Which of the following is unlikely to happen during the process of sugar breakdown (cellular respiration) in a cell?

• A. Release of carbon dioxide as a waste product
• B. Conversion of glucose to lactic acid under anaerobic conditions
• C. Synthesis of glucose from pyruvate
• D. Production of ATP from ADP and inorganic phosphate

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the process of cellular respiration, which is the metabolic pathway cells use to break down glucose and produce energy in the form of ATP. Cellular respiration typically involves glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation.
2. Step 2: Analyze the options provided. The release of carbon dioxide as a waste product occurs during the citric acid cycle, where pyruvate is broken down into carbon dioxide and energy-rich molecules. This is a normal part of aerobic respiration.
3. Step 3: Consider the conversion of glucose to lactic acid under anaerobic conditions. This process, known as lactic acid fermentation, occurs when oxygen is not available, allowing cells to regenerate NAD+ for glycolysis to continue. This is a common occurrence in certain cells, such as muscle cells during intense exercise.
4. Step 4: Evaluate the synthesis of glucose from pyruvate. This process, called gluconeogenesis, is not part of cellular respiration but rather a separate metabolic pathway that occurs primarily in the liver to produce glucose from non-carbohydrate precursors. It is unlikely to happen during sugar breakdown.
5. Step 5: Confirm that the production of ATP from ADP and inorganic phosphate is a key outcome of cellular respiration, occurring during oxidative phosphorylation in the mitochondria. This is a central purpose of the process.