Chapter 1 — ଜୈବ ବିବିଧତା (Biodiversity)

The word biodiversity is a short form of biological diversity. It means the variety of all living organisms found on the Earth or in a particular area: the different kinds of plants, animals, fungi and micro-organisms, the differences within each kind, and the different natural systems in which they live together. The term was popularised by the American biologist Edward O. Wilson in the 1980s, but the idea is as old as human observation of nature. A farmer in Odisha who grows several traditional varieties of paddy, a fisherman who knows the fifty kinds of fish in Chilika lake, and a tribal healer who can name a hundred medicinal plants of Similipal are all dealing with biodiversity.

Scientists describe biodiversity at three levels. Genetic diversity is the variation in genes within a single species. All human beings belong to one species, yet no two people are alike; all the mango trees of India belong to one species, yet Amrapali, Dasheri and Langra taste different. This variation is the raw material on which selection and breeding work. Species diversity is the number and abundance of different species in a region. A patch of rain forest in the Eastern Ghats holds far more species than a patch of the same size in a desert, so we say the forest has higher species diversity. Ecosystem diversity is the variety of habitats and ecological systems, such as forests, grasslands, wetlands, mangroves, coral reefs and rivers, each with its own community of organisms.

It is estimated that about 1.7 to 1.8 million species have been named and described so far, while the true number on Earth may be anywhere between 5 and 30 million. Insects alone account for more than half of the known species. India occupies only about 2.4 per cent of the world's land area, yet it holds nearly 7 to 8 per cent of all recorded species, which is why it is counted among the seventeen megadiverse countries. Within India, the Eastern Ghats and the coastal wetlands of Odisha are important pockets of this wealth.

Biodiversity matters for practical reasons as well as scientific ones. It provides food, fibre, timber, medicines and fuel; it keeps the soil fertile, purifies water and air, pollinates crops and regulates climate; and it has cultural and aesthetic value in our festivals, art and daily life. When a species is lost, the services it performed are lost with it, and the loss is permanent. That is why biodiversity is studied not only to satisfy curiosity but to protect the living support system of the planet.

Imagine a library with lakhs of books thrown into one heap. Finding a single book would be impossible. A library therefore arranges books by subject, author and title. Biologists face the same problem with millions of species, and the solution is the same: to arrange organisms into groups on the basis of similarities and differences. This process is called classification, and the branch of biology that deals with it is taxonomy (from the Greek taxis, arrangement, and nomos, law). The scientific study of the diversity of organisms and their relationships is called systematics.

Classification serves several purposes. It makes the study of an enormous number of organisms manageable, because knowing the features of a group tells us the features of every member of that group. It shows the relationships among organisms and gives a picture of how they evolved. It gives every organism a definite place and a definite name, so that scientists in Odisha, Japan and Brazil can be sure they are talking about the same creature. It also helps in identifying new organisms and in applied fields such as agriculture, medicine and forestry.

On what basis are organisms grouped? The earliest attempts used obvious, superficial characters. Aristotle divided animals into those with red blood and those without, and plants into herbs, shrubs and trees. Such systems are called artificial because they rest on one or two convenient characters. Modern classification is natural: it uses a large number of characters that reflect the fundamental design of the organism. The main criteria are:

• Cell structure: whether the cell has a true nucleus bounded by a membrane (eukaryotic) or not (prokaryotic).
• Body organisation: whether the organism is a single cell (unicellular) or made of many cells (multicellular), and whether the cells are organised into tissues and organs.
• Mode of nutrition: whether the organism makes its own food by photosynthesis (autotrophic) or depends on others (heterotrophic), and within heterotrophs whether it ingests food or absorbs it.
• Phylogeny: the evolutionary history and relationship of the group.

A character that appears earlier in evolution and is shared by a wide group of organisms is used first, and characters that arose later are used for finer divisions. For example, the presence of a nucleus separates bacteria from everything else; among nucleated organisms, multicellularity separates the protists from the rest; among multicellular organisms, the mode of nutrition separates plants from fungi and animals. The system that results is a nested set of groups within groups, which we study in the next topic.

Classification arranges organisms in a series of ranks or categories, each contained within the next larger one, like a set of boxes nested inside each other. This arrangement is called the taxonomic hierarchy. Carolus Linnaeus, the Swedish naturalist of the eighteenth century, used a small number of categories; later workers expanded the list to the seven obligate categories used today. From the largest to the smallest they are: Kingdom, Phylum (called Division in plants), Class, Order, Family, Genus and Species. Students often remember the sequence by the phrase 'King Philip Came Over For Good Soup'.

