Life on the Earth

  • Question 57

    Mention the difference between Desert-type vegetation and Tundra-type vegetation.


    Desert-type Vegetation

    Tundra-type Vegetation

    1. This vegetation is found in dry regions having low rainfall.

    2. This vegetation is found in tropical desert areas like north Africa.

    3. Cacti, thorny bushes and coarse grasses are the examples of desert-type vegetation.

    1. This vegetation is found in snow covered areas.

    2. This vegetation is found around North Pole in Eurasia and North America.

    3. Mosses, lichens and wild flowering shrubs are the examples of tundra-type vegetation.

    Question 58

    Distinguish between Tropical Grasslands and Mid-latitude Grasslands.


    Tropical Grasslands

    Mid-latitude Grasslands

    1. These grasslands occur in the interiors of continents in the tropical zone.

    2. These grasses are long grasses, about two metres in height.

    3. Major regions are the equatorial regions in Africa, parts of Brazilian plateau, Deccan plateau and northern Australia.

    4. These grasslands are known as Savanna in Africa and Pampas in Brazil.

    1. These grasslands occur in the interiors of continents in the middle latitudinal zone.

    2. These grasses are short grasses.

    3. Major regions are Russia, interiors of United States and Canada, South African plateau, coastal plains of Argentina and Uruguay in South America and Murray-Darling basin in Australia.

    4. These are known as steppes in Eurasia, Prairies in North America and Pampas in South America.

    Question 59

    What are biogeochemical cycles? Explain how nitrogen is fixed in the atmosphere.

    The cyclic movements of chemical elements of the biosphere between the living organisms and the environment are referred to as biogeochemical cycles.

    Bio refers to living organisms and geo refers to rocks, soil, air and water on the earth.

    Nitrogen is a major constituent of the atmosphere comprising of about 78% of the atmospheric gas.

    Ninety per cent of fixed nitrogen is biological. The principal source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil. Nitrogen can also be fixed in the atmosphere by lightning and cosmic radiation. In the oceans, some marine animals can fix it. After atmospheric nitrogen has been fixed into an available form, green plants can assimilate it.

    Question 60

    Describe the global distribution of biomes.

    Forests, grasslands, thorny shrubs and tundra are major plant biomes.

    Forest Types : Forests are classified into two types :

    (1) Evergreen and

    (2) Deciduous Forests.

    1. Evergreen Forests : These forests remain green throughout the year, as there is no mass shedding of leaves throughout the year. Evergreen forests are of the following types :

    (i) Tropical Evergreen Forests : These occur in equatorial regions and tropical coastal regions having heavy rainfall. There is a luxuriant growth and variety of vegetation. Trees have broad leaves. Mahogany, ebony and rosewood are of commercial value among tropical evergreen trees.

    (ii) Mid-latitude Evergreen Forests : These forests occur in western margins of continents in middle latitudes. Here rainfall is received in winter and the summer is dry. Plant have spiny, waxy or small leaves to reduce transpiration. Trees are widely spaced and shrubs occur in between. Cork, oak, olive and Chestnut are the examples.

    (iii) Coniferous Forests: They are found around the north polar region, Europe, Asia and North America. Trees are tall and conical in shape. They have thick needle-shaped leaves to reduce transpiration and to protect them from cold winter.

    2. Deciduous Forests : Trees shed their leases in a particular season to conserve loss of moisture. Deciduous forests are of the following types :

    (i) Tropical Deciduous Forests : These are found in subtropical regions with a distinct dry season. These forests have fewer species and are less dense. Teak is a valuable hardwood tree found in these forests. These are found in monsoon regions of Asia, central America, Brazil and northern Asia.

    (ii) Mid-latitude Deciduous Forests : These occur in coastal regions of cool climates. Trees shed their leaves in winter when temperature is below 6°C. These occur in the region of western Europe, north-eastern China, Japan, north-eastern United States etc.

    3. Grasslands: Grasses are shallow rooted plants which thrive under varying climatic conditions. They are divided into tropical grasslands and mid-latitude grasslands.

    (i) Tropical Grasslands : These occur in the interiors of continents in the tropical zone. These grasses are tall, about 2 metres in height. These are found in equatorial regions of Africa, Brazilian Plateau, Deccan Plateau etc.

    (ii) Mid-latitude Grasslands : These occur in the interiors of continents in mid-latitudes receiving moderate rainfall. These grasses are short and trees are absent. These are found in regions of Russia, U.S.A., Canada and South African plateau.

    4. Desert Vegetation : This vegetation occurs in regions of low rainfall. Short shrubs occur in patches. Cacti, thorny bushes and coarse grasses are found in deserts.

    5. Tundra Vegetation : This type of vegetation occurs around the North Pole in Eurasia and North America. Patches of mosses, lichens, wild-flowering shrubs are seen. The land is snow-covered during the long winters.

    Describe the global distribution of biomes.
    World Biomes

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