What is the chemical reaction between oxygen and glucose that releases energy into cells?

• A. Cellular respiration
• B. Fermentation
• C. Photosynthesis
• D. Combustion

Answer: (A)

Cellular respiration is the process by which cells harvest energy from glucose by using oxygen. In the mitochondria, glucose is broken down through a series of steps—glycolysis, the citric acid cycle, and the electron transport chain—to release energy that is captured as ATP, the cell’s usable energy. The overall result is glucose plus oxygen being converted into carbon dioxide, water, and ATP. This is the way inside cells that energy stored in glucose becomes available for activities like muscle movement, active transport, and biosynthesis.

Fermentation also releases some energy from glucose, but it does so without oxygen and yields far less ATP. Photosynthesis builds glucose using light energy, not releasing energy from glucose. Combustion is a rapid, uncontrolled burning outside living systems that releases energy as heat and light.