Succinic acid dehydrogenase is an enzyme used in the Krebs cycle.

Suggest one reason for the difference in the staining between the muscle fibres of the control mice and the trained mice.

The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice.

Explain why.

The scientists determined the mean diameter of muscle fibres in trained mice using an optical microscope to examine sections of muscle tissue. The circular area (πr2) of one field of view was 1.25 mm2. The diameter of this area was equal to the diameter of 15 muscle fibres.

Using this information, calculate the mean diameter in µm (micrometres) of muscle fibres in this section of tissue.

Answer ______________ µm

The scientists also compared the diameter of samples of muscle fibres taken from young mice and adult mice.

Describe two differences between these samples of muscle fibres.

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