Question

what happens to photosynthesis in a plant if there is no carbon dioxide present? photosynthesis will not change. photosynthesis will speed up. photosynthesis will stop.

Explanation:

Carbon dioxide ($\text{CO}_2$) is a core reactant in the photosynthesis process, which follows the chemical equation:
$$6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light energy}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$
Without this essential input, the reaction cannot proceed.

Answer:

Photosynthesis will stop.