Important Questions for Class 12 Chapter 14 - Ecosystem

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Important questions based on NCERT syllabus for Chapter 14 - Ecosystem:

Question-1: What is primary productivity? Give brief description of factors that affect primary productivity.

Solution: Primary productivity of an ecosystem is the amount of energy fixed or biomass synthesized by primary producers or green plants per unit area per unit time during photosynthesis. Factors affecting primary productivity are –
-Plant species inhabiting a particular area
-Sunlight
-Temperature
-Soil water
-Nutrients
lit deserts, sunlight is abundant but water is scarce or nutrients are lacking. Therefore, in such areas, water & nutrients supply become the limiting factors.

Question-2: Define decomposition and describe the processes and products of decomposition.

Solution: Decomposition is the breakdown of dead or waste organic matter by micro-organisms. Decomposition is both physical and chemical in nature.Process involved in decomposition are – fragmentation, catabolism & leaching.
•Fragmentation – The process primarily due to the action of detritus feeding invertebrate (detritivores) causes it to break into smaller particles. The detritus gets pulverized when passing through the digestive tracts of animals. Due to fragmentation, the surface area of detritus particles is greatly increased.
•Catabolism – Enzyme degradation of detritus into simpler organic substances by bacteria and fungi.
•Leaching – The process by which nutrients, chemicals or contaminants are dissolved & carried away by water, or are moved into a lower layer of soil.
Various inorganic and organic substances are obtained by decomposition. Inorganic substances are obtained in the process of mineralization while organic substances are obtained in humification. A dark coloured amorphous substance called humus is formed by decomposition. Humus is highly resistant to microbial action & undergoes extremely slow decomposition. It serves as a reservoir of nutrients.

Question-3: Give an account of energy flow in an ecosystem.

Solution: Flow of energy in an ecosystem is unidirectional.The ultimate source of energy is sun. The solar energy is captured by the green plants which utilize it in synthesizing their own food. The energy fixed by the green plants is transferred to herbivores which feed on them. The energy is then transferred to higher trophic levels (carnivores). At every step, considerable amount of energy is lost. According to 10% law, only 10% of total energy stored in a trophic level is transferred to the next trophic level of a food chain.