(a)[4]
Sarcomeres are the functional units within the myofibrils of the muscle fibres (muscle cells) in striated muscle. When an action potential reaches the sarcoplasmic reticulum of a striated muscle fibre, a sarcomere may shorten. This happens by the sliding filament model. Outline the sequence of events after stimulation of the sarcoplasmic reticulum that leads to shortening of a sarcomere.
(b)[4]
Scientists measured the diameters of samples of striated muscle fibres from young mice and adult mice. The findings are shown in Fig. 7.1. Using Fig. 7.1, describe two differences between the muscle fibres of young mice and adult mice and suggest how these differences may influence the sliding filament model.