Primary and secondary productionSpec C4.2.15, C4.2.16
In short
Primary production is the accumulation of carbon compounds in biomass by autotrophs. Secondary production is the accumulation of carbon compounds in biomass by heterotrophs. Both are measured as mass of carbon per unit area per unit time, usually g m⁻² yr⁻¹. Secondary production is lower than primary production because carbon compounds are lost as carbon dioxide and water in respiration.
- Primary production
- Accumulation of carbon compounds in biomass by autotrophs.
- Secondary production
- Accumulation of carbon compounds in biomass by heterotrophs.
Biomass accumulates when organisms grow or reproduce. Production is a rate, so its units are mass of carbon per unit area per unit time, usually g m⁻² yr⁻¹.
Biomes vary in their capacity to accumulate biomass. Production is high in tropical rainforests, where it is warm, wet and light all year, and low in deserts and tundra, where water or temperature limits photosynthesis and the growing season is short.
Secondary production is lower than primary production in an ecosystem. When carbon compounds are oxidised in cell respiration, they are converted to carbon dioxide and water and leave the organism, so that biomass is lost. Only the part of the food that is not respired, egested or excreted is built into new heterotroph biomass.
Production is not the same as biomass. Biomass is the mass present at one moment (g m⁻²); production is how fast it accumulates (g m⁻² yr⁻¹).
Written and checked against the IB Biology SL specification · Updated October 2026