Answers · Exercise and heart health

Exercise and the heart rate — answer key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. SQ1 · Practice

Model answer. During the stepping the heart rate rose quickly from 60 and levelled off near 145 beats per minute. When the stepping stopped it fell, fast at first and then more slowly, and took several minutes to get back to the resting rate.

A full answer includes

I chose: it rose quickly, then levelled off; after the stepping it fell back over several minutes.
I did not choose "fell back at once": the dots take several minutes to reach the resting rate.

Also accept

rose quickly, then levelled off; fell back to resting over several minutes

Watch for

“It rose steadily all through the stepping; when the stepping stopped it fell back at once.” — The line levels off before the stepping ends, and the dots take several minutes to fall back.
“It rose quickly, then levelled off; after the stepping it stayed level for several minutes.” — The dots after the stepping fall, minute by minute, until they reach the resting rate.
“It rose slowly at first, then faster; after the stepping it fell back over several minutes.” — The line is steepest at the start of the stepping, then it flattens.

2. SQ2 · Practice

Model answer. The stepping stopped at 4 minutes. The resting dot is at 60; the dot at 7 minutes (68) is still above it, and the count is first back at 60 at 8 minutes. So the recovery time was 8 − 4 = 4 minutes.

Checked automatically

Recovery time: 4 min (within ±0.5 min)
- Common wrong answer 8 min: That is the reading on the time axis. Subtract the 4 minutes before the stepping ended.
- Common wrong answer 3 min: Either that is the stepping time (1 to 4 min), or you stopped at 7 min, where the dot (68) is still above the resting dot.
- Common wrong answer 5 min: The count was already back at the resting rate at 8 min. Stop at the first dot level with the resting dot.

A full answer includes

I read the end of the stepping: 4 min.
I read when the count was first back at the resting 60: 8 min.
I worked out 8 − 4.
I wrote 4 minutes.
I did not give the time on the axis (8 min) as the answer.
I did not stop at 7 min: that dot (68) is still above the resting dot.

Also accept

4 min

Watch for

“8 minutes.” — That is the time on the axis. Count from the end of the stepping at 4 minutes.
“3 minutes, to the dot at 7 min.” — The dot at 7 minutes (68) is still above the resting dot. Look for the first dot level with it.
“5 minutes, to the dot at 9 min.” — The count was already back at 60 at 8 minutes. Stop at the first dot level with the resting dot.

3. SQ3 · Practice

Model answer. For a fair comparison only the activity changes. The same pupil does both, each lasts the same time, and he rests until his heart rate is back at the resting rate before each one. The activity is changed on purpose, and the heart rate just after each activity is what is measured.

A full answer includes

I chose the pupil who does both activities.
I chose how long each activity lasts.
I chose a rest back to the resting rate before each one.
I did not choose the activity: it is the one thing changed on purpose.
I did not choose the heart rate: it is what is measured.

Also accept

the same pupil; the same time for each activity; a rest back to resting before each

Watch for

“Which activity is done must stay the same.” — The activity is the one thing changed on purpose: skipping or jogging.
“The heart rate just after each activity must stay the same.” — The heart rate is what is measured, so it is expected to differ.

4. SQ4 · Practice

Options as numbered on the pupil sheet: 1 — cells in these muscles respire aerobically faster, using more oxygen and glucose; 2 — her thigh muscles contract harder to push the pedals round; 3 — her heart makes more energy and pumps it out to her thigh muscles; 4 — her heart beats faster and pumps more blood with each beat; 5 — each minute, more blood brings oxygen and glucose and takes away carbon dioxide.

Model answer. Her thigh muscles contract harder to push the pedals, so their cells respire aerobically faster, using more oxygen and glucose and making more carbon dioxide. Her heart beats faster and pumps more blood with each beat, so each minute more blood brings oxygen and glucose to the thigh muscles and takes away carbon dioxide. The step that does not belong is "her heart makes more energy": the heart only pumps blood. The blood brings glucose and oxygen, and the muscle cells release the energy from the glucose themselves, by respiration.

A full answer includes

Step 1: I put her thigh muscles contracting harder to push the pedals.
Step 2: I put the muscle cells respiring aerobically faster.
Step 3: I put her heart beating faster.
Step 4: I put more blood each minute bringing oxygen and glucose and taking away carbon dioxide.
I left out "her heart makes more energy": the heart pumps blood, and the muscle cells release the energy by respiration.
I did not put the heart beating faster first.

