Differentiate between gross and net primary production.

Differentiate between gross and net primary production.

• A. GPP is total energy captured by photosynthesis; NPP is GPP minus the energy used by producers for respiration.
• B. GPP is energy lost as heat; NPP is energy stored in glucose.
• C. GPP is the energy used by consumers; NPP is energy stored in glucose.
• D. GPP is net production; NPP is gross production.

Answer: (C)

The main idea is that gross primary production is the total energy plants capture through photosynthesis, while net primary production is what remains after the plants use some of that energy for their own respiration. In other words, NPP equals GPP minus the energy plants spend on respiration, and it represents the energy stored in new plant biomass that is available to herbivores. This clarifies why not all energy fixed by photosynthesis becomes biomass for the rest of the ecosystem. The other descriptions mix up where the energy goes or what GPP and NPP represent: energy used by consumers isn’t GPP, and NPP isn’t simply energy stored as glucose; and saying GPP is net production would invert the meanings.