ATP Photosynthesis Practice Test 2025 – Complete Exam Prep

Increasing concentrations of carbon dioxide (CO2) can enhance the rate of photosynthesis, particularly up to a certain point. Initially, as the concentration of CO2 rises, the rate of photosynthesis increases because CO2 is one of the key raw materials that plants use to convert light energy into chemical energy, specifically glucose. This process occurs in the chloroplasts of plant cells during the Calvin cycle, where CO2 is fixed into organic compounds.

However, this increase in the photosynthetic rate will not continue indefinitely. After a certain concentration of CO2 is reached, the rate levels off because other factors become limiting. These factors can include light intensity, temperature, and the availability of water or nutrients. When those other factors do not increase, there comes a point where the increase in CO2 does not result in a further rise in the rate of photosynthesis, causing the curve to plateau.

Thus, the correct answer indicates that while increasing CO2 concentrations initially enhance photosynthetic rates, this effect eventually stabilizes as other limiting factors come into play.