Question

18 primary productivity
key question: what is primary productivity, how does it differ
from net primary production, and why is it important?
what do we mean when we say that an ecosystem has a
(high or low) productivity? the energy accumulated by plants
or other producers in an ecosystem (or measured area) is
called primary production. it is the first - energy - storage step
in the food chain. the total amount of energy fixed by plants
through photosynthesis is the gross primary production (gpp).
however, some of this energy is required by the producers

1. (a) explain the difference between gross primary productivity (gpp) and net primary productivity (npp).

(b) write a simple word equation to show how npp is derived from gpp.
(c) what factors do you think could influence the gpp of ecosystems?
(d) why do you think it is important to distinguish between gpp and npp when studying the productivity of ecosystems?

Explanation:

(a) Gross primary productivity (GPP) is the total amount of energy captured by producers through photosynthesis per unit area (or volume) per unit time. Net primary productivity (NPP) is the biomass (energy) available to consumers after subtracting the energy used by producers for respiration from GPP.
(b) Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) - Respiration (R) by producers.
(c) Factors influencing GPP include light intensity and duration, availability of water, carbon - dioxide concentration, temperature, and nutrient availability. These affect the rate of photosynthesis in producers.
(d) Distinguishing between GPP and NPP is important as GPP shows the total energy capture by producers, while NPP indicates the energy available for the rest of the food web (herbivores, carnivores, etc.). It helps in understanding energy flow and ecosystem health, and in assessing the carrying capacity for consumers.

Answer:

(a) GPP is total energy captured by producers via photosynthesis; NPP is biomass available to consumers after subtracting producer respiration from GPP.
(b) NPP = GPP - Respiration by producers
(c) Light, water, CO₂, temperature, nutrients.
(d) GPP shows total energy capture, NPP shows energy available for the food - web, helps in understanding energy flow and ecosystem health.