Which of the following statements are correct?
(I) Gross primary productivity and net primary productivity are two components of productivity.
(II) Net primary productivity represents the biomass available for heterotroph consumption.
(III) Net primary productivity is calculated by subtracting respiration from gross primary productivity.
(IV) Energy flows in a unidirectional manner towards higher trophic levels, with some energy being lost as heat.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → I, II, III and IV
Primary productivity is the rate of biomass production by plants. It is divided into gross primary productivity (GPP) and net primary productivity (NPP), and the energy fixed this way moves up the trophic levels in one direction.
(I) Gross primary productivity and net primary productivity are two components of productivity. — True. Primary productivity can be divided into GPP and NPP.
(II) Net primary productivity represents the biomass available for heterotroph consumption. — True. NPP is the biomass available to heterotrophs, that is, herbivores and decomposers.
(III) Net primary productivity is calculated by subtracting respiration from gross primary productivity. — True. A good part of GPP is used by plants in respiration; GPP minus respiration losses (R) gives NPP.
(IV) Energy flows in a unidirectional manner towards higher trophic levels, with some energy being lost as heat. — True. Energy moves only towards the higher trophic levels, and part of it is lost as heat to the environment.
All four statements are correct.
NCERT Extract:
Productivity – “… It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). 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). GPP – R = NPP Net primary productivity is the available biomass for the consumption to heterotrophs (herbiviores and decomposers).”
Ecosystem – Structure and Function – “… There is unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.”