Class 11 Biology

Cardiac Output

Cardiac Output Definition: Cardiac output is the volume of blood pumped by each ventricle per minute.

Cardiac output depends on the frequency of heartbeat as well as the volume of blood ejected in one contraction.

It is expressed as minute volume or litres of blood per minute. The usual values of cardiac output for adults when at rest are 5 to 6 L/min or approximately 8% of body weight per minute.

With strenuous activity, an adult’s cardiac output can increase to almost 25 L/min to satisfy the body’s demands for nutrients and oxygen. Cardiac output is a product of heart rate (beats/ minute) and stroke volume.

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The amount of blood pumped by each ventricle with each heartbeat is called stroke volume.

In a healthy adult at resting condition, the stroke volume is 70 ml of blood. Cardiac output is calculated by the formula— Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR) So, the cardiac output is 70 x 72 = 5040 ml min’1 or approximately 5 litres min’1.

The cardiac output represents the volume of blood that is delivered to the body. It is an important factor in the determination of the effectiveness of the heart to deliver blood to the rest of the body.

Cardiac Index And Stroke Volume Index

Normal, resting cardiac output differs among individuals. Therefore, in clinical practice, measured values for cardiac output are often expressed as a flow (L/min) per body surface area (m2) which is called cardiac index.

It is the volume of blood released by each ventricle of the heart per minute to the body surface.

The surface area is estimated from calculations based on body weight and height. Cardiac index normally ranges from 2.6 to 4.2 L/min/m2.

The stroke volume index is the volume of blood released during each heartbeat with respect to the surface area of the body. The average value of stroke volume index in a healthy adult human is 47ml.

In 1870, German physiologist Adolf Fick contrived the first method for measuring cardiac output in animals and human beings.

The basis of this method is called Fick’s principle. This principle states that the amount of any substance received by an organ per unit of time is equal to the arterial level of the substance minus the venous level times the blood flow.

So Blood flow through an Organ In a given time =

Amount of substance removed from or added to blood during the same time period/ A- V difference of concentration of the substance/ml. of blood.

Over the past decades, many methods for cardiac output measurement have been developed like thermodilution method, oesophageal Doppler method, transoesophageal echocardiography, pulse contour cardiac output, lithium dilution cardiac output measurement, etc.

Factors Controlling Cardiac Output

Maintaining and regulating cardiac output is one of the most intricate functions of the circulatory system.

The cardiac output is the product of stroke volume and heart rate. Therefore, factors regulating stroke volume and/or heart rate are able to control it.

The key factors regulating cardiac output are given below—

Sympathetic stimulation: Increased sympathetic stimulation (due to fright, anger, etc.) increases the heart rate. It also increases stroke volume by increasing contractility, which results in a more complete ejection of blood from the heart.

Hence, cardiac output increases which is again brought to normal by increased parasympathetic activity after sympathetic stimulation.

Venous return: Cardiac muscle fibres are stretched by increased blood volume returning to the heart.

Increased stretch results in a greater force of contraction, which increases stroke volume and thereby cardiac output. Decreased venous return decreases cardiac output.

Heart rate: Increased heart rate decreases stroke volume but increases cardiac output. Excessive increase in the heart rate decreases cardiac output.

Myocardial contractility: Increased myocardial contractility results in increased cardiac output.

The strength of the force of myocardial contraction depends on the initial length of cardiac muscle fibres, nutrition and availability of oxygen, concentration of H+ ions, etc.

Peripheral resistance:

• The pressure against which ventricles pump blood is called afterload.
• This is determined by the resistance of arterioles to blood flow, which is called peripheral resistance.
• Increased peripheral resistance will reduce the volume of blood flow through the arteries and will in turn increase afterload.
• This will lower the stroke volume and thereby decrease cardiac output. Thus, peripheral resistance is inversely proportional to cardiac output.

Exercise: Exercise activates the sympathetic nervous system, increasing heart rate and contractility of the myocardium. Both of these actions increase venous return, contributing to increased stroke volume. Hence, cardiac output is increased.

Blood pressure

Blood pressure can be defined as the lateral pressure exerted by the flowing blood on the walls of the blood vessels (especially the arteries).

Types of blood pressure are—

Systolic blood pressure: The peak value of pressure exerted by the blood on the walls of the arteries during ventricular contraction or systole, is known as systolic blood pressure. Normal systolic blood pressure in an adult is in a range of 105-135 mm Hg (average 120 mm Hg) during each cardiac cycle.

Diastolic blood pressure: The minimum pressure exerted by the blood on the walls of the arteries during ventricular relaxation or diastole, is known as diastolic blood pressure. Normal diastolic blood pressure in an adult is about 80mm Hg (60 – 90 mm/Hg).

Pulse pressure: The term pulse refers to the alternating surges of pressure (expansion and then recoil) in an artery that occurs with each contraction and relaxation of the left ventricle. This difference between systolic and diastolic pressure is called pulse pressure.

Normally the pulse pressure is SBP-DBP = (120-80)= 40mm Hg.

Mean arterial pressure: Mean arterial pressure (MAP) is the average pressure during the cardiac cycle. The value of MAP varies at different levels of the circulatory system.

Blood pressure can be measured directly or indirectly

Direct measurement of blood pressure is done by cardiac catheter with the help of a pressure transducer or by putting a needle in an artery and connecting with a pressure transducer or simply a Hg manometer.

Indirect measurement of blood pressure involves auscultatory palpatory or oscillatory method by using a sphygmomanometer.

commonly called a blood pressure cuff, is an instrument used to obtain blood pressure readings by the auscultatory method.

Electrocardiogram [ECG]

Electrocardiogram Definition: The electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart recorded during the cardiac cycle.

Discovery: In 1887, Augustus D Waller recorded the first electrocardiogram. After that in 1903, Willem Einthoven studied the details of ECG and he is known as the father of ECG. After 1930, many advanced forms of ECG have been developed.

Description: The electrical activity of the heart is monitored and recorded on the ECG. The process of recording ECG is known as electrocardiography. An ECG configuration may consist of waves, and intervals recorded as voltage against time. A single waveform begins and ends at the baseline.

Electrocardiograph

Cardiac impulse, generated from the SA node, is transported to all tissues of the heart as electrical impulse via the AV node, a bundle of His, Purkinje fibre, etc., and all over the body through cells and blood.

So, the electrical activity of the heart can be observed by using electrodes at different parts of the body. The instrument used to measure these activities is known as electrocardiograph.

Einthoven’s triangle

During electrocardiography, an imaginary triangle is formed with three limb leads or electrodes (two shoulders and one left leg) by keeping the heart at the centre. This is known as Einthoven’s triangle

Methods of ECG recording: There are various methods for ECG recording. The electrodes that are used for the procedure, are placed in different parts of the body. Generally, there are two types of methods for electrocardiography—unipolar and bipolar ECG methods.

Waves Of Electrocardiogram

The ECG recorded on graph paper is composed of five types of waves— P, Q, R, S and T.

The P wave: The normal cycle of electrical activity in the heart begins with atrial depolarisation and is recorded as the P wave.

The shape of the P wave is usually symmetrical and upright. The normal duration of the P wave is 0.08 to 0.11 seconds.

The QRS complex: The QRS complex represents ventricular depolarization.

The QRS complex consists of three separate waveforms—

Q wave, R wave, and S wave. The first negative deflection (below the baseline) after the P wave is the Q wave.

The next tall positive deflection (above the baseline) is the R wave. The S wave is the small negative deflection (below the baseline) that follows the R wave. Under normal conditions, the duration of the QRS complex is less than 0.10 seconds.

The ST segment: The ST segment represents the time between ventricular depolarization and repolarization.

It begins at the end of the QRS complex (called the J point) and ends at the beginning of the T wave. Normally, it measures 0.12 seconds or less.

The T wave: The T wave represents ventricular repolarization, rest, and recovery. Its duration normally measures 0.20 seconds or less.

T waves are sensitive T indicators for the presence of a number of abnormalities.

The U wave: The U wave follows the T wave and has the same polarity (deflection) as the T wave. Its origin and mechanism are not known. Due to its low voltage, it is usually flat and almost not visible.

The PR interval: The PR interval starts at the beginning of the P wave and ends at the beginning of the QRS complex.

The normal duration of the PR interval is 0.12 to 0.20 seconds. The PR interval represents the total atrial (supraventricular) electrical activity prior to the activation of the bundle of His, ventricular branches, and Purkinje fibre system.

The QT interval: The QT interval is measured from the beginning of the QRS complex to the end of the T wave.

The QT interval represents total ventricular activity. The normal QT interval measures about 0.38 seconds and varies in males and females and with age.

Significance Of ECG

Electrocardiography is an indispensable tool in the diagnosis, prognosis and therapeutic aspect most of cardiac disorders.

From the ECG tracing, the following information can be determined—

1. Heart rate and heart rhythm,
2. Conduction abnormalities,
3. A prior heart attack,
4. Chances of coronary artery disease,
5. Abnormal thickness of heart muscle.

An electrocardiogram captures the electrical activity of the heart, so it can give information about the following conditions—

1. Myocardial Infarction,
2. Re-entry pathways in the electrical system,
3. Location of the heartbeat initiator, types of cardiac arrest (ventricular fibrillation, a systole, etc.) and other different changes in the electrical activity of the heart.

Double Circulation

Double Circulation Definition: When pathways, blood flows through called double the heart circulation.

Double circulation involves the movement of blood through the heart twice during each trip of the body.

The two pathways involved in this area—

Pulmonary circulation (i.e., transportation of blood from the heart to the lungs) and systemic circulation (i.e., transportation of blood from the heart to the rest of the body).

A double circulation must have a three or four-chambered heart. The right side of the heart receives deoxygenated blood from all over the body and pumps it to the lungs.

In the lungs, the blood loses CO₂ and receives O₂. The left side of the heart receives oxygenated blood from the lungs and transports it to all the body parts.

Amphibians, reptiles, birds and mammals have double circulation. Fishes have two-chambered hearts. They have a single circulation pathway.

Mechanism Of Double Circulation

The double circulation in human beings can be divided into— pulmonary circulation and systemic circulation.

Pulmonary Circulation

Pulmonary Circulation Definition: Pulmonary circulation is the movement of blood from the heart to the lungs, and then from the lungs back to the heart again. The pulmonary system begins with the pulmonary trunk and ends in the left atrium.

Pathway of circulation:

The pulmonary trunk originating from the right ventricle, divides into right and left pulmonary arteries which enter the right and left lung respectively.

These pulmonary arteries carry deoxygenated blood and divide into smaller arteries, arterioles and capillaries around the lung alveoli.

After gaseous exchange, oxygenated blood from the alveolar capillaries is carried by four pulmonary veins to the left atrium.

Systemic circulation

Systemic circulation Definition: The circulation, in which blood flows from the left ventricle to the body and again returns to the right atrium is known as systemic circulation.

Pathway of circulation:

The aorta originates from the left ventricle and then forms the arch of the aorta. It moves through the lungs as the dorsal aorta. This dorsal aorta crosses the diaphragm and moves into the abdominal cavity. Here, it is known as the abdominal aorta.

The aorta divides into many branches which form capillaries to supply oxygenated blood to different parts of the body.

The visceral capillaries join together to form venules and veins.

Veins combine together and form two main veins—superior vena cava and inferior vena cava. They drain deoxygenated blood into the right atrium from the visceral capillaries.

Regulation Of Cardiac Activity

Cardiac activity in humans is regulated mainly by—neural control and hormonal control.

Neural control: Neural control of the cardiovascular system involves two nerve centres— the cardioinhibitory centre (located in the medulla oblangata of the brain) and the cardioacceleratory centre (located in the vertebral column).

Parasympathetic nerves in the brain and sympathetic nerves in the spinal cord are involved in this regulation.

Stimulation of parasympathetic nerve fibres originating from the cardioinhibitory centre reduces heart rate and blood pressure. This nerve fibre is known as the vagus nerve or 10th cranial nerve.

This nerve fibre is distributed in the SA node, AV node and atrial muscles. Stimulation of sympathetic nerve fibres originating from the cardio accelerator centre of the spinal cord increases heart rate, blood pressure and contractility of cardiac muscles.

These nerve fibres are distributed in the SA node, AV node and the cardiac muscles.

Baroreceptors are a type of sensory neurons that are excited by the stretch of the blood vessel or increase in blood pressure.

They are present in different parts of the body. Due to their stimulation, the produced nerve impulse moves to the brain through the nerves.

As a result, the impulses from the cardioinhibitory centre come to the heart through the vagus nerve. This, in turn, reduces heart rate.

Hormonal control: Various hormones play a role in the control of the cardiovascular system.

Important sites of hormone secretion include the adrenal medulla, posterior pituitary gland, kidney, and atrium of the heart.

The major hormonal role is played by epinephrine and norepinephrine. Other hormones such as thyroxine, arginine, vasopressin and erythropoietin have some effect on the cardiovascular system.

Atrial muscle cells produce atrial natriuretic peptide which plays an important role in this.

Epinephrine and norepinephrine: When the sympathetic nervous system is activated, the adrenal medulla releases epinephrine (>90%) and norepinephrine (<10%), which circulate in the blood.

Epinephrine and norepinephrine have similar direct effects on the heart, but norepinephrine elicits a powerful baroreceptor reflex because it causes systemic vasoconstriction and increases mean arterial pressure.

Myogenic heart

• A myogenic heart is capable of generating an action potential, depolarization and consequent contraction from within the muscle itself instead of receiving any stimulus from a nerve.
• A healthy heart will perform myogenic rhythms that will allow it to beat 60 to 100 times per minute. Myogenic heart is found in animals like molluscs and vertebrates.

Neurogenic heart

The neurogenic heart refers to the highly specialized muscle cells that require neural input to initiate and maintain contractions. The neurogenic heart is found in animals like annelids and arthropods.

Atrial natriuretic peptide (ANP): Atrial natriuretic peptide is a 28-amino acid polypeptide synthesised and stored in the atrial muscle cells. They are released into the bloodstream when the atria are stretched. It decreases blood volume by increasing sodium excretion.

Other hormones: Thyroxine hormone directly affects the SA node of the heart and increases the heart rate.

Arginine vasopressin (AVP) exerts its major effect on the cardiovascular system by causing the retention of water by the kidneys, which regulates blood volume. Erythropoietin regulates RBC synthesis by stimulating bone marrow.

The decrease in hematocrit stimulates its release, which stimulates RBC synthesis.

Therefore, the increase in plasma volume is balanced with a larger RBC mass.

Disorders Related To Cardiovascular System

There are different types of abnormalities found in the function of the heart and in the circulation of blood.

Hypertension or high blood pressure

Hypertension is a transitory or sustained elevation of both the systemic and pulmonary arterial blood pressure to a level that induces cardiovascular damage.

If the blood pressure lies between 120/80 mm Hg and 139/89 mm Hg, it is called prehypertension (to denote increased risk of hypertension).

A blood pressure of 140/90 mm Hg or above is considered as hypertension.

Cause: Though the exact causes of hypertension are usually unknown, there are several factors including smoking, obesity, lack of physical activity, sedentary lifestyle, etc., which may be responsible for this condition.

Types of hypertension: There are two broad categories of hypertension—

Primary or essential hypertension and Secondary hypertension.