The species is the basic unit of classification. A species is a group of organisms that resemble one another closely, share a common ancestry and can interbreed in nature to produce fertile offspring. A horse and a donkey can mate, but their offspring, the mule, is sterile, so horse and donkey are separate species. Closely related species are grouped into a genus; the lion (Panthera leo), tiger (Panthera tigris) and leopard (Panthera pardus) belong to the genus Panthera. Related genera form a family (the cat family Felidae includes Panthera and the domestic cat genus Felis); related families form an order (Carnivora includes cats, dogs and bears); orders form a class (Mammalia); classes form a phylum (Chordata); and phyla form a kingdom (Animalia).

Two important trends run through the hierarchy. As we move up from species to kingdom, the number of organisms in the group increases, but the number of characters they share decreases. All members of the species Panthera leo share almost every feature; all members of Kingdom Animalia share only a handful, such as being multicellular, eukaryotic and heterotrophic. Conversely, as we move down the hierarchy, similarity increases and the group becomes smaller. This is why the species is the most natural and well defined unit, while the boundaries of higher categories are decided by taxonomists.

Between the obligate categories, taxonomists sometimes insert intermediate ones such as sub-phylum, sub-class or super-family when the diversity of a group demands it. Vertebrata, for instance, is a sub-phylum of Chordata.

The first systematic classification is credited to the Greek philosopher Aristotle (384–322 BC), who grouped living things into plants and animals, using habitat (land, water, air) and a few visible features. Carolus Linnaeus in 1758 formalised the two kingdom system, Plantae and Animalia, and gave us the binomial names still in use. For two centuries this arrangement served well, but as microscopes improved it became clear that many organisms did not fit. Bacteria have no nucleus; fungi look like plants but do not photosynthesise; euglena photosynthesises but swims and can feed like an animal; sponges were once thought to be plants. Ernst Haeckel in 1866 proposed a third kingdom, Protista, for such organisms, and Herbert Copeland in 1956 separated the bacteria as Monera, making four kingdoms.

In 1969 the American ecologist Robert H. Whittaker proposed the five kingdom classification, which is followed in this chapter. He used four criteria: (1) complexity of cell structure, prokaryotic or eukaryotic; (2) complexity of body organisation, unicellular or multicellular; (3) mode of nutrition, autotrophic (photosynthetic) or heterotrophic (absorptive as in fungi, or ingestive as in animals); and (4) phylogenetic relationship. On this basis all organisms are placed in five kingdoms:

The system has clear merits. It separates prokaryotes from eukaryotes, which is the deepest division in living things. It recognises fungi as a group distinct from plants, on the basis of their cell wall of chitin and absorptive nutrition. It places unicellular eukaryotes together in Protista instead of forcing them into plants or animals. It also reflects the evolutionary sequence: Monera gave rise to Protista, and from protists arose the three multicellular lines, Fungi, Plantae and Animalia, each with a different way of obtaining food.

The system is not perfect. Protista remains a mixed bag of organisms with little in common except being unicellular eukaryotes. Viruses, which are not made of cells and show life only inside a host, have no place in it. In 1990 Carl Woese proposed dividing Monera into two domains, Archaea and Bacteria, giving a three domain system. At the Class 9 level, however, the five kingdom scheme remains the standard framework, and the rest of this chapter follows it.

Kingdom Monera contains the prokaryotes, the simplest and most ancient living cells, which appeared on Earth about 3.5 billion years ago. The defining feature of a moneran is that its cell has no true nucleus: the genetic material is a single circular molecule of DNA lying naked in the cytoplasm in a region called the nucleoid, with no nuclear membrane around it. Membrane bound organelles such as mitochondria, chloroplasts, endoplasmic reticulum and Golgi bodies are also absent. Ribosomes are present but are smaller (70S) than those of eukaryotes. Most monerans have a rigid cell wall made of peptidoglycan (murein), not cellulose, and some are surrounded by a slimy capsule. Many move by means of one or more flagella.

