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Multiple Choice
What would be the expected effect on plants if the atmospheric CO$_2$ concentration was doubled?
A
The rate of photosynthesis would initially increase, leading to greater plant growth.
B
Plants would switch to using oxygen instead of CO$_2$ for photosynthesis.
C
There would be no effect on photosynthesis, as CO$_2$ is not a limiting factor.
D
Photosynthesis would stop completely due to CO$_2$ toxicity.
Verified step by step guidance
1
Understand the role of CO$_2$ in photosynthesis: CO$_2$ is a key reactant in the Calvin cycle, where it is fixed into organic molecules during the light-independent reactions of photosynthesis.
Consider the relationship between CO$_2$ concentration and photosynthesis: At lower CO$_2$ levels, photosynthesis is often limited by the availability of CO$_2$. Increasing CO$_2$ concentration can enhance the rate of photosynthesis up to a certain point.
Evaluate the potential effects of doubling atmospheric CO$_2$: Doubling CO$_2$ concentration would likely increase the rate of photosynthesis initially, as more CO$_2$ becomes available for fixation in the Calvin cycle.
Address the incorrect options: Plants do not switch to using oxygen for photosynthesis, as oxygen is not a reactant in the process. CO$_2$ is a limiting factor in many cases, so saying there would be no effect is incorrect. Additionally, CO$_2$ toxicity does not occur at doubled concentrations under normal conditions.
Conclude the expected outcome: The most plausible effect of doubling atmospheric CO$_2$ is an initial increase in the rate of photosynthesis, which could lead to greater plant growth, assuming other factors like water and nutrients are not limiting.