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Chapter 7 -Diversity in Living Organisms 1. What isthe basis of classification? Organisms differ in their form, structure and mode of living. Hence, based on their similarities theyshould be grouped. The grouping of related organisms helps us in studying theirevolutionary relationships. Classification is thedivision of organisms on the basisof characteristics intogroups and sub-groups. A characteristic may bea particular formor function. 2. Classification andEvolution Most life forms that we see today have arisen by an accumulation of changes in body design that allow the organism possessing them to survive better. There is a possibility that complexity in design will increase over evolutionary time, it may not be wrong to say that older organisms are simpler, whileyounger organisms aremore complex. 3. The hierarchy ofclassification groups Charles Darwin put forward the idea of evolution in 1859, in his book, The Origin of Species. Ernst Haeckel, Robert Whittaker and Carl Woese have tried to classify living organisms into broad categories, called kingdoms. Robert Whittaker, in 1969proposed ‘Five kingdoms classification’ of living organisms. The hierarchy can be represented as Kingdom sub grouping into Phylum for animals or Division for plants, Class, Order, Family, Genus and Species. Hence, the basic unit of classification is species. Species includes all theorganisms that aresimilar to breed and produce fertile offspring. 3.1 Monera It includes prokaryotic cells lacking organized nucleus and membrane bound cell organelles. Some of them have cell walls while some do not. Some of the Monerans are autotrophic and some of them are heterotrophic forms. Bacteria, cyanobacteria, blue-green algae, mycoplasma are some of the examples of Kingdom Monera. 3.2 Protista It includes algae, diatoms and protozoans. These areunicellular and thesimplest form of eukaryotes exhibiting both autotrophic and heterotrophic mode of nutrition. Locomotion and movement are possible by whip-like flagella andhair-like cilia or finger-like pseudopodia. Examples are unicellular algae, diatoms and protozoans. 3.3 Fungi These aremulticellular, eukaryotic saprophytes. The cell wallof fungi is made upof chitin. They feed on dead and decaying matter. They include mushrooms, rhizopus and mucor. Some fungi are symbiotic forming an association with algal cells. These symbionts are termed to be lichens.
3.4 Plantae It includes all the plants that are non-motile, multicellular and eukaryotic organisms with their cell wallsmade up of cellulose. Theseare complex organisms which can perform photosynthesis. Plants comprise cells with thick cellwalls. 3.5 Animalia It includes all the animals that are motile, multicellular, eukaryotic organisms with their cells possessing no cell walls. It exhibits species diversity. Members of this kingdom are complex organisms withtissue differentiation. 4. Plantae 4.1 Thallophyta Eichler classified the plant kingdom into two sub-kingdoms - Cryptogamae and Phanerogamae. Cryptogamae - This sub-kingdom includes plants with hidden reproductive organs and plants do not bearflowers or seeds. Cryptogams are further divided into threegroups: Thallophyta, Bryophyta and Pteridophyta. Thallophyta are the simplest of plants that do not have a well-differentiated body design. The plants in this group are commonly called algae. These are predominantly aquatic. Ex: Spirogyra, Ulothrix, Cladospora and Chara Bryophyta are often called amphibians of the plant kingdom as they require both aquatic and terrestrial conditions for the completion of their lifecycle. The plantbody is commonly differentiated to formstem and leaflike structures. e.g. Mossor Funaria Pteridophyta include fern plants which possess theplant body differentiated into stem, leaves androots. They alsopossess naked embryos in the formof spores underneath the leaf. Phanerogamae - This sub-kingdom includes plants that develop seeds and havewell-formed stem, leaves and roots. Phanerogams are further classified into Gymnosperms and Angiosperms. Gymnosperms were the firstplants to havea seed habit. These are theplants which possess naked seeds and areusually perennial, evergreen and woody. e.g. Pinus, cycas and deodar. Angiosperms are highly evolved plants with flowers, fruits and seeds. They are also called as flowering plants. These plants possess seeds enclosed inside the fruit. The seed germinates develops into a new plant. Plant embryos in seeds have structures called cotyledons. Cotyledons are called seed leaves and represent a bit of pre-designed plant in the seed. Angiosperms are divided into two groups, namely, monocots and dicots based on the number of cotyledons that they have.Ex: Paphiopedilum- Monocot, Ipomea- Dicot.