Monerans are unicellular, though some grow as chains or clusters of cells, and they are the smallest cells known, usually 1 to 10 micrometres in size. They are found everywhere: in soil, water, air, hot springs, salt pans, the intestines of animals and on human skin. In nutrition they show every possible mode. Some are autotrophic: the cyanobacteria (blue-green algae such as Nostoc and Anabaena) photosynthesise using chlorophyll scattered in the cytoplasm, and chemosynthetic bacteria such as the nitrifying bacteria obtain energy from chemical reactions. Most bacteria, however, are heterotrophic, living as saprophytes on dead organic matter or as parasites in living hosts.

Bacteria are named by shape: cocci are spherical (Streptococcus), bacilli are rod shaped (Lactobacillus, Escherichia coli), spirilla are spiral (Spirillum) and vibrios are comma shaped (Vibrio cholerae). They reproduce chiefly by binary fission, a single cell dividing into two, sometimes every twenty minutes, which is why a spoilt curry can carry crores of bacteria by morning. Under unfavourable conditions some bacilli form tough resting endospores that survive heat and drought.

Monerans are of enormous importance. Cyanobacteria and other nitrogen fixing bacteria such as Rhizobium in the root nodules of legumes convert atmospheric nitrogen into compounds that plants can use, enriching the soil. Decomposer bacteria break down dead bodies and return minerals to the earth. Lactobacillus turns milk into curd, and other bacteria are used to make vinegar, cheese, antibiotics such as streptomycin, and vitamins. On the other hand, bacteria cause diseases such as cholera, typhoid, tuberculosis, tetanus and leprosy in humans, and blight and wilt in crops. Mycoplasma, the smallest known cells, lack a cell wall altogether and cause diseases in plants and animals.

Kingdom Protista contains the unicellular eukaryotes: organisms made of a single cell that possesses a true nucleus with a nuclear membrane and the full set of membrane bound organelles, including mitochondria, endoplasmic reticulum, Golgi bodies and, in the photosynthetic forms, chloroplasts. Protists are therefore far more complex than monerans even though both are single celled. The single cell of a protist performs every function of life, feeding, moving, respiring, excreting and reproducing, so it is often described as a complete organism in one cell rather than a simple cell.

Protists live mainly in water: ponds, ditches, rivers, the sea, moist soil and the body fluids of other organisms. Many move by means of special locomotory structures, and the type of structure is used to group them. Amoeba moves by pushing out temporary finger like projections of cytoplasm called pseudopodia (false feet), which also surround and engulf food particles. Paramecium, the slipper animalcule, is covered with thousands of fine hair like cilia that beat in rhythm to propel it and to sweep food into its oral groove. Euglena moves with a long whip like flagellum and has a light sensitive red eyespot that guides it towards light. Plasmodium, the malarial parasite, has no locomotory organ in its adult stage and is carried in blood.

Nutrition in protists is remarkably varied. Photosynthetic protists such as Euglena, diatoms and dinoflagellates contain chlorophyll and are called protozoan algae or phytoplankton; they form the base of the food chain in oceans and lakes. Heterotrophic protists, the protozoa, ingest solid food by forming food vacuoles (holozoic nutrition), as in Amoeba and Paramecium. Some are parasitic: Plasmodium causes malaria, Entamoeba histolytica causes amoebic dysentery, Trypanosoma causes sleeping sickness and Giardia causes diarrhoea. Euglena is famous for being mixotrophic: it photosynthesises in light and absorbs organic food in darkness, showing both plant like and animal like characters.

Fresh water protists face the problem of water constantly entering the cell by osmosis; they expel it with a pulsating contractile vacuole. Reproduction is usually asexual by binary fission, but many protists also show sexual processes such as conjugation in Paramecium, where two cells exchange nuclear material. Under harsh conditions some form protective cysts.

Diatoms deserve special mention. Their cell walls are made of silica and form beautiful glass like shells that persist after death; deposits of these shells, called diatomaceous earth, are used in filters, polishes and toothpaste. Because protists include ancestors of fungi, plants and animals, the kingdom is a crucial link in the evolutionary story of life.

The fungi are eukaryotic, mostly multicellular organisms that were long mistaken for plants because they grow rooted in one place and reproduce by spores. Whittaker separated them into their own kingdom because they differ from plants in three fundamental ways. First, fungi have no chlorophyll and cannot photosynthesise. Second, their cell wall is made of chitin, the same tough substance found in the exoskeleton of insects, whereas the plant cell wall is cellulose. Third, they store food as glycogen, like animals, not as starch.

