OxfordAQA International GCSE Biology: Circulation in humans: heart, vessels, blood and transplants (9201) – Revision Notes

These notes condense section 3.2.3, Circulation in humans (statements a to t), of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams from May/June 2018 onwards. Full explanations and worked examples are in the study guide. Test yourself with the practice questions, tick off statements on the printable checklist, see the course hub, and find gaps with a free 10-minute diagnostic.

Key terms

Term	Meaning
Circulatory system	heart, blood vessels and blood
Double circulation	two circuits: heart to lungs and back, and heart to all other organs and back
Atrium	upper chamber; receives blood and pushes it into a ventricle
Ventricle	lower chamber; pushes blood out of the heart
Coronary arteries	supply the heart muscle with blood
Plasma	the fluid part of blood
Haemoglobin	red pigment in red cells; combines with oxygen
Oxyhaemoglobin	haemoglobin combined with oxygen
Fibrinogen	soluble protein changed into fibrin during clotting
Fibrin	fibres that form a network and trap cells in a clot
Antigen	protein on the surface of a cell
Rejection	the recipient’s antibodies attacking antigens on a donor organ

Heart and circulation (a, b, c, h, i)

• Heart wall is mostly muscle tissue; it pumps blood.
• Four chambers: right atrium, left atrium, right ventricle, left ventricle.
• Atria contract, forcing blood into ventricles. Ventricles contract, forcing blood out. Valves stop back-flow. Valve names are not needed.
• Arteries: heart to organs. Veins: organs to heart.

Route of blood, in steps

1. Vena cava
2. Right atrium
3. Right ventricle
4. Pulmonary artery
5. Lungs
6. Pulmonary vein
7. Left atrium
8. Left ventricle
9. Aorta
10. Body organs, then back to the vena cava

Vessel	To or from	Oxygen
Vena cava	body to right atrium	low
Pulmonary artery	right ventricle to lungs	low
Pulmonary vein	lungs to left atrium	high
Aorta	left ventricle to body	high
Coronary arteries	aorta to heart muscle	high

Must-know distinction: the pulmonary artery and pulmonary vein break the “arteries carry oxygenated blood” pattern. Name by direction (away from or towards the heart), not by oxygen content.

Why double? Blood goes back through the heart after the lungs, so it is pumped again before it reaches the other organs.

Vessels (j, k)

Vessel	Wall	Other features	Function link
Artery	thick; muscle and elastic fibres	carries blood away from the heart	withstands pressure; stretches and recoils
Vein	thinner	often has valves	valves prevent back-flow
Capillary	very thin	very narrow; found in organs	substances pass out of and into the blood through the wall

Blood (l to q)

Component	Nucleus?	Job
Plasma	not a cell	carries carbon dioxide (organs to lungs), soluble products of digestion (small intestine to organs), urea (liver to kidneys)
Red blood cell	no	carries oxygen as oxyhaemoglobin, from lungs to organs
White blood cell	yes	defence against microorganisms
Platelet	no (a cell fragment)	helps blood to clot at a wound

Oxygen carriage, in words: lungs: haemoglobin + oxygen → oxyhaemoglobin. Other organs: oxyhaemoglobin → haemoglobin + oxygen.

Clotting, in steps

1. A vessel is cut; platelets gather at the wound and help.
2. A series of enzyme-controlled reactions begins.
3. Fibrinogen is changed to fibrin.
4. Fibrin forms a network of fibres.
5. The network traps blood cells, forming a clot.

Heart problems and treatments (d, e, f, g)

Problem	Cause or description	Treatment	One advantage	One disadvantage
Irregular heart rate	natural pacemaker cells (right atrium) not keeping a steady rate	artificial pacemaker: electrical device	corrects the rhythm	needs surgery and a power source
Coronary heart disease	fatty layers narrow coronary arteries; less oxygen reaches heart muscle	stent holds artery open	restores blood flow without a donor	artery can narrow again; a procedure is needed
Stiff valve	tissue stiffens; valve does not open fully	replacement valve	restores one-way flow	see below
Leaky valve	valve lets blood flow backwards	replacement valve	restores one-way flow	see below
Heart failure	heart cannot pump enough	artificial heart (temporary) or transplant	keeps patient alive while waiting, or rests the heart	clots, infection, power and mechanical failure risks

Replacement valves

	Biological	Mechanical
Source	humans or other mammals	manufactured
Possible plus	usually less need for lifelong anticoagulant drugs	can last for a long time
Possible minus	can wear out and need replacing	blood may clot on it, so anticoagulant drugs are often needed

Antigens, transplants and blood groups (r, s, t)

• Antigens are proteins on the surface of cells.
• Transplant: a diseased organ is replaced by a healthy donor organ.
• Rejection: recipient’s antibodies attack the donor organ’s antigens because they are not recognised as the recipient’s own.
• Reduce rejection by (1) choosing a donor with a similar tissue type and (2) giving immune-suppressing drugs.

