Primary productivity is the rate of energy capture by which organisms?

• A. Rate of energy transfer between consumers
• B. Rate of energy capture by producers
• C. Rate of energy loss through respiration
• D. Rate of nutrient cycling

Answer: (A)

Primary productivity measures how quickly autotrophs, or producers, capture energy and store it as biomass through photosynthesis. These organisms—plants, algae, and photosynthetic bacteria—drive energy input into ecosystems by converting light energy into chemical energy. The rate is typically expressed as energy stored per unit area per unit time (for example, kJ/m^2/year). It’s useful to note the distinction between gross primary production (total energy captured) and net primary production (energy remaining after the producers use some for respiration). The other processes mentioned relate to energy flow after capture or to nutrient movement, not the act of capturing energy itself.