Fungi are heterotrophic with an absorptive mode of nutrition. They secrete digestive enzymes on to their food, break it down outside the body, and absorb the soluble products through their cell walls. Most fungi are saprophytes, feeding on dead and decaying matter such as fallen leaves, rotting wood, stale bread and dung; along with bacteria they are the great decomposers of the biosphere. Some are parasites on living plants and animals: Puccinia causes rust of wheat, Albugo causes white rust of mustard, and various fungi cause ringworm and athlete's foot in humans. A few live in symbiosis: lichens are a partnership between a fungus and an alga, and mycorrhizae are associations between fungal threads and the roots of trees such as sal and pine, in which the fungus supplies minerals and the tree supplies sugars.

The body of a typical fungus is not made of tissues but of a network of fine thread like filaments called hyphae; the whole tangled mass is the mycelium. In Mucor and Rhizopus (bread mould) the hyphae have no cross walls and contain many nuclei (coenocytic); in Penicillium and mushrooms the hyphae are divided by septa. The familiar mushroom is only the fruiting body; the real organism is the mycelium hidden in the soil or wood. Yeast (Saccharomyces) is an exception, a unicellular fungus that reproduces by budding.

Fungi reproduce vegetatively by fragmentation of the mycelium, asexually by enormous numbers of light spores (sporangiospores in Rhizopus, conidia in Penicillium) that are carried by wind, and sexually by fusion of hyphae followed by spore formation. The black powdery appearance of mould on bread is millions of sporangia.

Economically fungi are both friend and foe. Yeast ferments sugar to alcohol and carbon dioxide, giving us bread, idli and dosa batter, and beverages. Penicillium notatum gave the world its first antibiotic, penicillin, discovered by Alexander Fleming in 1928. Mushrooms such as Agaricus and the paddy straw mushroom widely cultivated in Odisha are nutritious food. Against this, fungi spoil stored grain, fruit and leather, cause crop diseases, and the poisonous toadstools can kill.

Kingdom Plantae includes all multicellular, eukaryotic, autotrophic organisms that possess chlorophyll and a cell wall of cellulose. Plants make their own food by photosynthesis and store it mainly as starch. The kingdom is divided on the basis of three questions: does the plant body have distinct root, stem and leaf, or is it an undifferentiated thallus? Does it have special tissues (xylem and phloem) to conduct water and food? Does it bear seeds, and are the seeds naked or enclosed in a fruit? The answers give five divisions, of which the two simplest are studied here.

Thallophyta are the simplest plants. The plant body is a thallus: it is not differentiated into root, stem and leaves, and it has no vascular tissue. Thallophytes are mostly aquatic and are commonly called algae. They range from single cells (Chlamydomonas), through unbranched filaments (Spirogyra, the pond silk, and Ulothrix), to large sea weeds many metres long (Laminaria, Sargassum). On the basis of their pigments they are grouped as green algae (Chlorophyceae, e.g. Spirogyra, Ulva), brown algae (Phaeophyceae, e.g. Fucus, Laminaria) and red algae (Rhodophyceae, e.g. Polysiphonia). Reproduction is vegetative by fragmentation, asexual by spores and sexual by fusion of gametes. Algae produce a large share of the oxygen of the atmosphere, are the food of aquatic animals, and yield agar (from red algae), iodine and alginate (from brown algae); Spirulina and Chlorella are cultivated as protein rich food.

Bryophyta are called the amphibians of the plant kingdom because, although they live on land, they need water for the male gametes to swim to the female gametes during fertilisation. They are small plants, seldom more than a few centimetres tall, growing in damp shady places on soil, rocks and tree trunks. The plant body is still thallus like or is differentiated into a stem like axis and leaf like structures, but it has no true roots; it is anchored by thread like rhizoids. There is no vascular tissue, so water moves from cell to cell, which limits their size. The dominant plant is the gamete producing generation (gametophyte); after fertilisation a small spore producing capsule (sporophyte) grows on it and remains dependent on it. Examples are the liverworts Marchantia and Riccia, which are flat and lobed, and the mosses Funaria and Polytrichum, which have tiny leaves in spirals. Mosses form the green carpet on old walls in the rainy season, prevent soil erosion, and Sphagnum moss forms peat and is used as packing material because it absorbs many times its weight in water.

