Question

photosynthesis and cellular respiration are important processes in the carbon cycle. the equations for the two processes show that the products of one are the reactants of the other, and vice versa. before humans began adding co₂ to the atmosphere mainly by burning fossil fuels, the concentration of co₂ in the atmosphere remained below 400 parts per million for hundreds of thousands of years.
how can the processes of photosynthesis and cellular respiration contribute to stable carbon dioxide concentrations in the atmosphere?
cellular respiration
c₆h₁₂o₆ + 6o₂ → 6co₂ + 6h₂o
photosynthesis
6co₂ + 6h₂o → c₆h₁₂o₆ + 6o₂

Explanation:

Photosynthesis (equation: \(6\text{CO}_2 + 6\text{H}_2\text{O}
ightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\)) takes in atmospheric \(\text{CO}_2\) to produce glucose and oxygen. Cellular respiration (equation: \(\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2
ightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}\)) releases \(\text{CO}_2\) back into the atmosphere. In natural ecosystems, these two processes are balanced: the \(\text{CO}_2\) released by respiration is taken up by photosynthesis, and the \(\text{O}_2\) released by photosynthesis is used in respiration. This balance helps maintain a stable concentration of \(\text{CO}_2\) in the atmosphere, as the amount of \(\text{CO}_2\) removed by photosynthetic organisms (like plants, algae) is roughly equal to the amount added by respiring organisms (plants, animals, microbes) over time. Before human - induced \(\text{CO}_2\) emissions (like burning fossil fuels), this natural balance kept \(\text{CO}_2\) levels stable.

Answer:

Photosynthesis absorbs \(\text{CO}_2\) from the atmosphere (using it to make glucose: \(6\text{CO}_2 + 6\text{H}_2\text{O}
ightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\)), while cellular respiration releases \(\text{CO}_2\) (breaking down glucose: \(\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2
ightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}\)). Their balanced exchange (respiration - produced \(\text{CO}_2\) is taken up by photosynthesis, photosynthesis - produced \(\text{O}_2\) is used in respiration) maintained stable atmospheric \(\text{CO}_2\) levels (pre - human fossil fuel burning).