ridge that runs from hilum to the strophiole of the seed, is known as raphe. It helps to absorb water into the seeds.

Kernel: It is the spherical fleshy structure present below the seed coat. It has three parts. They

1. Perisperm: The thin transparent membrane, that covers the endosperm, is known as the perisperm.
2. Endosperm: The thick, whitish-flat region below the perisperm is known as the endosperm. The endosperm provides nutrients to the embryo.
3. Embryo: It is the part that consists of two cotyledons and a tigellum or embryo axis.
   • Cotyledons: Cotyledons of this seed are thin leaf-like structures with veins and veinlets.
   • Embryo axis or tigellum: The minute rod-shaped structure attached to the cotyledons is known as the embryo axis or tigellum. The upper growing region of the embryo axis is known as plumule and the lower growing region is known as radicle. Both the radicle and plumule of these seeds are very small. Thus, the epicotyl and hypocotyl regions are not clearly visible.

Structure of endospermic monocotyledonous seed: Rice {Oryza sativa), wheat (Triticum aestivum), maize (Zea mays) are examples of endospermic monocotyledonous seeds. The structure of maize seed is discussed as follows.

Covering layer: The outer covering of the maize seed is formed by the combination of pericarp and seed coat. This is translucent, thick, and golden yellow in color.

Kernel: The part below the outer coat is known as the kernel. It has two parts—endosperm and embryo.

1. Endosperm: 75% of the kernel is the endosperm. This region stores a large amount of starch. Due to the presence of endosperm, this seed is known as endospermic seed. The endosperm is surrounded by a proteinaceous layer known as the aleurone layer.
2. Embryo: The embryo is present at the triangular swollen region, below the endosperm. The embryo is very small and formed of two parts.
   • Cotyledons: Maize contains only one cotyledon, known as scutellum. It is present between the embryo axis and endosperm. The scutellum supplies food from the endosperm to the embryo.
   • Embryo axis: A small rod-shaped embryo axis is present beside the scutellum. The upper part of the embryo axis is known as plumule and the lower part is known as radicle. The plumule is covered with a protective covering known as coleoptile. The covering of the radicle is known as coleorhiza.

Functions Of Different Parts Of A Typical Seed

The function of seed coat:

1. It protects the kernel from the external environment.
2. It helps in the absorption of water and oxygen.
3. It also provides the passage for the germ tube to come out during germination.

Function of cotyledons:

1. They provide nutrition to the embryo and help it to grow.
2. Cotyledon protects the embryo axis.
3. It also holds the embryo tightly.

The function of the embryo axis:

1. It joins the two cotyledons.
2. It helps in the formation of root from the radicle and shoot from the plumule.

Function of endosperm:

1. It provides nutrients to the embryo in the endospermic seed.
2. It helps in the development of the embryo.

Dispersal Of Fruits And Seeds

A plant bears numerous fruits and seeds. If all these fruits or seeds fall and germinate in the same place then all of them will compete with each other for necessary requirements, such as water, minerals, sunlight, etc., for survival.

Thus, they must be dispersed away from the mother plant to avoid overcrowding and unwanted struggle for existence. Fruits and seeds can not move by their own.

So, they depend on different agents such as water, animals, wind, etc., for dispersal. In this regard, they produce varied external outgrowths on bpsis of different dispersal agencies.

Dispersal Of Fruits And Seeds Definition: Seed or fruit dispersal is the process of carrying the seeds or fruits away from the parent plant for proper germination under suitable conditions.

Mechanisms of fruit and seed dispersal

Fruits and seeds are dispersed in various ways.

Dispersal by wind: The fruits or seeds that are dispersed by wind bear certain modified structures. Due to these structures, they can easily carried away by the wind. Some of these structures are discussed below.

Parachute mechanism: Some hairy appendages are found in certain fruits and seeds. These appendages help them to float in the air for a long time. These seeds are dispersed to greater distances.

These are of the following types—

Ucture is formed by the cluster of persistent hairy calyx. Pappi (plural) are present at the upper region of the fruits and help the fruit to float in the air. These are found in Mikania cordata, Helianthus annuus, etc.

Comma: The tuft of hairs is the outgrowth of the testa and is found on both sides of the seed. These tufts help them to float in the air just like a parachute. These are found in Calotropis procera, Alstonia scholaris, etc.

A hairy outgrowth of seeds: In some seeds, long hairy outgrowths develop from the testa and help them to float in the air. These hairy outgrowths are known as lint. These are found in Gossypium herbaceum, Bombax ceiba, etc.

Persistent feathery style: Some seeds contain persistent feathery styles, which help them to float with the wind. These are found in Clematis gouriana.

Balloon-like structure: In some plants, some floral parts become air-filled, swollen, balloon-like structures. These help the seeds to remain in the air for a longer period of time. These modifications are found in Cardiospermum halicacabum (inflated fruit), Physalis minima (inflated persistent calyx), etc.

Light and minute seeds: The seeds of some grasses and orchids are minute and lightweight. So, they can float in air very easily.

Seeds and fruits with wings: Seeds and fruits of many plants have wing-like appendages. They can be easily blown away In the air. Winged fruits are found In Shorea sp., Acer sp., and winged seeds are found In Moringa sp. (drumstick), Cinchona sp.

Censer mechanism: Fruits-like capsules of some plants have minute pores, from which a few seeds are dispersed when are being shaken by air. This mechanism is observed in Papaver somniferum (poppy), and Argemone maxicana.

Dispersal by water: The fruits and seeds of the plants, that grow near water bodies, are mainly dispersed through water. Such fruits and seeds must be provided with a waterproof, salt-resistant coat that will make the fruits and seeds buoyant.

Spongy thalamus: The thalamus of lotus (Nelumbo nucifera) is soft and spongy containing clusters of fruits. This helps the thalamus to remain afloat.

Water current carries it to a certain distance. The thalamus degenerates and the fruits are released. They settle down on the soil at the bottom of the water body and germinate.

Fibrous mesocarp: The fibrous mesocarp of coconut (Cocos nuclfera) fruit can entrap air. Its outer coat Is impermeable to water and keeps the fruit afloat for longer periods. Water current carries it to a certain distance.

Dispersal by animals: Some seeds and fruits are also dispersed by animals, birds, and human beings. There are different methods of fruit and seed dispersal by animals.

Some of these are described below—

Spiny outgrowth or appendages: Hard spiny outgrowths on the outer surface of the fruits are found in some plants such as Aristida sp., Chrysopogon aciculatus, etc. These fruits are attached to the animal’s body by the spiny outgrowths and are dispersed by them.

Hook-like appendages: Hooked appendages are found on the outer surface of the fruits in some plants such as Xanthium strumarium, Aerva aspera, etc. These appendages get anchored to the animal’s fur and are dispersed as the animals go to different places for grazing.

Secretion of sticky juice: Fruits of some plants such as Boerhavia repens, Gynandropsis gynandra, etc., secretes sticky juice from the glands present on their outer surface. This sticky substance helps the fruits to attach to the bodies of the grazing animals and get dispersed with them.

Remains of the food: The fruits of Azadirachta indica, and Ficus benghalensis, are usually eaten by animals and birds. But they cannot digest the seeds, as they have hard testa.

So, these seeds are dispersed through the excreta of animals or birds, many miles away from the place of their origin. In many cases, animals only eat the fleshy part of the fruit and throw away the seeds. Under favorable conditions, these seeds germinate.

Mechanical dispersal of fruits and seeds:

1. The fruits of Oxalis corniculata, Impatiens balsamina burst open suddenly when touched or due to air current and the seeds dispersed far away from the parent plant
2. The fruits of some plants such as Ruellia tuberosa Andrographis paniculate, and burst into two valves when get soaked in rain or dew thereby ejecting the seeds.
3. In Luffa aegyptiaca, a pore develops on the ripe fruits through which the seeds get dispersed out in the outer environment.
4. The fruits of Clitoria ternatea etc., twist after their pericarp bursts open, thus dispersing the seeds.

Semi-Technical Description Of Typical Flowering Plants

The following factors are important to describe a flowering plant—

1. Hierarchical position of the plant,
2. Habit and habitat,
3. The morphological features of root, stem, leaves, flower, fruits, etc.

Some other factors that are also important for describing a flowering plant are discussed below—

Dissection of a flower: A vertical and transverse section of a flower as well as its bud provide the shape of the thalamus and the arrangement of floral whorls on it,

1. Shape and size of the different floral whorls,
2. Adhesion or cohesion between different floral whorls,
3. Type of placentation,
4. The number of ovules in the locules of the ovary.

Floral formula: The representation of the number of floral whorls and their interrelationship by using digits, letters, and various symbols, is known as its floral formula.

By this formula, we get to know about the number of floral whorls, the number of bracts, the position of the floral whorls, the adhesion, and cohesion of different floral whorls, sexuality, and other characteristics of a flower.

Symbols used in floral formula: The following symbols are used in the floral formula—

Floral diagram: The floral diagram is the diagrammatic representation of the number and their relative arrangement of different floral whorls as observed in the transverse section of a flower bud, with respect to the mother axis (stalk of the flower).

Examples of floral formula and floral diagram: A sample floral formula and floral diagram are given below

Floral formula:

Description of the flora! formula:

1. The flower is ebracteate, complete, actinomorphic, and bisexual.
2. Calyx is polysepalous with 4 sepals arranged in two whorls. Hence, 2 sepals are present in each round.
3. The corolla is composed of 4 free petals.
4. There are six stamens, arranged in two whorls, 2 in one whorl and 4 in another.
5. The two groups of stamens may be of different lengths.
6. Gynoecium is bi-carpellary and fused
7. The ovary is superior.

