# Gross primary production and increase in biomass

Please help me calculate GPP, Increase in biomass, photosynthetic efficiency, etc., by explaining how you arrived at the final answer and showing all of the equations or formulas involved in each calculation. Kindly use the correct scientific units throughout the calculation, as well as in the final answer. Please use scientific notation and an appropriate number of significant figures in the final answers. Thank you.

In an ecological investigation of an area of European grassland, the energy values of organisms in the ecosystem were found. The ecologist summarized the results of the work thus:

The amount of solar energy reaching the grassland was 1.91 x 10^6 kJ m^-2 y^-1. The grasses of the area lost 36 x 10^2 kJ m^-2 y^-1 in respiration and showed a net primary productivity (NPP) of 20.4 x 10^3kJ m^-2 y-1.

1. What is the gross primary productivity (GPP) for this area? Please show all of your workings.

2. Calculate the photosynthetic efficiency, i.e., the percentage of solar energy reaching the vegetation that is converted to GPP.

3. Most of the NPP of the producers is lost by death or other pathways, but three particular groups of animals feeding on the grass were also studied:

a. field mice , which ingested 107 kJ m^-2y^-1 and lost 105 kJ m^-2y^-1 in respiration and faeces;

b. grasshoppers, which ingested 444 kJ m^-2y^-1 and lost 374.3 kJ m^-2y^-1 in respiration and faeces;

c. small birds, which ate grass seeds with an energy value of 60 kJ m^-2y^-1 and lost 59.2 kJ m^-2y^-1 in respiration and faeces;

CALCULATE the increase in biomass of each of the three groups: field mice, grasshoppers and small birds.

d. The energy value of the grasshopper population that is consumed by spiders is 0.8 kJ m^-2y^-1. In this habitat, grasshoppers do not survive beyond the end of the year. CALCULATE the percentage of the total energy value by grasshoppers lost by death and other pathways.

e. Some important groups of organisms found in each ecosystem have been omitted from this account . STATE what they are and their functions.

f. Please state the trophic level of each group of organism in this food web.

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#### Solution Preview

1. Gross Primary Production, GPP, is the total amount of CO2 that is fixed by the plant in photosynthesis.

Respiration, R, is the amount of CO2 that is lost from an organism or system from metabolic activity. Respiration can be further divided into components that reflect the source of the CO2.

Net Primary Production, NPP, is the net amount of primary production after the costs of plant respiration are included (NPP = GPP - R).

Therefore GPP = NPP + R = (20.4 x 10^3kJ m^-2 y-1)+ (36 x 10^2 kJ m^-2 y^-1) = 24.0 x 10^3kJ m^-3 y-1

2. Calculate the photosynthetic efficiency, i.e., the percentage of solar energy reaching the vegetation that is converted to GPP.

The photosynthetic efficiency is the fraction of light energy converted into other forms of ...

#### Solution Summary

Calculation of Gross Primary Production based on solar energy, respiration rates, and net primary productivity. Calculation of increase in biomass of field mice, grasshoppers and small birds.