The answer is a. formation of ATP from glucose during respiration.
Reduction is gain of electrons, and oxidation is loss of electrons.
During respiration, electrons are transferred from glucose to ATP. Since glucose loses electrons, this reaction is an oxidation reaction.
The formation of carbohydrates from carbon dioxide during photosynthesis must be a reduction reaction because carbon dioxide gains electrons to form carbohydrates.
The formation of oxygen from water molecules during photosynthesis is the reduction reaction. Water molecules are electron donors, but they give their electrons to chlorophyll molecules, not to oxygen. Oxygen forms in the photolysis of water.
