CBSE – 9th Standard Science

Class 9 Chapter 7 – Diversity in living organisms

  • Greek thinker Aristotle classified animals according to whether they lived on land, in water or in the air.
  • The characteristics of body design used for classification of plants will be very different from those important for classifying animals because the basic designs are different, based on the need to make their own food, or acquire it.
  • 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.
  • Charles Darwin first described this idea of evolution in 1859 in his book, The Origin of Species.
  • The classification Whittaker proposed has five kingdoms: Monera, Protista, Fungi, Plantae and Animalia.



  • These organisms do not have a defined nucleus or organelles, nor do any of them show multi-cellular body designs.
  • Some of them have cell walls while some do not.
  • The mode of nutrition of organisms in this group can be either by synthesizing their own food (autotrophic) or getting it from the environment (heterotrophic).
  • This group includes bacteria, blue-green algae or cyanobacteria, and mycoplasma.


  • This group includes many kinds of unicellular eukaryotic organisms.
  • Some of these organisms use appendages, such as hair-like cilia or whip-like flagella for moving around.
  • Their mode of nutrition can be autotrophic or heterotrophic.
  • Examples are unicellular algae, diatoms and protozoans.


  • These are heterotrophic eukaryotic organisms.
  • They use decaying organic material as food and are therefore called saprophytes.
  • They have cell-walls made of a tough complex sugar called chitin.
  • Examples are yeast and mushrooms.


  • These are multicellular eukaryotes with cell walls.
  • They are autotrophs and use chlorophyll for photosynthesis. Thus, all plants are included in this group.
  • Since plants and animals are most visible forms of the diversity of life around us.


  • These include all organisms which are multicellular eukaryotes without cell walls.
  • They are heterotrophs.
  • The first level of classification among plants depends on whether the plant body has well differentiated, distinct components.
  • The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances within it.



  • Plants that do not have well-differentiated body design fall in this group.
  • The plants in this group are commonly called algae.
  • These plants are predominantly aquatic. Examples are Spirogyra, Ulothrix, Cladophora and Chara.


  • These are called the amphibians of the plant kingdom.
  • The plant body is commonly differentiated to form stem and leaf-like structures.
  • However, there is no specialized tissue for the conduction of water and other substances from one part of the plant body to another.
  • Examples are moss (Funaria) and Marchantia.


  • In this group, the plant body is differentiated into roots, stem and leaves.
  • And has specialized tissue for the conduction of water and other substances from one part of the plant body to another.
  • Some examples are Marsilea, ferns and horse-tails.
  • The thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores.
  • The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’.



  • This term is made from two Greek words: gymnomeans naked and spermameans seed.
  • The plants of this group bear naked seeds and are usually perennial, evergreen and woody.
  • Examples are pines and deodar.


  • This word is made from two Greek words: angio means covered and spermameans seed.
  • The seeds develop inside an organ which is modified to become a fruit.
  • These are also called flowering plants. Plant embryos in seeds have structures called cotyledons.
  • Cotyledons are called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates.
  • The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed.
  • Plants with seeds having a single cotyledon are called monocotyledonous or monocots.
  • Plants with seeds having two cotyledons are called dicots.



  • These are organisms which are eukaryotic, multicellular and heterotrophic.
  • Their cells do not have cell-walls.
  • Most animals are mobile.
  • They are further classified based on the extent and type of the body design differentiation found



  • The word Porifera means organisms with holes.
  • These are non-motile animals attached to some solid support.
  • There are holes or ‘pores’, all over the body
  • These lead to a canal system that helps in circulating water throughout the body to bring in food and oxygen
  • These animals are covered with a hard outside layer or skeleton.
  • They are commonly called sponges, and are mainly found in marine habitats.
  • Examples are Euplectelea. Spongilla, Sycon.


  • These are animals living in water.
  • They show more body design differentiation.
  • There is a cavity in the body.
  • The body is made of two layers of cells: one makes up cells on the outside of the body, and the other makes the inner lining of the body.
  • Jellyfish and sea anemones are common examples.