Evaluate: mechanical device or transplant

	Device	Transplant
For	no donor wait; no rejection; no immune-suppressing drugs	real organ, no machinery to fail
Against	clots, infection, power or part failure	donor shortage; rejection risk; drugs raise risk of infection; major surgery

Group	Antigens	Plasma antibodies
A	A	anti-B
B	B	anti-A
AB	A and B	none
O	none	anti-A and anti-B

Recipient	Can receive from
O	O
A	O, A
B	O, B
AB	O, A, B, AB

Group O is the universal donor because its red cells have no A or B antigens. Blood typing is needed so that recipients are never given cells that their antibodies would attack.

Method boxes

Heart rate from a pulse count. Beats ÷ seconds × 60. Example: 31 beats in 20 s → 31 ÷ 20 × 60 = 93 beats per minute.

Volume pumped per minute. Volume per beat × beats per minute. Example: 72 cm³ × 75 = 5400 cm³ per minute (5.4 dm³).

Percentage change. (new − original) ÷ original × 100. Example: an artery narrows from 3.0 mm to 1.8 mm. (3.0 − 1.8) ÷ 3.0 × 100 = 40 per cent decrease.

Magnification. Image size ÷ real size, with both in the same unit. Convert micrometres to millimetres by dividing by 1000. Example: a cell of 5 µm drawn 40 mm wide: 40 ÷ 0.005 = × 8000.

Speed in a capillary. Distance ÷ time. Example: a red cell moves 0.9 mm in 4.5 s → 0.2 mm per second.

Linking ideas for longer answers

• Coronary heart disease to symptoms: narrowed coronary arteries mean less blood, so less oxygen and glucose reach the heart muscle, so less energy is released for contraction.
• Red cell to function: no nucleus leaves more room for haemoglobin; haemoglobin binds oxygen in the lungs and releases it in the organs.
• Capillary to exchange: a thin wall and narrow tube bring blood close to cells, so substances move between blood and cells easily.
• Antigen to rejection: a donor organ carries antigens that differ from the recipient’s, so the recipient’s antibodies treat it as foreign. A closer tissue type means fewer differences.
• Immune-suppressing drugs to infection: the drugs weaken the response that causes rejection, but they also weaken defence against microorganisms.

Quick self-test

1. Name the vessel that brings blood from the lungs to the heart.
2. Which chamber pumps blood out through the aorta?
3. State the function of the coronary arteries.
4. Give two differences between an artery and a vein.
5. A student counts 58 beats in 40 s. Calculate the heart rate.
6. Name the protein that fibrinogen is changed into.
7. A group AB patient needs red cells. Which donor groups are compatible?
8. State two ways of reducing the chance of organ rejection.
9. Give one disadvantage of a mechanical heart valve.
10. A stent opens an artery from 1.8 mm to 3.0 mm. Calculate the percentage increase in diameter.

Answers

1. Pulmonary vein.
2. Left ventricle.
3. They supply blood, and so oxygen, to the heart muscle.
4. Artery: thick wall with muscle and elastic fibres, carries blood away from the heart. Vein: thinner wall, often has valves, carries blood towards the heart.
5. 58 ÷ 40 × 60 = 87 beats per minute (87.0).
6. Fibrin.
7. O, A, B and AB.
8. Use a donor with a similar tissue type; give drugs that suppress the immune system.
9. Blood can clot on it, so anticoagulant drugs are often needed. (Any sensible disadvantage.)
10. (3.0 − 1.8) ÷ 1.8 × 100 = 66.7 per cent (3 s.f.).

Where marks are usually lost

• Calling the pulmonary vein “deoxygenated” or naming vessels by oxygen content.
• Writing “the blood” instead of the chamber or vessel by name when tracing the route.
• Saying a stent “unblocks” an artery completely, rather than holding it open.
• Giving a one-sided answer to an evaluate question: both options need an advantage and a disadvantage.
• Writing “the immune system rejects it” without naming antibodies attacking the antigens.
• Mixing up donor and recipient when reading the compatibility table.
• Forgetting the unit conversion in magnification, or using the wrong base for a percentage change.
• Saying platelets “make” the clot, with no mention of fibrinogen changing to fibrin.

Official syllabus

OxfordAQA International GCSE Biology (9201), specification Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA. These notes follow section 3.2.3, statements a to t.