Gross Primary Productivity and Net Primary Productivity
As autotrophs, such as plants and pytoplankton, convert solar energy to chemical energy through photosynthesis, they
perform primary production. The total chemical energy produced is called GROSS primary production. Autotrophs then
use this energy to perform cellular respiration. The energy that remains after respiration is called NET primary
productivity and is used to generate biomass (stems, roots, leaves) that can be consumed by herbivores. The rate at
which autotrophcs convert energy to biomass is called productivity and ecosystems whose plants convert solar energy
to biomass rapidly are said to have high net primary productivity.
To solve NPP/GPP problems you can use the following formula(s):
NPP + Respiration = GPP
GPP – Respiration = NPP
Net Primary
GPP – NPP = Respiration
Answer the following questions based on productivity
(refer to your notes if unsure):
1. Write the equation for photosynthesis.
2. Write the equation for cellular respiration.
3. What percent of the solar energy striking producers is captured by photosynthesis?
4. What percent of that solar energy is used for GPP?
5. Define Gross Primary Productivity
6. Define Net Primary Productivity
7. What happens to the energy that remains after respiration? Is this NPP or GPP?
8. Is the biomass available for primary consumers considered NPP or GPP?
9. What terrestrial ecosystems have a high NPP?
Gross Primary
10. What aquatic ecosystems have a high NPP?
11. In terrestrial ecosystems NPP tends to increase with which two abiotic factors?
12. In aquatic ecosystems, NPP tends to increase with which two abiotic factors?
Remember: NPP = GPP – Respiration or GPP = NPP + Respiration
13. The net annual productivity of a particular wetland ecosystem is found to be 8,000 kcal/m2. If respiration by the
aquatic producers is 12,000 kcal/m2 per year, what is the gross annual primary productivity for this ecosystem, in
kcal/m2 per year?
14. The NPP of an ecosystem is 1 kg C/m2/year and the GPP for the ecosystem is 2.5 kg C/m2/year and the energy
needed by the producers for their own respiration is 1.5 kg C/m2/year. What is the GPP of such an ecosystem?
15. If you measure the available biomass for a patch of forest as 10 kg C/m2/year and the GPP is 15 kg C/m2/year,
what was the amount of CO2 given off into the atmosphere ?
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