Question

select the correct answer from each drop - down menu.
during the day, plants produce
by splitting water molecules in the light - dependent reactions of photosynthesis. at the same
time, plants use cellular respirati
needed by the light - independent reactions to make sugars.
during the night, plants produce
because
takes place.

Explanation:

1. During the day, in photosynthesis (light - dependent reactions), plants split water molecules ($\ce{H_2O}$) and produce oxygen ($\ce{O_2}$). So the first blank should be "oxygen".
2. The light - independent reactions (Calvin cycle) need carbon dioxide ($\ce{CO_2}$) to make sugars. But at the same time as photosynthesis (daytime), cellular respiration also occurs. However, the key here is the product of splitting water in light - dependent reactions, which is oxygen. Then, for the part about what is needed for light - independent reactions, it's carbon dioxide, but the first drop - down (from the visible part) is about the product of splitting water, so oxygen. At night, plants do cellular respiration, which produces carbon dioxide, and since photosynthesis (which needs light) doesn't occur at night, the process that takes place at night related to gas production from plants (respiration) produces carbon dioxide. But for the first blank (product of splitting water in photosynthesis), the answer is oxygen.

Answer:

The correct option for the first drop - down (product of splitting water in light - dependent reactions of photosynthesis) is "oxygen". (Assuming the first drop - down is for the product of splitting water, the answer is oxygen. If there are more blanks, but based on the visible part and the process of photosynthesis: during the day, plants produce oxygen by splitting water molecules in light - dependent reactions of photosynthesis. At night, plants produce carbon dioxide because photosynthesis (which requires light) does not take place, and cellular respiration (which produces $\ce{CO_2}$) occurs.)