1.1. A group of 16-year-old students conducted a classroom experiment to study the effect of physical activity on heart rate.

The students selected four volunteers and measured each student's resting heart rate using a digital pulse monitor. Then, each student ran on a treadmill at a constant speed for 5 minutes. Immediately after the exercise, heart rates were measured again. The process was repeated after 10 minutes of rest to observe recovery.

Identify the independent and dependent variables in this investigation.

1.2. The results from the investigation in part (a) are shown in Table 1 below:

Table 1

Describe the changes in heart rate experienced by students immediately after exercise and after 10 minutes of rest.

1.3. Extended Tier Only

Explain why the heart rate changes during physical activity.

1.4. Suggest two ways to improve the validity of the results from the investigation described in part (a).