Grade 11 learners carried out an investigation to determine the effect of physical activity on the heart rate and breathing rate of humans.

here are the answers to your questions:

3.1.1
The independent variable in the investigation is the physical activity (e.g., rest, walking, running).
Answer: Physical activity

3.1.2
Two planning steps learners considered for this investigation are:

• Choosing learners of the same age to control for age-related physiological differences.
• Measuring the heart rate and breathing rate of each learner before physical activities to establish a baseline. Answer: Choosing learners of the same age; Measuring heart rate and breathing rate before activities

3.1.3
One way the learners ensured the validity of their investigation was by choosing 5 learners of the same age, which helps to control for a variable that could affect the results.
Answer: Choosing learners of the same age

3.1.4
Based on the table, running increases the breathing rate from 12 beats per minute (at rest) to 17 beats per minute.
Answer: Running increases the breathing rate from 12 to 17 beats per minute.

3.1.5
The breathing rate increases during running because the muscles require more oxygen for increased cellular respiration and produce more carbon dioxide as a waste product, which needs to be expelled.
Answer: Muscles require more oxygen and produce more carbon dioxide during running.

3.1.6
To calculate the difference in heart rate between rest and running: