May/June 2026 Paper 42

Mature red blood cells do not contain mitochondria. The only respiratory pathway carried out in red blood cells is glycolysis. The initial reaction in glycolysis is the phosphorylation of glucose using ATP. This reaction is catalysed by the enzyme hexokinase. An autosomal recessive gene mutation results in less hexokinase being produced, which can lead to hexokinase deficiency disease. Suggest the effect of the production of less hexokinase on red blood cells and suggest a possible symptom for a person with hexokinase deficiency disease.

Muscle cells contain mitochondria. This means that the Krebs cycle can take place in muscle cells. Outline the main events in the Krebs cycle.

If muscle cells do not receive enough oxygen, they may carry out respiration in anaerobic conditions. Describe respiration in anaerobic conditions in muscle cells.