Exercise and heart health — return questions key

1. MR1 · Return

Model answer. The valves make the lub and dub sounds as they close, so the doctor listens through a stethoscope; a leaking valve can be heard as a whooshing sound. An ECG records electrical activity through electrodes on the skin, and the pulse and the blood pressure are measured in the arteries.

A full answer includes

• I chose listening through a stethoscope.
• I did not choose the ECG: it records electrical activity, not the valves.

Also accept

• listening through a stethoscope

Watch for

• “recording an ECG from the chest” — An ECG records the electrical activity of the heart muscle. It does not pick up the valves closing.
• “counting the pulse at the wrist” — A pulse count gives the heart rate. It does not tell you how each valve closes.
• “measuring the blood pressure” — Blood pressure shows how hard the blood presses on the artery walls, not whether each valve shuts cleanly.

2. MR2 · Return

Model answer. 15 seconds is a quarter of a minute, so at 96 beats per minute a 15-second count should be 96 ÷ 4 = 24 beats. The pupil counted 20, so he missed 24 − 20 = 4 beats.

Checked automatically

• Count he should have got: 24 (within ±0.5)
  • Common wrong answer 384 : A 15-second count is smaller than a minute's beats: divide by 4.
  • Common wrong answer 6.4 : You divided by 15. A minute holds four 15-second counts: divide by 4.
• Beats missed: 4 (within ±0.5)
  • Common wrong answer 76 : You took 20 from 96, a rate per minute. Find the 15-second count first.

A full answer includes

• I worked out 96 ÷ 4 (or 96 × 0.25 min).
• I wrote 24 beats.
• I subtracted: 24 − 20.
• I wrote 4 missed beats.
• I did not subtract 20 from 96.

Also accept

• 24 beats; 4 beats missed

Watch for

• “96 − 20 = 76 missed beats.” — The 96 is per minute and the 20 is per 15 seconds. Turn the rate into a 15-second count first.
• “96 × 4 = 384 beats.” — A 15-second count is smaller than the beats in a minute: divide by 4.

3. MR3 · Return

Model answer. 100 beats take 60 seconds, so one beat, from one tall spike to the next, takes 60 ÷ 100 = 0.6 seconds.

Checked automatically

• Time between two tall spikes: 0.6 s (within ±0.02 s)
  • Common wrong answer 1.67 s: That is beats per second. Divide 60 s by 100 beats.
  • Common wrong answer 1.7 s: That is beats per second. Divide 60 s by 100 beats.
  • Common wrong answer 6000 s: You multiplied. Divide 60 s by 100 beats.

A full answer includes

• I worked out 60 ÷ 100.
• I wrote 0.6 s.
• I did not work out 100 ÷ 60.

Also accept

• 0.6 s

Watch for

• “100 ÷ 60 = 1.7 s.” — That is the number of beats in one second. Divide the time by the number of beats: 60 ÷ 100.
• “100 × 60 = 6000 s.” — A beat at this rate takes less than a second. Divide 60 s by 100 beats.

4. SR1 · Return

Model answer. The heart rate rises during the swim, from 62 to 146. After the swim it falls gradually: still raised at 1 minute (118) and back at the resting 62 by 8 minutes. Row C shows this.

A full answer includes

• I chose row C.
• I did not choose row B: the rate does not drop to resting in one minute.

Also accept

• C

Watch for

• “Row A: the rate stays at its highest after the swim.” — In row A the rate stays at its highest for 8 minutes. After exercise it falls back to resting.
• “Row B: the rate is back to resting 1 minute after the swim.” — In row B the rate is back to resting after only 1 minute. It falls gradually over several minutes.
• “Row D: the rate keeps rising after the swim.” — In row D the rate is higher 1 minute after the swim than at its end. It starts to fall as soon as the swim stops.

5. SR2 · Return

Model answer. The step height is changed on purpose, the recovery time is measured, and the stepping rate and the time spent stepping are kept the same. Row A shows this.

A full answer includes

• I chose row A.
• I did not choose row C: the stepping rate is kept the same, not measured.

Also accept

• A

Watch for

• “Row B: the recovery time is changed on purpose.” — Row B swaps the two: the pupil chooses the step height and measures the recovery time.
• “Row C: the stepping rate is measured.” — The stepping rate is set by the pupil, not measured, and the recovery time is what the pupil wants to find out.
• “Row D: the stepping rate is changed on purpose.” — The question asks about the step height, so the step height is what is changed on purpose.

