You're conducting an experiment to determine the effect of different wavelengths of light on the absorption of carbon dioxide as an indicator of the rate of photosynthesis in aquatic ecosystems. if the rate of photosynthesis increases, the amount of carbon dioxide in the environment will decrease, and vice versa. small aquatic plants are placed into three containers of water mixed with carbon dioxide. container a is placed under normal sunlight, b under green light, and c under red light. the containers are observed for a 24-hour period. carbon dioxide absorption is an appropriate indicator of photosynthesis because

The process of formation of sugar or carbohydrate by plants is known as photosynthesis.

It occurs in presence of light so the term "photo"

Here the plant uses carbon dioxide and it reacts with water to given glucose

The general reaction will be

6CO2(g)  + 6H2O(g)  + sunlight ---> C6H12O6  + 6O2

Thus the carbon dioxide is being converted to glucose

Higher the rate of absorption of carbon dioxide by plant more the rate of formation of glucose or more the rate of photosynthesis by the plant

The formation of glucose from carbon dioxide is a metabolic pathway which is a cycle known as Calvin cycle. Here actually the carbon is fixed into useful carbohydrates and this pathway is light independent.

Hence

Carbon dioxide absorption is an appropriate indicator of photosynthesis because  the main part of photosynthesis if fixation of carbon dioxide into useful carbohydrates by Calvin cycle (occurs in chloroplast of plant cells)