The difference between gross primary productivity and net primary productiviry is determined by the respiration of primary producers.
a. true
b. false

True

Explanation:

Gross primary productivity (GPP) of a system is defined as the rate by which the primary producers trap the solar radiation during the process of photosynthesis. The gross primary productivity is represented as total photosynthesis per unit area in a given time.

The net primary productivity (NPP) refers to the energy available to the plants for their growth after cellular respiration and is represented as plant growth per unit area in a given time.

Plants use part of the gross primary productivity in cellular respiration to produce the energy required to perform other vital functions. Hence, the energy consumed in cellular respiration differentiates the gross primary productivity and the net primary productivity.

NPP = GPP - Plant respiration

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.