Blood Vessels and Tissue Fluid: AQA A Level Biology Exam Questions by Topic

AQABlood Vessels and Tissue FluidExam Questions
Written by Tom Whitburn

Blood vessels and tissue fluid (part of AQA 3.3.4.1) come up on both Year 12 and A-level papers, usually as short explain questions worth two or three marks. You need to relate the structure of arteries, arterioles and veins to their function, explain why capillary beds are good exchange surfaces, and describe how tissue fluid is formed and how it returns to the circulatory system. The same section asks you to analyse data on risk factors for cardiovascular disease, weigh up conflicting evidence and tell a correlation from a causal relationship.

The examiners' reports show where the marks go. Students write that tissue fluid, plasma or blood is forced out of the capillaries when it is water and small molecules that leave, say tissue fluid returns by osmosis instead of water, describe the muscle in the aorta wall as a pump, and forget that arterioles change blood flow because the muscle in their walls contracts or relaxes. On the risk factor data, very few say that treated patients are still at a higher risk than normal.

Start with the blood vessels, then tissue fluid, and finish with the cardiovascular disease data. Answer each question on paper before you open the mark scheme. If you'd like help with this topic, my AQA masterclasses run online on Tuesdays at 5.15pm for Year 12 and on Wednesdays or Thursdays at 6.30pm for Year 13.

What you need from GCSE and Year 12

Each question on this page assumes you're secure on these GCSE and Year 12 ideas. If any of them feels shaky, revise it before you start.

  • GCSE: arteries carry blood away from the heart at high pressure and have thick, muscular, elastic walls; veins carry blood back at low pressure, have a wide lumen and valves; capillaries have walls one cell thick.
  • GCSE: risk factors for cardiovascular disease include smoking, high blood pressure, a high-fat diet and lack of exercise.
  • Year 12 (AQA 3.2.3): water moves by osmosis from a higher (less negative) to a lower (more negative) water potential across a partially permeable membrane.
  • Year 12 (AQA 3.3.4.1): contraction of the ventricles produces a high blood pressure that forces blood into the aorta and pulmonary artery.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Artery: a vessel carrying blood away from the heart; its thick wall has muscle and elastic tissue to withstand high pressure, and a smooth endothelium that reduces friction.
  • Elastic recoil: elastic tissue in an artery wall stretches as blood is pumped in, then recoils, which smooths the blood flow and maintains the pressure.
  • Arteriole: a small artery whose muscle contracts to narrow the lumen (vasoconstriction) or relaxes to widen it (vasodilation), controlling blood flow into capillaries.
  • Vein: a vessel carrying blood back to the heart at low pressure; it has a wider lumen, a thinner wall and valves.
  • Capillary bed: a network of capillaries with walls of thin endothelial cells and a large surface area, giving a short diffusion pathway for exchange with the tissues.
  • Tissue fluid: the fluid that bathes cells, formed when water and small molecules are forced out of the capillaries at the arteriole end.
  • Hydrostatic pressure: the blood pressure inside a capillary; at the arteriole end it is high enough to force water out.
  • Plasma proteins: large proteins such as albumin that stay in the capillaries, lowering the water potential of the blood so water returns by osmosis.
  • Lymphatic system: the vessels that drain excess tissue fluid and return it to the blood.
  • Risk factor: something linked with a higher chance of developing a disease, such as high blood pressure for cardiovascular disease.
  • Correlation: a link between two variables; it doesn't on its own show that one causes the other (a causal relationship).

What these questions cover (AQA 3.3.4.1, blood vessels, tissue fluid and cardiovascular disease)

The questions test these statements from the AQA AS and A-level Biology specification (7401/7402):

  • Blood vessels: The structure of arteries, arterioles and veins in relation to their function.
  • Capillaries and tissue fluid: The structure of capillaries and the importance of capillary beds as exchange surfaces. The formation of tissue fluid and its return to the circulatory system. (the lymphoedema, high blood pressure, salt and dengue questions all ask what makes tissue fluid build up)
  • Students should be able to analyse and interpret data associated with specific risk factors and the incidence of cardiovascular disease
  • Students should be able to evaluate conflicting evidence associated with risk factors affecting cardiovascular disease (the blood pressure treatment question asks you to weigh two treatments against risk data, and the fibre question asks you to judge a student's claim)
  • Students should be able to recognise correlations and causal relationships. (the fibre question tests whether a correlation in a large study shows that eating more fibre would lower one person's risk)

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 14 questions are worth 35 marks, so about 46 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Arteries, arterioles and veins (3.3.4.1)

Question 1

A level Paper 1 · June 2024 · Q08.1 · 2 marks · Hard

Give two features of the aorta wall and link each one to the aorta's function.

