Answers · Exercise and heart health

Watching the heart — answer key

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

1. MQ1 · Practice

Model answer. The activity of the heart can be monitored by an ECG (its electrical activity), by the pulse rate (felt in an artery) and by listening through a stethoscope to the sounds of the valves closing.

A full answer includes

I chose: an ECG, the pulse rate and listening to the valves closing.
I did not choose the list with the heart muscle contracting: the heart sounds come from valves.

Also accept

an ECG, the pulse rate and listening to the valves closing

Watch for

“an ECG, the pulse rate and listening to the heart muscle contracting” — The muscle contracting makes almost no sound you can hear. The lub and the dub are valves closing.
“an ECG, the breathing rate and listening to the valves closing” — The breathing rate is the activity of the lungs. The heart is counted at the pulse.
“the blood pressure, the pulse rate and listening to the valves opening” — Valves make their sound as they close, not as they open, and blood pressure is not one of the three ways.

2. MQ2 · Practice

Model answer. There are 4 lots of 15 seconds in a minute, so the heart rate is 20 × 4 = 80 beats per minute (or 20 ÷ 0.25 min = 80).

Checked automatically

Heart rate (beats per minute): 80 (within ±0.5)
- Common wrong answer 5 : You divided by 4. A whole minute holds four 15-second counts: multiply by 4.
- Common wrong answer 300 : You multiplied by 15. A minute holds 4 lots of 15 seconds: multiply by 4.

A full answer includes

I worked out 20 × 4 (or 20 ÷ 0.25 min).
I wrote 80 beats per minute.
I did not divide the count by 4.

Also accept

80 beats per minute

Watch for

“20 ÷ 4 = 5 beats per minute.” — A minute is longer than 15 seconds, so more beats happen in it: multiply by 4.
“20 × 15 = 300 beats per minute.” — Multiply by the number of 15-second lots in a minute, which is 4, not by 15.

3. MQ3 · Practice

Model answer. Each tall spike comes 0.8 s after the one before: 1.1 − 0.3 = 0.8 s (or from the 1st to the 5th spike, 3.5 − 0.3 = 3.2 s for 4 gaps, and 3.2 ÷ 4 = 0.8 s). One beat lasts 0.8 s, so a minute holds 60 ÷ 0.8 = 75 beats: 75 beats per minute. The same method works on a strip of any length, 4 seconds or 5 seconds.

Checked automatically

Time between two tall spikes: 0.8 s (within ±0.02 s)
- Common wrong answer 0.7 s: You divided 3.5 s by 5 spikes. Five spikes have four gaps, and the first is at 0.3 s.
Heart rate (beats per minute): 75 (within ±0.5)
- Common wrong answer 48 : You multiplied 0.8 by 60. Divide: 60 ÷ 0.8.
- Common wrong answer 86 : That comes from a gap of 0.7 s. Five spikes have only four gaps.

A full answer includes

I found the gap between spikes: 1.1 − 0.3 = 0.8 s.
I worked out 60 ÷ 0.8.
I wrote 75 beats per minute.
I did not divide 3.5 s by 5 spikes: five spikes have only four gaps.

Also accept

0.8 s; 75 beats per minute

Watch for

“3.5 ÷ 5 = 0.7 s between spikes.” — Five spikes have four gaps between them, and the first spike is at 0.3 s, not at 0. Subtract one spike's time from the next.
“0.8 × 60 = 48 beats per minute.” — Divide the minute by the time of one beat: 60 ÷ 0.8.

4. MQ4 · Practice

Options as numbered on the pupil sheet: 1 — the oxygen carried in the blood; 2 — the sounds of the valves closing; 3 — the sound of the heart muscle contracting; 4 — the electrical activity of the heart; 5 — the surge of blood stretching an artery wall.

Model answer. An ECG records, through electrodes on the skin, the electrical activity that spreads through the heart muscle before each contraction. A pulse is the surge of blood stretching the wall of an artery each time the left ventricle contracts. A stethoscope picks up the sounds of the valves closing.

A full answer includes

I matched ECG to the electrical activity of the heart.
I matched pulse to the surge of blood stretching an artery wall.
I matched stethoscope to the sounds of the valves closing.
I did not match the stethoscope to the heart muscle contracting.

Also accept

ECG electrical activity; pulse surge in an artery; stethoscope valves closing

Watch for

“The stethoscope picks up the heart muscle contracting.” — The muscle makes almost no sound you can hear. The lub and dub are the valves closing.
“The pulse is the heart beating in the wrist.” — The heart stays in the chest; the pulse is the artery wall stretched by a surge of blood.
“The pulse picks up the oxygen carried in the blood.” — Feeling a pulse tells you nothing about oxygen. You feel the artery wall stretch once at each beat.

