How is cardiac output worked out?

Heart rate times stroke volume, for example 80 beats times 75 mL gives 6 000 mL, or 6 litres a minute.

Why is blood in the pulmonary artery low in oxygen?

It leaves the right ventricle for the lungs to be oxygenated, so it is low in oxygen yet still an artery because it flows away from the heart.

S4 Biology: Human Transport System (Paper 4)

2026-11-01

Tutor Prep Guide · Primary English

The fourth paper combines cardiac output calculations, circulation routes, vessel structure and gas transport, working from daily pumping volume and the oxygen capacity of haemoglobin.

Direct answer　Cardiac output is heart rate times stroke volume, so convert to millilitres before litres; arteries and veins are named by direction, never by oxygen content.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S4 Biology: Human Transport System
Level	Four basic, three advanced, two challenge and one error-repair item

02　Questions (10 items)

FoundationHeart rate is 80 per minute and stroke volume is 75 mL. What is the cardiac output?
FoundationAn adult holds about 5 L of blood and the heart outputs 5 L a minute. Roughly how long does one full circulation take?
FoundationWhich type of vessel has the thickest, most elastic wall to withstand ventricular pressure?
FoundationIn what form is most carbon dioxide carried from tissues back to the lungs?
IntermediateHeart rate is 80 per minute and stroke volume is 80 mL. How many litres does the heart pump each minute?
IntermediateDuring exercise cardiac output rises from 5 to 20 litres a minute. How many times the resting value is that?
IntermediateBlood leaving the left ventricle, passing through the body and returning to the right atrium forms which circuit?
ChallengeHaemoglobin is 14 g/dL and each gram binds 1.34 mL of oxygen. How much oxygen can 100 mL of blood carry?
ChallengeHeart rate is 72 per minute with a stroke volume of 70 mL. How many litres are pumped in one day of 1 440 minutes?
Error redoA student says the pulmonary artery carries the most oxygen because arterial blood is oxygen-rich. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	6 000 mL per minute, or 6 litres per minute	Eighty beats times 75 mL gives 6 000 mL, or 6 litres a minute, which is a normal adult output.
2	About 60 seconds	Five litres divided by 5 litres a minute is one minute, so 60 seconds; exercise speeds this up to deliver oxygen faster.
3	Arteries	Arteries sit next to the heart and take the full systolic pressure, so their muscular and elastic layers are thickest.
4	As hydrogencarbonate ions dissolved in the plasma	Most carbon dioxide travels as hydrogencarbonate ions in the plasma, with only a small part dissolved or bound to haemoglobin.
5	6.4 litres	Eighty times 80 mL gives 6 400 mL, or 6.4 litres a minute; both ventricles must match or blood would pool.
6	Four times	Twenty divided by five is four, a 300 per cent rise, achieved by both a faster rate and a larger stroke volume.
7	The systemic circuit	The systemic circuit runs from the left ventricle through the body to the right atrium; the pulmonary circuit runs from the right ventricle to the lungs.
8	18.76 mL	Multiplying 14 by 1.34 gives 18.76 mL, so a low haemoglobin level directly cuts oxygen carriage.
9	About 7 258 litres	Seventy-two beats times 70 mL is 5 040 mL a minute, and 5.04 times 1 440 minutes gives about 7 258 litres.
10	Arterial means blood leaving the heart; the pulmonary artery carries deoxygenated blood to the lungs	Arteries and veins are named by direction, not oxygen level: the pulmonary artery carries deoxygenated blood to the lungs and the pulmonary vein returns oxygenated blood.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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