Answers · Exercise and heart health

Exercise and heart health — final check key

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

1. MK1 · Final check

Model answer. (a) An ECG records the electrical activity of the heart; the pulse rate is counted at an artery, such as at the wrist; a stethoscope picks up the sounds of the valves closing. (b) 10 seconds is a sixth of a minute, so the count is 90 ÷ 6 = 15 beats.

A full answer includes

(a) I wrote an ECG.
(a) I wrote the pulse rate.
(a) I wrote listening to the sounds of the valves closing.
(a) I did not write the sound of the heart muscle contracting.
(b) I worked out 90 × 10 ÷ 60 (or 90 ÷ 6).
(b) I wrote 15 beats.

Also accept

(a) ECG, pulse rate, sounds of the valves closing; (b) 15 beats

Watch for

“Listening to the heart muscle contract.” — The heart sounds are the valves closing.
“90 × 6 = 540 beats.” — A 10-second count is smaller than the beats in a minute: divide by 6.

2. MK2 · Final check

Model answer. From the first spike to the last is 5.6 − 0.4 = 5.2 s. Seven spikes have six gaps between them, so one beat lasts 5.2 ÷ 6 = 0.867 s. A minute holds 60 ÷ 0.867 = 69.2 beats. To the nearest whole number: 69 beats per minute. (Or: 6 beats in 5.2 s, so 6 × 60 ÷ 5.2 = 69.2.)

Checked automatically

Heart rate (beats per minute): 69 (exact value)
- Common wrong answer 75 : You divided 5.6 s by 7. Start from the first spike at 0.4 s, and count 6 gaps.
- Common wrong answer 81 : Seven spikes have six gaps: divide 5.2 s by 6, not by 7.
- Common wrong answer 64 : You divided 5.6 s by 6. Start from the first spike: 5.6 − 0.4 = 5.2 s.
- Common wrong answer 67 : You rounded the gap to 0.9 s first. Keep 0.867 s and round only at the end.
- Common wrong answer 70 : You rounded the gap down to 0.86 s first. Keep 0.867 s and round only at the end.

A full answer includes

I counted the gaps: 7 spikes have 6 gaps.
I found the time between spikes: (5.6 − 0.4) ÷ 6 = 0.867 s.
I worked out 60 ÷ 0.867 = 69.2.
I rounded to 69 beats per minute.
I did not divide by 7: seven spikes have only six gaps.

Also accept

69 beats per minute

Watch for

“5.6 ÷ 7 = 0.8 s for each beat, so 75 beats per minute.” — The first spike is at 0.4 s, not at 0, and seven spikes have only six gaps.
“5.2 ÷ 7 = 0.743 s for each beat, so 81 beats per minute.” — Seven spikes have six gaps between them, not seven: divide 5.2 s by 6.

3. SK1 · Final check

Model answer. (a) After ten weeks of training the resting rate was lower (about 56 instead of 76 beats per minute), the rate at the end of the stepping was lower (about 130 instead of about 155 on the lines; the first dots are 120 and 148) and the rate was back to resting sooner (back at 7 minutes instead of 11, so a recovery time of 3 minutes instead of 7): the heart muscle has become stronger and pumps more blood with each beat. (b) The pedal resistance, the pedalling speed, the time spent cycling and the way the pulse is counted stay the same; only the term of swimming lessons differs.

A full answer includes

(a) I gave two differences, each with values from the graph, from the three below.
(a) I could write: the resting rate was lower, about 56 instead of 76 beats per minute (54–58 instead of 74–78 is fine).
(a) I could write: the rate at the end of the stepping was lower, about 130 instead of 155 on the lines (or 120 instead of 148 from the first dots).
(a) I could write: the rate was back at resting sooner, about 3 minutes after the stepping instead of about 7 (2–3 instead of 6–7 is fine).
(b) I gave two things she keeps the same, from the four below.
(b) I could give: the pedal resistance.
(b) I could give: the pedalling speed.
(b) I could give: how long she cycles.
(b) I could give: how long she counts her pulse for.
(b) I did not give the heart rate: it is what is measured.

