What is the difference between primary productivity and secondary productivity in ecosystems?

What is the difference between primary productivity and secondary productivity in ecosystems?

• A. Primary productivity is energy captured by producers; secondary productivity is energy stored in consumer biomass from food eaten.
• B. Primary productivity is energy stored in consumers.
• C. Primary productivity is energy lost as heat.
• D. Primary productivity only occurs in oceans.

Answer: (A)

Energy flow in ecosystems involves two main ideas: how producers capture energy and how consumers convert that energy into their own biomass.

Primary productivity is the rate at which producers—like plants, algae, and some bacteria—capture energy from sunlight or inorganic chemical sources and turn it into organic matter. This is about the creation of new plant biomass, and it can be described as energy stored in producers per unit area per time (often expressed as GPP or NPP, with NPP accounting for plant respiration).

Secondary productivity, on the other hand, is the rate at which consumers accumulate biomass by eating producers or other organisms. It reflects how much of the ingested energy ends up stored as new consumer biomass, rather than used for metabolism or lost as heat.

So the statement that primary productivity is energy captured by producers and secondary productivity is energy stored in consumer biomass from food eaten best captures the difference. The other ideas don’t describe the definitions: energy stored in consumers describes secondary productivity (not primary); energy lost as heat is part of energy use but not the defining difference; and productivity occurs in many ecosystems, not only oceans.