Life on the Earth

  • Question 41

    What do you understand by the term ‘food web’ ? Give examples.

    A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community.

    For example a mouse feeding on grain may be eaten by different secondary consumers (carnivores) and these carnivores may be eaten by another set of different tertiary consumers.
    Question 42

    Describe the characteristics of Savanna biomes.

    Savannas are characterised by coarse grass and scattered trees on the margins of the tropics where rainfall is seasonal and wet seasons alternate with dry season. This biome supports the greatest variety of animals, such as zebra, giraffe, elephant, etc.
    Question 43

    What are photic and aphotic zones ?

    Photic zone : The vertical zone of the ocean are determined by availability of light for photosynthesis. The lighted upper 200 metres forms the photic zone.

    Aphotic zone : The next zone upto the depth of 2000 metres gets less light which is insufficient for photosynthesis. This layer is called aphotic zone.

    Question 44

    Why are the marine animals able to live at a great depths than the marine plants?

    The marine animals are able to live at great depths where there is a permanent darkness. The mjor fauna of marine comprise porifera, coelonterates, molluscs, marine worms, fishes and sea-snakes. The marine fishes have energetic organs, phophorescent organs, like glands and sensitive arms to live safely in the deep sea environment. As the marine animals do not need sunlight for their survival, they are able to live at great depths.

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