5. Animalia These are organisms which are eukaryotic, multicellular and heterotrophic. Their cells do not have cell wall. Most animals are mobile. Animals are classified on the basis of different features like cellular or tissue level of body organization, body symmetry, type of body cavity called as coelom, presence or absence of segmentation andpresence or absence of a backbone. Classification ofthe kingdom Animalia includes Invertebrata and Vertebrata. Invertebrata: It includes group of animals that do not possess a vertebral column. Invertebrata is classified intodifferent phyla such as Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca and Echinodermata. Porifera are multicellular organisms exhibiting minimal level of tissue organization. They lack nervous system. These are non motile. There are holes or pores all over the body. These animals are covered with a hard outside layer or skeleton. They are commonly called sponges. Porifera includes Sycon, Spongilla andEuplectella. Coelenterates are radially symmetrical organisms which live in water. Some are solitude and some arecolonial. They showmore body designdifferentiation. There is a cavity in the body. e.g. Corals, Hydra, sea anemone. Platyhelminthesare either freeliving or parasitic. They are bilaterally symmetrical and triploblastic animals. There is some degree of tissue body cavity or coelom. These are called flatworms. e.g. Planaria ( free living) liverfluke ( parasite). Nematoda are bilaterally symmetrical, triploblastic parasitic worms. Body iscylindrical. Pseudo coelom is present. Theycause diseases such as elephantiasis. e.g.Ascaris. Annelids are bilaterally symmetrical, triploblastic segmented animals. They havea true bodycavity. These are found in a variety of habitats. e.g.Earthworm, Nereis, leechetc. Arthropoda animals are bilaterally symmetrical, segmented, triploblastic animals with true coelom. They include Insects. They have jointed legs. Their circulatory system is open, so blood does notflow through blood vessels. Eg: prawns, butterflies etc. Molluscs are bilaterally symmetrical, triploblastic animals with reduced coelom. Locomotion in molluscs is by means of a muscular foot. They have little segmentation. They have an open circulatory system andkidney like organs for excretion. Eg.Pila, Unio, octopus Echinodermata animals are triploblastic with true coelomic cavity. Echinodermata are spiny skinned organisms. Skeletons of echinoderms are hard calcium carbonates. They exhibit radial symmetry. Eg: Starfish andsea urchins
Protochordata - These are bilaterally symmetrical, triploblastic and have a coelom and are primitive chordates. Protochordates possess a notochord during their early stage ofdevelopment. The notochord is a long rod-like support that runs all along the back of the animal separating the nervous tissue from the gut. These are marine animals. e.g. Balanoglossus, Herdmania and Amphioxus. Vertebrata: These are themost advanced groupof animals withtrue vertebral column and strong endoskeleton. Vertebrates are grouped into different classes based on bilateral symmetry, notochord, dorsal nerve cord, paired gill pouches, triploblastic, and coelomate. These classes are Pisces, Amphibia, Reptilia, Aves andMammalia. Pisces - includes all fish. These are aquatic cold blooded organisms and covered by scales. The body is streamlined and a muscular tailis used formovement. Fish breathe through their gills. Skeleton may be cartilaginous or bony in nature. They have two-chambered heart and reproduce by laying eggs. Eg: Torpedo, Mandarin fish, Stingray etc. Amphibians are cold-blooded animals. Amphibians can liveboth on landand in water. Respiration is by gulls and lungs. They possess a three-chambered heart. Amphibians reproduce by laying eggs.Eg: Frogs, toads and salamanders. Reptilia are cold-blooded animals have scales andbreathe through lungs. Heart is three- chambered except for crocodiles. Reptiles also reproduce by laying eggs. Eg: Snakes, turtles, lizards andcrocodiles. Aves are warm-blooded animals. Their fore limbs are modified for flight. Bones are hollow. Body is covered by feathers. Respiration is through lungs. They have four-chambered heart. They lay eggs. Eg: Crow, Ostrich, and Sparrow etc. Mammals are warm-blooded animals with four chambered hearts. Their skin is covered by hair, sweat glands and oil glands that regulate body temperature. Mammals give birth to young ones. They have mammary glands for the production of milk to nourish their young ones. Mammals like platypus lay eggs. Kangaroos give birth to under-developed young ones that are carried in theirmother’s abdominal pouch. Eg: Human, rat and cat etc.
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