Life on the Earth

  • Question 49

    Write short notes on the following:

    (i) Altitudinal biomes.

    (ii) Oligotrophic lakes.

    (iii) Boundaries of Eco-system.

    (i) Altitudinal biomes.

    Ans. A series of biomes can be noted along the slopes of high mountain ranges like the Himalayas, Andes and Rockies. These mountain ranges have the gradual change in the biome-type according to the altitude rather than the latitude. Temperature and precipitation rates are most important determinants of these biomes. In the tropical mountains the sequence of communities and conditions from the base of the mountain to the suow-line are tropical forest, deciduous forest, coniferous forest and Tundra.

    (ii) Oligotrophic lakes.

    Ans. The deep lakes with steep and rocky sides and poor in circulating nutrients such as phosphates are called oligotrophic lakes. The physical factors of the lakes contain saline or brackish water (Sambar lake of Rajasthan).

    (iii) Boundaries of Eco-system.

    Ans. An ecosystem is an area in which the living and non-living components can be demarcated by a boundary, for convenience in study. It is important to recognise that ecosystem are not strictly isolated. Their boundaries are indistinct and overlapping. Some movement always occurs from one eco-system to another in terms of energy and materials. This movement may be from an adjacent or distant eco-system. A pond may be separated from a grassland but some birds may break the barrier and feed on the fishes of the pond. The top soil from the Himalayas is washed down in massive amount by rivers. Siberian crane can migrate from Siberia to Bharatpur in India.

    Question 50

    Write a short note on Nektons.

    1. Nektons are the swimming organisms and include fishes, whales, dolphins, porpoises and other animals.
    2. Nektons feed primarily on zooplanktons which live below the surface where food is plentiful. Many plant-eating nektons come on the surface only at night to feed on planktons.
    3. Nektons always move from place to place and from one depth to another in search of food and for breeding.
    4. Some move in cold water and other either in warm water or in the entire ocean.
    5. Nektons are an advanced form of animals in relation to planktons and benthos.
    6. Dolphins and porpoises are among the most intelligent animals of the world. Dolphins have been successfully trained in some parts of the world to carry messages, mail and tools from one place to another.
    Question 51

    What is an ecological balance ? Discuss the important measures needed to prevent ecological imbalances.

    Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem.

    Ecological balance may be disturbed due to introduction of new species, natural hazards or man-made causes.

    Some measures should be taken to check these imbalances:

    i. Man’s interference should be rational.

    ii. Population should be controlled.

    iii. Afforestation should be encouraged.

    iv. Efforts should be made to preserve the species that are endangered.

    v. Prevention of extinction requires sound planning and management.

    Question 52

    Distinguish between Terrestrial and Aquatic Ecosystems.

    Terrestrial Ecosystem : Natural ecological groups of plants and animals extend over large areas. Each of major terrestrial ecosystem or terrestrial areas with their group of plants and associated animals, have different type of biomes including tropical rainforests, savanna, mediterranean, deciduous, grasslands, deserts, taiga and tundra.

    Aquatic Ecosystem : There are many kinds of aquatic ecosystems that differ widely with regard to abiotic factors. The aquatic ecosystems range from open ocean to small temporary puddles, have conditions of salinity, depth and fluctuations of temperature.

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