Question text: give two structural features of an aorta wall and explain how they are related to the function of an aorta, 2 marks.
Show the mark scheme Mark scheme, any two: smooth muscle withstands high blood pressure; elastic tissue stretches and recoils, maintaining or smoothing blood pressure; smooth endothelium reduces friction; protein (collagen) coat prevents the wall splitting. Reject contracts or relaxes for recoils.

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From the examiners' report: Fewer than 40% scored. Name the tissue and say what it does: muscle withstands high pressure, elastic tissue stretches and recoils. The muscle doesn't pump blood, and vasoconstriction belongs to arterioles.

Question 2

AS Paper 2 · November 2020 · Q03.1 · 2 marks · Hard

Explain how an arteriole can reduce blood flow into capillaries.

Question text: explain how an arteriole can reduce the blood flow into capillaries, 2 marks.
Show the mark scheme Mark scheme: muscle contracts; constricts or narrows the arteriole or its lumen. Accept vasoconstriction for 1 mark.

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From the examiners' report: Very few knew that the muscle in the arteriole wall contracts. Arterioles have no valves, and dilation increases flow, it doesn't reduce it.

Question 3

AS Paper 1 · November 2021 · Q06.2 · 2 marks

Identify a blood vessel in a micrograph and explain how you know.

Figure 6: optical micrograph of a section through two blood vessels; on the left a vessel with a thick wall and small round lumen, on the right, labelled M, a vessel with a thin wall and wide, flattened lumen.
Show the mark scheme Mark scheme: vein; wider lumen or thinner wall.

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From the examiners' report: No examiners' report for this part. Name the vessel, then give the feature you used, comparing it with the other vessel: a wider lumen or a thinner wall.

Question 4

AS Paper 2 · June 2023 · Q04.3 · 3 marks · Medium

Name the vessels that control blood flow to muscles and explain how they increase flow in exercise.

Question text: name the type of blood vessel that controls blood flow to muscles and explain how these blood vessels change blood flow during exercise, 3 marks.
Show the mark scheme Mark scheme: arteriole; circular or smooth muscle relaxes; vasodilation, or the lumen widens, so blood flow increases.

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From the examiners' report: Only a minority got all 3. Name arterioles, then say the muscle relaxes and the lumen widens. Constricting to raise pressure, or diverting blood elsewhere, doesn't answer the question.

Question 5

AS Paper 2 · June 2016 · Q09.4 · 2 marks · Easy

Suggest how widening blood vessels can lower ventricular blood pressure.

Question text: some drugs that reduce high ventricular blood pressure cause widening of blood vessels; suggest how this can reduce ventricular blood pressure, 2 marks.
Show the mark scheme Mark scheme, any two: larger lumen or volume of the blood vessels; reduces blood pressure in the vessels; less friction or resistance.

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From the examiners' report: Almost 90% got at least 1 mark. Link the larger lumen to lower pressure in the vessels; very few mentioned less friction or resistance.

Question 6

A level Paper 1 · November 2020 · Q03.2 · 2 marks · Hard

Explain the small rise in aortic pressure and blood flow at Q, and why it matters.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Figure 3: pressure in the left ventricle, pressure in the aorta near the heart and rate of blood flow in the aorta over 1 second in a dog; Q marks a small rise in aortic pressure and flow just after the ventricle pressure falls.
Show the mark scheme Mark scheme: elastic recoil of the aorta wall; smooths the blood flow, or maintains the rate of blood flow or the blood pressure. Reject muscle contracting.

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From the examiners' report: Only 11% gained any marks. It is elastic recoil of the aorta wall, not muscle contracting, and it smooths the blood flow. The aorta is not a second pump.

Capillaries and tissue fluid (3.3.4.1)

Question 7

AS Paper 2 · June 2025 · Q09.2 · 5 marks · Medium

Describe and explain how tissue fluid is formed and returned to the circulatory system.