Also accept

contract harder; respire aerobically faster; heart beats faster; more blood each minute brings oxygen and glucose and takes away carbon dioxide (left out: the heart makes energy)

Watch for

“The heart beats faster first, and that makes the muscles respire more.” — The muscles' need comes first; the heart responds to it.
“Her heart makes more energy and pumps it out to her thigh muscles.” — The heart pumps blood, not energy. The blood brings glucose and oxygen, and the muscle cells release the energy by respiration.

5. SQ5 · Practice

Model answer. At rest the heart rate was 60 beats per minute. During the first bout it rose quickly and levelled off at about 120. In the 2 minutes of rest it fell (116, then 92) but was still 80 when the second bout began, not back at 60. During the second bout it rose again, from 80 to about 120. After the second bout it fell, fast at first (116, 92, 76) and then more slowly (68), and was back at 60 at 11 minutes, 4 minutes after the stepping ended.

A full answer includes

I made at least four of the points below, each with a value from the graph.
I gave the resting rate: 60 beats per minute.
I said it rose quickly during the first bout, from 60.
I said it levelled off at about 120.
I said that in the rest between the bouts it fell only to 80, not back to the resting 60.
I said it rose again during the second bout, from 80 to about 120.
I said that after the second bout it fell fast at first, from about 116 to 76 in 2 minutes, then slowly, to 68 and 60.
I said it was back at 60 at 11 minutes, 4 minutes after the second bout ended.
I did not write that it was back at resting before the second bout: the dot at 5 min is 80.

Also accept

rest 60; about 120 in each bout; only down to 80 between the bouts; back at 60 at 11 min, 4 min after the second bout

Watch for

“It was back at the resting rate before the second bout began.” — The dot at 5 minutes is 80, above the resting 60. Two minutes' rest was not long enough to recover.
“The second bout raised the heart rate higher than the first.” — Both bouts level off at about 120. The second only starts from a higher rate, 80.

6. SQ6 · Practice

Model answer. P's rate is 15 × 4 = 60 beats per minute; Q's is 63. The volunteer's rate is steady, so nothing is lost by counting for longer. In P's count each beat missed changes the rate by 4 beats per minute; in Q's it changes it by only 1. So Q's one-minute count is the better value here. Straight after exercise, when the rate is falling, a short count is better.

A full answer includes

I chose: Q's 63 is better, because one missed beat changes it by only 1 beat per minute.
I did not choose "a 15-second count catches the rate at that moment": that matters only when the rate is changing.

Also accept

Q's 63 is better: at a steady rate one missed beat changes it by 1, not by 4

Watch for

“P's 60 is better: a 15-second count catches the rate at the moment it is taken.” — That matters when the rate is changing, as just after exercise. Here it is steady, so a longer count is more precise.
“P's 60 is better: in a short count there is less time to lose count of the beats.” — A beat can be missed in any count, but in 15 s each missed beat is multiplied by 4. In one minute it changes the rate by only 1.
“Both are equally good, because both have been turned into beats per minute.” — Both are in beats per minute, but 60 and 63 differ. Multiplying a count by 4 multiplies any missed beat by 4 too.

7. SQ7 · Practice

Model answer. To count her pulse by hand she needs a free hand and a still wrist, so she would have to stop pedalling for every count. A chest strap picks up the electrical activity of her heart and goes on recording while she moves, so she gets a reading every 30 seconds without stopping.

A full answer includes

I chose: counting needs a still wrist and a free hand; the strap goes on recording as she rides.
I did not choose "the wrist pulse is slower than the heart": there is one pulse for each heartbeat.

Also accept

counting needs a still wrist and a free hand; the strap goes on recording as she rides

Watch for

“The pulse at the wrist is slower than the heart, so a hand count would read too low.” — Each contraction of the left ventricle sends one surge of blood to the wrist, so the pulse rate is the heart rate.
“A count by hand must last a whole minute, so a reading every 30 seconds is impossible.” — A 15-second count × 4 gives beats per minute. The problem is counting while she rides.
“The strap counts only the lub sounds, so it can never miss a beat as a hand count can.” — A chest strap picks up the electrical activity of the heart, not its sounds.

8. SQ8 · Practice

Model answer. The heart does not make energy, and it does not pump energy: it pumps blood. The blood brings glucose and oxygen to the muscles, and the muscle cells release the energy from the glucose themselves, by aerobic respiration. During exercise the muscles respire faster, so the heart beats faster to bring more glucose and oxygen each minute and to take away the extra carbon dioxide.