Primary hypertension: It may develop as a result of environmental or genetic causes. It accounts for 90% of the total cases.

It is further divided into two types—

Benign or chronic hypertension: In this condition, blood pressure is usually higher than normal over a long time.

It increases the risk of heart attack, stroke, heart failure, or kidney disease.

Malignant or accelerated hypertension: It is caused by extremely high blood pressure. Immediate medical attention is required in malignant hypertension as it can quickly cause serious damage to the eyes, kidneys and brain.

Causes of malignant hypertension include any form of secondary hypertension, complications of pregnancy, use of cocaine, monoamine oxidase inhibitors (MAOIs), oral contraceptives, etc.

Several diseases such as cerebral oedema, and heart failure can be caused by this condition.

Malignant hypertension can be treated by using medicines such as anti-hypertensive drugs.

Secondary hypertension: High blood related to any other disorder or cause is known as secondary hypertension.

Diabetes, renal disease, renovascular hypertension, Cushing’s syndrome, obesity, and hormonal disorders are some common conditions related to secondary hypertension. Secondary hypertension can also occur during pregnancy.

Effects of hypertension: Most people with high blood pressure have no signs or symptoms. Although a few people with early-stage high blood pressure may experience dull headaches, dizzy spells, etc. Hypertension mainly destroys the heart, kidney, blood vessels and brain.

Effect on heart: Hypertension increases the rate and intensity of the contraction of the heart. This may increase the chances of ventricular hypertrophy and failure. It can also increase the risk of clotting of blood in the lungs and ischemic heart diseases. This affects the circulation of blood and O₂ in the body.

Effect on brain: Hypertension may cause haemorrhage, stroke, paralysis and ultimately death.

Effect on kidney: Hypertension causes high blood pressure in the kidneys. As a result, the renin-angiotensin system activates and ultimately causes kidney failure.

Prevention and treatment:

• This can be mainly prevented by changing lifestyle.
• It can also be prevented by avoiding the consumption of fatty food, cigarettes, alcohol, etc.
• The patient should take anti-hypertensive drugs.

Mainly, two types of medicines are used in case of hypertension—

Vasodilator drugs: These drugs increase the blood flow to the kidneys. This results in the elimination of excess water, thereby reducing blood pressure (by reducing blood volume).

Natriuretic or diuretic drugs: These drugs decrease the absorption of salt and water in the renal tubules and reduce blood pressure.

Hypotension

Abnormally low arterial blood pressure is known as hypotension. For an adult, less than 90 mm Hg systolic pressure and less than 60 mm Hg diastolic pressure describes hypotension.

Hypotension may result in loss of consciousness, nausea, fatigue, lightheadedness, dizziness, abnormalities in blood circulation, etc.

Circulation And Circulatory System

The Physiological process, by which digested food materials, oxygen, etc., are distributed throughout the body and hormones, enzymes, waste products, etc., are taken to their target sites through a particular fluid known as circulation.

The circulatory system is the organ system found in multicellular organisms that are concerned with the circulation of blood and consist of blood vessels and the heart.

Significance of animals do circulation: Multicellular not have most of their cells in contact with the external environment. Hence, they have developed oxygen, important metabolic substances and metabolic wastes. In the circulatory system, a fluid (blood) is driven through tubes (arteries, veins and capillaries) by a muscular pump (heart).

Transportation of useful substances to cells: Circulatory systems transport nutrients, waste products, hormones, respiratory gases, blood cells, antibodies and cells involved in the immune system in order to maintain homeostasis.

Transportation of respiratory gases: Circulation helps in the transportation of respiratory gases between the lungs and all the cells of the body.

When deoxygenated blood passes through the respiratory surfaces of the lungs, gaseous exchange takes place, i.e., carbon dioxide leaves the blood and oxygen enters into the blood.

The oxygen-rich blood goes back to the heart and is pumped from the heart into the blood vessels, that transport blood throughout the body. Oxygen reaches all the cells of the body through blood.

Transportation of excretory substances: It transports all the excretory substances like carbon dioxide, and non-protein nitrogenous waste materials and helps in their elimination from the body.

Transportation of hormones: Some cells synthesise substances like hormones which regulate different metabolic processes. The circulatory system transports these substances to their target cells.

Transportation of nutrients or other materials to storage organs: It helps to transport substances from the site of production to organs where they are stored.

Maintenance of internal equilibrium: It regulates internal temperature and contributes to thermal regulation by distributing heat from heat-producing sites
to areas of the body that cannot keep themselves warm.

Types of circulatory system: Depending upon the type of circulating fluid, there are two types of circulatory system— blood circulatory system and lymphatic system. These are discussed under separate heads.

Blood Circulatory System

The blood circulatory system is of two types—open and closed circulatory system.

Open blood circulatory system

The blood circulatory system in which the heart pumps blood (haemolymph) Into the Haemocoel (body cavity) So That Blood Directly Bathes The Living Cells, Is Called an Open Blood Circulatory System.

Examples: Open circulatory systems are found in animals such as arthropods, molluscs, and some other invertebrate groups.

Advantages of an open circulatory system:

1. Direct exchange of gases, nutrients, and waste products takes place between the living cells of the organiser Hence, less amount of energy is required.
2. Animals with an open circulatory system (with the exception of insects that carry out gaseous exchange independently from the circulation) are generally slower and have a low metabolic rate.
3. Blood pressure remains low.

Disadvantage of open circulatory system

This system is not very effective, because fluid is pumped under low pressure, so it circulates slower than in a closed circulatory system.

Closed Blood Circulatory System

The circulatory system in which the heart pumps the blood in the vessels, is called a closed blood circulatory system.

Lymphatic system

The lymphatic system is a network of tubular vessels or ducts and nodes through which lymph flows.

The lymphatic system is made up of the following structures—

Lymphatic capillaries: Lymphatic capillaries are tube-like structures. They have thin walls made of only a single layer of endothelial cells resting on a basement membrane.

They are closed at one end (blind end). They remain interwoven with blood capillaries but are not connected to them. They are wider than blood capillaries.

The lumens of these capillaries are filled with lymph and walls are permeable to interstitial fluid constituents, including protein Lymph vessels or lymph ducts Lymphatic capillaries join to form lymphatic vessels.

These vessels are structurally similar to the cardiovascular veins, though they have thinner walls and more valves. These valves prevent the backward flow of lymph as lymph flows toward the thoracic cavity.

Smaller lymphatic vessels unite to form larger lymphatic vessels. These larger vessels unite to form the two main lymphatic vessels or trunks.

They are called the thoracic duct and the right lymphatic duct.

The thoracic duct receives lymph from the entire body The thoracic duct receives lymph from the entire body The thoracic duct receives lymph from the entire body lymphatic duct.

This duct joins to the left subclavian vein near the left side of the heart. The right lymphatic duct is present on the right side of the thoracic region. It collects lymph from the right hand, throat and thorax.

This duct opens into the right subclavian vein Cistema chyli: A small, dilated sac found near the lower area of the thoracic duct in the lumbar region of the body is called the cistema chyli or receptaculum chyli. It is part of the lymphatic system into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow.

Lymph glands or lymph nodes: The lymph nodes are small bean-shaped structures that look like tiny bulbs and are found at intervals along the lymph vessels. They are masses of collagen and elastin fibres surrounded by a capsule made of fibrous tissue.

The afferent lymphatic vessels enter and efferent lymphatic vessels leave the lymphatic nodes.

Lymph nodes are especially abundant in specific regions such as armpits, neck and groins.

Axillary nodes, intercostal nodes, and inguinal nodes are some of the lymphatic nodes.

Besides these, some other glands such as the spleen, tonsils, etc., also consist of lymphatic tissues. The spleen is considered to be the largest lymphatic gland in the human body

Function Of Lymph Nodes

1. Lymph nodes filter different foreign particles such as bacteria, etc., from the lymph.
2. Lymphocytes are produced from the lymphoid cells present in the lymph glands. These lymphocytes are transported to the blood vessels through lymphatic vessels. They develop the immunity power of the body by producing antibodies.
3. Several antitoxins and antibiotics are produced from lymph nodes. These substances destroy the toxins that enter our body.

Spleen

1. It is the largest lymph gland present in our body. Some part of it is composed of lymphoid tissues.
2. It is located between the diaphragm and the fundus region of the stomach.

Function of spleen

1. Spleen is the graveyard of RBCs. The worn-out RBCs are phagocytised by the macrophages present in the spleen.
2. It works as a blood reservoir as it can store some amount of RBCs during rest.
3. Lymphocytes originate in the spleen.
4. It produces antibodies and antitoxins.

 

Lymph

Lymph Definition: The transparent, colourless or pale yellow tissue fluid that contains white blood cells (particularly modified lymphocytes) is called lymph.

This fluid circulates throughout the lymphatic system and returns to the venous blood by the thoracic and right lymphatic ducts. It transfers materials from blood to the body cells and vice versa.

Origin: In arteries, blood flows at a higher pressure than in veins. Due to this, blood plasma filters out from the arterial capillaries and moves into the intercellular space to form interstitial fluid.

This fluid contains water, glucose, amino acids, oxygen, carbon dioxide and several other electrolytes.

The exchange of different substances between blood and cells takes place via interstitial fluid.

Hence, its composition changes continuously. Some of this fluid is reabsorbed by the blood capillaries but most of it enters the lymph capillaries.

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This fluid collected inside the lymph capillaries is called lymph. At the time of formation, lymph is a clear watery liquid which has the same composition as that of interstitial fluid.

Composition Of Lymph

Lymph have a similar composition to blood plasma. Depending on the destination, lymph contains different concentrations of lymphocytes, proteins and fats. It has a large number of leucocytes (mostly lymphocytes) ranging from 500-75000/mm3. The lymph does not contain platelets.

The non-cellular portion of lymph contains water (94%) and solids (6%). The organic components of lymph include various proteins, fats, glucose and other non-protein nitrogenous substances urea, creatinine, enzymes, etc.).

Total protein content varies with the region from which the lymph drains. In fasting conditions fat content is low but after a fatty diet, it becomes higher. Inorganic components such as calcium, phosphorus, and chlorides are also present in lymph.

Functions Of Lymph

Transportation: Lymph is modified interstitial fluid, that is drained from the tissue and moved back to the circulatory system via the lymphatic network.

The lymphatic network transports important materials such as vitamins, digested food components, O₂ etc., in the body. They also take away the waste products such as CO₂, nitrogenous and non-nitrogenous wastes, etc., from the cells.

Removal of excess tissue fluid: Lymph returns protein and excess interstitial fluid to peripheral circulation.

Absorption: There are several small finger-like projections present on the inner wall of the small intestine, known as villi. Each of these villus consists of a lymphatic vessel, known as lacteal. Lacteal absorbs the digested fat and transports it to the bloodstream.

Disease prevention: The lymphatic system helps the body fight against diseases as the system contains a high concentration of lymphocytes in lymph nodes. The invading microorganisms and foreign particles are destroyed in the lymph nodes.

Human Circulatory System

The human circulatory system consists of the muscular heart, the network of blood vessels and blood. Blood is the circulating fluid which flows through the blood vessels after being pumped by the heart.

Types: Two types of circulatory systems are found in human beings— blood and lymphatic systems.

Heart

The heart is the main organ of the circulatory system. In vertebrates, it is located on the ventral side of the oesophagus. The human heart is more complex and the Function of lymph nodes advanced as compared to other organisms.

Heart Definition: A multi-chambered muscular organ, that pumps blood throughout the body in a rhythmic process, is known as the heart.

Location: The heart is situated in between the lungs in the middle of the thoracic cavity, slightly tilted to the left. The heart rests on the superior surface of the diaphragm, posterior to the sternum.

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Shape and size: The size of the heart is closely related to the size of the organism’s body.

The base of the heart is broad and flat, about 9 cm in breadth. The length of the heart of an adult is about 10-12 cm. Externally, the heart appears as a cone-shaped structure.

Shape and size: The size of the heart is closely related to the size of the organism’s body.

The base of the heart is broad and flat, about 9 cm in breadth. The length of the heart of an adult is about 10-12 cm. Externally, the heart appears as a cone-shaped structure

Wall of the heart

The wall of the heart is composed of the following layers—

Pericardium: The heart is enclosed in a double-layered sac, called pericardium. It is the fibrous outer wall made of dense connective tissue.

The pericardium is further divided into two layers —

Fibrous pericardium: It is the outer fibrous transparent sac that covers the heart.

Serous pericardium: The inner side of the pericardium is formed of a serous layer and is known as serous pericardium.

This serous pericardium is again divided into two layers, the inner layer—visceral pericardium and the outer layer—the parietal pericardium.

Visceral Pericardium: This layer is also called the epicardium. It is the innermost layer of the pericardium. It is composed of a single sheet of squamous epithelial cells overlying delicate connective tissue. This layer adheres to the heart.

Parietal Pericardium: This layer lies between the visceral pericardium and the fibrous pericardium.

The pericardial cavity lies between the visceral pericardium and the parietal pericardium. This cavity is filled with pericardial fluid which serves as a shock absorber and reduces friction between the pericardial membranes.

The primary function of the pericardium is to—

1. Protect The Heart
2. Anchor The Heart To The Surrounding Structures, Such As The Diaphragm And The Great Vessels; And
3. Prevent The Heart From Overfilling.

Myocardium: The myocardium is a thick contractile layer present just below the visceral pericardium.

It is composed of muscle cells, known as myocardiocytes. This layer is more thick in the ventricles than in the atria. This layer of the left ventricle is thicker than the right ventricle.

Endocardium: The endocardium is the innermost layer of the heart wall and lines the heart’s chambers.

It is made of squamous epithelium that rests on a thin connective tissue layer. It is continuous with the endothelium of the great blood vessels—the inferior and superior vena cava.

Chambers Of The Heart

The heart is a hollow, four-chambered, muscular organ that consists of the upper right and left atria (singular: atrium) and the lower right and left ventricles.

The atria are separated by a thin muscular wall called the interatrial septum and the ventricles are separated by a thick muscular wall called the interventricular septum.

There is a translucent, depression present in the septum between the right and left atrium, known as fossa ovalis. In the embryonic stage, there is an opening in place of the fossa ovalis.

It is known as foramen ovale. The heart actually functions as two separate pumps.

The right atrium and ventricle act as one pump to propel deoxygenated blood to the lungs. At the same time, the left atrium and ventricle act as another pump to propel oxygenated blood collected from the lungs towards the heart throughout the systemic circulation.

The right atrium and right ventricle: The inner surfaces of both atria are mostly smooth except for a low network of muscular ridges called musculi pectinati. The right atrium receives deoxygenated blood through the openings of the superior vena cava, inferior vena cava & coronary sinus.

The right atrium is connected to the right ventricle through an opening, known as the right atrioventricular orifice or aperture.

The right atrioventricular orifice is guarded by the right atrioventricular valve or tricuspid (formed of three flaps or cusps) valve.

This valve regulates unidirectional blood flow from the right atrium to the right ventricle and prevents the backflow of blood.

There are numerous muscular ridges on the inner wall of the right ventricle, known as columnae carneae.

