Which of the following statements is true regarding the process of glycolysis?
It both requires the input of ATP and produces ATP.
It produces ATP by oxidative phosphorylation.
It is an alternative to fermentation.
It involves changing 1 molecule of glucose into 1 molecule of pyruvate.
It occurs in the cell membranes of bacteria.
The Correct Answer and Explanation is:
Correct Answer: It both requires the input of ATP and produces ATP.
Explanation:
Glycolysis is a central metabolic pathway that occurs in the cytoplasm of cells (not in cell membranes, even in bacteria). It involves the breakdown of one glucose molecule (a six-carbon sugar) into two molecules of pyruvate (three-carbon compounds). This process is anaerobic, meaning it does not require oxygen, and it is the first step in cellular respiration.
The statement “It both requires the input of ATP and produces ATP” is true because glycolysis is divided into two main phases:
- Energy Investment Phase: In this phase, the cell uses 2 molecules of ATP to phosphorylate glucose and convert it into a more reactive form. This is necessary to destabilize the glucose molecule and prepare it for cleavage.
- Energy Payoff Phase: This phase generates 4 molecules of ATP and 2 molecules of NADH by substrate-level phosphorylation. Since 2 ATP were consumed earlier, the net gain is 2 ATP per glucose molecule.
Other options are incorrect:
- “It produces ATP by oxidative phosphorylation” is false because glycolysis produces ATP through substrate-level phosphorylation, not oxidative phosphorylation, which occurs in the mitochondria during later stages of respiration.
- “It is an alternative to fermentation” is false. Glycolysis actually precedes fermentation. When oxygen is absent, cells use fermentation to regenerate NAD⁺ so glycolysis can continue.
- “It involves changing 1 molecule of glucose into 1 molecule of pyruvate” is false. One glucose yields two pyruvate molecules.
- “It occurs in the cell membranes of bacteria” is false. Glycolysis takes place in the cytoplasm of all cells, including bacteria.
In summary, glycolysis requires ATP to initiate, but it also produces a net gain of ATP, making the correct statement: “It both requires the input of ATP and produces ATP.”
