Read GPP, NPP and Productivity Units
Productivity is a rate of biomass production; gross and net values differ by producer respiration.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Separate gross and net
Gross primary productivity (GPP) is total organic matter fixed by producers. Net primary productivity (NPP) = GPP − respiration and is available to consumers and decomposers. Report productivity per area per time, in mass or energy units.
Read ecosystem comparisons
Productivity per unit area is high in tropical forests and low in open ocean, though oceans cover a vast area and contribute substantially to global totals. The cited estimate is about 170 billion tonnes of global annual NPP, including roughly 115 billion tonnes terrestrial. GPP captures only a small fraction of PAR.
Distinguish primary from secondary production
The diagram assigns 7 kg of new plant biomass to primary production and 2 kg of new animal biomass to secondary production; decomposer biomass is not automatically secondary production. Both production rates use the same dimensional unit, mass per unit area per unit time. Thus the linked item supports statements A and C.
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- ✓NPP = GPP − respiration.
- ✓NPP supports consumers and decomposers.
- ✓Use area/time units.
- ✓Keep per-area productivity separate from global totals.
Do not swap GPP (total fixed) with NPP (after respiration).
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Practise 5 linked questions