5. MQ5 · Practice

Model answer. The lub comes just after the tall spike, as the ventricles start to contract. Their blood would be pushed back into the atria, so the valves between the atria and the ventricles shut: the lub. When the ventricles relax, blood in the aorta and the pulmonary artery would fall back into them, so the semilunar valves shut: the dub. Row B shows this.

A full answer includes

I chose row B.
I did not choose row A: the lub comes just after the spike, as the ventricles start to contract.

Also accept

Watch for

“Row A: the semilunar valves shut at the lub.” — Row A swaps the two. The lub comes as the ventricles start to contract, when blood would be pushed back into the atria.
“Row C: the valves open at each sound.” — Row C has the valves opening. A valve makes its sound as it shuts, not as it opens.
“Row D: the ventricle walls make the sounds.” — Row D has the muscle making the sounds. Contracting muscle makes almost no sound you can hear; both sounds are valves shutting.

6. MQ6 · Practice

Model answer. 20 seconds is a third of a minute (20 ÷ 60). Beats counted = heart rate × time in minutes = 87 × 1/3 = 29 beats.

Checked automatically

Beats counted in 20 seconds: 29 (within ±0.5)
- Common wrong answer 261 : That is a count for 3 minutes. 20 seconds is a third of a minute: divide by 3.
- Common wrong answer 1740 : You multiplied by 20 seconds, but the rate is per minute. Divide by 3.
- Common wrong answer 4.35 : You divided by 20. 20 seconds is a third of a minute: divide by 3.

A full answer includes

I worked out 87 × 20 ÷ 60 (or 87 ÷ 3).
I wrote 29 beats.
I did not multiply 87 by 3.

Also accept

29 beats

Watch for

“87 × 3 = 261 beats.” — That would be a count for 3 minutes. 20 seconds is shorter than a minute, so the count is smaller than 87.
“87 × 20 = 1740 beats.” — The rate is per minute, not per second. Change 20 seconds to a third of a minute first.

7. MQ7 · Practice

Model answer. One beat lasts 0.9 seconds, so 60 seconds hold 60 ÷ 0.9 = 66.7 beats: about 67 beats per minute.

Checked automatically

Heart rate (beats per minute): 66.7 (within ±0.5)
- Common wrong answer 54 : You multiplied. A minute holds 60 ÷ 0.9 beats.
- Common wrong answer 0.015 : You divided the wrong way round. Work out 60 ÷ 0.9.

A full answer includes

I worked out 60 ÷ 0.9.
I wrote 67 beats per minute (66.7).
I did not multiply 0.9 by 60.

Also accept

67 beats per minute (66.7)

Watch for

“0.9 × 60 = 54 beats per minute.” — Multiplying gives the seconds taken by 60 beats, not the beats in a minute. Divide: 60 ÷ 0.9.
“0.9 ÷ 60 = 0.015 beats per minute.” — That is the wrong way round. Work out how many 0.9 s gaps fit into 60 s.

8. MQ8 · Practice

Model answer. Each time the left ventricle contracts, it pushes one surge of blood into the aorta and the arteries. Each surge stretches the artery wall once, felt as one pulse, so there is one pulse for each heartbeat.

A full answer includes

I chose: each contraction of the left ventricle sends one surge of blood to the wrist.
I did not choose the right ventricle: it pumps blood to the lungs.

Also accept

each contraction of the left ventricle sends one surge of blood to the wrist

Watch for

“Each heartbeat makes a lub and a dub, and each sound is felt as one pulse.” — Then the pulse rate would be twice the heart rate. The sounds are heard, not felt; a pulse is a surge of blood.
“Each contraction of the right ventricle sends one surge of blood to the wrist.” — The right ventricle pumps blood to the lungs. The surge in the arteries of the body comes from the left ventricle.
“Each heartbeat sends one electrical signal along the nerves to the wrist.” — The electrical signal spreads through the heart muscle and is picked up by an ECG. A pulse is a surge of blood.

9. MQ9 · Practice

Model answer. The heart beats 78 times in 60 seconds, so 26 beats take 26 ÷ 78 = a third of a minute. A third of 60 seconds is 20 seconds. (Or: one beat takes 60 ÷ 78 s, so 26 beats take 26 × 60 ÷ 78 = 20 s.) Check: 26 beats in 20 s is 26 × 3 = 78 beats per minute.

