Chapter 1 — The Living World

Ask a child what is alive and the answer comes at once: the dog, the tree, the ant; not the stone, the table, the river. Yet when a biologist tries to write down a definition of life that includes every organism and excludes every object, the task turns out to be hard. The usual approach is to list the characteristics of living organisms and then ask which of them are defining, that is, which are found in every living thing and in no non-living thing.

The commonly listed characteristics are: growth, reproduction, metabolism, cellular organisation, consciousness (the ability to sense and respond to the environment), self-replication, self-organisation, interaction and emergence. Each of these needs to be examined, because some of them fail the test of being exclusive to life.

Consider growth. A crystal grows, a sand dune grows, a mountain grows by accumulation. Growth by itself, therefore, is not a defining feature. Consider reproduction. Many organisms, such as mules, sterile worker bees and infertile human couples, do not reproduce, yet they are certainly alive. Reproduction too is not defining. What remains? Metabolism, the sum of all chemical reactions occurring inside a living body, is found in every living organism and never occurs in isolation outside a living system. Cellular organisation, the fact that every organism is made of one or more cells, is likewise universal. Consciousness, the capacity to sense the environment and respond, is exhibited by all organisms, from a bacterium swimming toward sugar to a sunflower turning with the sun. These three are the defining properties of living organisms.

Two more ideas round off the picture. A living organism is a self-replicating, evolving and self-regulating interactive system capable of responding to external stimuli. And life shows emergent properties: the whole is more than the sum of its parts. Water is not alive, nor are proteins, but a cell built from them is; a tissue has properties none of its cells has alone; an organism has properties no tissue has. This hierarchy of organisation, from molecules to cells, tissues, organs, organ systems, organisms, populations, communities and the biosphere, is the framework within which biology is studied.

Finally, the organisms we see today are the product of evolution; every living thing is a link in an unbroken chain of self-replication that began about 3.5 billion years ago. That historical dimension is part of what it means to be alive, and it is why the study of diversity in this chapter and of classification in the next is also, at bottom, a study of common descent.

Growth is an increase in mass and an increase in the number of individuals or cells. In living organisms both kinds occur, and they occur from inside the body: a plant grows because its cells divide and enlarge, and the new material is manufactured by the organism's own metabolism. This is called intrinsic growth or growth from within.

Non-living things also 'grow', but by accretion, the accumulation of material on the surface. A crystal enlarges as ions from solution attach to its faces; a sand dune enlarges as wind deposits more sand; a stalactite lengthens as calcium carbonate is added drop by drop. The material comes from outside and is merely stuck on; no internal process manufactures it. This difference, growth from inside versus growth by external deposition, is the main distinction between living and non-living growth, and it is why growth alone cannot be the defining property of life.

Within living organisms, plants and animals differ in the pattern of growth. In plants growth continues throughout life at the tips of roots and shoots, where meristematic tissues keep dividing, and in the cambium that thickens stems. A banyan tree that is centuries old is still adding leaves and roots. Plant growth is therefore said to be indeterminate. In animals, growth occurs only up to a certain age, after which it stops, although cells continue to be replaced. Animal growth is determinate.

In unicellular organisms such as bacteria, yeasts and Amoeba, growth and reproduction cannot be separated, because the cell grows and then divides into two, and division is at once an increase in cell number and the making of new individuals. Here the increase in number of cells is counted as growth as well as reproduction. In multicellular organisms the two are distinct: a rose bush grows by making more cells, and it reproduces by making seeds or cuttings that become new plants.

Growth in plants can be measured as increase in length, area, volume, fresh weight, dry weight or cell number, and its rate follows a characteristic sigmoid or S-shaped curve: slow at first, then rapid, then slowing as maturity approaches. The later chapters of the course on plant growth and development treat this quantitatively. For now the essential points are: living things grow from inside by cell division and enlargement; non-living things grow only by accretion; plants grow throughout life while most animals stop; and in unicellular forms growth and reproduction coincide.

A frequent examination question asks whether growth can be taken as a defining property of living organisms. The answer, argued as above, is no: because non-living objects also grow, growth is a characteristic of life but not its defining criterion. Only when growth is intrinsic and accompanied by metabolism does it point unmistakably to a living organism.

Reproduction is the production of new individuals of the same kind, so that the species persists beyond the life of any one organism. In multicellular plants and animals it may be sexual, involving the fusion of gametes and giving offspring that combine the characters of two parents, or asexual, in which one parent alone produces offspring genetically identical to itself. Plants show a rich variety of asexual reproduction: fungi multiply by millions of asexual spores; yeast and Hydra bud; Planaria regenerates whole individuals from fragments; the filamentous algae and the fungi and the protonema of mosses multiply by fragmentation, each piece growing into a new organism; potato tubers, ginger rhizomes and Bryophyllum leaf margins produce new plants vegetatively.

In unicellular organisms such as bacteria, unicellular algae and Amoeba, reproduction is by cell division, and the same event is also growth; the two are not separable, as noted in the previous topic.

Is reproduction a defining property of life? Many living organisms never reproduce: mules, sterile worker bees, and infertile individuals of any species. They are unquestionably alive. Reproduction is thus a characteristic of the species but not an unfailing criterion for the individual, and so it cannot serve as a definition of life.

Metabolism is the sum total of all the chemical reactions taking place in a living organism. All living organisms, from a single bacterium to a banyan tree, are made of chemicals of many kinds and sizes, and these are constantly being made and broken down. Reactions that build complex molecules from simpler ones are anabolic (for example photosynthesis and protein synthesis); reactions that break complex molecules down, usually releasing energy, are catabolic (for example respiration). Together these thousands of reactions, proceeding in an orderly and regulated way, constitute metabolism.

No non-living object exhibits metabolism. It is true that isolated metabolic reactions can be carried out in a test tube outside the body; such reactions are called in vitro (in glass) reactions. But such a reaction in a test tube is neither living nor non-living; it is merely a living reaction. Only the complete, integrated set of reactions inside a cell constitutes the metabolism that characterises life. Hence metabolism is a defining feature of all living organisms without exception.

A related idea is cellular organisation. Every living organism is composed of cells, and metabolism occurs within cells. A virus, which has no cells and no metabolism of its own, tests this boundary; it is generally regarded as being at the border of the living and the non-living, alive only inside a host cell. The exclusive features of life, then, are the properties of the cell as a metabolising, self-regulating system; and reproduction and growth, though characteristic, are consequences of that system rather than its definition.

The most obvious and technically the most complicated feature of living organisms is their ability to sense the environment and respond to it. Biologists use the word consciousness for this capacity, in a broader sense than the everyday meaning. All organisms, prokaryotic and eukaryotic, unicellular and multicellular, plant and animal, respond to environmental stimuli, whether physical (light, temperature, gravity, touch, water), chemical (nutrients, toxins, hormones) or biological (other organisms). Plants respond to light by growing toward it, to gravity by sending roots downward, to touch by twining tendrils, to day length by flowering, and to pathogens by producing defensive chemicals. Human beings are the only organisms aware of themselves, that is, with self-consciousness; but every organism has consciousness in the sense of responsiveness, and this is a defining property of life.

Closely connected is self-organisation and self-regulation. A living body keeps its internal conditions steady in the face of changing surroundings, a capacity called homeostasis. It repairs damage, replaces worn-out parts, and coordinates the activities of its parts through chemical messengers. All this happens without any external designer; the system organises itself from the information encoded in its genes.

This brings in the idea of hierarchy and emergence. Living organisms are organised in levels: atoms form molecules, molecules such as proteins and nucleic acids form organelles, organelles form cells, cells form tissues, tissues form organs, organs form organ systems, and systems form the organism. At each level new properties appear that were not present at the level below. A mixture of the right chemicals in the right proportions is not a cell; a heap of cells is not a leaf; a leaf cannot do what a whole plant does. These new properties are said to be emergent. Life itself is the supreme emergent property, arising from the interactions of components that are individually non-living.

Because organisms are organised hierarchically and interact with one another, the study of living things extends beyond the individual to populations (all individuals of one species in a place), communities (all the populations in a place), ecosystems (communities together with their physical environment) and the biosphere, the sum of all ecosystems on Earth. Interactions between organisms, such as competition, predation, parasitism and symbiosis, are as much a part of being alive as the internal chemistry.

Bringing the threads together: living organisms are self-replicating, evolving and self-regulating interactive systems capable of responding to external stimuli. They grow, reproduce and metabolise, are made of cells, and show consciousness; among these, metabolism, cellular organisation and consciousness are the defining features, and the rest are characteristic. That sentence is the summary the examiner expects when asking 'What is living?'

Step out of doors anywhere in Telangana and the variety of living things is overwhelming: neem, tamarind and palmyra trees; grasses, sedges and weeds; lichens on rocks and mosses on walls; mushrooms after rain; insects, birds, lizards, frogs and cattle; and invisible microbes in every handful of soil. Extend this to the whole planet and the number of different kinds of organisms is vast. The number of species known and described so far is between 1.7 and 1.8 million, and estimates of the total, including species not yet discovered, run to many millions more. This variety of living organisms, at the level of species, of genes within species and of ecosystems, is called biodiversity.

Diversity on this scale creates a problem. In every region and in every language, local names are given to organisms, and the same plant may have dozens of names while one name may refer to several different plants. The plant known in Telugu as vepa is neem in English, nimba in Sanskrit and nim in Hindi; and 'lily' in English is applied to plants of several unrelated families. Communication between scientists in different countries would be impossible on such a basis. Hence the first need is to give every organism a single, universally accepted scientific name.

The second need is to organise the known kinds into groups so that they can be studied. It is impossible to study 1.8 million species one by one, but if organisms are placed in groups sharing common features, knowledge of one member tells us much about the others. This grouping is classification, and the science of it is taxonomy.

Before a new organism can be named or classified it must be identified: its characters must be described and compared with those of known organisms to decide whether it matches one of them or is new. Identification, nomenclature and classification are the three processes of taxonomy, and they are applied in that order to any organism encountered for the first time.

Classification also serves purposes beyond convenience. It reveals relationships: organisms placed in the same group are usually related by descent, so a good classification is also a summary of evolutionary history. It allows prediction: a newly found plant of the family Solanaceae is likely to contain alkaloids, because its known relatives do. It supports applied work in agriculture, forestry, medicine and conservation, where knowing exactly which species one is dealing with is essential. And it makes possible the recording of biodiversity, so that the loss of species can be measured and slowed.

The organisms of the earth were not all described at once; the work of naming and classifying has been going on for centuries and is far from finished, especially for insects, fungi and microbes. Every year thousands of new species are described, and the system of names and groups explained in the following topics is what allows this enormous, never-ending inventory to be kept in order.

Nomenclature is the standardised naming of organisms so that a given organism has one name that is recognised the world over. For plants the rules are laid down by the International Code for Botanical Nomenclature (ICBN), now called the International Code of Nomenclature for algae, fungi and plants; for animals by the International Code of Zoological Nomenclature (ICZN). Every scientific name is assigned only after the organism has been correctly identified and described, and the rules ensure that each name is used for one organism only and each organism has only one correct name.

The system used is binomial nomenclature, given to biology by Carolus Linnaeus in the eighteenth century. Each name has two components: the generic name (the name of the genus) followed by the specific epithet (the name of the species within the genus). The scientific name of mango is Mangifera indica: Mangifera is the genus, indica the specific epithet. Together the two words form the name of the species.

The universal rules of binomial nomenclature are:

• Biological names are generally in Latin or Latinised, whatever their origin, and are written in italics when printed.
• The name has two words; the first is the genus and the second the specific epithet.
• When handwritten, both words are underlined separately to indicate their Latin origin, since italics cannot be written by hand.
• The generic name begins with a capital letter; the specific epithet begins with a small letter. Thus Mangifera indica, never Mangifera Indica.
• The name of the author who first described the species is written after the specific epithet in an abbreviated form, in Roman (not italic) type: Mangifera indica Linn. (or L.). This tells the reader who published the name and helps trace the original description.
• The specific epithet may be repeated in animals (a tautonym such as Naja naja) but not in plants under the botanical code.

