Choose the correct statements about productivity from the following:
A. Primary production is expressed in terms of weight (g m−2) or energy (kcal m−2).
B. Net primary productivity is the available biomass for the consumption to heterotrophs, that is, herbivores and decomposers.
C. A considerable amount of gross primary productivity is utilised by plants in photosynthesis.
D. Secondary productivity is defined as the rate of formation of new organic matter by producers.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A and B only
Gross primary productivity (GPP) is the rate at which plants make organic matter in photosynthesis. Plants use up a large part of it in their own respiration (R). What is left, GPP − R, is the net primary productivity (NPP), and this is the food available to the next levels.
A. Primary production is expressed in terms of weight (g m−2) or energy (kcal m−2). — True. Production can be given as mass of organic matter or as the energy held in it, per unit area.
B. Net primary productivity is the available biomass for the consumption to heterotrophs, that is, herbivores and decomposers. — True. NPP is what remains after the plants’ own respiration, so it is the part that herbivores and decomposers can use.
C. A considerable amount of gross primary productivity is utilised by plants in photosynthesis. — False. GPP is the product of photosynthesis. A considerable amount of it is used by plants in respiration, which is why NPP = GPP − R.
D. Secondary productivity is defined as the rate of formation of new organic matter by producers. — False. Secondary productivity is the rate of formation of new organic matter by consumers. Formation by producers is primary productivity.
NCERT Extract:
Productivity – “… Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (gm–2) or energy (kcal m–2). … Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). … Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers). Secondary productivity is defined as the rate of formation of new organic matter by consumers.”