Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water and carbon dioxide to produce oxygen and energy in the form of sugar. It occurs in two stages: in stage one, chloroplasts in plant cells capture sunlight and use its energy to power stage two, where carbon dioxide and water are converted into oxygen and glucose using an enzyme-driven process. Cellular respiration is the process by which cells generate energy by breaking down glucose molecules in the presence of oxygen. It also occurs in two stages: in stage one, glucose is broken down into smaller molecules in the cytoplasm, and in stage two these molecules are further broken down in the mitochondria to release energy, carbon dioxide and water.