Question

counting beats and breaths
muscles need oxygen to function. when a person breathes, oxygen enters the lungs and is then carried by blood. the heart pumps this oxygen - rich blood to the body’s muscles. if muscles do not receive enough oxygen, they can feel tired because they cannot produce the energy they need efficiently.
students in a school collect data about their heart rates before and after an activity. they each flipped a coin to determine if their activity would be to run for 1 minute or sit still for 1 minute. the students measured their heart rates immediately before and immediately after the activity. graph 1 shows the results.
graph 1. heart rate data
which type of feedback loop is triggered during exercise, and why?
a positive feedback loop because
a negative feedback loop because
a positive feedback loop because
a negative feedback loop because the heart rate changes to correct a change in blood gas levels.

Explanation:

To determine the correct feedback loop during exercise, we analyze the options:

• Positive feedback loops amplify a change, while negative feedback loops counteract a change to maintain homeostasis.
• During exercise, muscles need more oxygen, so blood gas levels (e.g., oxygen and carbon dioxide) change. The heart rate increases to deliver more oxygen - rich blood and remove carbon dioxide, correcting the blood gas imbalance. This is a negative feedback loop as it works to restore normal conditions.
• Option A: Positive feedback is incorrect as exercise - related heart rate increase is not amplifying a change but correcting it.
• Option B: The description about “the activity” is not a correct reason for negative feedback.
• Option C: The reason about “the couple instead of the muscles” is incorrect and not related to the feedback loop in exercise.
• Option D: Correctly states that the heart rate changes (increases) to correct the change in blood gas levels, which is a negative feedback loop.

Answer:

D. A negative feedback loop because the heart rate changes to correct a change in blood gas levels.