The advantage of a Latin name is that Latin is a dead language: it belongs to no country, changes no more, and is neutral between all modern tongues. The advantage of a two-word name is that it is short, unique and informative: the genus name groups related species together, so that Solanum tuberosum (potato), Solanum melongena (brinjal) and Solanum nigrum (black nightshade) are seen at a glance to be relatives.

A name may be changed only under the rules, for example when a species is found to belong to a different genus, in which case the original author's name is placed in brackets and the reviser's name follows; and the earliest validly published name has priority. Common names, by contrast, are unregulated and may be used freely in ordinary speech, but they have no place in a scientific description.

Students should practise writing names correctly: Triticum aestivum Linn. for wheat, Oryza sativa Linn. for rice, Azadirachta indica for neem, Homo sapiens for humans, Panthera tigris for tiger. A name printed upright or with the epithet capitalised loses marks.

Classification is the process by which organisms are grouped into convenient categories on the basis of easily observable characters. Plants, animals, dogs, cats, insects, mammals are all such categories. In scientific classification the categories are called taxa (singular taxon), and each taxon represents a rank in a hierarchy: a mango is a member of the taxon Mangifera at the rank of genus, of Anacardiaceae at the rank of family, of the taxon Plantae at the rank of kingdom. Note the distinction: 'genus' is a category or rank; 'Mangifera' is a taxon at that rank.

The science of classification is taxonomy. It is based on the study of external and internal structure, cell structure, developmental process and ecological information of organisms, and it comprises the processes of characterisation, identification, classification and nomenclature. Taxonomy has ancient roots; human beings have always needed to know which plants were edible, medicinal or poisonous, and early systems, such as those of Theophrastus in Greece and the Indian Vedic and Ayurvedic texts, classified plants by use or by habit (trees, shrubs, herbs). Linnaeus in the eighteenth century gave the first comprehensive, rule-based system.

Systematics is a wider term. The word comes from the Latin systema, meaning a systematic arrangement of organisms; Linnaeus used Systema Naturae as the title of his great work. Systematics takes into account not merely the description and classification of organisms but their evolutionary relationships. Modern systematics, sometimes called new systematics or biosystematics, uses evidence from morphology, anatomy, embryology, cytology, palynology, phytochemistry, molecular biology (DNA and protein sequences) and ecology to reconstruct the phylogeny, the family tree, of organisms and to build classifications that reflect it. Some authors treat taxonomy and systematics as synonyms; strictly, taxonomy is the part of systematics concerned with the theory and practice of classification and naming.

Three kinds of classification systems are recognised in botany:

• Artificial systems use one or a few easily seen characters, such as habit (trees, shrubs, herbs) or the number of stamens, as in Linnaeus's sexual system. They are convenient but group unrelated plants together.
• Natural systems use many characters, especially of the flower and fruit, and group plants by overall similarity, which usually reflects true relationship; Bentham and Hooker's system, still used in Indian herbaria, is the best-known example.
• Phylogenetic systems arrange organisms according to their evolutionary descent, primitive groups before advanced ones; Engler and Prantl, Hutchinson and, most recently, the Angiosperm Phylogeny Group are examples.

A further modern approach is numerical taxonomy, in which hundreds of characters are given equal weight and the similarity between organisms computed statistically; and cytotaxonomy and chemotaxonomy, which use chromosome number and structure or chemical constituents respectively.

The essential point for this chapter is that classification is not arbitrary. Organisms are grouped because they share characters, and shared characters, in the modern view, point to shared ancestry. The taxonomic hierarchy described next is the framework on which any of these systems is hung.

The species is the basic unit of classification. Every organism that has been described belongs to a species, and the species is the only taxonomic category that has a reality in nature independent of the taxonomist, because its members actually breed with one another. All the higher categories are groups of species assembled by comparison.

