In cellular respiration, atp molecules must be input to initiate the process of glycolysis.

2 ATP molecules

Explanation:

Glycolysis is the initial stage of cell respiration, which is a series of reactions that produce energy for cell metabolic functions.

In glycolysis, the glucose molecule breaks down, this reaction consumes 2 ATP, so the glycolysis reaction has an energy balance of 2 ATP (This is the only step of cellular respiration that consumes ATP)

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.