NCERT Solutions for Class 11 Biology Chapter 4 - Animal Kingdom

Answer:

Common fundamental features like symmetry, germ layers, segmentation, coelom etc. provide a guide to classify animals on the basis of unique features which they possess. In the absence of such characteristics, the placing of animals in particular groups would be difficult and haphazard. Examples of convergent evolution, adaptive radiations, presence of vestigial organs etc. will provide problems for classification of animals. All animals placed under one group by taxonomists exhibit a variety of common fundamental features which make their recognition and description easy.

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1. Finding out whether it is an animal or a plant.
   If it is an animal, the following steps are followed further :
2. Study of level of organisation—cellular or tissue or organ or organ system level.
3. Study of symmetry—Radial or bilateral symmetry.
4. Presence or absence of body cavity and if present, it is pseudocoelom or eucoelom.
5. Study of type of segmentation—internal or external metamerism.

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The presence or absence of a cavity between the body wall and the gut wall is very important in classification. The body cavity, which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomates e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates. In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates e.g., aschelminthes.
The animals in which the body cavity is absent are called acoelomates e.g., platyhelminthes.

Showing Coelom (a) Coelomate (b) Pseudocoelomate (c) Acoelomate

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In many animals, the hatched organism resembles an adult, except that it is small in size and is often called a juvenile. The juvenile undergoes growth and sexual development only. Such a type of development is called direct development.
e.g. Ascaris, Pheretima, reptiles and birds.
In certain animals, the egg develops into a strikingly different organism from the adult that leads an independent free life and is called the larva. The larva undergoes drastic changes to form the adult by a process called metamorphosis. Such a kind of development is called indirect development.

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Features of parasitic platyhelminthes

1. Presence of hooks and suckers.
2. Platyhelminthes absorb nutrients from the host directly through their body surface.
3. Digestive system is absent.
4. Skeletal, respiratory and circulatory systems are absent.
5. Well developed reproductive organs.
6. Development is indirect with many larval stages.

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Success of arthropods. It is largely due to their unique cuticle, segmentation and presence of jointed appendages. It is called arthropodization.

1. The cuticle is composed of protein and the polysaccharide chitin. It may be strengthened by deposition of minerals (calcium phosphate and carbonate) in it. Being tough it protects the arthropods against pedators and forms jointed exoskeleton for muscle attachment. Being light, it does not add to body weight. Being impervious to water, it checks drying up of the body. It is termed sclerotization. This has enabled the arthropods to survive on land in almost any environment. The chitinous wings of the insects enable them to fly and cross barriers which other animals cannot cross.
2. Striated muscles provide quick movements and tracheal respiration supplies energy rapidly.
3. Groups (tagmata) of segments allow arrangement of organs.
4. Jointed appendages have become specialized for a great variety of functions. This provides division of labour among the regions.

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(c) Echinodermata.

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The chordates are characterized by the presence of a notochord at some stage of life cycle. Later this notochord may or may not get replaced by a cartilaginous or bony vertebral column. Those chordates in which the vertebral, column appears are called vertebrates and those chordates in which the vertebral column does not appear as protochordates. However they are chordates but not vertebrates. Thus all vertebrates are chordates but all chordates are not vertebrates.

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1. The air bladder acts as a buoyancy regulator by altering the pressure in it. It enables the fish to stay at a particular depth without expending energy in swimming, thus conserving energy. 2. Air bladder also acts as an accessory respiratory organ.

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1. The fore-limbs are modified into wings to provide a large surface area formed by the structures called feathers which are light in weight.
2. The sternum is extended to form a keel. Large flight muscles are attached to the keel.
3. Powerful flight muscles named pectorales majoris are present.
4. The body is streamlined.
5. Weight is kept to a minimum by the possession of a very light skeleton with hollow bones (pneumatic bones) and air sacs.
6. The efficient flight is achieved by the birds taking advantage of vertical air movement i.e. by gliding and soaring.
7. The coracoid bones are well developed transmit the ‘‘lift’’ of the wings to whole body.
8. Brain is well developed.
9. The metabolic rate of birds is relatively high to provide the energy required for flight.
10. Urinary bladder is absent.

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No. The number of eggs produced by oviparous animals is much higher than viviparous animals because the chances of fertilization and development are low. In viviparous animals the development of the embryo depends upon the mother ; so only one or few could be supported. In oviparous animals, some eggs may not get the favourable conditions for development and hatching and may degenerate. So a large number of eggs are produced.

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(c) Annelida.

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1. (d) 2. (c) 3. (b) 4. (a)

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Prepare a list of some animals parasitic on human beings.

1. Itch-Mite
2. Schistosoma
3. Taenia
4. Ascaris
5. Hookworm
6. Wuchereria
7. Pinworm
8. Trichinella
9. Dracunculus
10. Leech.