Taxonomic Description Of Some Plants Of Selected Angiospermic Families

Descriptions of some selected angiosperm families are given below along with their economic importance. One member from each family is also described.

Description of Solanaceae Family

Distinguishing Characteristics

1. Plants are mostly terrestrial. Some are aquatic (For example Solanum tampicense).
2. Plants are mostly herbs, some are shrubs, and rarely soft woody trees (For example Solanum grandiflorum). They are either annual or perennial.
3. Plants have a tap root system.
4. Aerial stem is herbaceous or woody, erect or prostrate (For example Solanum surattense), climbing (For example Solanum dulcamara), branched, with solid internodes, hairy or with prickles. The underground stem is tuberous (For example Solanum tuberosum).
5. Leaves are either simple or pinnately compound, exstipulate, entire or incised, petiolate or sessile, alternate or opposite, unicostate type of reticulate venation.
6. The inflorescence is either solitary or axillary cyme helicoid cyme or cymose pannicle.
7. Flowers are bracteate or ebracteate bisexual, actinomorphic or zygomorphic (Example Schizanthus sp., sp.), hypogynous, and pentamerous. Floral whorls are arranged in a tetracyclic pattern.
8. Calyx is made of five, green colored sepals. It is gamosepalous, rotate, tube or bell-shaped, aestivation valvate. Sepals are hairy, persistent, or accresent (Example Physalis sp.).
9. Corolla is usually made of five petals. It is gamapetalous, may have hair, rotate or campanulate or tubular or infundibuliform in shape. Aestivation valvate or imbricate.
10. Stamens are five and epipetalous. Anthers are pithecoid, basifixed, or dorsifixed and dehiscence by an apical pore or longitudinal slit.
11. Gynoecium bicarpellary and syncarpous. Nectarine glands are present at the base. Stigma is bifid or capitate and style is simple and terminally placed. Ovary oblique, superior, bi- or trilocular, placentation axile, ovule numerous.
12. Fruit usually berry, sometimes capsule (Example Datura).
13. Seeds are dicotyledonous and with endosperm.

Economic Importance:

The economic importance of the Solanaceae family is as follows—

1. There are many food-yielding plants belonging to the family Solanaceae. Examples Solanum tuberosum (potato), Solanum melongena (brinjal), Capsicum annum (chilli), Lycopersicum esculentum (tomato), etc.
2. Tobacco is obtained from leaves and branches of Nicotiana tabacum and Nicotiana rustica.
3. Various alkaloids are obtained from Datura stramonium, anoxia, and Hyoscymous niger.
4. Several medicinally important plants belong to this family. Examples are Datura, Withania somnifera, Solanum xanthocarpum, Atropa belladonna (yield atropine), etc.
5. Cestrum nocturnum, Petunia sp., etc are some of the ornamental plants belonging to this family.

Description of a member of the Solanaceae family

Scientific name: Solanum nigrum

Common name: Indian nightshade

Systematic position:

Class—Dicotyledonae

Sub-class—Gamopetalae

Series—Bicarpellatae

Order—Polemoniales

Family—Solanaceae

Genus—Solanum

Species—nigrum

Description of the plant

1. Habit and habitat: Annual, wild herb, that grows mainly in shaded regions.
2. Root: Tap root.
3. Stem: Herbaceous, aerial, erect, cylindrical, hard and branched.
4. Leaves: Simple, exstipulate, unicostate reticulate venation, petiolate, oval-shaped, acute apex, entire leaf margin, smooth leaf surface, and arranged in alternate phyllotaxy.
5. Inflorescence: Cymose, scorpioid, uniparous with 5-8 flowers (rhipidium).
6. Flower: Bracteate, pedicellate, complete, bisexual, actinomorphic, hypogynous, white-colored, valvate aestivation.
7. Calyx: 5 sepals, gamosepalous, persistent
8. Corolla: 5 petals, gamopetalous, white-coloured.
9. Androecium: 5 stamens, polyandrous, epipetalous stamens, basifixed, long filament, dehiscence of anther occurs through terminal pores.
10. Gynoecium: Bicarpellary, syncarpous, obliquely placed superior ovary, thick placenta, containing multiple ovules, axile placentation, elongated pistil, flattened stigma.
11. Fruit: Fleshy, indehiscent, berry type with persistent stalk.
12. Floral formula: 

 

Description of floral formula: Ebr—Ebracteate;

—Actinomorphic flower;

Bisexual, K(5)— 5 Sepals and gamosepalous;

—Epipetalous stamen where the number of petals is 5, gamopetalous, 5 free stamens;

—2 pistils, joined and ovary superior.

Description of Fabaceae family

The description of the Fabaceae family is given below along with its economic importance.

