Citation:
NPP refers to the amount of energy that remains after plants have used some of their captured energy for their own respiration.
GPP is the total amount of energy captured by plants through photosynthesis before any deductions.
Respiration is the process by which organisms, including plants, release stored energy from organic compounds to carry out life functions.
Trophic levels represent different levels in a food chain or food web where organisms obtain their energy and nutrients.