They contain some finger-like muscular projections, known as papillary muscles. The cusps or leaflets of the tricuspid valve are attached to the wall of the right ventricle by strong, elastic threads, known as chordae tendineae. The opening and closing of the tricuspid valve are controlled by the papillary muscles through the chordae tendineae.

The pulmonary artery originates from the right ventricle. There is a seminular valve present at the juncture of the pulmonary artery and right ventricle.

Left atrium and left ventricle: The left atrium and left ventricle are also connected to each other through an opening known as the left atrioventricular orifice or aperture.

The left atrioventricular orifice is guarded by the bicuspid (formed of two cusps) or mitral valve.

The left atrium receives four pulmonary veins, two from the left and two from the right lung.

These pulmonary veins bring oxygenated blood from the lungs. They do not have any valve to regulate the blood flow. Blood flows obliquely from the atrium to the ventricle which is regulated by the mitral valve.

The left ventricle which is larger than the right ventricle, has much thicker walls. Like the right ventricle, it also possesses columnae carneae and papillary muscles. Chordae tendineae are also seen.

The lower part of the left ventricle receives blood from the left atrium. The upper part, which has mainly fibrous walls, is termed the aortic vestibule, and it ends in the aorta, the largest artery of the body.

The junction of the vestibule and aorta contains dense fibrous tissue that encircles the aortic valve and is continuous with the cardiac skeleton.

Cardiac grooves

• All the different chambers of the heart are separated from each other by grooves. These grooves are known as cardiac grooves.
• The left and right atria are separated from each other by an interatrial groove. Atria and ventricles are separated from each other by the coronary sulcus or atrioventricular groove.
• The grooves by which two ventricles are separated from each other are known as anterior interventricular sulcus and posterior interventricular sulcus.

Junctional Tissues Of Heart

Junctional Tissues Of Heart Definition: The tissues of the cardiac muscles, responsible for the origin and conduction of cardiac impulses (waves of electric potential generated by stimulation of cardiac muscles by specific stimulus), are known as junctional tissues of the heart.

Junctional Tissues Of Heart Types:

1. Sino-atrial (SA) Node,
2. Atrioventricular (AV) node,
3. Bundle of His,
4. Purkinje fibres,
5. Internodal tract.
6. Sinoatrial (SA) node

Location: Situated on the right wall of the right atrium, near the entrance of the superior vena cava.

Characteristics: The SA node is a small mass of muscle tissue, about 3.0 mm in width.

Function: This is known as the “Natural Pacemaker” or heartbeat regulator. It initiates impulses automatically at a more rapid rate than any other
part of the conduction system.

Its rate of discharge of impulses determines the rate of heartbeat. The electrical signal spreads out over the walls of the atria, causing them to contract.

Atrioventricuiar (AV) node

Location: It is located in the right posterior portion of the interatrial septum.

Characteristics: Muscles of AV nodes are cardiac muscle fibres. It contains a very small amount of myofibrils.

AV muscle fibres are comparatively smaller than the SA node. The AV node and the conduction tissue surrounding it are known as the AV junctional tissue.

The AV node is also called the ‘reserve pacemaker of heart’ because during functional inactivity of the SA node, it can initiate heartbeats, but at a slower rate.

Function: The action potential spreading through the right atrium causes depolarization of the AV node.

When the impulses reach the AV node, there is a slight delay that allows the atria to finish their contraction before the ventricles begin their contraction.

The AV node then conducts impulses to the muscles of the ventricles through a bundle of His and Purkinje fibres.

Bundle of His and its branches

Location: It is a band of nerve fibres that originates from the posterior part of the AV node, and then passes along the interventricular septum to the ventricles.

Characteristics: A Swiss physician, Wilhelm His, first described this tissue. It divides into right and left branches which proceed along the right and left sides of the interventricular septum to the tips of the two ventricles. It is also called an AV bundle.

Function: These specialised fibres conduct the impulses at a very rapid velocity (about 2 m/sec). The bundle of His constitute the only electrical link between the atria and the ventricles.

Purkinje fibres

Location: The Purkinje fibres, named after their discoverer Johannes von Purkinje, are the tree-like terminal branchings of right and left bundles of His.

Characteristics: Cells of these fibres consist of high amount of glycogen-containing sarcoplasm. There are thousands of myofibrils present around the cells.

Function: Purkinje fibres conduct the impulses at high velocity (about 4 m/sec) throughout the ventricles. During the ventricular contraction, they carry the impulses from both the left and right branches of the bundle of His to the myocardium of the ventricle.

Internodal tract

Location: These are located between the SA node and the AV node.

Characteristics: There are three internodal tracts connecting the SA node and AV node—the anterior tract of Bachman, a middle tract of Wenckebach and the posterior tract of Thorel.

Function: Their main function is to carry impulses from the SA node through the right atrium to the AV node.

As the impulses pass along the internodal tracts, the right atrium contracts, pushing the blood it contains, through the tricuspid valve into the right ventricle.

Myocardial tissue has four main characteristics that integrate the heart’s electrical and mechanical activity

Automaticity: It is the ability to initiate an impulse or stimulus. The pacemaker cells (SA node) of the cardiac conduction system spontaneously depolarize in the absence of external stimulation. The AV-junctional tissue and the His-Purkinje network also possess the property of automaticity.

Excitability: It is the ability to respond to an impulse or stimulus. The cells are electrically irritable because of an ionic imbalance across the cell membranes.

Cells thus respond to external stimuli from chemical, mechanical or electrical sources. Atrial and ventricular myocardial fibres respond to the impulse generated by the pacemaker cells of the cardiac conduction system by depolarization and repolarization.

Conductivity: It is the ability to transmit impulses to other areas of the heart. Cells of the conduction system and the myocardial muscle fibres, both have this property.

Contractility: It is the ability of cardiac muscles to shorten, responding to stimuli with mechanical action. Myocardial fibres respond mechanically to electrical stimulation by contracting.

The course of circulation of blood through the human heart The circulation of blood through the human heart occurs through periodic systole and diastole.

They are discussed below—

Atrial diastole: This is the relaxation time of both the atria. During this time deoxygenated blood enters into the right atrium through superior and inferior vena cava and oxygenated blood from the lungs enters into the left atrium through pulmonary veins.

The mixing of the blood is prevented due to the presence of an interatrial septum between the atria.

Auricular or atrial systole: This is contraction time for both atria. The deoxygenated and oxygenated blood move from the right and left atria respectively to the corresponding ventricles.

The tricuspid and bicuspid valves present at the atrioventricular grooves open to guide the flow of blood.

Ventricular diastole: This is the relaxation time of the ventricles. During this time, the left ventricle receives oxygenated blood from the left atrium and the right ventricle receives deoxygenated blood from the right atrium.

Ventricular systole: It is the time for contraction of both the ventricles. The deoxygenated blood in the right ventricle flows to the lungs through the pulmonary artery.

The oxygenated blood from the left ventricle flows to different parts of the body through the aorta.

The bicuspid and tricuspid valves close during this time and prevent the backflow of the blood to the atria. At the same time the semilunar valves open and guide the blood flow to the respective blood vessels and prevent the backflow of the blood to the ventricles.

Erythropoietin

It is a glycoprotein hormone which controls erythropoiesis. It is produced in the interstitial fibroblast cells closely associated with peritubular capillary and proximal convoluted tubule in the kidney (90%), liver and other organiser:

Rouleaux formation

Sometimes RBCs are stacked on each other and form a structure like stacked dinner plates. This condition is known as rouleaux formation.

These stacked structures can move easily through broad blood vessels but cannot move through narrow blood vessels, and sometimes become barriers in blood circulation.

Site of rupture: After completing their lifespan, RBC rupture in the liver and spleen. The spleen is known as the graveyard of RBC.

Haemolysis and fate of RBCs: At the end of their lifespan, the plasma membrane of the RBC ruptures and releases their content including haemoglobin in the surrounding fluid. This process is known as haemolysis.

Functions of RBC: These are as follows—

Transportation of O₂ and CO₂: RBCs collect oxygen from the lungs and release it to the cells and tissues.

They take up carbon dioxide from the cells and tissues and release it to the lungs.

Haemoglobin found in the red blood cells helps in the transport of oxygen and carbon dioxide between the lungs and the cells.

Regulation of acid-base balance: Haemoglobin present in RBC acts as a buffer and regulates the carbonate ion concentration.

Regulation of viscosity of blood: RBCs help to regulate the viscosity of the blood.

Maintenance of ionic balance: In the RBCs, carbon dioxide either binds to haemoglobin or reacts with water.

In reaction with water, it produces carbonic acid, which when dissociates, produces hydrogen ions. The deoxygenated haemoglobin is a stronger base and is capable of taking up these hydrogen ions. Hence, they are buffered by haemoglobin.

Other functions: RBCs carry the blood group antigens and Rh factor.

Erythrocyte sedimentation rate (ESR) The erythrocyte sedimentation rate (ESR) is the rate at which red blood cells settle down in a tube containing blood under standardized conditions and is a measure of inflammation or abnormal proteins in the body.

ESR commonly increases with any condition that gives rise to inflammation, such as infection, arthritis, or cancer.

It plays a very important role in the detection of any disease. According to the Wintrobe method, the normal ESR value is 0-9mm/h for males and 0-20mm/h for female

Haemoglobin: The red, oxygen-carrying, iron-containing pigment, comprising of a haem group and globin protein, that is found in the red blood cells of vertebrates is called haemoglobin.

Structure of haemoglobin: Haemoglobin (Hb) is a molecule made up of four subunits. Each subunit contains a haem moiety conjugated to a polypeptide. There are two pairs of polypeptides in each haemoglobin molecule.

Haem is an iron-containing porphyrin derivative. The polypeptides are collectively referred to as globin.

Instruments for measuring haemoglobin

The concentration of haemoglobin can be measured by using different instruments and methods. This includes Helden’s haemoglobinometer and Gauhar’s haemoglobinometer. Nowadays, a spectrophotometer is used to measure the concentration of haemoglobin.

RBC ghost

After hypotonic haemolysis of RBCs, all the cytoplasm along with the haemoglobin comes out from the cells. If these cells are observed under a microscope, then a spectrin-rich endoskeleton is found in these cells. These cells are known as RBC ghosts.

Location: Haemoglobin is found in the RBCs of human beings and other vertebrates.

Types: Normally there are two types of haemoglobin found in human beings, these include HbA and HbF.

HbA: HbA (Adult haemoglobin) is found in adult human beings. It has 2 alpha and 2 beta polypeptide chains and comprises 97% of normal adult haemoglobin.

HbA is again of two types: HbA₂ and HbA₂ The globin portion of HbA-! consists of four polypeptide chains—2ar chains and 2/3 chains.

Each chain contains 141 amino acid molecules. Each chain contains 146 amino acid molecules.

Thus, HbA is designated as α2δ2. Not all the haemoglobin in the blood of normal adults is HbA HbA₂ consists of two a and two 6 chains.

Thus, HbA2 is designated as α2δ2. The β chains also contain 146 amino acid molecules, but 10 individual residues differ from those in the chains.

About 98% of the total haemoglobin in adults is HbAi and 2-2.5% is HbA₂.

HbF: HbF is normal foetal haemoglobin. It has 2 alpha and 2 gamma polypeptide chains mainly found in the embryonic stage.

Variants of normal haemoglobin are formed when there are genetic changes in the globin genes.

Amount: The amount of haemoglobin present in 100 ml of blood is 14-17g in healthy adult males and 12-16g in healthy adult females.

Chemical nature: Haemoglobin is formed of iron-containing pigment haem (4%) and globin protein (96%). Haem consists of Fe²⁺ or ferrous ions in the centre of heterocyclic organic compounds, called porphyrins.

The molecular weight of haemoglobin is 68000 Da.

Fate of haemoglobin: Old RBCs are destroyed by the macrophages. Breakdown of haemoglobin occurs by the action of the enzyme haem oxygenase.

This generates haem and globin molecules. The haem is then converted to bilirubin and biliverdin. These pigments get released in the bile. The iron group of the haem portion is reused in the formation of haemoglobin.

Functions of haemoglobin: The functions of haemoglobin are discussed below.

Helps to transport respiratory gases: During respiration in vertebrates and in higher animals, the inhaled oxygen combines with haemoglobin to form oxyhaemoglobin. This oxyhaemoglobin moves through blood capillaries and reaches the tissues.

Similarly, the carbon dioxide produced in the tissues combines with haemoglobin and form carbaminohaemoglobin, which reaches the alveoli of the lungs through the blood capillaries.

In this way, haemoglobin helps in the transportation of oxygen and carbon dioxide.

Maintains the acid-base balance in blood: Haemoglobin acts as a buffer and maintains the acid-base balance of the body.

Produces pigment materials: The haemoglobin found in dead RBCs forms pigments such as biliverdin, bilirubin, sercobilinogen, etc.

These give colour to the faeces. Haemoglobin also produces the pigment urochrome, which gives a straw colour to the urine.

White Blood Corpuscle or Leucocyte or WBC

White Blood Corpuscle or Leucocyte or WBC Definition: White blood cells (WBCs) are colourless nucleated blood cells which lack haemoglobin and participate in reactions against invading pathogens or foreign particles in the body.

Structural characteristics:

1. WBC do not contain any pigment so, they are colourless.
2. They contain cytoplasm and a persistent nucleus. The cytoplasm of WBC can be granular or smooth (agranular). The nucleus can be of different shapes, such as spherical, kidney-shaped, etc.
3. All the white blood cells are capable of amoeboid movement.
4. WBCs are rich in nucleoprotein. Their cytoplasm consists of lipids, glycogen, cholesterol, vitamin C and different enzymes.
5. Mitochondria, Golgi apparatus and other organelles are present in the cytoplasm of WBCs.

Size: WBCs do not have a fixed diameter. Their average diameter is 8-18 pm.

Lifespan: The average lifespan of WBC is 1-15 days.

Number: The total WBC count is normally about 4,000 – 11,000 per mm3 of blood.

Origin of WBC: WBC originates in bone marrow, spleen and lymph nodes. White blood cells are produced from pluripotent haemopoietic stem cells—myeloblast, lymphoblast and monoblast.

Types: Depending on the presence and absence of granules in the cytoplasm, WBCs are categorised into two main groups— Granulocytes (including neutrophils, eosinophils and basophils) and Agranulocytes (including lymphocytes and monocytes).

This classification depends on whether granules can be distinguished in their cytoplasm using a light microscope and conventional staining methods. WBCs can also be divided into two broad groups—the phagocytes and the immunocytes.

Granulocytes, which include three types of cells— neutrophils, eosinophils and basophils, together with monocytes comprise the phagocytes.

The lymphocytes, their precursor cells and plasma cells make up the immunocyte population. The types of WBCs (granulocytes and agranulocytes) are discussed under separate heads.

Granulocytes: The white blood cells that contain granules in their cytoplasm are known as granulocytes.

According to the characteristics of granules, granulocytes are categorised into three types— neutrophil, eosinophil and basophil.

The granulocytes have lobed nuclei which have varying shapes from cell to cell. Hence granulocytes are also known as polymorphonuclear leucocytes.

Neutrophil: The granular WBCs which can be stained with neutral stain are called neutrophils.

Structural features:

The cytoplasm of the neutrophils consists of numerous granules and they can be stained with neutral stain. They get stained with both basic (methylene blue) and acidic (eosin) dyes. Hence, they appear purple in colour.

