The smooth ER differs from the rough ER in that:

What is the difference between the rough and smooth ER? Rough ER's have ribosomes on the surface and produce large amounts of proteins for export. Smooth ER's contain a collection of specialized enzymes and does not have ribosomes on its surface.

Explanation:

photosynthesis makes the glucose that is used in cellular respiration to make atp. the glucose is then turned back into carbon dioxide, which is used in photosynthesis. while water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water.

for a different answer set the answer would be because the oxygen in the water had depleted (apex)