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.

Answer: (A)

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.
2. 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.
3. 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.
4. 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.
5. 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.