Scientists investigated the effect of regular exercise on skeletal muscle fibres in mice - AQA - A-Level Biology - Question 3 - 2017 - Paper 1

Trained mice can sustain prolonged exercise due to increased muscle efficiency. Regular exercise enhances aerobic respiration, resulting in greater ATP production. This allows trained mice to perform longer periods of activity without fatigue, as they rely less on anaerobic processes that lead to lactate accumulation.

First, calculate the effective diameter of the field of view by determining the area per fibre. If the area of one field is 1.25 mm² for 15 fibres, the total area per fibre is:

$\text{Area per fibre} = \frac{1.25 \text{ mm}^2}{15} \approx 0.0833 \text{ mm}^2$

Assuming that the muscle fibres are circular, the area of a circle is given by:

$A = \pi r^2$

To find the radius, we rearrange that to find:

$r = \sqrt{\frac{A}{\pi}}$

Substituting the area per fibre into the equation yields:

$r = \sqrt{\frac{0.0833}{\pi}} \approx 0.1625 \text{ mm}$

To find the diameter in micrometres, we use:

$d = 2r = 2 \times 0.1625 \text{ mm} = 0.325 \text{ mm} = 325 \text{ µm}$

1. The muscle fibres from young mice tend to exhibit larger diameters compared to those from adult mice, indicating a difference in muscle development.
2. Young mice muscle fibres may show a greater range of variation in diameter than those from adult mice, suggesting that muscle fibre maturation stabilizes size.

1. The distribution of muscle fibre diameters in young mice is typically wider, with some fibres significantly larger than those in adult mice, indicating developmental growth stages.
2. Adult mice muscle fibres may exhibit more uniformity in diameter compared to young mice, reflecting a more consistent and mature muscle structure.