Taxonomic studies define a species as a group of individual organisms with fundamental similarities. Two related species can be distinguished from each other on the basis of distinct morphological differences. Mangifera indica, Solanum tuberosum and Panthera leo are species; in each name the second word is the specific epithet and the first the genus, and a genus may contain one or many species. Panthera contains the lion (P. leo), tiger (P. tigris) and leopard (P. pardus); Solanum contains hundreds of species; Mangifera contains the mango and several wild relatives. Human beings are the single species Homo sapiens.

The biological species concept, formulated by Ernst Mayr, defines a species as a group of actually or potentially interbreeding natural populations that is reproductively isolated from other such groups. Members of one species can mate and produce fertile offspring; members of different species either cannot mate, or produce sterile hybrids such as the mule (horse × donkey). This concept works well for sexually reproducing animals and plants but is hard to apply to organisms that reproduce asexually, such as many bacteria and fungi, or to fossils; for these, morphological, chemical or molecular criteria are used instead.

Within a species there is variation: no two individuals are identical, and populations from different areas may differ in size, colour or physiology. When such differences are consistent and geographically based, the populations may be recognised as subspecies or, in plants, as varieties, written as a third word after the specific epithet: Oryza sativa var. indica. Cultivated forms selected by farmers and breeders are cultivars, written in single quotes: Mangifera indica 'Banganapalli'.

The species is not fixed for all time. Populations that become isolated, by a mountain range, a river or a change of habitat, accumulate differences until they can no longer interbreed, and a new species has arisen. Speciation in this sense is the source of the diversity that taxonomy records, and the reason why a classification of species is also a picture of evolutionary history.

In practice a taxonomist recognises a species by comparing a specimen with descriptions and with type specimens preserved in herbaria, looking for the combination of characters that the species shows and its relatives do not. The examination usually asks for the definition of a species and for examples, and sometimes asks the student to explain why the species is the basic unit; the answer is that it is the lowest rank at which organisms interbreed and the unit from which every higher taxon is built.

Classification is not a single step but a process involving a hierarchy of steps, in which each step represents a rank or category. Since a category is a part of the overall taxonomic arrangement, it is called a taxonomic category, and all the categories together constitute the taxonomic hierarchy. Each category is a unit of classification and represents a rank; a group placed at that rank is a taxon. The categories in ascending order are species, genus, family, order, class, division (phylum in animals) and kingdom.

Species. The lowest category, defined in the previous topic: a group of individuals with fundamental similarities. Mangifera indica, Solanum tuberosum, Panthera leo. The specific epithets are indica, tuberosum and leo.

Genus. A genus comprises a group of related species that have more characters in common with one another than with the species of other genera. Genera are thus aggregates of closely related species. Potato (Solanum tuberosum), tomato (Solanum lycopersicum) and brinjal (Solanum melongena) are three different species of the genus Solanum; lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) belong to the genus Panthera, which differs from the genus Felis that contains the domestic cat. A genus may contain a single species (monotypic) or hundreds.

Family. A family is a group of related genera with fewer similarities than the species of a genus have. Families are characterised on the basis of both vegetative and reproductive features, especially of the flower, fruit and seed in plants. The genera Solanum, Petunia and Datura are placed in the family Solanaceae because they share regular pentamerous flowers, alternate leaves, bicarpellary ovary with oblique septum and berry or capsule fruits. Among animals, the genus Panthera (lion, tiger, leopard) and the genus Felis (cats) are placed in the family Felidae. Similarly the cat and the dog, though both carnivores, show enough differences to be placed in different families, Felidae and Canidae.

Plant family names, under the botanical code, end in -aceae: Solanaceae, Poaceae, Fabaceae, Anacardiaceae. A few older names are conserved as alternatives (Gramineae for Poaceae, Leguminosae for Fabaceae, Cruciferae for Brassicaceae, Compositae for Asteraceae, Umbelliferae for Apiaceae, Labiatae for Lamiaceae, Palmae for Arecaceae), and both forms are acceptable.