Pteridophyta are the first plants with a body clearly differentiated into true roots, stem and leaves and with vascular tissue, xylem for conducting water and phloem for conducting food. This internal plumbing allowed them to grow tall; the coal deposits of the world are largely the remains of giant pteridophyte forests of the Carboniferous period. They have no flowers and no seeds; they reproduce by spores borne in sporangia, usually clustered in brown patches called sori on the underside of leaves. Like bryophytes they need water for fertilisation, so most live in moist shady places. Here the spore bearing plant is the main plant, and the gametophyte is a tiny heart shaped prothallus. Examples are the ferns (Pteris, Dryopteris, Adiantum or maidenhair fern), the horsetail Equisetum, the clubmoss Lycopodium, and Marsilea, the four leaved water fern common in Odisha paddy fields.

Thallophyta, Bryophyta and Pteridophyta together are called cryptogams (Greek: hidden marriage), because their reproductive organs are inconspicuous and they produce no seeds. The remaining two groups produce seeds and are called phanerogams or spermatophytes. The seed, an embryo packed with food and protected by a coat, freed plants from dependence on water for reproduction and allowed them to conquer dry land.

Gymnosperms (Greek: naked seed) bear seeds that are not enclosed in a fruit. The ovules lie exposed on the scales of woody cones; there are no flowers and no ovary. They are mostly evergreen trees and shrubs with needle like leaves, well adapted to cold and dry conditions, and they form the vast coniferous forests of the Himalaya and northern lands. Examples are Pinus (pine), Cedrus (deodar), Cycas (which looks like a palm and is grown in Odisha gardens) and Ginkgo. They give timber, resin, turpentine and paper pulp.

Angiosperms (Greek: enclosed seed) are the flowering plants, the most advanced, most diverse and most successful group with about 2.5 lakh species. The reproductive organs are borne in flowers; the ovules are enclosed in an ovary which after fertilisation becomes the fruit, and the seeds lie inside it. Angiosperms range from tiny duckweed to giant banyan trees and dominate every land habitat. On the basis of the number of cotyledons (seed leaves) in the embryo they are divided into two classes:

Kingdom Animalia includes multicellular eukaryotic organisms that are heterotrophic, take in food by ingestion, lack a cell wall and chlorophyll, and are usually capable of movement. The kingdom is divided into phyla on the basis of a series of characters: whether the cells are organised into tissues; whether the body is symmetrical, and if so radially (like a wheel) or bilaterally (with a left and a right half); the number of germ layers, two (diploblastic) or three (triploblastic); the presence and type of body cavity or coelom; whether the body is segmented; and whether a notochord is present. We begin with the three simplest phyla.

Phylum Porifera (pore bearers) is the phylum of sponges. These are the simplest multicellular animals; their cells are loosely arranged and do not form true tissues or organs, and for centuries they were thought to be plants because they are fixed to rocks (sessile). The body is a hollow sac or vase perforated by countless minute pores called ostia; water is drawn in through them by flagellated collar cells, food particles and oxygen are taken from it, and the water leaves through a large opening, the osculum. This canal system is the hallmark of the phylum. The body is supported by a skeleton of needle like spicules of calcium carbonate or silica, or by fibres of spongin, the soft bath sponge. Sponges are mostly marine and asymmetrical, and reproduce by budding and by gametes. Examples: Sycon, Spongilla (a fresh water sponge) and Euspongia.

Phylum Coelenterata (or Cnidaria) includes hydra, jellyfish, sea anemones and corals. The body is radially symmetrical and diploblastic, made of two cell layers, ectoderm and endoderm, with jelly like mesoglea between them. For the first time there is a true tissue level of organisation. The body is a sac with a single opening, the mouth, surrounded by tentacles that carry stinging cells called cnidoblasts, used to paralyse prey and for defence; a jellyfish sting is these cells at work. Digestion occurs in the central gastrovascular cavity. Two body forms occur: the fixed cylindrical polyp (hydra, sea anemone) and the free swimming umbrella shaped medusa (jellyfish). Corals are colonial polyps that secrete a limestone skeleton and build reefs.

