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Ch. 53 - Ecosystems and Global Ecology
Chapter 52, Problem 5

If the GPP of a grassland is 5000 kcal/m2/year and 55 percent is used up by cellular respiration, what is the NPP? a. 2250 kcal/m2/year b. 2750 kcal/m2/year c. 5000 kcal/m2/year d. need more data

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1
Calculate the amount of energy used up by cellular respiration by multiplying the GPP by the percentage used in respiration: 5000 kcal/m2/year * 55% = 2750 kcal/m2/year.
Subtract the energy used in respiration from the GPP to find the NPP: 5000 kcal/m2/year - 2750 kcal/m2/year = 2250 kcal/m2/year.
Match the calculated NPP with the provided options to find the correct answer.
The correct answer is 2250 kcal/m2/year, which corresponds to option a.
Thus, the NPP of the grassland is 2250 kcal/m2/year.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gross Primary Productivity (GPP)

Gross Primary Productivity (GPP) refers to the total amount of energy captured by photosynthetic organisms in a given area over a specific time period. It represents the total biomass produced through photosynthesis before any energy is used for respiration. In this question, GPP is given as 5000 kcal/m²/year, which serves as the starting point for calculating net productivity.
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Cellular Respiration

Cellular respiration is the process by which organisms convert glucose and oxygen into energy, carbon dioxide, and water. This process consumes a portion of the energy produced during photosynthesis. In the context of the question, 55 percent of the GPP is used for cellular respiration, indicating how much energy is lost to metabolic processes, which is crucial for determining Net Primary Productivity (NPP).
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Net Primary Productivity (NPP)

Net Primary Productivity (NPP) is the amount of energy that remains after accounting for the energy used in cellular respiration by primary producers. It is calculated by subtracting the energy used for respiration from GPP. NPP is a key indicator of ecosystem productivity and health, and in this case, it can be calculated as NPP = GPP - (GPP * respiration percentage).
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