Checked automatically

Time the coach counted for: 20 s (within ±0.5 s)
- Common wrong answer 3 s: That is 78 ÷ 26, the number of 26-beat counts in a minute. Work out 26 ÷ 78 of a minute instead.
- Common wrong answer 0.33 s: That is the time in minutes. Multiply by 60 for seconds.
- Common wrong answer 0.333 s: That is the time in minutes. Multiply by 60 for seconds.
- Common wrong answer 34 s: You worked out 26 × 78 ÷ 60. The time is 26 ÷ 78 of 60 seconds.

A full answer includes

I worked out the time in minutes: 26 ÷ 78 = 0.333 min (a third of a minute).
I changed it to seconds: 0.333 × 60.
I wrote 20 s.
I did not work out 78 ÷ 26 = 3 and give 3 s.

Also accept

20 s

Watch for

“78 ÷ 26 = 3 s.” — That is how many lots of 26 beats fit into one minute, not a time. The count took 26 ÷ 78 of a minute.
“26 ÷ 78 = 0.33 s.” — That is the time in minutes. Multiply by 60 to change it to seconds.

10. MT1 · Apply

Model answer. Each heartbeat makes two sounds, a lub and a dub, so 54 sounds are 54 ÷ 2 = 27 beats. A minute holds 3 lots of 20 seconds, so the heart rate is 27 × 3 = 81 beats per minute.

Checked automatically

Heart rate (beats per minute): 81 (within ±0.5)
- Common wrong answer 162 : You counted each sound as a beat. A lub and a dub make one beat: halve first.
- Common wrong answer 27 : That is the number of beats in 20 seconds. Multiply by 3.
- Common wrong answer 108 : You doubled the sounds. Two sounds make one beat, so halve them, then multiply by 3.

A full answer includes

I halved the sounds: 54 ÷ 2 = 27 beats in 20 seconds.
I multiplied by 3: 27 × 3.
I wrote 81 beats per minute.
I did not count each sound as one beat.

Also accept

81 beats per minute

Watch for

“54 × 3 = 162 beats per minute.” — Each beat makes two sounds, a lub and a dub. Halve the number of sounds first.
“54 ÷ 2 = 27 beats per minute.” — Those 27 beats took only 20 seconds. Multiply by 3 for a minute.

11. MT2 · Apply

Model answer. The "dub" is the sound of the semilunar valves closing as the ventricles relax. If it is replaced by a whooshing sound, blood may be leaking back through semilunar valves that do not close properly.

A full answer includes

I chose the semilunar valves.
I did not choose the valves between the atria and the ventricles: they make the normal lub.

Also accept

the semilunar valves

Watch for

“The valves between the atria and the ventricles.” — Those make the "lub", which sounds normal here.
“The muscle in the walls of the ventricles.” — The muscle contracting makes almost no sound you can hear. The dub is a sound of valves closing.
“The air moving in and out of the lungs.” — Breathing sounds come with each breath, not in place of the dub in every heartbeat. The dub is the sound of valves closing.

12. MT3 · Apply

Model answer. 14 is far below 21 and 23: the pupil probably lost the pulse for a few seconds, so it is anomalous and is left out. The mean of the other two counts is (21 + 23) ÷ 2 = 22 beats in 15 seconds. A minute holds 4 lots of 15 seconds, so the mean heart rate is 22 × 4 = 88 beats per minute. Repeated counts are what show up an anomalous one.

Checked automatically

Anomalous count: 14 (exact value)
- Common wrong answer 21 : 21 is close to 23. Look for the count that is far from the other two.
- Common wrong answer 23 : 23 is close to 21. Look for the count that is far from the other two.
Mean heart rate (beats per minute): 88 (within ±0.5)
- Common wrong answer 77 : You included the anomalous 14. Leave it out of the mean.
- Common wrong answer 77.3 : You included the anomalous 14. Leave it out of the mean.
- Common wrong answer 176 : You multiplied the total of two counts by 4. Find the mean count first.
- Common wrong answer 44 : Those beats took 30 seconds. Find the mean 15-second count and multiply by 4.

A full answer includes

I identified 14 as the anomalous count.
I found the mean of the other two: (21 + 23) ÷ 2 = 22 beats in 15 s.
I multiplied by 4: 22 × 4.
I wrote 88 beats per minute.
I did not include 14 in the mean.

Also accept

anomalous count 14; 88 beats per minute

Watch for

“The mean of all three: (21 + 14 + 23) ÷ 3 × 4 = 77 beats per minute.” — The count of 14 is anomalous and pulls the mean down. Leave it out.
“21 + 23 = 44 beats per minute.” — Those 44 beats were counted in 30 seconds. Find the mean count for 15 seconds, then multiply by 4.