The important idea running through these ranks is that the number of shared characters decreases as one goes up the hierarchy. Two species in a genus share many characters; two genera in a family share fewer; two families in an order share still fewer. Conversely the number of organisms included increases: a species contains only its own individuals, a genus contains all its species, a family all its genera. This inverse relation between rank and similarity is the key to answering questions on the hierarchy.

Order. Just as genera are assembled into families on the basis of shared characters, families are assembled into orders. An order is the assemblage of families that exhibit a few similar characters; the similar characters are fewer than those shared by different genera of a family. The plant families Convolvulaceae and Solanaceae are included in the order Polemoniales (in some systems Solanales) mainly on the basis of floral characters such as regular, pentamerous, gamopetalous flowers with epipetalous stamens. In animals the order Carnivora includes the families Felidae and Canidae. Plant order names typically end in -ales.

Class. A class includes related orders. The order Primata, comprising monkeys, gorillas and gibbons, is placed in the class Mammalia along with the order Carnivora, which includes animals like tigers, cats and dogs, because all have hair and mammary glands. In flowering plants, the two classes Dicotyledonae (Magnoliopsida) and Monocotyledonae (Liliopsida) are separated by the number of cotyledons, venation, root system, vascular bundle arrangement and floral formula in threes or fours and fives. Solanales belongs to Dicotyledonae; Poales, containing the grasses, belongs to Monocotyledonae.

Division (Phylum). Classes comprising animals like fishes, amphibians, reptiles, birds and mammals constitute the next higher category, the phylum Chordata, on the basis of common features such as the presence of a notochord and a dorsal hollow neural system. In plants the corresponding rank is the division, and its names end in -phyta: Angiospermae (Magnoliophyta or Anthophyta), Gymnospermae, Pteridophyta, Bryophyta, and the algal divisions Chlorophyta, Phaeophyta and Rhodophyta. Dicotyledonae and Monocotyledonae are the two classes of the division Angiospermae.

Kingdom. All animals belonging to various phyla are assigned to the highest category, the kingdom Animalia; all plants to the kingdom Plantae. In the five-kingdom system of Whittaker, studied in the next chapter, the other kingdoms are Monera, Protista and Fungi. Kingdom is the highest rank in classical taxonomy; a still higher rank, the domain (Bacteria, Archaea, Eukarya), has been proposed on molecular evidence.

Intermediate categories. Where the hierarchy is not fine enough, taxonomists insert sub- and super-ranks: subspecies, subgenus, subfamily, suborder, subclass, subdivision, and superfamily, superorder and so on. In the classification of angiosperms, for example, the classes are divided into subclasses (Polypetalae, Gamopetalae, Monochlamydeae in Bentham and Hooker) and then into series before the orders are reached.

The complete hierarchy for two common plants and one animal, as required in the examination, is set out below; a student should be able to reproduce it and to name the rank of any term.

Reading the table downward, each row contains fewer organisms and more shared characters than the row above; reading across, mango and wheat part company at the class, while man is separate from the kingdom downward.

Taxonomic studies of various species of plants, animals and other organisms are useful in agriculture, forestry, industry and in general in knowing our bio-resources and their diversity. Such studies require correct classification and identification, and identification requires intensive laboratory and field work, and above all comparison with reliably named material. Over the centuries taxonomists have developed taxonomical aids: techniques, procedures and stores of information and specimens that make identification possible. The principal aids for botanists are the herbarium, the botanical garden, the museum, the zoological park and the identification key, together with published floras, manuals, monographs and catalogues.

Herbarium. A herbarium is a storehouse of collected plant specimens that are dried, pressed and preserved on sheets. The procedure is: collect the plant in flower or fruit with a note of locality, date and habitat; press it between blotting papers in a plant press until dry; poison it against insects and fungi; mount it on a standard herbarium sheet (about 29 × 42 cm) with glue or strips; and attach a label giving the date and place of collection, the English, local and botanical names, the family, the collector's name and number, and field notes on habit and habitat. The sheets are then arranged according to a universally accepted system of classification, usually Bentham and Hooker in Indian herbaria, and stored in cabinets.

