Choose the correct option:

(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 option.

I, II, III and IV

The correct answer is Option (4) - I, II, III and IV

Statement I: Productivity can be divided into gross primary productivity and net primary productivity. This statement is true. Productivity refers to the rate at which energy is captured and converted into biomass by producers in an ecosystem. Gross primary productivity (GPP) is the total amount of energy captured by producers through photosynthesis. Net primary productivity (NPP) is the energy available for consumption by heterotrophs after accounting for the energy used by the producers themselves during respiration.

Statement II: Net primary productivity is the available biomass for the consumption by heterotrophs. This statement is true. Net primary productivity represents the biomass or energy that is available for consumption by heterotrophs, which are organisms that obtain their energy by consuming other organisms. It reflects the actual amount of energy that is transferred from producers to the rest of the ecosystem.

Statement III: Net primary productivity is equal to gross primary productivity minus respiration. This statement is true. Net primary productivity is calculated by subtracting the energy lost through respiration by producers from the total energy captured during gross primary productivity. The difference between gross primary productivity and respiration gives the net primary productivity, which represents the surplus energy available for the rest of the ecosystem.

Statement IV: There is unidirectional movement of energy towards higher trophic levels and its dissipation and loss as heat to the environment. This statement is true. Energy flow in an ecosystem is unidirectional, moving from lower trophic levels (producers) to higher trophic levels (consumers). As energy is transferred from one trophic level to the next, a significant portion of it is lost as heat through metabolic processes and other inefficiencies. This loss of energy limits the overall biomass and number of individuals at higher trophic levels.

Therefore, the correct option is (4) I, II, III, and IV.