• The nucleus appears purple due to staining and is divided into two to five segments or lobes.
• The lobes are divided into two to five segments or lobes.
• The lobes are connected by a thin strand or filament of nuclear material,

Neutrophils have 3 types of granules—

• Azurophilic or primary granules,
• Specific or secondary granules,
• Gelatinase-containing granules or tertiary granules.

Diameter: 10-12 pm

Lifespan: A few hours to a few days (2-4 days).

Number: Neutrophils are the most abundant type of WBCs in our body. They make up 50-70% of the total amount of WBCs. There are about 3000-6000 neutrophils present per mm3 of blood.

Functions: Neutrophils act as the first line of defence against pathogens. They are motile and phagocytic (destroy damaged tissues). They contain enzymes like protease, elastase, metalloproteinase, NADPH oxidase and antibody-like substances, defensins.

These antimicrobial peptides are active against bacteria and fungi. They secrete Platelet Aggregation Factor (PAF) which accelerates the aggregation of platelets at the injured site of blood vessels.

Reasons for the increase in the neutrophil count

The following reasons are responsible for the increase in the neutrophil count—

1. Infection,
2. Destruction of cells and tissues due to burns, myocardial infarction, etc., © leukaemia,
3. Excess smoking, taking contraceptive pills, etc.

Eosinophil: The granulated WBCs where the granules can be stained with acidic dye (eosin) are known as eosinophils.

1. Structural features:
   1. Usually, eosinophils have a bilobed nucleus. The cytoplasm is packed with large, coarse, retractile, orange-red granules containing histamine. The granules are referred to as eosinophilic because they take up the acidic dye, eosin.
   2. Eosinophils are produced in the bone marrow and circulate in the bloodstream for about 6 hours before migrating to the tissues.
2. Diameter: 10-12 pm
3. Lifespan: A few days (8-12 days).
4. Number: There are 150-300 eosinophils per mm3 of blood. They constitute about 1-4% of the total WBCs.
5. Functions:
   1. Eosinophils respond to chemotactic stimuli and are phagocytic. They can kill ingested organisms,
   2. Eosinophils also take part in allergic reactions. They also produce histaminase and aryl sulphatase B. These are the enzymes that inactivate two inflammatory agents released by mast cells,
   3. Eosinophils take part in dissolving blood clots in blood vessels.

Basophil: The granular WBCs where the granules are stained with basic dyes (methylene blue) are known as basophils.

1. Structural features:
   1. The nucleus of basophil is 2-3 lobed. The cytoplasm has fewer number of coarse granules,
   2. The granules are called basophilic because they take up basic stains (such as methylene blue). Upon staining the granules take up bluish purple color against pale blue cytoplasm.
2. Diameter: 8-10 pm.
3. Lifespan: 12-15 days.
4. Number: They are the rarest type of white blood cell, making up only 0.4% of the total white blood cells, found in a blood smear. 0-100 basophils are present per mm3 of blood.
5. Functions: They have a role in allergic and inflammatory responses.

Basophil granules release some important substances such as—

1. Proteases: Exaggerate inflammation,
2. Hyaluronic acid: Necessary for deposition of ground substances in the basement membrane,
3. Heparin: Prevents intravascular blood clotting,
4. Histamine: Mediate’s acute hypersensitivity reaction—vascular changes, increased capillary permeability
5. Serotonin: Acts as vasoconstrictor.

Agranulocytes: The white blood cells that do not have any granules in their cytoplasm are known as agranulocytes.

Agranulocytes are mainly of two types—

1. Monocytes and
2. Lymphocytes.

Monocyte: The large agranulated cells, capable of phagocytosis are known as monocytes.

1. Structural features:
   1. Monocytes are amoeboid in appearance. The nucleus is round or oval-shaped when cells are young.
   2. But as they grow older, the nucleus becomes convoluted, kidney-shaped or horse-shoe-shaped.
   3. The cells have a large amount of dear non-granular cytoplasm, maybe, with vacuoles in it.
   4. These cells are mainly formed in the bone marrow.
2. Diameter: About 16 – 18 pm in diameter.
3. Lifespan: About 2-4 days.
4. Number: 300-600 monocytes per mm3 of blood.
5. Functions:
   1. Monocytes in the circulation are precursors of tissue macrophages that are actively phagocytic.
   2. Monocytes circulate in the blood for 1-3 days and then migrate to body tissues, where they transform into macrophages.
   3. They destroy dead cells and bacteria by the process of phagocytosis,
   4. They secrete some signalling proteins like interleukin 1 (IL-1), which increase the body temperature during infections and help in the production of T-lymphocytes.

Lymphocyte: The granulated white blood cells which produce antibodies are known as lymphocytes.

1. Structural features:
   1. Lymphocytes form an essential component of the immune system and are derived from haemopoietic stem cells.
   2. On the basis of nuclear size, the lymphocytes are of two types. These are—
      1. Small lymphocytes: These are more common in normal blood. They have a large, dense, round nucleus which occupies the major portion of the cell.
      2. Large lymphocyte: The nucleus may be round and indented. The cytoplasm is basophilic and thicker than that of the small lymphocyte and forms a wider zone around the nucleus.
2. Diameter: A small lymphocyte is slightly larger than a red blood cell and the diameter is about 7.5pm. The diameter of large lymphocytes is about 12 p.m.
3. Lifespan: About 2-3 days.
4. Number: These are the second most common WBC (25-35%), and are easy to find in blood smears 1500-4000 lymphocytes are present per mm3 of blood.
5. Functions:
   1. They produce immunoglobulins or antibodies,
   2. Lymphocytes are mainly concerned with the production and transport of antibodies and they take an active part in the response to a wide range of antigens,
   3. They attack viruses, cancer cells, etc.
   4. Certain lymphocytes are part of the generalised response of the innate immune system, responding quickly to threats. Others act against specific pathogens or infected cells and are part of the adaptive immune response,
   5. Lymphocytes of the adaptive immune system are specific to a particular antigen—substances foreign to the body

General functions of WBCs

1. Destruction of germs: The neutrophils and monocytes destroy the ingested pathogens and foreign materials by phagocytosis. They help to protect the body from harmful agents.
2. Production of antibodies: The lymphocytes increase the defensive mechanism of the body by producing antibodies.
3. Prevention of allergies: Eosinophils play an important role in allergic reactions by producing histamine.
4. Secretion of heparin: Basophils prevent intravascular blood coagulation by secreting heparin.
5. Trephone production: From plasma proteins, the monocytes produce a chemical substance, known as trephone. It provides nourishment to the tissues.

Thrombocyte Or Platelet

Definition: Platelets or thrombocytes are small, granulated and anucleated blood corpuscles, which are involved in blood clotting. (Greek. Thrombos= lump or clot and cyta= vessel; the word cute is derived from it and used to name these cells)

Platelets are membrane-bound fragments of cells that form when larger cells in the bone marrow break apart. Platelets do not contain nuclei and help in coagulation and clotting of blood at the wound.

Structural features:

1. Platelets are actually not true cells but merely circulating fragments of cells.
2. They are non-nucleated, round or oval, plate or disc-shaped structures, which is the reason behind their nomenclature.
3. Platelets are formed from the terminal end of the pseudopodia of megakaryocytes (large bone marrow cells will lobed nuclei).
4. They are surrounded by selectively permeable membranes.
5. They appear somewhat smaller in the microscope. This is because their cytoplasm is divided into two zones—an outer hyalomere, which hardly stains, and an inner granulomere, which contains granules, that appear bluish in colour when stained.

Size: The mean diameter of platelets varies in different individuals, ranging from approximately 2-4 m.

Lifespan: These break down in the blood within 7 to 10 days after their formation.

Number: The platelet count in the circulating blood is normally between 2,00,000 and 5,00,000 per mm3 of blood. Newborn babies have a slightly lower level of platelets, which normally attain the adult range within three months from birth.

Functions: These are as follows—

Blood clotting and coagulation: Platelets play a key role in blood clotting, which prevents excessive blood loss after an injury.

Storage of important biomolecules: Platelets also act as the storage for several substances, including serotonin, epinephrine, histamine, and thromboxane and also help in their transportation.

Repairing of wounds: Upon activation, they release specific molecules which initiate constriction of local blood vessels, which facilitates clot formation.

 

• The Living World
  • The Living World Notes
• Biological Classification
  • Classification System Of Living Organisms Notes
  • Archaebacteria Characteristics and Types Notes
  • Biological Classification Important Notes
• Plant Kingdom
  • Algae – Definition, Characteristics, Types Notes
  • Chlorophyceae – Definition, Distribution and Characteristics Notes
  • Red Algae General Characteristics Notes
  • Bryophyta -Definition and Characteristics Notes
  • Characteristics And Classification Of Gymnosperms
  • Plant Kingdom – Classification and Characteristics Notes
• Animal Kingdom
  • Animal Kingdom Notes
• Structural Organisation in Plants and Animals
  • Types And Functions Of Epithelial Tissues Notes
  • Endothelium Definition and Function Notes
  • Glandular Epithelium – Definition, Structure and Functions Notes
  • Muscular Tissue – Structure, Functions and Types Notes
  • Nervous Tissue – Characteristics, Structure, Function Notes
  • Number Of Longitudinal Tracheal Trunks In Cockroach Notes
  • Haemocytes In Insects Notes
  • Morphology Anatomy Of An Insect Cockroach Notes
  • Structural Organization In Animals Notes
• Morphology of Flowering Plants
  • Plant Stem – Structure and Functions Notes
  • Root System – Roots, Types of Roots and Functions of Roots Notes
  • Morphology of Leaf – Structure, Types, Parts & Modifications
  • Bud – About, Types, Example Notes
  • Phyllotaxy Notes
  • What Is Aestivation ? Describe Various Types Of Aestivation
  • Morphology Of Flowering Plants Notes
• Anatomy of Flowering Plants
  • Shoot Apex Notes
  • Permanent Tissue Notes
  • Anatomy Of Flowering Plants Notes
• Cell:Structure and Function
  • Cell Cycle And Cell Division Notes
• Cell – The Unit of Life
  • Nucleoplasm – Function, Components Notes
  • Erythopoietin Notes
  • Human Circulatory System Notes
  • Lymph Notes
  • Cardiac Output Notes

• Diversity of Living Organisms
  • Biological Classification Multiple Choice Question and Answers
  • Plant Kingdom Multiple Choice Question and Answers
  • Animal Kingdom Multiple Choice Question and Answers
• Structural Organisation in Plants and Animals
  • Morphology of Flowering Plants Multiple Choice Question and Answers
  • Anatomy of Flowering Plants Multiple Choice Question and Answers
• Cell:Structure and Function
  • Biomolecules Multiple Question and Answers
  • Cell Cycle and Cell Division Multiple Choice Question and Answers
• Plant Physiology
  • Transport in Plants Multiple Question and Answers
  • Photosynthesis in Higher Plants Multiple Choice Question and Answers
  • Respiration in Plants Multiple Choice Question and Answers
  • Plant Growth and Development Multiple Choice Question and Answers
• Human Physiology
  • Digestion and Absorption Multiple Choice Question and Answers
  • Breathing and Exchange of Gases Multiple Choice Question and Answers
  • Body Fluids and Circulation Multiple Choice Question and Answers
  • Excretory Products and Their Elimination Multiple Choice Question and Answers
  • Neural Control And Coordination Multiple Choice Questions And Answer
  • Chemical Coordination Multiple Choice Question And Answers

Biology Class 11 WBCHSE Structural Organisation In Animals Question And Answers

Question 1. What are animal tissues?
Answer: The cells in an animal body which are identical in structure, origin and function, organise to form animal tissues.

Question 2. What is histology?
Answer: The branch of science that deals with the structure, origin, function, variation etc., of tissues is called histology.

Question 3. Name the four main tissues in an animal body. State the embryonic origin of these tissues.
Answer: The four main animal tissues are—epithelial tissue, connective tissue, muscular tissue and nervous tissue.

The embryonic origin of these tissues is—

1. Epithelial tissue—ectoderm, endoderm, mesoderm
2. Connective tissue—mesoderm
3. Muscular tissue—mesoderm
4. Nervous tissue—ectoderm.

Question 4. Which tissue lacks blood vessels?
Answer: Epithelial tissue lacks blood vessels. The cells of epithelium obtain nutrition and other necessary substances through diffusion from the intercellular fluid.

Read and Learn More WBCHSE Solutions For Class 11 Biology

Question 5. What is a brush border?
Answer: In most cases, the free surface of epithelial tissue folds to form tiny finger-like structures which are known as microvilli.

Class 11 Biology Solutions

The epithelium that is lined by microvilli appears like a brush and so is called a brush border.

Question 6. Which chemical constituent is secreted by goblet cells?
Answer: Goblet Cell Mainly Sexreates Mucin.

Question 7. Compare the secretion process of holocrine, apocrine and merocrine glands.
Answer:

Question 8. What are the main parts of connective tissue?
Answer: The main components of connective tissue are- cells, matrix and fibres. Besides, blood vessels are associated with connective tissue. gill

Question 9. Name some immune cells of connective tissue.
Answer: Macrophages, mast cells etc., are some immune cells of connective tissue.

Question 10. What fibres are present in areolar connective tissue?
Answer: Two types of fibres are seen in areolar connective tissue

White fibres: Collagen-containing, white, unbranched, thick fibres.

Yellow fibres: Elastin-containing, yellow, branched, thin fibres.

Question 11. Name three main cartilages.
Answer: Three main cartilages are—hyaline cartilage, fibrous cartilage and elastic cartilage.

Question 12. What are red and white muscles?
Answer: Mammals have two types of striated/skeletal muscles—red muscles and white muscles.

Class 11 Biology Solutions

Myoglobin containing red-coloured, slow-contracting muscles are called red muscles. These muscles work slowly for a long time without getting fatigued. Example muscles of the back.

Myoglobin lacking pale-coloured, fast-contracting muscles are called white muscles. These muscles work fast for a short time. Example muscles of eye orbit.

Question 13. Why is skeletal muscle called striated?
Answer: Skeletal muscle fibres have alternate light and dark bands. So, skeletal muscle is called striated muscle.

Actually, the parts of the muscle fibres that have more actin protein appear dark. Again, the parts of the muscle fibres that have more myosin protein appear light.

Question 14. Which contractile protein fibres are present in striated muscles?
Answer: Striated muscle has two contractile protein fibres— thin fibres or actin fibres and thick fibres or myosin fibres.

Question 15. Name the neuroglial cells of the nervous system,
Answer: The neuroglial cells are—oligodendrocytes, astrocytes, microglia and ependymal cells.

Question 16. What are the divisions in each body segment of a cockroach?
Answer: Each body segment of a cockroach has four chitinous parts—tergum (dorsal), sternum (ventral), and pleurite (two lateral parts).

Question 17. What is elytra?
Answer: A pair of chitinous wings that originate from the j dorsal surface of the mesothorax is called elytra. It helps the cockroach to change direction.

Question 18. State the position of crop and gizzard.
Answer: In cockroaches, the crop is located at the posterior part of the alimentary canal and gizzard is located next to the crop.

