What you need to know
- 1.6Circulation meets the demands of tissues.
- 1.8Cardiac function.
- 1.15–1.16Interpretation and evaluation of health evidence.
All numerical values are fictional and the cardiac-output equation is supplied. This activity explains physiology, not personal diagnosis or treatment.
By the end, you should be able to…
- Use cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. in a supplied calculation.
- Link pumping to tissue supply.
- Avoid diagnosing from one measurement.
Build your understanding
Start with the mechanism
Heart failure means the heart cannot pump enough blood to meet the body’s needs, or can do so only under abnormal filling conditions. It does not mean the heart has necessarily stopped. Detailed clinical classification is enrichment.
A fictional comparison
You are given cardiac outputThe volume of blood pumped by one ventricle per minute: cardiac output = stroke volume × heart rate. = heart rateThe number of heartbeats per minute. × stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat.. In this illustration, person A has 70 beats min⁻¹ and 70 cm³ per beat; person B has 90 beats min⁻¹ and 40 cm³ per beat. Outputs are 4,900 and 3,600 cm³ min⁻¹ respectively. The higher heart rate does not compensate completely for the lower stroke volume.
Explain what the numbers leave out
Blood flow affects delivery of oxygen and substrateThe molecule that binds to an enzyme’s active site and is changed in the reaction., but delivery also depends on blood oxygen content and where blood is distributed. These invented values cannot diagnose a real person. An investigation needs comparable conditions, repeated measurements and relevant clinical context.
Make your reasoning visible
Multiply compatible units
Beats min⁻¹ × cm³ beat⁻¹ gives cm³ min⁻¹; divide by 1,000 for litres per minute.
Separate outcome from compensation
A faster heart rateThe number of heartbeats per minute. can compensate for reduced stroke volumeThe volume of blood pumped out of one ventricle in one heartbeat., but the product determines output in the supplied model.
Avoid this misconception
The claim: A faster heart rate always means more blood pumped per minute.
The correction: Stroke volume matters too; calculate both factors.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Calculate the two cardiac outputs in litres per minute.
Show suggested answer
A = 4.9 L min⁻¹; B = 3.6 L min⁻¹.
Practice question
Retrieval and explanation · suggested answer
Give one reason the two measurements alone cannot establish a diagnosis.
Show suggested answer
Activity, measurement conditions, body size and other physiological factors may differ. A diagnosis needs additional evidence.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Using the supplied model, what heart rate would produce 4,900 cm³ min⁻¹ with a stroke volume of 40 cm³? Why is this only a mathematical prediction?
Show a hint
Divide desired output by stroke volume.
Explore the reasoning
4,900/40 = 122.5 beats min⁻¹. This assumes stroke volume remains constant; physiological changes with heart rate may invalidate that assumption.
Recall this lesson
Lesson recall questions
Question 1 of 5: When diffusion is too slow to meet metabolic ________, a ________ system provides ________ transport.
Why mass transport is needed
Practice question
Retrieval and explanation · suggested answer
When diffusion is too slow to meet metabolic ________, a ________ system provides ________ transport.
Lesson: 1B 1: The Principles of Circulation
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Measuring function rather than guessing
1C · Thinking Bigger: Heart FailureNHLBI describes heart failure as a problem with the heart’s ability to supply the body. Measurements help connect symptoms to mechanisms. Heart rate counts beats, whereas cardiac output…Specification 1.6 · 1.8Read & use the scienceClose article
Why this matters
NHLBI describes heart failure as a problem with the heart’s ability to supply the body. Measurements help connect symptoms to mechanisms. Heart rate counts beats, whereas cardiac output describes the volume moved each minute. The same rate can accompany different stroke volumes, and tissues depend on adequate delivery rather than the count alone. Cardiac physiology therefore uses measurements that address pumping and filling as well as rhythm. This is an application of transport biology, not a diagnostic exercise. A numerical change needs a physiological interpretation and a comparison with other observations before it can explain someone’s symptoms.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
Use the science
Why might measuring heart rate alone miss a pumping problem?
Explore a possible response
It does not measure the volume ejected per beat or whether the blood flow meets tissue needs.
Explore the source
- NHLBI: heart failureNHLBI
The scientist who runs a temporary circulation
1B · The Principles of CirculationDuring some heart operations, a clinical perfusionist operates equipment that temporarily supports circulation and gas exchange. This professional monitors the system rather than merely switching on a pump.…Specification 1.6 · 1.8Read & use the scienceClose article
Why this matters
During some heart operations, a clinical perfusionist operates equipment that temporarily supports circulation and gas exchange. This professional monitors the system rather than merely switching on a pump. Blood must reach tissues, acquire oxygen and release carbon dioxide while the surgical team works. Your distinction between mass transport and diffusion explains the division of labour: the machine moves blood over long distances, while exchange still depends on gradients across a thin barrier. The career combines physiology, measurements and rapid communication with other specialists. It also shows why a functioning oxygenator is not enough if blood is not reaching the organs.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.6 understand why many animals have a heart and circulation (mass transport to overcome the limitations of diffusion in meeting the requirements of organisms)
- 1.8 know the cardiac cycle (atrial systole, ventricular systole and cardiac diastole) and relate the structure and operation of the mammalian heart, including the major blood vessels, to its function
Use the science
The oxygenator works normally but the rate of blood flow falls substantially. Explain why tissue oxygen supply can still fall.
Explore a possible response
Oxygen content per volume is not the same as delivery per minute. Lower flow supplies fewer oxygenated red cells and may fail to maintain the tissue diffusion gradient.
Explore the source
- PerfusionRoyal Brompton & Harefield hospitals, NHS