  • The body of animals in this group is far more complexly designed than in the two other groups we have considered so far.
  • The body is bilaterally symmetrical, meaning that the left and the right halves of the body have the same design.
  • There are three layers of cells from which differentiated tissues can be made, which is why such animals are called triploblastic.
  • The body is flattened from top to bottom, which is why these animals are called flatworms.
  • They are either free-living or parasitic.
  • Some examples are free-living animals like planarians, or parasitic animals like liverflukes.


  • The nematode body is also bilaterally symmetrical and triploblastic.
  • However, the body is cylindrical rather than flattened.
  • There are tissues, but no real organs, although a sort of body cavity or a pseudocoelom, is present.
  • These are very familiar as parasitic worms causing diseases, such as the worms causing elephantiasis (filarial worms) or the worms in the intestines.
  • Some examples are Ascaris, wuchereria.


  • Annelid animals are also bilaterally symmetrical and triploblastic, but in addition they have a true body cavity.
  • This allows true organs to be packaged in the body structure
  • There is, thus, extensive organ differentiation. This differentiation occurs in a segmental fashion, with the segments lined up one after the other from head to tail.
  • These animals are found in a variety of habitats– fresh water, marine water as well as land.
  • Earthworms and leeches are familiar examples.


  • This is probably the largest group of animals.
  • These animals are bilaterally symmetrical and segmented.
  • There is an open circulatory system, and so the blood does not flow in well defined blood vessels
  • The coelomic cavity is blood-filled. They have jointed legs.
  • Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs.


  • In the animals of this group, there is bilateral symmetry.
  • The coelomic cavity is reduced. There is little segmentation.
  • They have an open circulatory system and kidney-like organs for excretion. There is a foot that is used for moving around.
  • Examples are snails and mussels.


  • In Greek, echinos means hedgehog, and derma means skin. Thus, these are spiny skinned organisms.
  • These are exclusively free-living marine animals.
  • They are triploblastic and have a coelomic cavity.
  • They also have a peculiar water-driven tube system that they use for moving around.
  • They have hard calcium carbonate structures that they use as a skeleton.
  • Examples are starfish and sea urchins.


  • These animals are bilaterally symmetrical, triploblastic and have a coelom.
  • In addition, they show a new feature of body design, namely a notochord, at least at some stages during their lives.
  • The notochord is a long rod-like support structure that runs along the back of the animal separating the nervous tissue from the gut.
  • Examples are Balanoglossus, Herdmania and


  • These animals have a true vertebral column and internal skeleton.
  • This allows a completely different distribution of muscle attachment points to be used for movement.
  • Vertebrates are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs.
  • Vertebrates are grouped into five classes.


  • These are fishes. They are exclusively aquatic animals.
  • They obtain oxygen dissolved in water by using gills.
  • The body is streamlined, and a muscular tail is used for movement.
  • They are cold-blooded and their hearts have only two chambers.
  • They lay eggs.


  • These animals differ from the fish in the lack of scales, in having mucus glands in the skin, and a three-chambered heart.
  • Respiration is through either gills or lungs.
  • They lay eggs. These animals are found both in water and on land.
  • Frogs, toads and salamanders are some examples.


  • These animals are cold-blooded, have scales and breathe through lungs.
  • Most of them have a three-chambered heart except crocodiles, they have four heart chambers.
  • They lay eggs with tough coverings and do not need to lay their eggs in water, unlike amphibians.
  • Snakes, turtles, lizards and crocodiles fall in this category.


  • These are warm-blooded animals and have a four-chambered heart.
  • They lay eggs.
  • There is an outside covering of feathers, and two forelimbs are modified for flight.
  • They breathe through lungs.
  • All birds fall in this category.


  • Mammals are warm-blooded animals with four-chambered hearts.
  • They have mammary glands for the production of milk to nourish their young.
  • Their skin has hairs as well as sweat and oil glands.
  • Most mammals produce live young ones.