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The Oxygen Cycle:
i. Oxygen is the main by-product of photosynthesis.
ii. It is involved in the oxidation of carbohydrates with the release of energy, carbon dioxide and water.
iii. The cycling of oxygen is a highly complex process. Oxygen occurs in a number of chemical forms and combinations.
iv. It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.
v. Much of oxygen is produced from the decomposition of water molecules by sunlight.
There are two types of biogeochemical cycles:
i. The gaseous - In the gaseous cycle, the main reservoir of nutrients is the atmosphere and the ocean.
ii. The sedimentary cycle - In the sedimentary cycle, the main reservoir is the soil and the sedimentary and other rocks of the earth’s crust.
Who are decomposer? State two scavengers.
What are two types of ecosystems?
Ecosystems are of two major types:
i. terrestrial
ii. aquatic.
Mention the classes of the aquatic ecosystem.
Aquatic ecosystems can be classed as:
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On what factors does the nature of biome depend ?
1. Complexity of cell structure.
2. Complexity of organism's body.
3. Mode of obtaining nutrition.
Two components of an ecosystem are:
(i) Biotic components
(ii) Abiotic components.
1. Plant kingdom. 2. Animal kingdom.
There are two major types of ecosystems :
(i) Terrestrial and
(ii) Aquatic ecosystem.
The five kingdoms are as under:
i. Monera (Single cell microscopic organisms).
ii. Protista (Unicellular, mainly aquatic organisms).
iii. Plantae (Multicellular photosynthetic plants).
iv. Fungi (Multicellular decomposers).
v. Animalia (Multicellular animal consumers).
Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem.
2. Man is at the top of the ecological pyramid. The pyramid has a large base.
3. It represents primary producers. From base to the top, the numbers go on deceasing at each trophic level.
4. All green plants and other producers occupy the first trophic level. Herbivores which feed on plants occupy the second trophic level. Carnivores that eat herbivores are at the third trophic level.
5. At each level, the flow of energy is reduced; because only a fraction of energy is transferred from lower to higher level.
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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.
The fresh water bodies are lakes and ponds. They vary in size from less than a hectares to hundreds of hectares. The relatively shallow lakes called eutrophic lakes have a rich accumulation of organic products.
Streams and rivers: They differ widely in volume of water, speed of flow and oxygen content, etc. The nature and composition of flora and fauna depends on the source of the river and the land environment. Floating population of planktons are generally absent in such waters. Sediments are deposited on the river bed. The total volume of water is also larger. The surface gets more sunlight raising the temperature of water. The water often is muddy cutting down light at the river bed. Many reptiles, mammals and birds obtain their food from the water therein.
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.
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.
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.
Fresh water environment : Lakes and ponds are stagnant fresh water bodies and occur particularly in every biome. They vary in size from less than a hectare to hundreds of hectares. The relatively shallow lakes called eutrophic lakes, have a rich accumulation of organic products. The fresh water ponds are called autotrophs and have microscopic phytoplanktons.
Streams and rivers differ in volume, temperature etc. The nature and composition of flora and fauna depend on the source of river and the land environment.
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Taiga |
Tundra |
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1. These are coniferous forests. 2. Pine, fur, cedar and spruce are the prevalent trees. 3. In some areas, trees are so dense that little light reaches the floor. 4. This biome is good habitat for elks, deer, geese, rabbits, pumas, lynx and many insects. |
1. Tundra consists of plains characterised by snow and ice. 2. There is poor light and extremely low temperature. Snowfall is scanty. 3. Vegetation is so sparse that it is also called the arctic desert. 4. This biome is virtually treeless. |
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Mid-latitude Evergreen Forests |
Mediterranean Forests |
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1. These forests are found in the sub-tropical belts. 2. These forests are found in the eastern margins of the continents. 3. In these forests, plants have broad leaves. 4. No shrubs are found in between the trees. 5. Oak, eucalyptus and wattle are the examples of such forests. |
1. These forests are found in the middle latitudes. 2. These forests are found in the western margins of the continents. 3. Trees of these forests have small leaves. 4. Shrubs occur in between the trees. 5. Cork, oak, olive and chestnut are the examples of Mediterranean forests. |
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Tropical Deciduous Forests |
Mid-latitude Deciduous Forests |
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1. These forests occur in sub-tropical regions with a distinct dry season. 2. Trees shed their leaves in the dry season. 3. They are found in the regions of Western Europe, North-Eastern China, Japan, North-Eastern U.S.A, Southern China and New Zealand. |
1. These forests occur in the coastal regions of cool climates. 2. Trees shed their leaves in winter season. 3. They are found in the monsoon regions of Asia, parts of central America, Brazil and northern Australia. |
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Desert-type Vegetation |
Tundra-type Vegetation |
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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. |
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Tropical Grasslands |
Mid-latitude Grasslands |
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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. |
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.
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.