Question text: describe and explain how tissue fluid is formed and how it is returned to the circulatory system, 5 marks.
Show the mark scheme Mark scheme, max 5: water and small molecules forced out of the capillary; by high hydrostatic pressure at the arterial end; plasma proteins remain; proteins lower the water potential of the blood; water moves back by osmosis; excess tissue fluid enters the lymph.

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From the examiners' report: About 20% got all five. Pressure forces water out at the arteriole end; osmosis only comes in at the venule end. The best answers fitted the first four points into one sentence.

Question 8

AS Paper 1 · June 2017 · Q04.3 · 2 marks · Hard

Explain the role of the heart in the formation of tissue fluid.

Question text: explain the role of the heart in the formation of tissue fluid, 2 marks.
Show the mark scheme Mark scheme: contraction of the ventricles produces high blood or hydrostatic pressure; this forces water and some dissolved substances out of the capillaries. Reject blood, plasma or tissue fluid forced out.

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From the examiners' report: 74% scored zero. Say the ventricles contract (not just 'the heart pumps') and that water is forced out of the capillaries, not tissue fluid, plasma or blood.

Question 9

AS Paper 1 · June 2017 · Q04.4 · 1 mark

Suggest how a blocked lymphatic system could cause swelling in the legs.

Question text: lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system; suggest how, 1 mark.
Show the mark scheme Mark scheme: excess tissue fluid cannot be reabsorbed or drained, so it builds up. The idea of excess is needed.

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From the examiners' report: 73% scored zero, and many wrote about blood clots. The lymphatic system drains excess tissue fluid; if it is blocked, the excess builds up.

Question 10

AS Paper 2 · June 2016 · Q09.3 · 2 marks · Hard

Explain why a high ventricular blood pressure makes tissue fluid build up.

Question text: some people produce a much higher ventricular blood pressure than normal, which can cause tissue fluid to build up outside the blood capillaries; explain why, 2 marks.
Show the mark scheme Mark scheme: more fluid forced out of the capillaries due to high pressure; less fluid returns to the capillaries, or the lymphatic system cannot drain away all the excess. Reject more tissue fluid forced out.

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From the examiners' report: Almost two-thirds scored nothing, mostly by describing how tissue fluid forms. Explain the build-up: more fluid out, less back. Write 'more fluid', not 'more tissue fluid'.

Question 11

A level Paper 1 · June 2017 · Q03.3 · 2 marks

Explain how a high salt concentration in the blood can make tissue fluid build up.

Question text: high absorption of salt from the diet can give a higher than normal salt concentration in the blood plasma entering capillaries, which can lead to a build-up of tissue fluid; explain how, 2 marks.
Show the mark scheme Mark scheme, either pair: lower water potential of the tissue fluid, so less water returns to the capillary by osmosis; or higher blood pressure or volume, so more fluid forced out at the arteriole end. Don't mix and match.

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From the examiners' report: No examiners' report for this part. Pick one route and finish it: either water potential and osmosis at the venule end, or blood pressure and more fluid forced out at the arteriole end.

Question 12

A level Paper 1 · June 2023 · Q09.6 · 2 marks · Easy

Explain how blood proteins leaking into tissue fluid affect its return to the capillaries.

Question text: the dengue virus damages capillaries so that blood proteins move out into the tissue fluid; explain how this would affect the return of tissue fluid into the capillaries, 2 marks.
Show the mark scheme Mark scheme: increases the water potential of the blood, or decreases the water potential of the tissue fluid; so less water returns to the capillaries by osmosis, or more leaves. Ignore tissue fluid for the second point.

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From the examiners' report: This discriminated well. Say where the water potential changes and which way water moves. It is water that moves by osmosis, not 'tissue fluid'.

Cardiovascular disease risk factors (3.3.4.1)

Question 13

AS Paper 2 · June 2022 · Q06.3 · 4 marks · Hard

Evaluate two blood pressure treatments for reducing the risk of cardiovascular disease.

Figure 6: relative risk of cardiovascular disease against blood pressure from 10 to 22 kPa, flat across the low and ideal ranges (up to 16 kPa) then rising through pre-high and high. Figure 7: mean blood pressure fell by about 1.7 kPa with treatment 1 and 4 kPa with treatment 2.
Show the mark scheme Mark scheme, max 4: treatment 2 reduces bp or risk more; neither reaches ideal bp; treatment 1 leaves patients at high bp (20.3); treatment 2 leaves them pre-high (18), still above normal risk; no statistical test; side effects and duration unknown; large sample. Reject 'results are significant'.