Phylum Platyhelminthes (flatworms) marks three advances: the body is bilaterally symmetrical, triploblastic (a third layer, mesoderm, lies between ectoderm and endoderm), and it has organs. There is no body cavity (acoelomate), and the body is flat like a leaf or ribbon, which allows oxygen to reach every cell by diffusion. Most are parasites with hooks and suckers, and most are hermaphrodite, carrying both male and female organs. Examples: Planaria, a free living flatworm famous for regenerating a whole body from a fragment; the liver fluke Fasciola which infests sheep; and the tapeworm Taenia solium, which lives in the human intestine and is contracted by eating undercooked pork.

Phylum Nematoda (Aschelminthes) contains the roundworms, which have a cylindrical, unsegmented body tapering at both ends and covered by a tough cuticle. They are bilaterally symmetrical and triploblastic, and they show a body cavity, but it is not lined by mesoderm and is called a pseudocoelom. Unlike flatworms they have a complete digestive tube with mouth and anus, and the sexes are separate. Many are parasites of great medical importance. Ascaris lumbricoides, the common roundworm, infects the human intestine through contaminated food and water and is common in children; Wuchereria bancrofti, spread by Culex mosquitoes, blocks the lymph vessels and causes filariasis (elephantiasis), which was widespread in coastal Odisha; hookworm and pinworm are other examples. Free living nematodes are abundant in soil.

Phylum Annelida (ringed worms) brings two major advances. The body is divided into a series of similar ring like segments (metameric segmentation), visible as the rings of an earthworm, and there is a true coelom lined with mesoderm, in which organs are suspended. Annelids have a closed circulatory system with blood vessels, an excretory system of nephridia, and a nerve cord. Locomotion is by muscles of the body wall aided by tiny bristles called setae. Examples are the earthworm Pheretima, which aerates and enriches the soil and is called the farmer's friend; the leech Hirudinaria, a blood sucking ectoparasite of cattle and man; and Nereis, the marine sandworm.

Phylum Arthropoda (jointed feet) is the largest phylum, containing over two thirds of all known animal species. The distinguishing characters are a segmented body usually grouped into head, thorax and abdomen; jointed appendages (legs, antennae, mouth parts); and a hard external skeleton of chitin which is shed periodically as the animal grows (moulting). The coelom is reduced and the blood flows freely in body spaces, an open circulatory system with a cavity called the haemocoel. Respiration is by gills in aquatic forms, by tracheae (air tubes) in insects and by book lungs in spiders and scorpions. The main classes are Insecta (three pairs of legs, usually two pairs of wings: cockroach, butterfly, honey bee, mosquito, housefly), Crustacea (prawn, crab), Arachnida (four pairs of legs: spider, scorpion) and Myriapoda (centipede, millipede). Arthropods pollinate crops, give silk, honey and lac, and also destroy crops and carry diseases such as malaria and dengue.

Phylum Mollusca (soft bodied) is the second largest phylum. The body is soft and unsegmented, with a muscular foot for creeping or burrowing, a visceral mass containing the organs, and a fold of skin called the mantle which secretes a calcareous shell in most forms. The coelom is reduced and circulation is open. Respiration is by gills in a mantle cavity. Examples are the snail Pila, the garden slug, the pearl oyster and the freshwater mussel Unio (with a two part shell), and the octopus and squid, in which the foot is modified into arms and the shell is internal or absent. Oysters give pearls, and the shells of the Chilika lake mussels are burnt to make lime.

Phylum Echinodermata (spiny skinned) contains exclusively marine animals such as the starfish (Asterias), sea urchin, brittle star, sea cucumber and sea lily. Their skin bears spines and plates of calcium carbonate that form an internal skeleton just under the skin. The adults are radially symmetrical, usually with five arms or five fold pattern, although the larva is bilateral, showing that they evolved from bilateral ancestors. The unique feature of the phylum is the water vascular system: sea water enters through a sieve plate and is pumped into hundreds of hollow tube feet that stretch and contract to move the animal, hold prey and breathe. Echinoderms are triploblastic and coelomate, have no head or brain, and show remarkable power of regeneration; a starfish can regrow a lost arm, and in some species a single arm regrows a whole starfish. Starfish are a pest on oyster beds and coral reefs.

Phylum Chordata is the phylum of the most familiar animals, including ourselves. Every chordate, at some stage of its life, shows three characters: a notochord, a flexible rod of cells running along the back which supports the body and in vertebrates is replaced by the backbone; a hollow dorsal nerve cord lying above the notochord, from which the brain and spinal cord develop; and pharyngeal gill slits, openings in the wall of the pharynx which persist as gills in fishes and disappear in land vertebrates, where they are seen only in the embryo. Chordates are bilaterally symmetrical, triploblastic and coelomate, with a closed circulation and a post anal tail at some stage.

