Which step of cellular respiration can occur without the presence of oxygen?

• A. Oxidative phosphorylation
• B. Glycolysis
• C. Electron transport chain
• D. Citric acid cycle (Krebs cycle)

Answer: (B)

Verified step by step guidance

1. Understand the process of cellular respiration, which consists of glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation (including the electron transport chain). Oxygen plays a critical role in some of these steps.
2. Recognize that glycolysis is the first step of cellular respiration and occurs in the cytoplasm. It does not require oxygen and is therefore anaerobic.
3. Learn that glycolysis involves the breakdown of glucose into two molecules of pyruvate, producing a small amount of ATP and NADH. This process can occur in both aerobic and anaerobic conditions.
4. Understand that the citric acid cycle (Krebs cycle) and oxidative phosphorylation (including the electron transport chain) require oxygen to function efficiently. These steps occur in the mitochondria and are part of aerobic respiration.
5. Conclude that glycolysis is the only step of cellular respiration that can occur without the presence of oxygen, making it essential for energy production in anaerobic conditions.