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From the examiners' report: Under 2% got all 4. Read the new blood pressure off each bar, then place it on Figure 6: both groups are still at higher than normal risk. The stem says a large number of patients, so use it.

Question 14

A level Paper 1 · June 2019 · Q02.2 · 4 marks

Evaluate a student's claim that 10 g more fibre a day would significantly lower his risk of CVD.

Figure 3: relative risk of cardiovascular disease against mass of fibre eaten from 5 to 60 g per day, falling from about 1.3 to 0.65, with dashed lines showing ±2 standard deviations that widen at low and high fibre intakes.
Show the mark scheme Mark scheme, max 4: negative correlation; the student's current intake isn't known; significance depends on whether the ±2 SD lines overlap; between 5 and 30 g a significant fall, between 30 and 50 g not; correlation does not mean causation; little data at high intakes; wide SDs; no statistical test.

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From the examiners' report: No examiners' report for this part. It depends where the student starts: compare the SD lines 10 g apart, and say that a correlation doesn't show causation.

Where students lose marks (from AQA examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Muscle in the aorta resists pressure; it doesn't pump: Fewer than 40% scored on two features of the aorta wall. Many said the muscle pumps blood or 'maintains' blood pressure, or described vasoconstriction, which happens in arterioles, not the aorta.

    ✔ Gains credit: "(Smooth) muscle absorbs / resists / withstands high (blood) pressure."

  • Elastic tissue stretches and then recoils: Only 11% scored on the small rise in pressure and flow in the aorta; many thought the aorta acts as a second pump. On the aorta wall question most gave recoil only, or said recoil increases blood pressure.

    ✔ Gains credit: "Elastic recoil (of the aorta wall)"; "elastic tissue stretches and recoils, maintains / smooths blood pressure".

  • Arterioles change flow through their muscle: Most students didn't know that muscle in the arteriole wall controls blood flow; some gave arterioles valves. On exercise, many wrote about constricting the lumen to raise pressure instead of widening it.

    ✔ Gains credit: "Muscle contracts; constricts / narrows the arteriole"; for exercise, "(circular / smooth) muscle relaxes; vasodilation increases blood flow".

  • Water is forced out, not tissue fluid: 74% scored zero on the role of the heart in forming tissue fluid. Most repeated the stem, or said 'tissue fluid', 'fluid', 'plasma' or even 'blood' left the capillaries.

    ✔ Gains credit: "Contraction of ventricle(s) produces high blood / hydrostatic pressure; (this) forces water (and some dissolved substances) out (of blood capillaries)."

  • Explain the build-up, don't describe formation: Almost two-thirds scored nothing on why high blood pressure makes tissue fluid build up. Many described how tissue fluid forms, and wrote that 'more tissue fluid' is forced out.

    ✔ Gains credit: "More fluid forced / filtered out of capillary (due to high pressure)"; "lymphatic system cannot drain away all excess fluid".

  • Pressure pushes water out; osmosis brings it back: About 20% got all five marks for tissue fluid formation and return. Errors included water forced out at the arteriole end 'by osmosis' and leaving osmosis out of the return at the venule end.

    ✔ Gains credit: "High hydrostatic pressure forces water out; (plasma) proteins remain and lower the water potential; water moves (into the blood) by osmosis."

  • Water moves by osmosis, and say where the water potential changes: In the dengue question, many said 'tissue fluid' returns by osmosis instead of water, and didn't say where the water potential had changed or which way the water moved.

    ✔ Gains credit: "Decreases water potential of tissue fluid; (so) less water returns to blood / capillaries (by osmosis)."

  • Lower blood pressure can still mean higher risk: Under 2% got all 4 marks on the blood pressure treatments. Most saw that treatment 2 worked better, but few said patients were still above normal risk, and the 'large number of patients' in the stem was ignored.

    ✔ Gains credit: "With treatment 2, patients (are) in pre-high bp / 18 bp so (still) at higher risk than normal"; "large sample size so results representative".

Download the questions

Download the PDF pack (14 questions, mark schemes at the end)

Keep practising

Questions, mark schemes and examiners' report extracts © AQA.

Tom Whitburn
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