1.1. Lab technicians investigated the impact of regular exercise on the skeletal muscle fibres of guinea pigs.  The muscle fibres of exercised guinea pigs (who had 8 weeks of regular exercise) were compared with those of non-exercised guinea pigs. The muscle fibres from both sets of guinea pigs were stained with a specific chemical to show up succinic acid dehydrogenase activity. The darker and more intense the stain, the greater the succinic acid dehydrogenase activity. Figure 1 shows a set of results that they obtained.

Figure 1

Succinic acid dehydrogenase is an important enzyme that is used during the Krebs cycle. 

Suggest two reasons for the difference in the staining seen between the muscle fibres of the exercised guinea pigs vs the non-exercised guinea pigs.

1.2. Lab technicians decided to investigate the endurance capabilities of the different guine pigs. They had the guinea pigs carry out prolonged exercise and compared the length of time that the exercised guinea pigs and non-exercised guinea pigs could continue for. The exercised guinea pigs were able to exercise for a significantly longer time than the non-exercised guinea pigs. Explain why.

1.3. The lab technicians determined the mean diameter of muscle fibres in exercised guinea pigs by using an optical microscope to examine sections of muscle tissue. The circular area (πr² ) of a single field of view was 1.5 mm². The diameter of this area was equal to the diameter of 10 muscle fibres. Use this information to calculate the mean diameter in μm (micrometres) of a single muscle fibre in this sample of tissue.

1.4. The scientists also compared the diameter of samples of muscle fibres taken from male and female guinea pigs. The results are shown in Figure 2 below.

Figure 2

Describe two differences between the two samples of muscle fibres.