Question 19. Name the parts of the mouth of a cockroach.
Answer: The parts of the mouth of a cockroach are- maxillae (1 pair), mandible (1 pair), labium, labrum, and hypopharynx.

Question 20. Why isn’t a respiratory pigment present in cockroaches?
Answer: Cockroaches lack any respiratory pigment. It is because atmospheric air enters the body through spiracles and is directly transported to tissues through the trachea and tracheoles. So, it does not require any pigment.

Question 21. What type of metamorphosis occurs in cockroaches? What is the name of the moulting hormone?
Answer: Metamorphosis in cockroaches is of hemimetabolous type and the moulting hormone is ecdysone.

Question 22. What are Ostia? Mention their function.
Answer: Ostia: Openings in the lateral surface of each cavity of the heart in cockroaches are called ostia. These are covered by valves.

Function: Valves allow the flow of haemolymph from the pericardium to the heart through the ostia but prevent its backflow.

Class 11 Biology Solutions

Question 23. What are alary muscles?
Answer: These are a kind of muscles, located on both sides of the heart of a cockroach. They help the heart to contract and relax. Cockroach possesses 12 pairs of alary muscles.

Question 24. What is the collateral gland?
Answer: The branched gland present within the fat bodies in the ovariole of female cockroaches is called the collateral gland. The secretions from this gland form ootheca.

Question 25. What is hepatic caecae?
Answer: The eight fine tubules present at the junction of the gizzard and mesenteron are called hepatic caecae.

The frontal end of these tubules is closed and the distal ends open into the alimentary canal. Digestive juices are secreted by these glands.

Biology Class 11 WBCHSE Structural Organisation In Animals Multiple Choice Questions

Question 1. Which type of tissue correctly matches its location?

Answer: 4.

Question 2. Which of the following features is not present in Periplaneta americana?

1. Indeterminate and radial cleavage during embryonic development
2. Metamerically segmented body
3. Schizocoelom as body cavity
4. Exoskeleton composed of N-acetylglucosamine

Answer: 1. Indeterminate and radial cleavage during embryonic development

Question 3. The body cells in cockroaches discharge their nitrogenous waste in the haemolymph mainly in the form of—

1. Calcium carbonate
2. Ammonia
3. Potassium urate
4. Urea

Answer: 3. Potassium urate

Question 4. Choose the correctly matched pair—

1. The inner lining of salivary ducts—ciliated epithelium
2. The moist surface of the buccal cavity—glandular
3. Epithelium
4. Tubular parts of nephrons—cuboidal epithelium
5. The inner surface of bronchioles—squamous epithelium

Answer: 3. Tubular parts of nephrons—cuboidal epithelium

Class 11 Biology Solutions

Question 5. Choose the correctly matched pair—

1. Tendon—Specialised connective tissue
2. Adipose tissue—Dense connective tissue
3. Areolar tissue—Loose connective tissue
4. Cartilage—Loose connective tissue

Answer: 4. Cartilage—Loose connective tissue

Question 6. The inner surface of the bronchi, bronchioles and fallopian tubes are lined by—

1. Cuboidal epithelium
2. Columnar epithelium
3. Squamous epithelium
4. Ciliated epithelium

Answer: 4. Ciliated epithelium

Question 7. What type of cartilaginous tissue is found in the intervertebral discs?

1. Costal cartilage
2. Hyaline cartilage
3. White fibrous cartilage
4. Yellow elastic cartilage

Answer: 3. White fibrous cartilage

Question 8. The lining of intestine and kidneys in humans is—

1. Keratinised
2. Brush border
3. Ciliated
4. None of these

Answer: 2. Brush border

Question 9. The vagina, oesophagus, and urethra contain which type of tissue?

1. Stratified squamous epithelium
2. Simple squamous epithelium
3. Ciliated epithelium
4. Columnar epithelium

Answer: 1. Stratified squamous epithelium

Class 11 Biology Solutions

Question 10. The inner lining of the ducts of sweat glands and pancreatic duct is formed by this epithelium—

1. Stratified cuboidal
2. Stratified non-keratinised squamous
3. Transitional
4. Pseudostratified

Answer: 1. Stratified cuboidal

Question 11. Dense regular connective tissue is present in—

1. Ligament and tendons
2. The joint capsule and Wharton’s jelly
3. Periosteum and endosteum
4. Pericardium and heart valves

Answer: 1. Ligament and tendons

Question 12. The structural unit of bone is—

1. Chondrin
2. Cyton
3. Osteon
4. Ossein

Answer: 3. Osteon

Question 13. Read the following statements and choose the correct answer—

1. Gap junctions cement adjacent cells together.
2. Areolar tissue contains fibroblasts, macrophages and mast cells.
3. Tight junctions facilitate the cells to communicate with each other.
4. Adhering junctions helps to stop substances from leaking across tissues.
5. Cells of connective tissue except blood secrete fibres of structural proteins called elastin,

Choose the Correct Option

1. 1, 2 and 3 only are incorrect
2. 2, 3 and 4 only are incorrect
3. 3 and 5 only are incorrect
4. 1, 2 and 5 only are incorrect
5. 2, 4 and 5 are incorrect

Answer: 1. 1, 2 and 3 only are incorrect

Class 11 Biology Solutions

Question 14. Which of the following is not a sensory structure in cockroaches?

1. Antennae
2. Eyes
3. Anal cerci
4. Maxillary palps
5. Proventriculus

Answer: 5. Proventriculus

Question 15. Choose the wrongly matched pair regarding the position of reproductive structure in earthworms.

1. Testes—10th and 11th segments
2. Spermatheca—6th and 9th segments
3. Male genital pore—9th segment
4. Ovaries—Intersegmental septum of 12th and 13th segments

Answer: 3. Male genital pore—9th segment

Question 16. Female genital pore—14th segment In cockroaches, arthrodial membrane—

1. Forms the hind wings
2. Covers the compound eyes
3. Forms the hypopharynx
4. Forms the tegmina
5. Joins the sclerites

Answer: 5. Joins the sclerites

Question 17. Which of the following animals has enucleated erythrocytes?

1. Earthworm
2. Sepia
3. Frog
4. Rat

Answer: 4. Rat

Question 18. The outer covering of cartilage is called—

1. Peritoneum
2. Periosteum
3. Endosteum
4. Perichondrium

Answer: 4. Perichondrium

Question 19. Bone marrow is absent in—

1. Reptiles
2. Amphibians
3. Fishes
4. Birds

Answer: 4. Birds

Class 11 Biology Solutions

Question 20. Debove’s membrane is a layer of—

1. Muscular tissue
2. Epithelial tissue
3. Connective tissue
4. All of these

Answer: 3. Connective tissue

Question 21. Cardiac muscle is found in—

1. Pericardium
2. Endocardium
3. Myocardium
4. Peritoneum

Answer: 3. Myocardium

Question 22. The H-zone in skeletal muscle fibre is due to—

1. The absence of myofibrils in the central portion of a band
2. The central gap between myosin filaments in the a-band
3. The central gap between actin filaments extending through myosin filaments in the a-band
4. Extension of myosin filaments in the central portion of the a-band

Answer: 3. The central gap between actin filaments extending through myosin filaments in the a-band

Class 11 Biology WBCHSE Structural Organisation In Animals Short Answer Type Questions

Question 1. What is a basement membrane?
Answer: The layer of collagenous fibres present between the upper epithelial layer and lower subepithelial loose connective tissue is called the basement membrane.

Question 2. What is epithelial tissue?
Answer: The animal tissue which forms the covering of the body and the inner and outer walls of some organs is called the epithelial tissue.

Question 3. What is germinal epithelium?
Answer: The epithelial tissue that helps in the formation of gametes and lines the testis and ovary is called germinal epithelium.

Question 4. What is endocardium?
Answer: The squamous epithelium in the inner wall of the heart is called endocardium.

Question 5. What are the cellular components of blood?
Answer: The cellular components of blood are red blood corpuscles (RBCs), white blood corpuscles (WBCs) and blood platelets.

Question 6. What type of tissue occurs in hairs, nails and horns?
Answer: Stratified cornified squamous epithelial tissue {occurs in hairs, nails and horns.

Question 7. Which is the hardest structure in our body?
Answer: Bone is the hardest structure in our body.

Question 8. State the function of Malphighian tubules,
Answer: Malpighian tubules are the main excretory organs of cockroaches. They collect excretory substances from body fluid and transport them to the alimentary canal.

Question 9. What is endothelium?
Answer: All tissue on the inner wall of blood vessels and lymphatic vessels is called endothelium.

Question 10. What is glandular tissue?
Answer: The epithelial tissue that takes part in secretory functions is called glandular tissue.

Question 11. What is a mixed gland? Give an example.
Answer: The glands which are constituted of both endocrine and exocrine components are called mixed glands. For example, the pancreas is a mixed gland.

Question 12. What do you mean by synapse?
Answer: The junction between the axon of one neuron and the dendron of another neuron where neurotransmitters are released is called a synapse.

Question 13. Mention the main function of epithelial tissue.
Answer: The main function of epithelial tissue is to provide protection from injuries.

Question 14. What is a bipolar neuron?
Answer: The neuron which has one dendron and one axon extending from the cyton is called a bipolar neuron.

Question 15. What is astrocyte?
Answer: Supporting cells of the peripheral nervous system that provide nutrition to a neuron are called astrocytes.

Question 16. What is myosin?
Answer: The contractile protein of myofilaments in muscles is called myosin.

Question 17. What is a sarcomere?
Answer: The contractile unit of muscles is known as sarcomere.

Question 18. Name one plasma protein.
Answer: y-globulin protein is a plasma protein.

Question 19. Mention the name of the contractile proteins of the muscles.
Answer: Actin and myosin are the contractile proteins in the muscles.

Question 20. Mention the function of adipose cells.
Answer: Adipose cell stores fat and provides insulation to the body, thereby preventing loss of heat.

Class 11 Biology WBCHSE

Question 21. What is a neurilemma?
Answer: The outermost covering made up of Schwann cells, that surrounds the axon is called neurilemma.

Question 22. What is an intercalated disc?
Answer: Sarcolemma of the cardiac muscle fibre is thickened at intervals to form plate or disc-like structures called intercalated discs.
They appear as dark lines that separate the individual cardiac muscle cells from one another.

Question 23. Mention the scientific name of the American cockroach.
Answer: The scientific name of the American cockroach is Periplaneta americana.

Question 24. Mention the phylum and class of cockroaches.
Answer: Cockroach belongs to the phylum Arthropoda and class Insecta.

Question 25. What role is played by the gizzard of cockroach?
Answer: Gizzard contains chitinous teeth which cut and chum the food into pieces.

Question 26. How many spiracles are found in a cockroach?
Answer: 10 pairs of spiracles are found in cockroaches.

Question 27. Name the different mouth parts of the cockroach.
Answer: The labrum, mandible, maxillae, labium and hypopharynx are the mouth parts of cockroaches.

Question 28. How many segments are found in the thorax of a cockroach?
Answer: Three segments are present in the thorax of the cockroach.

Question 29. How many segments are present in the abdomen of a cockroach?
Answer: Ten segments are present in the abdomen of cockroaches.

Question 30. Name the different digestive glands of cockroaches.
Answer: The digestive glands of cockroaches are salivary gland, glandular cells of midgut epithelium and hepatic caecae.

Question 31. What is the function of the mandible of a cockroach?
Answer: The mandible acts as the palate and helps in chewing, crushing and grinding the food.

Question 32. How many segments are there in the leg of cockroach?
Answer: The leg of the cockroach has five segments.

Question 33. What do you mean by haemocoel?
Answer: The haemolymph-filled body cavity of a cockroach is called a haemocoel.

Class 11 Biology WBCHSE

Question 34. What is anal style?
Answer: The paired appendages articulated with a ninth abdominal segment of male cockroaches are called anal style.

Question 35. Where are the sclerites present in cockroaches?
Answer: Sclerites are present in the exoskeleton of cockroaches.

Question 36. Which mouth part of the cockroach is comparable to our tongue?
Answer: The Hypopharynx of cockroaches is comparable to the human tongue.

Question 37. What is the use of crops of cockroach?
Answer: Crop stores food for cockroaches.

Question 38. How many sinuses are found in cockroaches?
Answer: Three sinuses are present in cockroaches. They are dorsal, middle and ventral sinuses.

Question 39. A muscular fibre tapers at both ends and does not show striations. Name the muscle fibre.
Answer: Smooth or non-striated muscle fibres taper at both ends and do not show striations.

Question 40. How does a gap junction facilitate the intercellular communication?
Answer: Gap junction connects adjacent cells through the cytoplasm and thus allows cellular communication.

Question 41. Justify the name ‘pseudostratified epithelium’.
Answer: In the case of pseudostratified epithelium, all tire cells touch the basement membrane but may or may not reach the free surface.

The nuclei of these cells are arranged in different planes. As a result, they seem to form several layers, giving a pseudostratified appearance.

• Diversity of Living Organisms
  • The Living World Question and Answers
  • Biological Classification Question and Answers
  • Plant Kingdom Question and Answers
  • Animal Kingdom Question and Answers
• Structural Organisation in Plants and Animals
  • Morphology of Flowering Plants Question and Answers
  • Anatomy of Flowering Plants Question and Answers
  • Structural Organisation in Animals Question and Answers

• Cell:Structure and Function
  • Cell – The Unit of Life Question and Answers
  • Biomolecules Question and Answers
  • Cell Cycle and Cell Division Question and Answers
• Plant Physiology
  • Transport in Plants Question and Answers
  • Mineral Nutrition Question and Answers
  • Photosynthesis in Higher Plants Question and Answers
  • Respiration in Plants Question and Answers
  • Plant Growth and Development Question and Answers
• Human Physiology
  • Digestion and Absorption Question and Answers
  • Breathing and Exchange of Gases Question and Answers
  • Body Fluids and Circulation Question and Answers
  • Excretory Products and Their Elimination Question and Answer
  • Locomotion And Movement Question And Answers
  • Neural Control And Coordination Questions And Answer
  • Chemical Coordination Question And Answers

 

The Living World

What Is Living?

• The living world, that we see around us, has a large amount of variety. It includes different types of animals, plants, and microorganisms, that live in varied habitats such as mountains, lakes, oceans, forests etc.
• A roaring tiger, a flying bird, or a blooming flower, all of them are so different yet they are parts of the same living world! Such an extent of diversity makes us wonder— what is life? Let us find out what it is.
• What is life? Can it be defined? It is very difficult to define life. Life may be regarded as a property of living things which distinguishes them from non-living things,  Again, scientists have tried to define life on the basis of a  number of characteristic features. These features include metabolism, reproduction, etc.
• Anything that exhibits these characteristics is called living. There are several unanswered questions about life. For example, how did life originate? Which species was the first to originate on Earth? Hence, there is ample scope for research in this field. The branch of science which studies all the aspects of life is called life science or biology.

