NCERT Solutions for Class 11 Geography Chapter 15 Life On the Earth

Ans : (i) (b) all living and nonliving organisms
(ii) (b) the savannas
(iii) (c) iron oxides
(iv) (c) carbohydrates 

Ans : (i) Ecology is a scientific study of the interactions of organisms with their physical environment and with each other.


(ii) The interactions of a particular group of organisms with abiotic factors within a particular habitat resulting in clearly defined energy flows and material cycles on land, water and air, are called ecological systems.
Ecosystems are of major types:
 Terrestrial
 Aquatic


(iii) These sequence of eating and being eaten and the resultant transfer of energy from one level to another is known as the food-chain.
Grass (first level) is eaten by deer (intermediate level) is eaten by lion (last level).


(iv) A network of food chains mixed together to form a food web. For example, a mouse feeding on grain may be eaten by different secondary consumers (carnivores) and these carnivores may be eaten by other different tertiary consumers (top carnivores).


(v) A biome is a plant and animal community that covers a large geographical area. 

Ans : (i) The balance of the chemical elements is maintained by a cyclic passage through the tissues of plants and animals. The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water and soil through decomposition. These cycles are largely energised by solar insolation. The cyclic movements of chemical elements of the biosphere beüeen the organism and the environment are referred to as biogeochemical cycles. Bio refers to living organisms and geo to rocks, soil, air and water of the earth.
Ninety per cent of fixed nitrogen is biological. The principal source of free nitrogen is the action of soil microorganisms 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.


(ii) Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable.
Ecological imbalances: Ecological balance may be disturbed due to the introduction of new species, natural hazards or human causes.
The important measures to prevent ecological imbalances are:
 By not interfering in nature.
 By controlling population.
 By reusing and recycling things.
 By using natural resources judiciously.
 Afforestation should be encouraged.
Proper knowledge and management are necessary for protecting and conserving the ecosystems.