Also accept

(a) two of lower resting rate, lower peak, shorter recovery, with data; (b) two of pedal resistance, pedalling speed, cycling time, counting method

Watch for

“The heart rate must stay the same.” — The heart rate is what is measured.

4. SK2 · Final check

Model answer. (a) The rowing muscles contract more often and more strongly, so they carry out more aerobic respiration. They need more oxygen and glucose and make more carbon dioxide, so the heart beats faster to pump more blood to them each minute. (b) In the hard race the muscles also made lactic acid. The heart rate stays raised while the blood carries the lactic acid to the liver, where it is broken down using oxygen, and carries the extra carbon dioxide to the lungs.

A full answer includes

(a) I wrote that the rowing muscles contract more often and more strongly.
(a) I wrote that their cells carry out more aerobic respiration.
(a) I wrote that they need more oxygen and glucose.
(a) I wrote that they make more carbon dioxide.
(a) I wrote that the heart beats faster to pump more blood to the muscles each minute.
(a) I did not write that the heart makes energy for the muscles.
(b) I wrote that the muscles made lactic acid in the hard race.
(b) I wrote that the blood carries the lactic acid to the liver to be broken down.
(b) I wrote that the extra carbon dioxide is still being carried to the lungs.
(b) I did not write that lactic acid is breathed out.

Also accept

(a) more aerobic respiration; more oxygen and glucose needed, more carbon dioxide; heart faster, more blood per minute; (b) lactic acid carried to the liver; carbon dioxide removed

Watch for

“The heart makes more energy for the rowing muscles, so it beats faster.” — The heart pumps blood, not energy. The blood brings the muscles glucose and oxygen, and their cells release the energy by respiration.

5. HK1 · Final check

Model answer. (a) In coronary heart disease fatty deposits build up in the coronary arteries and narrow them; a blood clot can block them. The heart muscle beyond the block gets too little oxygen and glucose, so it cannot respire and contract, and may die (a heart attack). (b) Diet, lack of exercise, stress, smoking, genetic predisposition, age and sex.

A full answer includes

(a) I wrote that fatty deposits build up in the coronary arteries.
(a) I wrote that the deposits narrow the arteries.
(a) I wrote that a blood clot can block the narrow space.
(a) I wrote that the heart muscle beyond gets too little oxygen and glucose.
(a) I wrote that this muscle cannot respire or contract, and may die (a heart attack).
(a) I did not write that the valves are blocked.
(b) I named four of: diet, lack of exercise, stress, smoking, genetic predisposition, age, sex.

Also accept

(a) coronary arteries narrowed or blocked, heart muscle short of oxygen; (b) four risk factors

Watch for

“CHD is a blockage of the heart's valves.” — It is a blockage of the coronary arteries.

6. HK2 · Final check

Model answer. (a) Eating less salt keeps blood pressure lower. Eating less fatty meat and butter lowers the saturated fat in his diet, so his blood cholesterol falls and fewer fatty deposits form in his coronary arteries. Regular exercise helps to keep his blood pressure and body mass down. (b) His age or his sex. (c) Diet and exercise only reduce the risk: his age and sex stay the same, and coronary heart disease has several causes at once.

A full answer includes

(a) I gave two different changes, each with how it lowers the risk, from the three below.
(a) I could write: eating less salt keeps his blood pressure lower.
(a) I could write: less fatty meat and butter (less saturated fat) lowers his blood cholesterol, so fewer fatty deposits form in his coronary arteries.
(a) I could write: regular exercise helps to keep his blood pressure down.
(a) With exercise I could also write: it helps to keep his body mass down, so he does not become obese.
(a) I did not give stopping smoking: it is not a change to diet or exercise.
(b) I identified his age (58) or his sex (male).
(c) I wrote that some risk factors, such as age and sex, cannot be changed.
(c) I did not write that diet and exercise prevent coronary heart disease.

Also accept

(a) two of less salt, less saturated fat, regular exercise, each with its effect; (b) age or sex; (c) some risk factors cannot be changed

Watch for

“Diet and exercise prevent coronary heart disease.” — They reduce the risk; other risk factors remain.
“His smoking cannot be changed.” — He can stop smoking. His age and his sex are what he cannot change.