A full answer includes

I wrote that the heart does not make energy: it pumps blood.
I wrote that the blood brings glucose and oxygen to the muscles.
I wrote that the muscle cells release the energy from glucose by aerobic respiration.
I wrote that a faster heart rate brings more glucose and oxygen to the muscles each minute.
I wrote that it also takes away more carbon dioxide each minute.
I did not write that the energy is released in the heart or in the blood.

Also accept

the heart pumps blood, not energy; the blood brings glucose and oxygen; the muscle cells release the energy by aerobic respiration; a faster rate brings more glucose and oxygen each minute and takes away more carbon dioxide

Watch for

“The heart makes energy and pumps it to the muscles.” — The heart pumps blood. The muscle cells release the energy from glucose by respiration.
“The blood releases the energy and passes it on to the muscles.” — Respiration happens inside the muscle cells. The blood only brings the glucose and oxygen that they use.

9. SQ9 · Practice

Model answer. Both columns fall together: the heart rate from 126 to 65 beats per minute and the lactic acid from 12.0 to 1.2 mmol per dm³, and both are close to their resting values only after about an hour. This fits the heart rate staying raised while the blood carries the extra lactic acid to the liver, where it is broken down using oxygen (removing the oxygen debt). The table rules out the two statements in which one falls before the other, and lactic acid is not breathed out: carbon dioxide is.

A full answer includes

I chose: her heart rate stays raised while her blood still has extra lactic acid to take to the liver.
I checked both columns: they fall together, and both are near resting only after about an hour.
I did not choose "breathed out": lactic acid is broken down in the liver.

Also accept

her heart rate stays raised while her blood still has extra lactic acid to take to the liver

Watch for

“The lactic acid is breathed out in the lungs, so it falls as her breathing slows down again.” — Lactic acid is not breathed out. The blood carries it to the liver, where it is broken down. The lungs remove carbon dioxide.
“Her heart rate is back at its resting value well before the lactic acid begins to fall.” — At 45 minutes her heart rate is still 75, above the resting 62, and the lactic acid has fallen since the first reading.
“The lactic acid stays at its highest until her heart rate is back at resting, then falls.” — The lactic acid falls from the first reading on, 12.0, 9.0, 5.0, at the same time as the heart rate.

10. ST1 · Apply

Model answer. The harder the activity, the higher the heart rate: 74 beats per minute sitting, 98 walking, 136 jogging and 172 running fast.

A full answer includes

I wrote that the harder the activity, the higher the heart rate.
I quoted the lowest value: 74 sitting.
I quoted the highest value: 172 running fast.
I did not write that it rises by the same amount each time.

Also accept

the harder the activity, the higher the heart rate (with data)

Watch for

“Heart rate goes up by the same amount for each activity.” — Look at the differences: 24, 38 and 36. They are not equal.

11. ST2 · Apply

Model answer. More than one thing changed: the step height, the time spent stepping and the volunteer. A difference in recovery time could be caused by any of them, so the results cannot show the effect of one alone.

A full answer includes

I named the step height as different.
I named the stepping time as different.
I named the volunteer as different.
I wrote that a difference in recovery time could be caused by any of these.
I did not write that one group's result is wrong.

Also accept

more than one variable differs (height, time, volunteer), so the cause of any difference is unknown

Watch for

“Group 2 worked harder, so its recovery time is wrong.” — Neither result is wrong; the two tests are just not the same test.

12. ST3 · Apply

Model answer. With the bag, the leg muscles contract more strongly, so their cells carry out more aerobic respiration. They use more oxygen and make more carbon dioxide each minute, so the heart beats faster to pump more blood through them. Row C shows all three higher.

A full answer includes

I chose row C.
I did not choose row A: more aerobic respiration makes more carbon dioxide, not less.

Also accept

Watch for

“Row A: more oxygen is used, but less carbon dioxide is made.” — Aerobic respiration that uses more oxygen also makes more carbon dioxide. The two rise together.
“Row B: the muscles respire the same; only the heart rate rises.” — The heart does not beat faster because the bag presses on it. It beats faster because the leg muscles respire more.
“Row D: the muscles respire more, but the heart rate stays the same.” — To bring much more oxygen each minute, more blood must flow through the muscles, so the heart beats faster.