Distinguishing Characters

1. Plants are mostly terrestrial, but some are aquatic (For example Neptunia natans).
2. Plants are mostly herbs, some are shrubs or woody trees. They are either annual or perennial.
3. Most plants have a tap root system. Roots bear nodules which carry symbiotic nitrogen fixing bacteria Rhizobium sp.
4. Stem erect, twinning or climbing, herbaceous or woody, hair may present.
5. Leaves are simple or pinnately compound, alternately arranged, stipulated, leaf base pulvinus, venation reticulate, whole leaf or upper leaflets of the compound leaf may modify into tendrils.
6. Inflorescence was racemose or rarely solitary axillary.
7. Flowers are bracteate or ebracteate, pedicellate or sessile bisexual, complete, zygomorphic, hypogynous or perigynous, cyclic, and pentamerous.
8. Calyx is made of five, green colored sepals. It is either free or gamosepalous, aestivation imbricate, and often persistent.
9. Corolla is usually made of five petals. It is polypetalous and may be papilionaceous (For example Pisum sativum), aestivation imbricate (For example Mimosa pudica), or vexillum (For example Clitoria ternate)
10. The androecium is composed of 10 or more stamens present. Stamens are either free or united (monadelphous or diadelphous), vitreous, and basifixed.
11. Gynoecium monocarpellary. Stigma is simple or capitate. The style is long and flattened. Ovary superior, unilocular, elongated, placentation marginal, with many ovules.
12. Fruit legume or pod, rarely lomentum (Example Desmodium sp.)
13. Seeds are dicotyledonous and non-endospermic.

Economic Importance:

The economic importance of the Fabaceae family is as follows—

1. There are many members of Fabaceae that yield pulses. Examples are Pisum sativum (pea), Cicer arietinum (gram), Lens culinaris (lentil), Vigna radiata (green mung), etc.
2. Green young pods of Dolicos lablab, Vicia faba, etc., are used as vegetables.
3. Glycine max (soybean) and Archls hypogea (groundnut) are important sources of cooking oil. Soybean is used to extract soya milk which Is a substitute for milk.
4. Fibers are obtained from the stem of Crotolaria juncea, and Sesbania bispinosa. These fibers are used to prepare ropes, canvas, mats, etc.
5. Timber is obtained from Delbargia sisso, latifolia, Pterocarpus sp., etc.
6. Roots of Glycyrrhiza glabra (licorice), leaves and seeds of Abrus sp., flowers of Sesbania grandiflora, etc., are known to have different medicinal properties.
7. Different dyes are obtained from plants like Indigofera tinctoria, Pterocarpus santalinus, Sophora japonica, etc.
8. Lathyrus odoratus, Clitoria ternatea, etc., are used as ornamental plants.

Description of a member of the Fabaceae family

Scientific name: Pisum sativum

Common name: Sweet pea

Systematic position:

Class—Dicotyledonae

Sub-class—Polypetalae

Series—Calyciflorae

Order—Rosales

Family—Fabaceae

Genus—Pisum

Species—sativum

Description of the plant

1. Habit and habitat: Annual, climbing herb
2. Root: Branched tap root, nodules present.
3. Stem: Herbaceous, weak, branched, hollow, green colored, climber, glabrous.
4. Leaf: Arranged in alternate phyllotaxy, sessile, foliaceous stipules, compound imparipinnate, leaf apex is transformed into tendrils. Leaves are oval-shaped with unicostate reticulate venation. The entire margin with acute leaf apex.
5. Inflorescence: Racemose or solitary inflorescence.
6. Flower: Bracteate, ebracteolate, pedicellate, bisexual, zygomorphic, complete, cyclic, partially perigynous, variously colored.
7. Calyx: 5 sepals, gamosepalous, valvate aestivation, green-colored, hairy, persistent.
8. Corolla: 5 petals, papilionaceous, vexillary aestivaion.
9. Androecium: Stamens 10, diadelphous, 9 stamens fused to form a sheath around the pistil and the tenth stamen remains free. Anther is dithecous, basifixed.
10. Gynoecium: Monocarpellary, unilocular, superior ovary, marginal placentation with many ovules, style is long and curved, single hairy stigma.
11. Fruit: Legume or pod.
12. Floral formula:
    
    
13. Description of the floral formula: Br—Bracteate; flower; K₍₅₎ -5  sepals, gamosepalous; C_1+2+(2) Corolla consists of one single large petal (standard), two free petals (wings) and two fused petals (keel), A₍₉₎₊₁—9 fused stamen and1 free stamen; G(1)—Monocarpellary, superior ovary.

Description ofLiliaceae family

The description of the Liliaceae family is given below along with its economic importance.

Distinguishing characters

1. Plants are mostly perennial or annual herbs. Some are shrubs (Example Yucca, Dracaena, etc.) or climbers (Example Smilax sp.). Trees are rare (For example, Xanthorhoea sp.).
2. Roots are adventitious, generally, fibrous roots and fasciculated tuberous roots may present (Example Asparagus sp.).
3. Stem aerial or underground. Aerial stems may be erect or climbing. Underground stems may be rhizomes, bulbs or corms. Internodes were solid or fistular. Stem branches may be modified into cladode (Example Aspergus sp.)
4. Leaves are either simple, stipulate or exstipulate, sessile or petiolate with sheathing bases, cauline or cylindrical, alternate, whorled or opposite, leaves may be fleshy and leathery (Example Yucca sp.), or reduced to scales (Example Ruscus sp.), leaf margin may be entire or spiny, venation mostly parallel.
5. The inflorescence may be solitary terminal (For example tulip.), solitary axillary (For example glory lily.), racemose (For example Yucca sp.), panini (For example Asphodelus sp.), or umbel (For example Allium sp.)
6. Flowers are bracteate or ebracteate, bisexual or unisexual, actinomorphic or zygomorphic, hypogynous, incomplete, and trimerous.
7. Perianth is composed of 4-8 tepals, gamophyllous to form a tube or polyphyllous (For example tulip, glory lily, etc.). Tepals are petaloid or sapaloid, arranged in 2 whorls, aestivation valvate or imbricate.
8. The androecium is composed of 3-12 stamens. Stamens polyandrous, monadelphous, arranged in two whorls, antitepalous. Anther basifixed or versatile, bithecous and dehiscence longitudinal or by apical pore.
9. Gynoecium bi- ortricarpellary and syncarpous. Ovary superior, bi- or trilocular, placentation parietal, ovules two or many. Style simple, united, or free. Stigma is often trilobed.
10. Fruits berry (For example Asparagus sp.) or capsule (For example Asphodelus sp.)
11. Seeds are monocotyledonous and endospermic.

Economic Importance:

The economic importance of the Liliaceae family is as follows—

1. Leaves and pedicels of Allium cepa, A. ascolium, tender shoots and roots or Asperagus sp., bulbs of Allium cepa, and A. sativum are used in cooking.
2. Fibers are obtained from leaves of Yucca sp., Agave sp., Phormium sp., etc.
3. Several medicinally important plants belong to this family. Examples are Aloe vera, Smilax sp., Asparagus sp., Gloriosa sp., Colchicum sp., etc.
4. Corms of Colchicum autumnale are used to yield colchicine used to stain chromosomes and to induce polyploidy in organisms.
5. There are many important ornamental plants that belong to this family. Examples Tulipa (tulip), Lilium (tiger lily), Gloriosa (glory lily), etc.

Description of a member of the LlUiaceac family

Scientific name: Allium cepa

Common name: Onion

Systematic position:

Class—Monocotyledonae

Series—Coronarieae

Order—Liliales

Family—Liliaceae

Genus—Allium

Species—cepa

Description of the plant

1. Habit and habitat: Annual, herbs, cultivated plants.
2. Root: Adventitious, fibrous.
3. Shoot: Underground tunicated bulb, disc-like stem is present at the lower portion of the bulb. The floral axis is leafless and known as a scape.
4. Leaf: Leaves bear in whorls, fleshy and scaly leaves arise from small bulbs, aerial leaves green, cylindrical, leaf base, hollow, venation parallel.
5. Inflorescence: Umbel.
6. Flower: Ebracteate, pedicellate, ebracteolate, incomplete, bisexual, white in color, cyclic, trimerous.
7. Perianth: The number of tepals is 6, present in alternately placed two whorls, 3 tepals in each whorl. Tepal is white in color, petaloid.
8. Androecium: Stamens 6, arranged in two whorls. Each whorl contains 3 stamens. The base of the stamens may be free or attached to the perianth. Anther is dithecous.
9. Gynoecium: Tricarpellary and fused, superior ovary, trilocular, axile placentation, each locule bears two ovules, short style, and minute stigma.
10. Fruit: Capsule.
11. Seed: Monocotyledonous endospermic seed.
12. Floral formula:
    
13. Description of floral formula:
    • —Actinomorphic (regular) flower;
    • —bisexual;
    • P₃₊₃—Perianth consists of 6 free tepals, arranged in two whorls, each whorl has 3 tepals;
    • A₃₊₃—6 free stamens, arranged in two whorls;
    • G(3)— Tricarpellary, fused, superior ovary.

Morphology Of Flowering Plants Notes

• Alkaloids: Any of a class of nitrogenous organic compounds of plant origin that have pronounced physiological actions on humans. These may include drugs or poisons.
• Canopy: The upper layer or habitat zone, formed by mature tree crowns and biological organisms (For example epiphytes, lianas, and arboreal animals).
• Definitive nucleus: The diploid nucleus found in the center of the embryo sac, produced after the fusion of the two haploid polar nuclei.
• Epiphyte: A plant that grows harmlessly upon another plant and drives its moisture and nutrients from the air.
• Funiculus: A slender rope-like stalk attaching an ovule to the ovary wall.
• Gynofaasic style: A style that appears to be inserted at the base of the ovary because of the infolding of the ovary wall.
• Hilum: A scar or mark left on a seed coat by the former attachment to the ovary wall or to the funiculus.
• Integuments: A tough outer protective layer of the ovule.
• Line of suture: A fairly rigid joint between two anther lobes, through which anther dehisces.
• Micropyle: A small opening in the surface of an ovule, through which the pollen tube penetrates the ovule.
• Nectaries: A nectar-secreting glandular organ found mainly in flower and also on leaf or stem.
• Staminode: A sterile or abortive stamen, frequently resembling a stamen.

Points To Remember

1. Assimiiatory roots of Tinospora and epiphytic roots of Venda can synthesize food by photosynthesis.
2. The flowering plant that lacks root is called epiposium. Example duckweed.
3. Solanum tuberosum (potato) is a modified stem, but Ipomoea batatus (sweet potato) is a modified root.
4. Asparagus sp. is a diode.
5. A rhizome with weak, horizontal, and longer internodes, is called sobole. Example Cynodon dactylon (durba ghas).
6. When two leaves originate opposite to each other from the same node with a difference in size between them, this condition is called anisophilly. ExampleGoldfussia.
7. The small, flattened ear-like outgrowths that develop from two sides of the junction of leaf base (hypopodium) and leaf lamina (epipodium) in monocot leaves, is called auricle.
8. The epipodium of Dischidia rafflesiana gets modified into a pitcher and stores rainwater. This stored water is utilized later as required. This type of modified leaf is called a water reservoir.
9. Phyllotaxy in Acalypha hispida is of a special type due to its variable length of petiole. This type of phyllotaxy is known as leaf mosaic.
10. The plants in which bisexual flowers, unisexual flowers, and neuter or neutral flowers grow in a single inflorescence, is called polygamous plant. Example mango.
11. Bisexual, incomplete flower is found in Polianthes tuberosa.
12. Coconut sap is the liquid endosperm.
13. The smallest flowering plant is duckweed (Lemna sp.).
14. The smallest flower is Wollfia microscopic.
15. The largest flower is Rafflesia arnoldii.
16. The world’s largest inflorescence is that of Puya Raimondi (about 32ft).
17. The dicotyledonous plant that lacks cotyledon is Cuscuta reflexa.
18. The banana plant is the largest perennial herb.
19. Double fertilization occurs in angiosperms.
20. Growth in width occurs in dicot plants but not in monocot plants.
21. The modified underground stem of potatoes is used as seeds. Underground roots of the stripped gourd is used as plantlets. New plantlets also develop from the stem of rose, berry, etc., and from the leaves of Bryophyllum sp., Begonia sp.
22. The phenomenon of opening of flower buds is called anthesis.
23. The junction point of the flagellum and cotyledon is called the nodal zone.
24. Fleshy scale leaves or cataphylls are present in Allium cepa (onion).
25. When different types of flowers grow in the same plant, then the condition is known as heterophylly. Example Sagittaria sp., Limnophila sp.

 

Biology Class 11 WBCHSE Morphology Of Flowering Plants Some Important Questions And Answers

1. What is the difference between a root cap and a multiple root cap?
Answer: The root cap is single-layered and regenerates again after its disintegration. On the other hand, multiple root caps contain multiple layers of cells but can not be produced again.

2. Is it possible for a plant to absorb minerals and water from the soil, if the root hairs of its primary root get degenerated?
Answer: Yes. This is because root hairs are also present in the branched roots (secondary and tertiary roots). So, after the degeneration of the root hairs of the primary root, the plant can absorb water and minerals through the root hairs of the branched roots.

3. Why is the root hair region of the main root temporary?
Answer: The root hair region of the main root has a definite lifespan. After that, the root hairs degenerate and secondary roots grow from that region.

Read and Learn More WBCHSE Solutions For Class 11 Biology

4. Write about the distribution of roots in a dome-shaped tree.
Answer: The roots of these trees move deep into the soil, Besides these roots, some branch roots are also found near the lower surface of the trunk. The branch roots remain scattered at the base of the trunk to provide mechanical support to the tree.

Class 11 Biology Solutions

5. Name the two functions of the plants that are performed only by the adventitious roots but not by the true roots.
Answer: Reproduction and respiration, are the two functions performed only by the adventitious roots.

6. What type of root is a beetroot? Name the pigment present in this root. Name the substance in which the pigment is soluble.
Answer: Beetroot is a napiform root. The pigment is betacyanin. It is soluble in water.

7. Name the plant, in which photosynthesis occurs through the roots.
Answer: Tinospora sp., and Trapa sp., are the two plants, in which photosynthesis occurs through the roots.

8. Name the plants in which buds are produced by adventitious roots.
Answer: The adventitious roots of Trichosanthes sp., and Dalbergia sp., can produce buds.

9. Write down the characteristics of roots in Orchid-like plants.
Answer:

Orchid-like plants bear two types of roots. They are—

1. Clinging root and
2. Aerial roots. The clinging root helps the plant to remain attached to the support. Aerial roots absorb water vapor from the air. They provide the required amount of water for photosynthesis to the plants.

10. What kind of root is found in sweet potato? Write down a special feature of this root.
Answer: Tuber-like roots are found in sweet potatoes which are known as tuberous roots. Special feature: These roots do not have any definite shape.

11. What do you mean by vegetative and reproductive organs of plants?
Answer: Vegetative organs perform functions other than reproduction. Whereas, reproductive organs take part in sexual reproduction to form new individuals.

Class 11 Biology Solutions

12. Give two examples of rootless plants.
Answer: Wolffia sp., and Utricularia sp.

13. Why do potatoes store a large amount of starch in them?
Answer: Vegetative reproduction in potatoes occurs by the axillary buds. These buds require glucose for their development. This glucose is provided by the starch stored in the potatoes. So, potatoes store a large amount of starch.

14. Why should plants be described morphologically?
Answer: The description of morphological features helps in identifying and assigning any plant to its proper taxonomical hierarchy and nomenclature.

15. What is the difference between the thorns of an Indian stone apple and a rose?
Answer: The thorns of the Indian stone apple are modified part of the aerial stem and develop endogenously. In the case of a rose, the thorns are outgrowths of the stem epidermis and develop exogenously. They are actually prickles.

16. Write down the mode of reproduction in Amorphophallus paeoniifolius (oal) and Zingiber officinale (ginger).
Answer: These two plants reproduce by axillary buds which help in vegetative reproduction. These axillary buds are produced in favorable conditions and gradually develop into new plants.

17. Why do biennial plants require two seasons to complete their life cycle?
Answer: In the first season, these plants germinate from their seeds and attain maturity gradually. In this stage, they produce roots, shoots, etc., (vegetative growth). In the next season, they complete their life cycle by producing flowers and fruits (reproductive growth).

18. Why do the pine and Himalayan Cedar (deodar) become cone-shaped?
Answer: The main axis of these trees grows indefinitely with a racemose branching pattern. The branches of the lower regions are longer than the branches of the upper region. So, these trees appear cone-shaped.

19. Why is an onion known as a shoot-less plant?
Answer: Usually shoot of this plant is not visible. The disc-shaped shoots do not have any aerial region and thus, they are not visible above the ground. The small shoot is not visible clearly even under the soil. So, this plant is known as the shoot-less plant.

20. Name the edible part of the onion.
Answer: The edible part of the onion is mainly the modified, fleshy scale leaves.

Class 11 Biology Solutions

21. How will you identify that the underground part of a plant is a stem?
Answer: The underground part of the plant should not bear any root hair, root cap, or adventitious roots. But it should have a node, internode, axillary bud, apical bud, and scale leaves.

22. Give examples of plants with amplexicaul and semi-amplexicaul leaf bases.
Answer: Amplexicaul: Aethusa cynapium. Semi-amplexicaul: Musa paradisiaca.

23. Name the plant parts that are modified to form the following—thorns of Indian stone apple and Argemone sp.
Answer: Thorns of Indian stone apple: Modified axillary buds.

Thorns in Argemone sp. Modified leaves.

24. When you will find rachis in a leaf?
Answer: The leaf rachis is found in a compound leaf.

25. What are sessile flowers? Give example.
Answer: The flowers without pedicel are known as sessile flowers. Example Polianthes tuberosa.

26. Write down the differences between pome and drupe.
Answer: The differences between pome and drupe are

27. Name the factors responsible for the amount of light absorbed by the leaves.
Answer: The factors are the shape of the leaf, location, and phyllotaxy.

28. Pea plants have foliaceous stipules. Why?
Answer: The leaves of the pea plant are compound pinnate leaves. The upper leaflet of the rachis gets modified into tendrils, hence the number of leaves is reduced. As a result, the rate of photosynthesis as well as the growth rate becomes low. So, in this case, the stipule enlarges and becomes foliaceous. This stipule helps in photosynthesis to overcome the problems.

29. Write about the submerged leaves of this Limnophilla sp.
Answer: The submerged leaves of this plant are linear, narrow, and dissected. These leaves reduce the hydrostatic pressure. They also help in the absorption of oxygen, soluble in water.

Class 11 Biology Solutions

30. What is the basic difference between a simple leaf and a leaflet?
Answer: The axil of the simple leaf bears axillary buds but axillary buds are not found at the axil of leaflets.

31. Write about the modification of the petiole to carry out physiological functions.
Answer: Winged petiole: In some plants such as in Citrus sp., the petioles become broad, like foliar leaves, to carry out the process of photosynthesis. Phyllode: In some plants such as in Acacia sp., the compound leaves shed off in early stages. So, the petioles become broad and flattened to carry out the process of photosynthesis, like the foliage leaves.

