Answer:
Beginning with energy sources obtained from their environment in the form of sunlight and organic food molecules, eukaryotic cells make energy-rich molecules like ATP and NADH via energy pathways including photosynthesis, glycolysis, the citric acid cycle, and oxidative phosphorylation.
Cells have an organelle known as 'mitochondria' which has ATP molecules in it. These ATP molecules generates energy for the cell to function properly.
Cells need a source of energy, they get this energy by breaking down food molecules to release, the stored chemical energy.
This process is called 'cellular respiration'.
The process is happens in all the cells in our body.
Oxygen is used to oxidize food, main oxidized food is sugar(glucose).