NCERT Gist: Diversity In Living Organisms | Additional Study Material for UPSC PDF Download

- Organisms which have ancient body designs that have not changed very much.
- The warm and humid tropical regions of the earth, between the tropic of Cancer and the tropic of Capricorn, are rich in diversity of plant and animal life. This is called the region of megadiversity.
- Of the biodiversity of the planet, more than half is concentrated in a few countries - Brazil, Colombia, Ecuador, Peru, Mexico, Zaire, Madagascar, Australia, China, India, Indonesia and Malaysia.
- a species includes all organisms that are similar enough to breed and perpetuate.

Protista

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

Fungi

- These are heterotrophic eukaryotic organisms.
- They use decaying organic material as food and are therefore called saprophytes.
- Many of them have the capacity to become multicellular organisms at certain stages in their lives.
- They have cell-walls made of a tough complex sugar called chitin.
- Examples are yeast and mushrooms.
- Some fungal species live in permanent mutually dependent relationships with bluegreen algae (or cyanobacteria).
- Such relationships are called symbiotic. Symbiotic life forms are called lichens.
- We have all seen lichens as the slow-growing large coloured patches on the bark of trees.

Plantae

- Multicellular eukaryotes with cell walls.
- Autotrophs and use chlorophyll for photosynthesis.
- All plants are included in this group.
- Since plants and animals are most visible forms of the diversity of life around us, we will look at the subgroups in this category later.

Animalia

- These include all organisms which are multicellular eukaryotes without cell walls.
- They are heterotrophs.

Thallophyta

- 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 tr.
- Examples are Spirogyra, Ulothrix, Cladophora and Chara.

Bryophyta

- 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.

Pteridophyta

- In this group, the plant body is differentiated into roots, stem and leaves and has specialised 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.
- Plants with well differentiated reproductive tissues that ultimately make seeds are called phanerogams.

Gymnosperms

- This term is made from two Greek words: gymno-means naked and sperma-means seed.
- The plants of this group bear naked seeds and are usually perennial, evergreen and woody.
- Examples are pines, such as deodar, pinus, cycas.

Angiospenns

- This word is made from two Greek words: angio means covered and sperma-means 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 geminates.
- Thus, cotyledons represent a bit of pre-designed plant in the seed.
- 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.

Animalia

- These are organisms which are eukaryotic, multicellular and heterotrophic.
- Their cells do not have cell-walls.

Porifera

- The word 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.
- The body design involves very minimal differentiation and division into tissues.
- They are commonly called sponges, and are mainly found in marine habitats.
- Example: Euplectelia, Sycon, Spongilla.

Coelenterata

- 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.
- Some of these species live in colonies (corals), while others have a solitary like-span (Hydra).
- Jellyfish and sea anemones are common examples.

Platyhelminthes

- 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.
- This allows outside and inside body linings as well as some organs to be made.
- There is thus some degree of tissue formation.
- However, there is no true internal body cavity or coelom, in which well-developed organs can be accommodated.
- The body is flattened dorsiventrally, meaning from top to bottom, which is why these animals are called flatworms.
- They are either freeliving or parasitic.
- Some examples are freeliving animals like planarians, or parasitic animals like liverflukes

Nematoda

- 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 (roundworm or pinworms).
-  Example: Ascaris, Wuchereria.

Annelida

- 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, Nereis and leeches are familiar examples.

Anthropoda

- 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 (the word “arthropod” means, jointed legs).
- Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs.

Mollusca

- 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. Chiton, Octopus, Pila & Unio.

Echinodermata

- 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 Asterias (starfish) and sea urchins

Protochordata

- 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 (chord=string) that runs along the back of the animal separating the nervous tissue from the gut.
- It provides a place for muscles to attach for ease of movement.
- Protochordates may not have a proper notochord present at all stages in their lives or for the entire length of the animal.
- Protochordates are marine animals.
- Examples are Balanoglossus, Herdemania And Amphioxus

Vertebrata

Pisces

- These are fish.
- They are exclusively water-living animals.
- Their skin is covered with scales/plates.
- 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, unlike the four that humans have.
- They lay eggs.
- We can think of many kinds of fish, some with skeletons made entirely of cartilage, such as sharks, and some with a skeleton made of both bone and cartilage, such as tuna or rohu.

Amphbia

- 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

Reptilia

- These animals are cold-blooded, have scales and breathe through lungs.
- While most of them have a three-chambered heart, crocodiles 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.

Aves

- 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.

Mammalia

- 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 familiar to us produce live young ones.
- However, a few of them, like the platypus and the echidna lay eggs, and some, like kangaroos give birth to very poorly developed young ones.