Read and Learn More: WBCHSE Notes for Class 11 Biology

• The history of biology traces the study of the living world from ancient to modern times. Biological sciences emerged from traditional disciplines of medicine and J natural history, dating back to the works of Aristotle and Galen in ancient Greece.
• The term ‘biology’ in its modern f sense appears to have been introduced independently by Thomas Beddoes (in 1799), and Kar Friedrich Burdach (in  Life originated on earth from non-living matter. These non-living matters include the different inorganic elements. Simple organic molecules are formed from these inorganic elements.
• For example, when inorganic elements C, H, N, and O combine, they form organic compounds such as amino acids, nucleotides, etc. These were organised into larger molecules like proteins, nucleic acids, etc. Gradually, through these molecules, life came into existence. Life originated on earth, probably around 3.8 to 4 billion years ago.
• The origin of life had been discussed in Rig Veda, Manu Samhita, Agni Purana, and other Indian texts about 3000-3500 years ago. Charak, the principal contributor to the ancient science of ayurveda, tried to define life.
• Attempts to define life were also made by great European scholars like Aristotle and Darwin. In general, life is considered a unique and complex organization of molecules, ions, and even cells. It manifests itself through various characteristics such as growth, development, metabolism, and reproduction.

Characteristics of living organisms:

The major characteristics of living organisms are as follows—

Growth and development: 

1. Growth is a; fundamental characteristic of all living organisms. A single-celled zygote grows into a multicellular organism, Multicellular organisms show growth through repeated cell divisions.
2. Growth can be characterized by increase in mass and number of cells in an organism. Cell increases in mass due to the aggregation of protoplasmic I material in them.
3. In plants, growth takes place throughout their life, but in animals, it occurs up to a certain age.
4. Development is a post-zygotic phase in  which an organism expresses itself through cell division, cell differentiation, and cell rearrangement.
5. Non-living things do not show growth and development. They may also increase in size due to the deposition of materials on their surfaces. This is known as accretion. This is seen in case of sand dunes in desert. They grow in size due to the deposition of sand.

 Differences between growth and development:

Shape and size:

1. The shape and size of the organisms are determined by their genes.
2. Organisms are either macroscopic or microscopic. Macroscopic organisms can be observed through the naked eye. In nature, microscopic- organisms can be observed only through a microscope. Microscopic organisms are much more in number than the macroscopic ones.
3. A young organism grows into an adult. An adult organism does not show non-living things, on the other hand, remains same in shape and size.
4. Giant sequoia (redwood tree) is the world’s largest tree and the largest living organism by volume. They grow to an average height of 50-95m and are over 17 m in diameter.

Reproduction:

1. Reproduction is the process by which an organism produces its young ones. It is one of the unique characteristics of the living organisms. By this process, an organism can transmit hereditary traits or characters to its subsequent generations.
2. Reproduction may be vegetative, asexual and sexual.
3. Vegetative reproduction is usually found in plants.
4. Most plants and animals reproduce through asexual or sexual methods.
5. Non-living things cannot reproduce.

Metabolism:

1. Metabolism is an important characteristic of living organisms.
2. The body of each living organism is constituted of different chemical compounds. A large number of chemical reactions take place in the living cells. These reactions are known as biochemical reactions.
3. All such chemical reactions, that occur in an organism, are collectively known as metabolism. This process helps to generate energy within a living body.
4. Sun is the ultimate source of energy on earth. Green plants can harvest solar energy and convert it into chemical energy, in the form of food through a process called photosynthesis. Herbivorous animals or herbivores feed on these green plants and acquire energy. Carnivorous animals or carnivores get their energy by feeding on the herbivores.
5. This energy is also required for other processes like transport, growth, etc., in living organisms.
6. Metabolism is of two types—anabolism and catabolism.
7. Through anabolism, the living cell synthesises complex organic biomolecules from simple inorganic or organic raw materials at the expense of energy. Consequently, the dry weight of the cell or organism (i.e., weight after removal of all of its water content) increases. These anabolic processes include processes like photosynthesis, protein synthesis from amino acids, nucleic acid synthesis, etc.
8. Through catabolism, large and complex molecules break up into simpler components, mainly to liberate energy. As a consequence, the dry weight of the cell or organism decreases. An important example of catabolism is respiration, in which food matters break up to release energy, C02 and H20.

Differences between anabolism and catabolism:

Organisation

Cellular organisation:

1. Every living body is made up of microscopic structures called cells. It is the structural and functional unit of. a living organism.
2. Each cell contains a jelly-like substance called protoplasm.
3. The protoplasm of a cell contains a globular body called the nucleus, that regulates all activities of the cell. The part of the protoplasm surrounding the nucleus is the cytoplasm. It contains cell organelles.
4. The protoplasm of a cell is enclosed by a membrane known as the cell membrane.
5. The activity of a cell depends on the structure and function of the protoplasm.
6. The cell as well as protoplasm is absent in non-living things.

Structural organisation:

1. The body of an organism may be unicellular to multicellular.
2. In unicellular organisms, all biological functions are performed by a single cell.
3. In multicellular organisms, a cell is the structural and functional unit. Groups of cells are organised to form tissues. Tissues are further organised into an organ and several organs collectively constitute an organ system.
4. An external stimulus and the response to it, both occur in the form of a signal. These signals pass through each part of the body. There is a system within the body, that changes one form of signal to the other. This is called a signal transducing system.

Consciousness:

1. Consciousness refers to the ability to sense the external environment and to respond to environmental stimuli.
2. There are continuous interactions between an organism and its environment. The environment sends different external stimuli to the organism, who in turn responds to those stimuli.
3. The ability to generate a response to such stimuli is called sensitivity.
4. The degree of response varies from one organism to another.
5. It is observed in both plants and animals. E.g., Mimosa pudica is a seismonastic (sensitive to touch) plant. In this plant, the leaves droop in response to wind, vibration or touch. Rapid closing of eyes in response to high light intensity is another example of sensitivity.
6. Non-living things neither show sensitivity nor respond to stimuli.

Apart from these major features, living organisms also have many other features that differentiate them from non-living things. These are as follows—

Genetic material: Every living organism contains deoxyribonucleic acid (DNA) as the genetic material. The genetic material determines the characteristics and functioning of the organism. It also contains units of heredity called genes. It also transmits these characteristics from one generation to the next. Hence is called the hereditary material.

In some organisms such as viruses, RNA (Ribonucleic acid) is present instead of DNA, as the genetic material. No such genetic material is present in a non-living object.

Mutation:

1. Any sudden alteration in the structure of DNA that brings about permanent, heritable change(s) in the characteristics of the organism, is called mutation.
2. Mutations act as raw materials of evolution.

Coordination:

1. All the physiological events in a living body are correlated and all the organs cooperate with each other for proper functioning of the body. Due to this correlation, living organisms maintain a balance in all their activities.
2. This leads to continuous exchange of information between internal and external environments of organisms.
3. In plants, coordination is maintained through different hormones.
4. In animals, coordination takes place through nerves, hormones, etc.

Homeostasis: 

1. Homeostasis refers to the ability of maintaining a stable internal condition despite of changing external conditions.
2. Examples of homeostasis are — in plants, opening, and closing of stomata regulate the process of transpiration and entry of C02; In humans, regulation of blood pressure, heart beat, concentration of components of blood, levels of Ca2+ in body, etc.

Adaptation:

1. Living organisms modify themselves according to environmental changes and requirements. This is known as adaptation. This results in morphological, physiological, biochemical, and molecular changes within the organisms.
2. These changes are generally inherited over generations, for survival under adverse conditions.
3. Adaptation is the inherent characteristic of all living organisms.
4. Without adaptation, no species can survive in this changing world.

It has been observed that adaptations over long periods of time, could cause an ancestral species to give rise to several descendant species. This may occur if one population is fragmented into several subpopulations and each inhabiting different habitats.

• In cases of geographically isolated populations, one species can diverge rapidly into multiple species through adaptation when new resources are available due to environmental changes. This is called adaptive radiation. This may be demonstrated through the famous example of adaptive radiation as seen with Darwin’s finches.
• In this case, it was observed that several new species of birds (finches) originated from a common ancestor Darwin collected specimens of these birds during his visit to the Galapagos Islands, 900 km off the Pacific coast of South America, in 1835.
• These species of birds (more commonly called finches) differed on the basis of ecology, song, and morphology, specifically the nature of the beaks.
• These birds remain scattered throughout the islands, which signified that populations of the same species became isolated geographically and evolved separately. One major difference among the different species within the same island is the shape and size of the beak.
• Due to adaptation to different food and resources, the finches developed different kinds of beaks. This difference in the beaks, brought about by adaptive radiation helps several species of finches to survive in the same environment, without competition or lack of resources. This further increases the biodiversity in the respective region.

Life cycle:

1. The series of changes that take place in an organism from its birth to death is called its life cycle. Birth, growth, development, reproduction, senescence or ageing and death are the changes involved in a life cycle
2. The time period from birth to death of an organism is its life span. It varies among

organisms of different species from a few hours to several hundred or several thousand of years.

Ageing and death

1. After reaching the adult stage, the body of an organism gradually begins to grow old. This is known as senescence or ageing.
2. It continues up to a certain age after which the organism dies.

• Morphogenesis: It is the process of development of different germ layers, organs, and parts of an organism. This includes formation of morula from zygote. The morula grows into a blastula. The blastula gradually transforms into gastrula which ultimately gives rise to a tiny organism.
• Healing and repair: All living organisms have the ability to heal their wounds. In other words, they have the ability to repair the injured tissues. For example, wounds on our skin get healed by growth of new skin. The wounded parts of the plants also get healed by activities of a tissue called cambium.
• Excretion: Along with useful products, several waste products are also produced by the process of metabolism. Removal of these waste products from the body is known as excretion.
• Self-regulation: A regulatory system operates within every living organism. It controls the functioning (such as metabolism, excretion, and reproduction) of the body. Non-living organisms do not have any such self-regulatory mechanism.
• Movement: Movement includes motion of any part of the body and that of the whole body. Movement of the whole body from one place to another is called locomotion.
• Animals show both movement and locomotion while plants show only movement. Movements that occur due to internal forces are called autonomic movements. Movements that occur due to external stimuli are called paratonic movements.

Evolution: It is the gradual modification of one species over successive generations, into new species. For example, primitive apes have undergone evolution over numerous generations, to give rise to modern man.

Concept Check:

1. Who is known as the ‘Father of Biology’?
2. Name two ancient texts in which ‘Origin of Life1 had been discussed about 3000-3500 years ago.
3. What is life? What is the relation between growth and life?
4. Explain loss in protoplasmic dry weight, with an example.
5. Name the ways by which sensitivity is helpful to man.
6. What is homeostasis?
7. Reproduction is intimately related to life.1—explain.

Diversity In The Living World

• We find a large variety of living organisms around us. Some of them are large, while some are small. Some of them are so tiny that they cannot be seen through the naked eye. The variability among the organisms found on earth is known as biodiversity.
• About 1.7-1.8 million species of organisms have been found on earth till now and several more are yet to be discovered.
• Biodiversity is the healthy and effective basis of the ecosystem. Biodiversity exists due to the difference in genes among the individuals of a species, and that between different species. Biodiversity deals with the degree of nature’s variety in the biosphere.
• Definition: Biodiversity may be defined as a large diversification of the biological world due to the diversification of gene pool, species, and ecology.
• In other words, the diverse types of organisms j present as a whole, in a region at a particular time, is called the biodiversity of that region at that time.
• Thus, biodiversity may be observed at three levels as follows— 0 genetic diversity,  species diversity, ecological or community diversity.

Genetic diversity:

• Members of any plant or animal species differ widely in their genetic constitution. It is due to heredity that every individual gets a set of specific characteristics. Thus, for example, within a human population, each one is different from others in that population as well as from all other organisms.
• This genetic diversity is essential for a population of any species. This genetic variety in wild species constitutes the ‘gene pool’ from which modern-day crops and domestic animals have evolved over the course of thousands of years.
• Today new variety of plants with more productivity are being developed by using wild relatives of the existing crop plants. This process is also adapted to develop new breeds of domestic animals with desirable and improved features.
• However, If the number of individuals is reduced in a  species, the genetic diversity is reduced.

Species diversity:

• Species is a basic unit of classification. It is defined as a  group of similar organisms that mate and produce progeny of the same type with further variations thus, sharing a common lineage.
• Various species of plants and animals present in a region constitute its species diversity. This diversity is seen both in natural ecosystems and in agricultural ecosystems.
• Some areas are richer in species diversity than others. Natural undisturbed tropical forests have much greater richness of species than plantations. At present scientists have been able to identify and categorize about 1.75 million species on earth.
• However, many new species are being continuously identified, especially in the group of flowering plants and insects.
• Areas that are rich in species diversity are called ‘hotspots’ of diversity. India is among the world’s 15 nations that are exceptionally rich in species diversity.

Ecological or community diversity:

• There is a large variety of different ecosystems on earth. Each has its own distinctive interlinked species based on the differences in the habitat.
• Ecosystem diversity can be described for a specific geographical region, or a political entity such as a country, a state, or a district.
• Distinctive ecosystems include landscapes such as forests, grasslands, deserts, mountains, etc., and aquatic ecosystems such as rivers, lakes, and the sea. Ecosystems are mostly natural in wilder areas.
• If natural ecosystems are overused or misused, their productivity eventually decreases and they are then said to be degraded. India is exceptionally rich in ecological diversity.

This kind of diversity is again observed at three levels – Alpha (α), Beta (β), Gamma (γ) diversity.

Alpha diversity:

It is the biodiversity within a particular area, community, or ecosystem. It is usually expressed by the number of species (i.e., species richness) in that ecosystem. This can be measured by counting the number of taxa (distinct groups of organisms such as families, genera, and species) within the ecosystem.

Beta diversity:

• Beta diversity is a measure of biodiversity which is done by comparing the species diversity between ecosystems or habitats. This comparison involves the number of taxa unique to each of the ecosystems.
• It is the rate of change in species composition across habitats or among communities. It gives a quantitative measure of diversity of communities that experience changing environments.

Gamma diversity:

It refers to the total species richness over a large area or region. It is a measure of the overall diversity for the different ecosystems within a region.

It is the sum of the diversity of component ecosystems and the diversity between component ecosystems. Gamma diversity can be expressed in terms of the species richness of component communities as follows

γ= SI + S2 – c

Where, SI = the total number of species recorded in the first community, S2 = the total number of species recorded in the second community, c = the number of species common to both communities.

Significance of biodiversity:

The present-day biodiversity on earth is the outcome of nearly 3.5 billion years of evolution. In the period before the appearance of humans, the earth supported more biodiversity than any other period in geological history. However, since the dominance of mankind, biodiversity showed begun a rapid decline, with one species after another suffering extinction.

Biodiversity should be conserved for the following important reasons—

Ecological value: Every species carries out a particular function within an ecosystem. Some of them can capture and store energy. Some of them produce food and others decompose organic material.

• There are species that help to recycle water and nutrients throughout the ecosystem, fix atmospheric gases, or help to regulate climate.
• Ecosystems with immense biodiversity provide different sources of food. These also provide services without which we can not survive.
• These include decomposition of wastes, purification of the air and water, stabilization and moderation of the climate, reducing chances of flood, drought, and other environmental disasters.
• More diverse an ecosystem, the better it can withstand environmental stress and become more productive.

Economic value: For mankind, biodiversity is first a resource for daily life. Crop diversity is very important for mankind as a food source and is also called agrobiodiversity. Biodiversity is also viewed as a reservoir of resources like food, pharmaceuticals, and other necessary products. Thus resource shortages may be related to the loss of biodiversity.

