Describe how C4 plants are able to fix carbon dioxide in the process of photosyn

Question

Describe how C4 plants are able to fix carbon dioxide in the process of photosynthesis with little or no photorespiration in the heat of summer, while C3 plants have significant amounts of photorespiration under similar conditions. Address the following:

a) What enzyme is used to fix atmospheric carbon dioxide for C4 plants and C3 plants?
b) Which plants have Kranz anatomy?
c) Where, specifically, is PEP carboxylase found in the leaves of C4 plants?
d) Where specifically, is rubisco found in the leaves of C4 plants and C3 plants?
e) Under what conditions does rubisco act more like an oygenase than a carboxylase?
f) What is photorespiration, and why is it a "seemingly wasteful process"?
g) Under what conditions do C4 plants tend to outcompete C3 plants?
h) Under what conditions do C3 plants tend to outcompete C4 plants and why is this the case?

Explanation / Answer

a. In C3 plants, RuBisCo is the enzyme used to fix atmospheric carbon dioxide and in C4 plants PEP carboxylase is the enzyme. b. C4 plants have Kranz anatomy c. PEP carboxylase is found in the mesophyll cells of C4 plants d. RuBisCo is found in the bundle sheath cells of C3 and C4 plants e. RuBisCo acts as an oxygenase under very hot and dry conditions, when nitrogen and CO2 levels are low and when temperatures are high f. Photorespiration is a process where RuBisCo acts as an oxygenase and adds oxygen to RuBP rather than carbon dioxide. This reduces the rate of photosynthesis. It seems a wasteful process as it leads to a loss of carbon and nitrogen from the plant which may limit the growth of the plant g. C4 plants tend to outcompete C3 plants under hot and dry conditions h. When temperature and sunlight is moderate, when ground water is plentiful and when carbon dioxide concentrations are around 200 ppm or higher, C3 plants tend to outcompete C4 plants.

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