Under anaerobic conditions, a culture of yeast cells metabolizes 4 molecules of glucose vi… — JAMB UTME

Under anaerobic conditions, a culture of yeast cells metabolizes $4$ molecules of glucose via alcoholic fermentation. What is the total net number of ATP molecules generated from this process?

$8$ ATP moleculesAnswer
B
$16$ ATP molecules
C
$144$ ATP molecules
D
$4$ ATP molecules

Answer

The total net yield is

8

ATP molecules.

During anaerobic alcoholic fermentation in yeast, each glucose molecule undergoes glycolysis to produce

2

molecules of pyruvate, yielding a net total of

2

ATP molecules via substrate-level phosphorylation. For

4

glucose molecules, the total net ATP yield is

4 \times 2 = 8

ATP molecules.

Step-by-Step Solution

Identify the respiratory pathway and conditions

Alcoholic fermentation is an anaerobic pathway in yeast occurring in the cytoplasm.

Without oxygen, pyruvate does not enter the mitochondria for the Krebs cycle or electron transport chain.

Determine the net ATP yield per glucose molecule

Glycolysis yields

4

ATP molecules gross minus

2

ATP molecules invested, giving

2

net ATP molecules per glucose.

Substrate-level phosphorylation in glycolysis provides the sole net ATP gain during fermentation.

Calculate net ATP for 4 glucose molecules

4 \text{ glucose molecules} \times 2 \text{ ATP/glucose} = 8 \text{ ATP molecules}

Multiplying single-molecule net yield by total glucose input.

Key Concept

Net ATP yield difference between anaerobic fermentation and aerobic respiration

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