Why does anaerobic respiration have a lower ATP yield than aerobic respiration? (4 marks)

During anaerobic respiration only glycolysis can occur as oxygen is not present to act as the final electron acceptor in oxidative phosphorylation, therefore only substrate level phosphorylation can occur. In order for glycolysis to continue, in animal cells, pyruvate is is reduced so NADH becomes NAD allowing glycolysis to continue which provides 2 ATP and keeps the cell alive until areobic respiration resumes.