Which process releases energy by breaking down glucose in the presence of oxygen?

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

Answer: (B)

The main idea is aerobic cellular respiration—the process that releases energy from glucose when oxygen is present. In this pathway, glucose is gradually broken down through glycolysis, then the citric acid cycle, and finally the electron transport chain in mitochondria. Oxygen serves as the final electron acceptor in the chain, enabling a large amount of ATP to be produced. This makes aerobic respiration the most energy-efficient way cells harvest energy from glucose, with carbon dioxide and water as byproducts.

Other options don’t fit the situation as well. Photosynthesis uses energy from light to build glucose, not release energy. Fermentation occurs without oxygen and yields far less ATP. Glycolysis is the first stage and can occur without oxygen, but by itself it doesn’t fully break down glucose to release the bulk of its energy.