What is the key difference between gross primary productivity and net primary productivity?

Gross primary productivity (GPP) refers to the total amount of energy captured by photosynthesis in a given area over a specific time period. It measures the overall energy production by plants, without accounting for energy expenditure. In contrast, net primary productivity (NPP) represents the energy available to the next trophic level after plants have used some of that energy for their own metabolic processes, primarily respiration. Therefore, NPP is calculated by subtracting the energy used in respiration from GPP.

This distinction is vital in ecology as NPP indicates the amount of energy that can be stored as biomass and ultimately supports herbivores, carnivores, and decomposers in the ecosystem. Understanding this difference helps in analyzing energy flow within an ecosystem and the productivity of different environments.

While other choices touch on aspects related to productivity, they do not accurately define the core distinction. Gross productivity does not specifically measure energy used; it reflects total energy produced. The statement about gross productivity counting only plant energy is misleading because it overlooks the broader context of energy capture by all primary producers. Additionally, NPP does not relate directly to secondary producers; rather, it focuses on the energy available to support them. Thus, the correct understanding centers on how respiration factors into the