Mitochondrial DNA (mtDNA) is a small circular DNA molecule located in mitochondria - AQA - A-Level Biology - Question 4 - 2019 - Paper 3

The student's conclusion that training has a positive effect on VO₂(max) and CS activity can be evaluated by examining the data presented in Figures 4 and 5.

1. First, it’s important to recognize that both groups showed an increase in VO₂(max) and CS activity after training. However, without statistical analysis (like a t-test), we cannot definitively conclude that these differences are significant.

2. Additionally, the fact that both groups underwent the same training program for 8 weeks suggests that any observed increases could be attributed to the training rather than the genetic differences alone. Thus, while the data may suggest a positive effect of training, the lack of significant statistical evidence limits the strength of the student's conclusion.

1. In Group C, the presence of cytosine at nucleotide position 16 519 may result in less mitochondrial replication or production, thereby reducing the overall capacity for energy production.

2. The mutation could also lead to less effective transcription of the genes necessary for mitochondrial proteins and citrate synthase, resulting in lower CS activity as shown in Figure 5.

The conclusion that 'Having thymine at nucleotide position 16 519 in Group T causes an increase in ability to exercise for longer' is a complex claim that requires careful consideration of the data.

1. From Figure 5, it can be observed that Group T did have increased CS activity compared to Group C, which may indicate improved aerobic capacity. However, purely attributing this improvement to the mutation at position 16 519 without considering the influence of the 8-week training program and other factors could be misleading.

2. Furthermore, correlation analysis presented in Figure 6 may or may not show a relationship between percentage changes in VO₂(max) and CS activity in Group T, which suggests that other variables could be impacting exercise capacity. Therefore, while the mutation may play a role, it is not the sole factor determining the increased ability to exercise longer.