32. The flowers of the fig are not visible. Why?
Answer: In Fig, the inner wall of the receptacle contains male, female, and sterile flowers. As the flowers are covered with the receptacle, they are not visible.

33. Identify true fruit and false fruits among the following—paddy, fig, cucumber, lemon, jackfruit.
Answer: True fruits—Cucumber, lemon, and paddy. False fruits—Jackfruit and fig.

34. Mention two points of importance of the floral diagram.
Answer:

Two points of importance are—

1. Floral diagrams provide information about a number of flower parts, fusion among them, etc.
2. It also provides information about the arrangement of floral whorls on the thalamus with respect to the mother axis.

Biology Class 11 WBCHSE Morphology Of Flowering Plants Very Short Answer Type Question

Question 1. What type of roots are present in leguminous plants?
Answer: Nodulated root

Question 2. Write the type of venation in monocotyledonous plants.
Answer: Parallel venation

Question 3. Give an example of tap root, modified to store food.
Answer: Conical root of carrot

Question 4. Name the special tissue present in the aerial roots of orchids.
Answer: Velamen

Question 5. Give two examples of fruits whose seeds are dispersed by explosive mechanism.
Answer: Atidrographis paniculate (kale), Impatiens balsamina (dopant flower)

Question 6. What type of venation is seen in leaves of dicotyledonous plants?
Answer: Reticulate venation

Class 11 Biology WBCHSE

Question 7. Which part of the grapevine modifies into a tendril?
Answer: Terminal end of branches

Question 8. Name the edible part of the orange.
Answer: Juicy hairs developed from endocarp

Question 9. What type of fruit is pomegranate?
Answer: Balausta

Question 10. Give an example of heterogamous capitulum inflorescence.
Answer: Sunflower

Question 11. What is the outermost covering of the seed?
Answer: Testa

Question 12. Give an example of a dicot non-endospermic seed.
Answer: Pea

Question 13. Write two examples in which bilateral cyme inflorescence is seen.
Answer: Dyanthus, Silene

Question 14. Name one cultivated plant which does not bear fruit and seed.
Answer: Sugarcane

Question 15. What types of modifications are observed in the roots of carrots, radishes, and dahlia?
Answer: Conical, napiform, and fasciculated roots respectively

Question 16. Write the floral formula of Solanum nigrum.
Answer: 

Question 17. Name one plant in which chlorophyll is synthesized in its adventitious roots and thus, carry out photosynthesis.
Answer: Trapa, Tinospora

Question 18. Name one flowering insectivorous plant that lacks a root.
Answer: Utricularia

Question 19. What are the different parts of a seed coat?
Answer: Testa and tegmen

Question 20. Which type of leaf possesses stomata mainly on its lower epidermis?
Answer: Generally in the dorsiventral leaf

Question 21. Give two examples of false fruit.
Answer: Apple and pear

Question 22. Write one example of a flowering plant that lacks green leaves.
Answer: Capparis aphylla

Question 23. Which is the edible part of ginger?
Answer: Rhizome of ginger

Question 24. Name the root of Cuscuta sp. that helps the plant to invade the tissue of host plant.
Answer: Haustoria

Question 25. Why do the leaves of Aloe and Agave become fleshy?
Answer: These plants mainly grow in dry and hot places. So, their leaves become fleshy by storing water to resist drought.

Class 11 Biology WBCHSE

Question 26. Why is the calyx of a pea described as gamosepalous?
Answer: In peas, the calyx is gamosepalous because all the sepals remain united.

Question 27. In swampy areas like the Sunderbans in West Bengal, plants bear special kinds of roots called?
Answer: Pneumatophores

Question 28. In aquatic plants like Pistia and Eichornia, leaves and roots are found near________
Answer: Water surface

Question 29. Roots obtain oxygen from air in the soil for respiration. In the absence or deficiency of O₂, root growth is constricted or completely stopped. How do these plants growing in marshlands or swamps obtain the oxygen required for root respiration?
Answer: They respire through pneumatophores

Question 30. Reticulate and parallel venations are characteristics of _________ and __________ respectively.
Answer: Dicotyledons, monocotyledons

Question 31. Write the floral formula of an actinomorphic, bisexual, hypogynous flower with five united sepals, five free petals, five free stamens, and two united carpels with superior ovary and axile placentation.
Answer:

Question 32. An inflorescence is found in a hanging position. Identify and in which plant it is present.
Answer: Catkin, mulberry

Question 33. Coleoptile and coleorhiza are absent in which seeds?
Answer: In dicotyledonous seeds

Question 34. Nimmi ate dal and potato fry for lunch. Name the families, with which these two plants are associated.
Answer: Fabaceae, Solanaceae respectively

Question 35. Name the main parts of a typical leaf.
Answer: Leaf base, petiole, and leaf lamina