The herbarium serves as a quick referral system in taxonomical studies. A botanist with an unknown plant compares it against named sheets; a specimen on which a species was first described, the type specimen, is the permanent reference for that name. Herbaria also record the distribution of species through their labels, preserve material of plants that have since become rare or extinct, supply material for anatomical, chemical and DNA study, and provide the raw data for floras. The largest herbaria hold millions of sheets; India's national herbarium is the Central National Herbarium at Kolkata under the Botanical Survey of India.

Botanical gardens. These are specialised gardens that have collections of living plants for reference. Each plant is labelled with its botanical or scientific name and its family, and often its origin. The garden may include glasshouses for tropical or desert plants, an arboretum of trees, sections for medicinal, economic and endangered plants, and a seed bank. Botanical gardens are used for identification by comparison with living material, for the study of plants through their life cycles, for introducing and acclimatising useful plants, for the ex situ conservation of threatened species, for education and for research in horticulture and plant breeding. The famous botanical gardens are the Royal Botanic Gardens at Kew in England, the Indian Botanical Garden (now the Acharya Jagadish Chandra Bose Indian Botanic Garden) at Howrah, and the National Botanical Research Institute at Lucknow.

A herbarium preserves what a plant looked like on a given day in a given place; a botanical garden preserves the living plant itself. Together they let a taxonomist see both the permanent record and the growing organism, and both remain indispensable even in the age of DNA barcoding, because a sequence has to be tied to a named specimen before it can identify anything.

Museums. Biological museums are generally set up in educational institutes such as schools and colleges. They have collections of preserved plant and animal specimens for study and reference. Specimens are preserved in containers or jars in preservative solutions such as formalin or alcohol; plant and animal specimens may also be preserved as dry specimens; insects are preserved in insect boxes after collecting, killing and pinning; larger animals such as birds and mammals are usually stuffed and preserved. Museums often have collections of skeletons of animals too. The museum's value for a botanist lies in the preserved fruits, seeds, woods, fungi and algae that cannot be represented on a herbarium sheet.

Zoological parks. These are places where wild animals are kept in protected environments under human care, which enables us to learn about their food habits and behaviour. All animals in a zoo are provided, as far as possible, with conditions similar to their natural habitats. Zoological parks are the animal counterpart of botanical gardens: living collections for study, breeding of endangered species and public education. The Nehru Zoological Park at Hyderabad is one of the largest in India.

Key. A key is a taxonomical aid used for the identification of plants and animals based on the similarities and dissimilarities of their characters. The commonest form is the dichotomous key, which presents a series of numbered pairs of contrasting statements called couplets. Each statement in a couplet is a lead. The user reads both leads of the first couplet, chooses the one that fits the specimen, and is directed to another couplet or to a name. Since one character is chosen at each step, one of the two alternatives is accepted and the other rejected, until only one name remains. Separate keys are required for each taxonomic category such as family, genus and species. Keys are generally analytical in nature, and a well-made key uses characters that are easy to observe and constant within the group.

An example of a short key to four genera of common plants:
1a. Leaves parallel-veined; flowers in threes ......... 2
1b. Leaves reticulate-veined; flowers in fours or fives ......... 3
2a. Stem hollow, jointed; fruit a caryopsis ......... Triticum
2b. Stem solid; fruit a capsule ......... Lilium
3a. Fruit a drupe; leaves simple, alternate ......... Mangifera
3b. Fruit a berry; flowers with plicate corolla ......... Solanum

Flora, manuals, monographs and catalogues. A flora contains the actual account of the habitat and distribution of plants of a given area, with keys and descriptions, providing an index to the plant species found there; the Flora of British India by Hooker and the various state and district floras are examples. Manuals are useful in providing information for identification of names of species found in an area, often with practical keys. Monographs contain information on any one taxon, treating a family or a genus exhaustively over its whole range. Catalogues list the taxa of a region or a collection with their names and references. These publications, together with the specimens in herbaria and museums, make up the working library of the taxonomist.

The examiner commonly asks the student to define a key and to name its parts (couplet and lead), to distinguish a flora from a monograph, and to state the function of a herbarium or a botanical garden. All these are short-answer questions and the definitions above answer them directly.