Some of the economically important commodities that biodiversity supplies to humans are as follows.

• Food: Biodiversity provides a variety of food sources like — crops, livestock, forestry, and fishes.
• Medicine: Several plant species have been used for medicinal purposes since the prehistoric times. For example, quinine (to treat malaria) comes from the bark of the Cinchona plant; morphine (used as pain reliever) comes from the Poppy plant. It is estimated that out of 250,000 known plant species, only 5,000 have been explored so far, for possible medical applications.
• Commercial products: Biodiversity is a source of different products that have commercial use. For example, fibers (used for making cloth), wood (for making furniture), etc.
• Other such products are oils, lubricants, perfumes, paper, waxes, rubber, latexes, resins, and cork. All of these can be derived from various plant species. Products of animal origin are wool, silk, fur, leather, lubricants, waxes.
• Transport: Different animals may also be used as modes of transport. Tourism and recreation: Biodiversity also facilitates tourism and provides a source of recreation as well. Ecotourism, in particular, is a growing outdoor recreational activity.
• Environmental value: The adverse effects of environmental pollution may be prevented through more and more biological diversification.
• Ethical value:  Each and every organism has the j full right to survive in the world. This has been accepted in the announcement of United Nations Environment Programme in 1982. Therefore, it is the duty of man to save and conserve all the species in the world.
• Laws for conservation of biodiversity: Several lav/s have been framed, both nationally as well as,  internationally for conservation of biodiversity. Some famous law for conservation of biodiversity in India are The wildlife (protection) act, 1972. 2) The Forest (conservation) act, 1980. 3) The environment (protection act), 1986. 4) Biological diversity act, 2002.

Taxonomy And Systematics

• Each organism on earth is known by different local names at different places. This gives rise to confusion. To avoid this, a universal name is given to each organism. This name is used to refer to the organism, irrespective of its local name.
• This system of providing a universal name to an organism is known as nomenclature. The science of naming, classification, and identification of different organisms by their names and characteristic features is called taxonomy. The term was coined by de Candolle in 1813.
• Carolus Linnaeus is known as the Father of Taxonomy. Taxonomy is a part of a broader branch of study called systematics. Systematics is defined as the scientific study of organisms regarding their identification, naming, and classification.
• The term was coined by Linnaeus in 1751. Simpson had defined systematics as— the study of diversity of organisms and all their comparative and evolutionary relationships, based on the studies of anatomy, ecology, physiology, and biochemistry.

Taxonomy And Systematics Identification:

Taxonomy And Systematics Definition: Identification is the process of differentiating one organism from others with the help of its specific features.

Necessity of identification:

1. An organism should be identified, in order to be placed in the appropriate taxon (unit of classification like genus, species, etc.).
2. Correct identification is essential because further studies on the organism depend on it.

Procedure of identification:

• Generally, it is carried out directly by comparing the organism to be identified with other organisms of known identity. It can also be carried out indirectly by comparing the features of the organism with those of similar organisms, as mentioned in books and other scientific literature.
• Sometimes, a specimen may not resemble any previously identified one. In that case, the specimen is considered as a new one.

Nomenclature:

• Nomenclature Definition: Nomenclature is defined as the scientific and international system of naming any organism.
• Nomenclature Necessity: People of a particular place know the local plants and animals by their common or vernacular names. But these names vary from place to place. To overcome this problem, it is essential that each organism should have a universally accepted scientific name. Scientific names do not vary with region and help to identify a particular organism in any place, around the world.
• Nomenclature Types: All organisms on earth have two names— common name or vernacular name and scientific name. Carolus Linnaeus introduced scientific names of plants and animals in his books, Species Plantarum (1753) and Systema Naturae (1758, 10th Ed.) respectively. He named the plants and animals by laying down certain rules.

Common or vernacular name:

• Common or vernacular name Definition:  Common name or vernacular name is the name that is based on the local language of a particular place.
• Example:  The cockroach, which is found everywhere in the world, is known by different names in different places. In Hindi, it is known as Tilachatta and Aarshola in Bengali.
• Common or vernacular name Advantages:  Common names are easy to pronounce. A layman (person without any scientific knowledge) can identify an organism easily by its common name.
• Common or vernacular name Disadvantages:  Common names are not the same in every language. So it is difficult to identify an organism in different places by its common name if the local language is not known.

Scientific name

Scientific name Definition: Scientific name is the name given to each organism following the rules of international system of nomenclature.

Example: The scientific name of onion is Allium cepa. Onion is scientifically identified by this name, all over the world.

Scientific name Advantages:

1. A scientific name helps to avoid the confusion that arises due to different local names of the same organism, around the world.
2. Scientific names are universally accepted.
3. The rules of scientific naming or nomenclature are the same all over the world.

Method of naming: There are three common methods of nomenclature.

• Binomial nomenclature:  Latin term bi means two and nomen means name. This type of naming includes two levels—genus and species.
• Binomial Definition: The scientific system of naming of any organism by using two words, where the first word is the generic name (genus) and the second word is the specific name (species), is known as binomial nomenclature.
• Example: Mangifera indica, where Mangifera is the genus and indica is the species.
• Caspar Bauhin (1560-1624) was the first to implement a system of naming, which was the precursor of the binomial system of nomenclature. Later on, this was followed by Carolus Linnaeus who used binomial nomenclature for the plants in his book Species Plantarum (1753) and for the animals in his book Systema Naturae. He is considered the Father of modern taxonomy and binomial nomenclature.

Rules for binomial nomenclature:

• The rules for binomial nomenclature are framed and standardised by some international scientific organisations. These rules are followed all over the world. International rules for naming plants are called International Code of Botanical Nomenclature (ICBN).
• International rules for naming animals are called International Code of Zoological Nomenclature (ICZN). There are international rules for naming other organisms as well, such as International Code of Nomenclature of Bacteria (ICNB) for naming bacteria, International Code of Viral Nomenclature (ICVN) for naming viruses, etc.

Common recommendations

Some common recommendations for binomial  nomenclature are

1. Every organism should have one scientific name, that is composed of two Latin words. The first word should be genus and the second is species.
2. The scientific name should always be typed in italics.  In case it is handwritten, both generic and specific epithets should be underlined separately.
3. The generic name should always start with capital letter while the specific epithet should start with small letter.
4. In some cases, the name is further followed by the name of the; author (the taxonomist who first described the species; and named it). If the author’s name is too long, the abbreviated form is used. For example, the complete  scientific name of a human being is Homo sapiens (L.).  Here, T denotes the name of the author Linnaeus.
5. Organisms of different kingdoms such as animals and plants, should be named differently. Genus names of two different types of organisms belonging to the same kingdom should not be the same. But the same species name can be used with different genus names. For example, Cyriocosmus elegans is the scientific name of a spider species (tarantula) and Centruroides elegans is the: scientific name of a scorpion.

Some information related to nomenclature

• Homonym: If the names of two different organisms are pronounced and spelled in the same way, then they are known as homonyms.
• According to international code for biological nomenclature, the older of the two homonyms is accepted while the other name is rejected. For example, the Astragalus rhizanthus Boiss (1843) is a homonym of Astragalus rhizanthus Royle (1835).
• Toponym: When an organism is named after its habitat or geographical location, then this type is known as toponym. For example, Myiagra caledonica is a bird found in New Caledonia. This bird is sometimes known as the New Caledonian flycatcher.
• Tautonym: If the genus and species name of any organism are same, then it is an example of tautonym. Example, Gorilla gorilla. This type of name is not permitted in botanical nomenclature but is accepted in zoological nomenclature.

Scientific names of India’s national tree, animal and bird:

Scientific names of some plants:

Scientific names of some animals:

• Trinomial nomenclature: In this type of naming, scientific names include genus names, species names, and subspecies (subgroups under a species) names.
• Example: The scientific name of house crow is Corvus splendens. The subspecies of house crow are differentiated using trinomial nomenclature. E.g., Corvus splendens splendens, Corvus splendens insolens and Corvus splendens protegatus. Here splendens, insolens, and protegatus are the subspecies.
• Polynomial nomenclature: In this type of nomenclature organisms are named by using a series of 1 descriptive words, hence, it is known as polynomial j nomenclature. It was in use before the publication of Systema Naturae by Linnaeus.
• Example: Caryophyllum saxatilis folis gramineus umbellatis corymbis is the full scientific name of the plant Caryophyllum. The name says that this plant grows on the rocks, its leaves are grass-like, and floral arrangement is umbellate corymb (flowers are arranged 1 to form an umbrella-like shape).

Some information related to nomenclature Classification: Diverse types of living organisms are present on earth. Each year a number of new species are added to the list of identified organisms. Many fossils have also been discovered in recent times. To study the different types of living organisms easily, scientists have classified them into various groups or categories.

Some information related to nomenclature Definition: The system of categorisation of different organisms into different groups on the basis of their significant characteristics and relationship is known as classification.

Need for classification:

1. Classification is necessary as it makes the study of diverse organisms very much convenient.
2. It helps to identify any organism.
3. It helps us to get an idea about the organisms belonging to a particular group, by studying only a few organisms representing that group.
4. It helps us to understand the relationship among different groups of organisms.
5. It provides information about organisms belonging to any specific geographical region.
6. It also helps to study fossils and to identify extinct species.
7. It also helps to understand the evolutionary trends (nature of evolution) across different groups of organisms.

Three domains of life:

Living organisms are divided into three groups or domains, on the basis of genetic constitution. These are called the Three Domains of Life. The three domains of life are — Archaea, Bacteria, and Eukarya. This is actually a system of biological classification that was propounded by American microbiologist Carl Woese in 1990. This system has been discussed in detail in (Biological Classification).

Concept Check:

1. Who coined the term ‘taxonomy’?
2. What is binomial nomenclature? Give example.
3. Define taxonomy.
4. Define systematics.
5. What do you understand by classification? .
6. What do you understand by identification in terms of biology?

Taxonomic Categories

Classification of organisms involves various grouping levels. These levels are known as categories or taxonomic categories. The system of arranging categories one above the other is known as hierarchy or taxonomic hierarchy. Each level of this hierarchy is a unit of classification and represents a rank. These ranks are commonly known as taxon (plural: Taxa). For example, Division Angiospermae, here Division is the category, and ‘Angiospermae’ is the taxon. Details are given in the following table.

Different categories and taxa:

Some definitions related to taxonomic hierarchy

• Monotypic genus: A genus which includes only one species is known as monotypic genus. For example, sapiens is the only species under the genus Homo.
• Polytypic genus: The genus which includes more than one species are known as polytypic genus. For example, tigris and leo are two species present under the genus Panthera.
• Monotypic species: The species which are not divided j into subspecies, varieties, and races, are known as monotypic species. For example, in Ginkgo biloba, biloba is the monotypic species.
• Polytypic species: The species which are divided into two or more subspecies, varieties, or races are known as polytypic species. For example, there are many subspecies of Panthera tigris. They are— P. tigris altaica (Siberian tiger), P. tigris tigris (Bengal tiger),  P. tigris jacksoni (Malayan tiger), etc.
• Species: It is the lowest taxonomic category. The j genetically different but morphologically similar groups of organisms, which are capable of interbreeding, are known as species. Each genus may have one or more species. For example, Panthera leo (lion) and Panthera | tigris (tiger) have different specific epithets (leo and j tigris), but same genus (Panthera). Different species j under the same genus have morphological similarities j but are reproductively isolated.
• Genus: Genus (PI. genera) is the taxonomic category j that comes above the species. It comprises of j morphologically related species. All the species under j the same genus have a common ancestor. A genus may contain one or more species. For example, lion (Panthera leo), tiger (Panthera tigris), jaguar (Panthera onca), and leopard (Panthera pardus) belong to the same genus (Panthera).
• Family: It is the taxonomic category that comes above genus. A family contains one or more related genera. For example, Felis (genus of cats) and Panthera (genus of tiger, leopard, lion, and jaguar) are under the same family, Felidae. The suffix used for families are different. For plants, the family name ends with -aceae, while that for animals, the family name ends with -idae.
• Order: It is the taxonomic category that comes above family. An order comprises one or more related families. For example, families Felidae (family of cats) and Canidae (family of dogs) belong to the same order Carnivora (members of both the families are carnivores and have large canine teeth).

Intermediate Categories

• Hierarchy categories are of two types— obligate and intermediate categories. The categories which are always used to define the taxonomic position of an organism are known as obligate categories.
• This includes kingdom, phylum or division, class, order, family, genus, species. Some categories are also added in between obligate categories to make the taxonomic position more precise. These categories are known as intermediate categories. For example, sub-division, superclass, etc.

Class: It is the taxonomic category that comes above order. A class comprises one or more related orders. For example, orders Rodentia (rats), Primata (monkeys) and Carnivora (cats, dogs, etc.) belong to the same class Mammalia (have hairs and milk glands).

Phylum/Division: The next taxonomic category that comes above class is called phylum (in case of animals) or division (in case of plants). It comprises related classes. For example, phylum Chordata includes classes Amphibia, Reptilia, Aves, etc.

Kingdom: The highest category of taxonomic hierarchy is kingdom. Each kingdom consists of same type of phyla/divisions. For example, all the animals are placed under kingdom Animalia, and all plants under kingdom Plantae.

Examples of hierarchical classification:

Different suffixes used in different hierarchy levels:

Concept of species:

• Species is the basic unit of taxonomy. It is the lowest unit of taxonomic hierarchy. It includes genetically different but morphologically similar groups of organisms. These organisms are capable of interbreeding.
• They cannot breed with organisms of other species. This feature of any species is termed reproductive isolation. Each genus may have one or more species under it. For example, Panthera leo (scientific name of lion) and Panthera tigris (scientific name of tiger) have different specified names (leo and tigris), but same genus (Panthera).
• The characteristic of interbreeding is important for a species. However, a species cannot be delimited solely on its basis.
• This is due to two reasons—0 In some cases, members of different species may interbreed. However, the progeny produced are generally sterile. For example, mule (male ass + mare) and hinny (horse + female ass) are two such sterile offsprings.
• In some cases of interspecific mating, fertile offsprings such as tigon (male tiger + female lion) and liger (male lion + female tiger) may be produced. 0 Sexual reproduction is absent in organisms like prokaryotes and protists. Hence, the phenomenon of interbreeding is absent in them. In such cases, morphological, anatomical, cytological and other characteristics are considered for categorizing a species.
• A species may be further divided into subgroups. These subgroups are known as subspecies or varieties. They have characteristic features that distinguish them from other subspecies.
• Sexual reproduction is an important point in the definition of a species. It produces offsprings that are different from parents.
• These variations over a course of time may cause a species to change. Thus, species are really dynamic groups and not static as was considered earlier.

Concept Check:

1. What is the meaning of the word ‘hierarchy?
2. Name the seven categories of taxonomic hierarchy.
3. What do you understand by the word ‘family?
4. What do you understand by the word ‘order?
5. What is the meaning of the word ‘taxon?

Taxonomical Aids

• To study the vast diversity of the biological world, we need to identify and classify the organisms correctly. To do this, we need to carry out both fieldwork and laboratory studies.
• These are carried out by collection and conservation of biological specimens (dead or living) by proper means.
• The specimens are conserved for further studies. There are several taxonomical aids that help in these studies. These include botanical gardens, herbaria, museum,s and zoological parks.

