IGCSE Biology Paper-4: Specimen Questions with Answers 99 - 99 of 120

Question number: 99

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What is the role of productivity in an ecosystem. How net primary productivity is different from gross primary productivity


The rate of synthesis of organic compounds by any trophic level per unit area and per unit time is called as productivity and the study of productivity is called as production ecology. Productivity can be of two types –primary productivity and secondary productivity.

In primary productivity the amount of energy accumulation in plants as organic matter through the process of photosynthesis per unit time and per unit area. In addition, when the rate of synthesis of organic matter by the consumer it is called as secondary productivity. Primary productivity may be of two types-

(i) Net primary productivity

(ii) Gross primary productivity

Table shows difference between NPP and GPP

Table shows difference between Net primary productivity and gross primary productivity

(i) Net primary productivity

(ii) Gross primary productivity

Amount of organic matter store by producers

Amount of organic matter synthesize by producers

It is equal to the organic matter make in photosynthesis minus utilization in respiration and other loss

It is equal to the rate of increase in body weight of producer plus loss due to respiration and damage

It depend on GPP

It depends upon photosynthetic efficiency of producers, availability of solar energy