The Living World Notes

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.

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• 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.

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• 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.

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 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.

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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.

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Differences between anabolism and catabolism:

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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.