6. SR3 · Return

Model answer. B's muscles could not get enough oxygen, so they also respired anaerobically and made lactic acid. After the run his heart rate stays raised for longer while his blood carries the lactic acid to the liver, where it is broken down using oxygen (removing the oxygen debt). A's gentle jog was mostly aerobic, so A's rate falls back sooner.

A full answer includes

• I chose: B's stays raised longer, because his blood must take lactic acid to the liver.
• I did not choose "both recover in the same time": the two exercises are not equally hard.

Also accept

• B, because his blood must carry lactic acid to the liver

Watch for

• “Both recover in the same time, because they exercised for the same 5 minutes.” — The same time is not the same effort. B's fast run left lactic acid to remove.
• “A's stays raised for longer, because aerobic respiration makes more carbon dioxide.” — B's muscles worked harder and made lactic acid too. That takes longer to remove.
• “B's falls sooner, because the lactic acid makes his heart muscle relax and slow.” — Lactic acid does not slow the heart. It must be carried to the liver, which keeps the rate raised.

7. HR1 · Return

Model answer. A heart attack at rest means that the heart muscle beyond the artery got no blood at all, not just too little for exercise. It came suddenly, so the artery closed within minutes. A fatty deposit grows over years, but a blood clot can form on the deposit within minutes and fill the narrow channel that is left. Row C shows this.

A full answer includes

• I chose row C.
• I did not choose row A: a fatty deposit builds up over years, not in a few minutes.

Also accept

• C

Watch for

• “Row A: the fatty deposit grew larger in a few minutes.” — Row A has the deposit closing the artery that evening. Fatty deposits build up slowly, over years; only a clot forms in minutes.
• “Row B: enough blood still reached the muscle while she rested.” — Row B leaves blood reaching the muscle at rest. Then she would not have had a heart attack while sitting still.
• “Row D: the clot took several years to close the channel.” — Row D gives the clot years. A clot forms within minutes; it is the deposit that took years.

8. HR2 · Return

Model answer. Smokers: 40 ÷ 500 × 100 = 8 %. Non-smokers: 15 ÷ 500 × 100 = 3 %. The smokers were 40 ÷ 15 = 2.67 (about 2.7) times as likely to develop coronary heart disease. Still, 92 % of the smokers did not develop it in the ten years: a risk factor raises the chance.

Checked automatically

• Smokers who developed coronary heart disease: 8 % (within ±0.1 %)
  • Common wrong answer 40 %: There were 500 smokers, not 100. Work out 40 ÷ 500 × 100.
  • Common wrong answer 0.08 %: That is the fraction. Multiply by 100 for a percentage.
• Times as likely: 2.67 (within ±0.05)
  • Common wrong answer 25 : That is the difference, 40 − 15. "How many times" means divide: 40 ÷ 15.
  • Common wrong answer 0.375 : You divided the wrong way round. Work out smokers ÷ non-smokers: 40 ÷ 15.

A full answer includes

• I worked out 40 ÷ 500 × 100.
• I wrote 8 %.
• I worked out 40 ÷ 15.
• I wrote about 2.7 times (2.67).
• I did not subtract: 40 − 15 = 25 is a difference, not "how many times".

Also accept

• 8 %; about 2.7 times

Watch for

• “40 − 15 = 25 times as likely.” — 25 is how many more smokers developed it. "How many times" means divide: 40 ÷ 15.
• “40 % of the smokers developed it.” — There were 500 smokers, not 100: 40 ÷ 500 × 100 = 8 %.

9. HR3 · Return

Model answer. He takes in 1500 kJ a day more than he uses. The extra energy is stored, mostly as fat, so over many months his body mass rises. Obesity raises blood pressure and makes coronary heart disease more likely. Matching energy intake to energy use helps to avoid this.

A full answer includes

• I chose: his body mass rises, and obesity raises his blood pressure and his risk.
• I did not choose "passes out as waste": energy taken in but not used is stored, mostly as fat.

Also accept

• his body mass rises; obesity raises blood pressure and the risk

Watch for

• “His body mass rises, but only the saturated fat he eats can change his risk.” — Obesity raises blood pressure, which makes CHD more likely, whatever the fat in his diet.
• “His body mass stays the same, because his heart uses up the extra energy.” — The heart's work is already part of the 10 000 kJ he uses. The extra 1500 kJ a day is stored, mostly as fat.
• “His body mass stays the same, because the extra energy passes out as waste.” — Food that is digested and absorbed but not used is stored, mostly as fat. It is not passed out.