The lower chordates, or protochordates, keep the notochord and have no backbone. Sub phylum Urochordata includes the sea squirt Herdmania, and sub phylum Cephalochordata includes Amphioxus (Branchiostoma), a small fish like animal in which the notochord runs the whole length of the body and which is regarded as a model of the ancestral chordate. In the sub phylum Vertebrata the notochord is replaced during development by a vertebral column of separate bones or cartilages, the brain is enclosed in a skull (cranium), and there is a well developed head with paired sense organs and usually two pairs of limbs or fins. Vertebrates are divided into five classes, Pisces, Amphibia, Reptilia, Aves and Mammalia, on the basis of their skeleton, breathing organs, heart, body covering, temperature regulation and mode of reproduction, which the next topic takes up in detail. The vertebrates include the largest animals that have ever lived, the blue whale in the sea and the dinosaurs on land, and the animals of greatest importance to human beings as food, labour and companions.

The sub phylum Vertebrata is divided into five classes. Their distinguishing characters are asked for again and again in examinations, so they should be learnt as a comparison.

Class Pisces (fishes) are aquatic, cold blooded (poikilothermic, body temperature varies with the surroundings) vertebrates. The body is streamlined and covered with scales; they swim with fins and breathe dissolved oxygen through gills. The heart has two chambers, one auricle and one ventricle. Most lay eggs (oviparous) and fertilisation is usually external. Cartilaginous fishes (sharks, rays) have a skeleton of cartilage, gill slits without a cover and a mouth on the underside; bony fishes (rohu, catla, hilsa, seer fish) have a bony skeleton, gills protected by an operculum and an air bladder for buoyancy.

Class Amphibia (frogs, toads, salamanders) live both in water and on land, and return to water to breed. The skin is moist, glandular and without scales, and takes part in breathing. The larva (tadpole) breathes by gills; the adult breathes by lungs and skin. The heart has three chambers, two auricles and one ventricle. They are cold blooded and lay jelly covered eggs in water, with external fertilisation.

Class Reptilia (lizards, snakes, turtles, crocodiles) are the first fully terrestrial vertebrates. The body is covered with dry, horny scales that prevent water loss. They breathe entirely by lungs, are cold blooded and creep or crawl on short limbs or on the belly. The heart is three chambered with the ventricle partly divided, except in crocodiles which have four chambers. Fertilisation is internal, and they lay shelled eggs on land. The olive ridley turtle that nests at Gahirmatha and the saltwater crocodile of Bhitarkanika are reptiles.

Class Aves (birds) are warm blooded (homeothermic, constant body temperature), with the body covered in feathers and forelimbs modified into wings. The bones are hollow to reduce weight, the jaws form a toothless beak, and the heart is four chambered. Air sacs connected to the lungs give a continuous flow of air. Fertilisation is internal and they lay hard shelled eggs which they incubate. Examples: crow, pigeon, peacock, and the flightless ostrich and kiwi.

Class Mammalia are warm blooded vertebrates whose skin bears hair and whose females have mammary glands to feed the young with milk. They have a four chambered heart, a muscular diaphragm separating chest and abdomen, external ears (pinnae), teeth of different kinds, and lungs. Most give birth to living young (viviparous) nourished before birth through a placenta; the exceptions are the egg laying platypus and echidna, and the pouched kangaroo. Examples: man, cat, cow, elephant, bat (a flying mammal) and whale and dolphin (aquatic mammals).

Every organism is known by a local name, and this causes confusion. The bird called kaua in Odia is kauwa in Hindi, kaakam in Tamil and crow in English; the same word 'lily' is used for several unrelated plants; and a single species may have a dozen names in different districts of one state. Scientists need one name, understood everywhere, for each species. The system that provides this is binomial nomenclature (two name naming), introduced by Carolus Linnaeus in his book Species Plantarum (1753) and Systema Naturae (1758). Under this system the scientific name of every organism consists of two words: the first is the generic name (the genus) and the second is the specific epithet (the species). Thus the scientific name of man is Homo sapiens, of the mango Mangifera indica, of the tiger Panthera tigris, of rice Oryza sativa and of the housefly Musca domestica.