Museums

• Museums Definition: A museum is an institution that preserves and exhibits objects of scientific, artistic, cultural, or historical importance.
• Museums Types: Museums may be classified according to the nature of the objects they preserve. They may be historical museum, natural history museums, etc. The Museum of natural history mainly preserves plants and animals.
• Working procedure: Museums provide information about various plants and animals to the researchers and students. The working procedures of museums are discussed below.
• Keeping a record of the sample: Museums keep a record of the samples which they preserve. The Global Biodiversity Information Facility (GBIF), an international organization, maintains the records of the specimens and samples in museums all over the world.
• Preservation: Preservation methods vary according to the objects that are to be preserved. Plant or animal specimens are preserved in liquid preservatives in jars. The liquid preservative is a mixture of alcohol and formalin. Some large animals are preserved in stuffed forms. Some insects are preserved by drying and mounting in boxes.
• Exhibition: Science exhibitions in the museum are unique resources for informal education. These help us to remember facts and develop skills in science. They are places to discover, explore, and get ideas about the natural world.

Importance

1. Museums preserve specimens of plants and animals from various parts of the world. It provides information about these species.
2. It also helps in the comparative study of different organisms.
3. Specimens of newly discovered species may also be preserved in some museums as type specimen.
4. Museums help to draw attention of the common people towards endangered and extinct species.
5. Biological museum of schools and colleges help the students to study different plant and animal species.

Some famous museums:

Zoological Parks

• Zoological Parks Definition: A zoological park or garden is a place where living animals are kept in enclosures for study and exhibition.
• Zoological Parks Types: According to the nature of the conserved animals and their habitat, zoological gardens or parks are of several types such as, open-range zoo, animal theme park, aquarium, etc.

Working procedure:

1. The area of a zoological park is made comfortable for the animals to live and reproduce.
2. In the zoological gardens, a diet chart is prepared and followed for all the animals, according to their feeding habits, health condition, and behavior.
3. There are trained veterinary doctors who take care of the wounded and diseased animals.
4. The scientific names, common names, and habitat of the animals, etc., are displayed in front of their enclosures. This helps the people gather information about the animals.
5. A map is provided inside the zoo for helping the tourists.

Importance: 

1. Zoological parks or gardens are examples of ex-situ conservation. Main scientific purpose of a zoological park is the conservation and breeding of endangered species and subsequent increase in their numbers. This is done to prevent their extinction.
2. It plays an important role in taxonomic research, identification, and observation of different animals.  It creates awareness among the people regarding the conservation of animals.
   Names of some famous international and national zoological gardens are given in the following table.

Names of some famous zoological gardens or zoos:

Herbarium

Herbarium Definition: The collection of dried plant specimens mounted on a sheet of paper, so as to preserve it in such a way that it provides information about the actual plant, is called a herbarium.

Preparation of herbarium sheet: A thick sheet of paper, on which the dried samples of the plants are mounted, is called the herbarium sheet. Following are the steps involved in the preparation of a herbarium sheet.

Collection of specimen: 

1. This is the first step involved in the preparation of a herbarium (plural: herbaria).
2. Specimens are carefully collected at different seasons, as well as from different environments. They are also collected at different stages of their life cycle.
3. The plant which is to be preserved should have all its parts (leaves, flowers, roots, etc.). In case of flowering plants, their different parts such as fruits, inflorescence, stem, etc., may give different information. Hence, in case of these plants, separate parts of the plant may be collected as specimens at different stages of their development.

Materials required for specimen collection:

1. Knife,
2. scissors or cutter (small and big),
3. old newspapers,
4. blotting papers and cotton,
5. forceps,
6. magnifying glass,
7. polythene bags,
8. small shovel or spade or sickle,
9. field notebook,
10. vasculum (a kind of case or box),
11. empty jars and bottles with FAA solution (mixture of formaldehyde, glacial acetic acid and alcohol),
12. pen or pencil and measuring tape,
13. brush (small and big),
14. pieces of cloth,
15. plant press machine.

Drying: 

1. Healthy shoots of a certain length, with leaves, flowers and fruits are collected from the plants.
2. These are properly placed within two blotting papers immediately after collection. These are again kept between two sheets of old newspaper or magazine.
3. Now these are kept in plant press machine.
4. To make the specimen dehydrated, without any damage, the blotting papers have to be regularly changed. It is kept in this condition for 24/48/72 hours.
5. The succulent parts are stored in bottles with FAA solution for faster dehydration.
6. Sometimes, specimens may be dried by applying heat on moist parts.
7. Smaller specimens are dried by placing them within folded cloth and pressing it with hot electric iron.

Mounting the sample: 

1. After drying, the specimen is mounted on a herbarium sheet.
2. Herbarium sheets are generally white, large, thick pieces of papers, with dimensions of about 29 x 41 cm or 30 x 45 cm.
3. The specimens are attached to the herbarium sheet by applying glue.
4. A single specimen is placed on a single herbarium sheet.

Labelling: After mounting, a label (identity card) is placed below the specimen, towards the lower right hand corner of the hebarium sheet. The label contains the following information

1. Flora of
2. Collection No
3. Date of Collection
4. Locality of collection
5. Altitude
6. Habitat
7. Habit
8. Distribution
9. Abundance
10. Collector
11. Scientific name of the specimen
12. Local name of the specimen
13. Family
14. Identifier
15. Remarks

Preservation:

1. Herbarium sheets are preserved in herbarium cases made of wood or steel.
2. These are stored in cupboards to protect them from insects.
3. The specimens are arranged according to the families. They may also be arranged according to their scientific names or the name of their species, both alphabetically.

Protection:

1. Herbarium sheets are destroyed mostly by moulds and fungi. Hence the herbarium sheets and cases must be kept clean and proper measures should be taken to prevent the growth of fungi and moulds.
2. 0.1% mercuric chloride, DDT spray, napthalene dust, carbon disulphide spray etc., must be used to prevent growth of harmful organisms.
3. Sometimes warm vapours may also be used to destroy the harmful organisms.
4. To prevent the fungal growth, the moisture of the room must be regulated.

Importance: 

1. It helps in the comparative study of different plant species. It also provides primary information about the plant and its corresponding parts.
2. It helps to identify similar samples of the plants and helps in taxonomic studies.
3. It draws attention to economically important plants.
4. It helps to conserve the newly discovered plants and their wild species.
5. It helps to study the extinct plant species.
6. It provides reference material for research.

The term herbarium is also used to refer to the building that houses the actual herbarium. Some of the famous herbaria are given in the following table.

Some famous herbaria:

Botanical Carden

Botanical Carden Definition: Botanical gardens are the enclosed places where a wide variety of plants are scientifically cultivated and conserved.

General features:

1. Different species of plants are cultivated and conserved in these gardens.
2. Most of the botanical gardens are linked to several research centers, greenhouses, rock gardens, palm houses, orchid houses, herbariums, museum, etc.
3. Botanical gardens help to educate people on conservation issues and the role of humans in environmental changes.

Do You Know:

The world’s first botanical garden was the University Gardens of Italy established in the 16th and 17th centuries. These gardens were used only for the academic study of medicinal plants.

Importance:

1. Climate change, habitat destruction, invasive alien species, and over-exploitation are some direct threats to plant survival and the earth’s biodiversity. Botanical gardens have been set up as safe haven for plants, where they would remain safe from the above-mentioned threats. Botanical gardens are also useful for taxonomic research.
2. Botanical gardens maintain ex-situ conservation of plants, often displayingseveral plant species. This helps to maintain a living store of genetic diversity that can support conservation and research.
3. Botanical gardens conserve plants that might become extinct in the wild. These plants may also have commercial values.
4. Botanical gardens store the seeds or germplasm of plants for future use, research and propagation. This is another method of ex-situ conservation of plants. It is known as seed banking.
5. Botanical gardens make people aware about plant and biodiversity conservation. It encourages the sustainable use of plants for the benefit of all. Names of some famous international and national botanical gardens are given in the following table.

Some famous botanical gardens:

The international body of botanical gardens:

• Following its establishment in 1987, the IUCN Botanic Gardens Conservation Secretariat (BGCS) began to build its membership of botanic gardens worldwide and develop a program in support of botanic gardens. In 1989, The Botanic Gardens Conservation Strategy was published.
• In the following year, BGCS became independent from IUCN and subsequently came to be known as Botanic Gardens Conservation International (BGCI).
• A primary concern of BGCI is to provide a means for botanic gardens in all parts of the globe to share information and news about their activities, programmes that may benefit conservation.

Acharya Jagadish Chandra Bose Indian Botanic Garden:

• Howrah Acharya Jagadish Chandra Bose Indian Botanic Garden (formerly known as Indian Botanic Garden or Royal Botanic Garden, Calcutta) is situated at Shibpur, Howrah, near Kolkata.
• It is the largest botanical garden in India as well as in south east Asia and one of the oldest botanic gardens in the world.
• The garden exhibits a wide variety of rare plants and a total collection of over 12,000 specimens on a piece of over 109 hectares of land on the bank of the Hooghly river.
• It also houses of largest herbarium of India, Central National Herbarium. It is under the administration of Botanical Survey of India (BSI).

Taxonomic Key

Taxonomic Key Definition: Taxonomic key is a tool that helps scientists to identify an unknown organism on the basis of morphological similarities and dissimilarities.

Characteristics:

1. The key is an important taxonomic aid for identification of plants and animals based on similarities and dissimilarities.
2. It is an artificial device by which each type of taxonomic category can be identified.
3. Keys are based on contrasting characters which are generally placed in pairs called couplets. Of the contrasting characters one is accepted while the other is rejected. Thus, the couplet represents the choice between the two options. Each statement in a key is called a Lead.
4. Separate keys are needed for each taxonomic category (or a taxon) like family, genus, or species.
5. Keys are more useful in identification of unknown organisms.

Importance: 

1. Unknown organisms can be m identified quickly by using taxonomic key, since it provides a structure for sorting different species by different information given on it.
2. During identification, it helps j to skip other species automatically that do not resemble  the species on the basis of their characteristic features.

Types of Taxonomic Key: Taxonomic keys are of two types—punched card key and dichotomous key. The latter are of two types—indented key and bracketed key.

Punched card key:

• A punched card key consists of a card on which holes are | punched. It may be of two types— edge-punched key | and body-punched key (polyclave). In edge-punched key, the holes are punched along the perimeter of the card.
• While in body-punched key, holes are punched in rows on the main body of the card. In edge-punched key, attributes are represented by holes while in body-punched key, attributes are represented by the card.
• The main advantage of using punched keys is that the attributes to be used for identification may be chosen by the user.

Importance: 

1. Unknown organisms can be identified quickly by using taxonomic key since it provides a structure for sorting different species by different information given on it.
2. During identification, it helps to skip other species automatically that do not resemble the species on the basis of their characteristic features.

Dichotomous key:

The term dichotomous means divided into two parts. This key gives two choices in each step. The dichotomous key consists of a pair of contrasting characteristics i.e., couplets and each statement of a couplet is called a lead (characteristic). Each lead should be numbered and easily observable. The dichotomous key is of two types—

Indented or Yoked key

Characteristics:  Indented key provides a series of two or more alternate characters arranged in successive manner. An organism may be identified by careful selection of the characters.

Example:  Some fish are identified using indented key.

1. Bony endoskeleton

1. Body is covered with scales
2. Barbell present ———–Labeo calbasu
3. Barbell absent———— Labeo rohita

2. Body is not covered with scales

1. Dorsal fin large———– Clarias gariepinus
2. Dorsal fin small————- Heteropneustes fossilis

1. Cartilaginous endoskeleton

1. Horizontally flat body, long tail with  spine————– Myliobatoidei
2. Cylindrical body, heterocercal tail without  spine————- Selachimorpha

Bracketed or Parallel key:

Characteristics:  In this type, both the leads of each couplet always remain together. The characters are not further divided into sub-divisions.  Each lead of the couplets is given a number in the brackets. According to these numbers, different plants and animals can be identified.

Example: Some fish are identified using bracketed key.

1. Bony endoskeleton————-
2. Cartilaginous skeleton—————
3. Body is covered with scales———-
4. Body is not covered with scales————
5. Barbell present Labeo calbasu—————-
6. Barbell absent Labeo rohita————
7. Dorsal fin large Clarias gariepinus——-
8. Dorsal fin small Heteropneustes fossilis——-
9. Long and narrow tail with spine Myliobatoidei———-
10. Heterocercal tail without spine Selachimorpha———-

Advantages and disadvantages of taxonomic key: 

1. The punched card key is useful for beginners e.g., college students, who are interested in taxonomy. But the system is costly.
2. Dichotomous key is suitable for the taxonomists and it costs much less. The indented key gives a visual representation of the group and the users can readily obtain a clear picture about the taxon.

Concept Check:

1. Define taxonomic key.
2. Define museum and botanical garden.
3. Name the tools required for the preparation of herbarium.

The Living World Notes

• Biomolecules: Molecules involved in different metabolic processes of living organisms.
• Blastula: An early stage of animal embryo; appears as a hollow sphere of cells.
• Dry weight: Weight of the body excluding its water content.
• Ecology: The branch of biology that deals with environment and its interrelationship with all the living and non-living component of it.
• Gnstrula: This is another stage of development of animal embryo and it comes after the blastula stage.
• Gene pool: All the genes present in a particular group of organism at a given time.
• Germ layer; Group of cells present in the embryo which helps in the formation of all organs.
• Germplarm: Living genetic resources such as seeds, conserved for breeding of an particular organism.
• Macromolecules: Large biomolecules such as proteins.
• Morula: This is an early stage of animal embryo development; appears as a sphere of cells.
• Specimens: Organisms or objects used for scientific studies.
• Type specimen: The specimen that serves as the reference when a new plant species is discovered and first named.

Points To Remember:

1. The living and non-living things can be distinguished on the basis of a main feature called life. Living things have life while non-living things do not.
2. Important characteristics of living organisms include shape and size, cellular and structural organisation, growth and development, metabolism, sensitivity, reproduction, homeostasis, coordination etc.
3. The diversity observed in different organisms worldwide is known as biodiversity.
4. All the cells contain their genetic material within the nucleus, mainly in the form of DNA, rarely RNA.
5. The ability of maintaining stable internal condition, irrespective of the external environmental condition, is called homeostasis.
6. The term ‘Taxonomy’ is composed of two Greek words ‘Taxis’ and ‘Nomos’. ‘Taxis’ means arrangement and ‘Nomos’ means law.
7. Systematics is the branch of biology which reveals relationship among all the organisms by identification, naming, description and classification.
8. The systematic framework of classification where taxonomic categories are arranged in specific order is known as taxonomic hierarchy.
9. There are total seven taxonomic categories present in Linnaean hierarchy or taxonomic hierarchy and the smallest category is the species.
10. The nomenclature that includes two categories, genus and species, is known as binomial nomenclature.
11. Carolus Linnaeus is known as the Father of Binomial nomenclature.
12. If one organism has more than one scientific name, then the first effectively and validly published name should be accepted. The other names are known as synonyms. This is known as the Law of Priority.
13. Each unit of classification is known as taxon.