Dual Enrollment Biology Practice Test

Which statement describes the overall impact of photosynthesis on atmospheric CO2?

Plants release CO2, increasing atmospheric CO2

Plants remove CO2 from the atmosphere and convert it to organic matter, acting as carbon sinks

Photosynthesis acts as a carbon sink by taking carbon dioxide from the air and turning it into organic matter in plant tissues. During this process, CO2 is fixed with water to form glucose (and other carbohydrates) using light energy, so carbon is stored in plants rather than remaining in the atmosphere. As plants grow, they accumulate biomass that contains carbon, reducing atmospheric CO2 levels. The other ideas don’t fit because photosynthesis uses CO2 rather than releasing it, and the splitting of water in the light reactions produces oxygen, not CO2.

Photosynthesis does not affect atmospheric CO2

Photosynthesis increases CO2 as water splits