The rules for writing scientific names are fixed by international codes, the International Code of Botanical Nomenclature (ICBN) for plants and the International Code of Zoological Nomenclature (ICZN) for animals, and are as follows:

• The names are in Latin or are Latinised, because Latin is a dead language and does not change.
• The generic name begins with a capital letter and the specific epithet begins with a small letter: Panthera leo, never Panthera Leo.
• When printed, the two words are written in italics; when handwritten, each word is underlined separately.
• The generic name is a noun and the specific epithet is usually an adjective describing the organism (indica, of India; sativa, cultivated; domestica, of the house).
• The name of the author who first described the species may be added after the name in abbreviated form, for example Mangifera indica L., where L. stands for Linnaeus.
• No two genera in the same kingdom may have the same name, and no two species in one genus may have the same epithet.

The advantages are clear. A scientific name is unique and universal. It shows relationship: Panthera leo, Panthera tigris and Panthera pardus are at once recognised as close relatives. It is stable and does not depend on language or region. Sometimes a subspecies or variety is indicated by a third word, making the name trinomial: the Bengal tiger is Panthera tigris tigris, and modern man is sometimes written Homo sapiens sapiens.

Common scientific names a Class 9 student should know include: neem Azadirachta indica, banyan Ficus benghalensis, potato Solanum tuberosum, pea Pisum sativum, wheat Triticum aestivum, frog Rana tigrina, peacock Pavo cristatus, cow Bos indicus, dog Canis familiaris and the malarial parasite Plasmodium vivax.

Odisha is one of the most biologically rich states of India. It has a coastline of about 480 km, the mangrove delta of the Mahanadi and Brahmani rivers, the Eastern Ghats running through its interior, and the northern plateau bordering Jharkhand; this variety of landscape produces a corresponding variety of life. Forests cover roughly a third of the state and are mostly tropical moist and dry deciduous forests dominated by sal (Shorea robusta), with teak, bamboo, mahua, kendu and a wealth of medicinal plants. The state has recorded more than 2,700 species of flowering plants, over 550 species of birds, about 90 species of mammals, over 100 reptiles and hundreds of species of fish.

Several places are famous for particular treasures. Chilika, Asia's largest brackish water lagoon, is a Ramsar wetland of international importance; it hosts about ten lakh migratory birds every winter, flamingos, pelicans, ducks and waders that fly from Siberia and Central Asia, and it is home to the Irrawaddy dolphin. Similipal in Mayurbhanj is a tiger reserve and a UNESCO biosphere reserve with tigers, elephants, leopards, gaur, a rare melanistic (black) tiger population, more than 1,000 plant species and about 100 species of orchids. Bhitarkanika in Kendrapara is the second largest mangrove forest of India, the stronghold of the saltwater crocodile, and shelters king cobras, water monitors and heronries. Gahirmatha beach nearby is the world's largest mass nesting ground (arribada) of the olive ridley sea turtle, where lakhs of females come ashore on a few nights each year; Rushikulya in Ganjam is a second rookery. Elephants roam Chandaka near Bhubaneswar, blackbuck live in the grasslands of Ganjam, and Nandankanan zoo has bred white tigers and gharials.

This wealth is under threat. Forests are cleared for mining, industry, roads and cultivation; wetlands are drained or polluted; sea turtles are killed in trawler nets and disoriented by lights on the coast; elephants are electrocuted and die on railway tracks; rare orchids and medicinal plants are collected illegally; and invasive species such as water hyacinth choke Chilika. The loss of habitat is the biggest single cause of extinction, followed by over exploitation, pollution, introduced species and climate change.

Conservation takes two forms. In situ (on site) conservation protects species in their natural habitat through national parks, wildlife sanctuaries, biosphere reserves and tiger reserves; Odisha has two national parks (Similipal and Bhitarkanika) and nineteen sanctuaries. Ex situ (off site) conservation keeps species outside their habitat in zoos, botanical gardens, seed banks and gene banks; Nandankanan and the Regional Plant Resource Centre at Bhubaneswar are examples. Laws such as the Wildlife (Protection) Act 1972 and the Biological Diversity Act 2002 back these efforts, and the traditional wisdom of communities that protect sacred groves and village forests is equally important. Every student can contribute by planting native trees, refusing products made from wild animals, and reporting poaching.