Transport in Animals (3.1.2): OCR A Level Biology Exam Questions by Topic

OCRExchange and TransportExam Questions
Written by Tom Whitburn

Transport in animals is one of the biggest spec points in Year 12, and it turns up on every OCR A paper. Spec point 3.1.2 asks why animals need transport systems, how single, double, open and closed systems differ, and how arteries, arterioles, capillaries, venules and veins suit their jobs. It also covers tissue fluid, the structure of the heart and its dissection, the cardiac cycle, how the heartbeat is coordinated, ECG traces, and how haemoglobin carries oxygen and carbon dioxide.

The examiners' reports for these questions point to a handful of habits that cost marks. Students reverse the SA:V idea, can't say what oncotic pressure is, write 'brachycardia', or read a Bohr shift as an increase in affinity. In error-spotting questions they quote the student's text without saying what is wrong, and in calculations they divide instead of multiplying or give cardiac output in cm3/bpm.

Work through the twenty questions below in order. They start with recall of vessels, the heart and haemoglobin, move on to applying it to pressure graphs, ECGs and dissociation curves, and finish with a heart drawing and pregnancy data. If you'd like to go through questions like these with me each week, my OCR A masterclasses run on Wednesdays at 5.15pm for Year 12 and on Tuesdays at 6.30pm or Thursdays at 5.15pm for Year 13.

What you need from GCSE

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

  • The heart has four chambers: two atria and two ventricles. The right side pumps blood to the lungs and the left side pumps it to the body.
  • Arteries carry blood away from the heart at high pressure, veins carry it back at low pressure and have valves, and capillaries are where substances are exchanged.
  • Red blood cells contain haemoglobin, which carries oxygen from the lungs to the tissues.
  • Larger organisms have a smaller surface area to volume ratio, so they need transport systems to move substances to and from their cells.
  • The heart's natural pacemaker is a group of cells in the right atrium.

Key terms

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

  • Single and double circulation: in a single circulation blood passes through the heart once per circuit of the body (fish); in a double circulation it passes through twice (mammals).
  • Open and closed circulation: in a closed system blood stays inside vessels; in an open system (insects) haemolymph bathes the organs directly.
  • Hydrostatic pressure: the pressure of the blood against the capillary wall, which pushes fluid out of the capillary.
  • Oncotic pressure: the tendency of water to move into the blood by osmosis, because large plasma proteins give the blood a lower water potential.
  • Cardiac output: the volume of blood pumped by the heart per minute: heart rate × stroke volume, in cm3 min−1.
  • Myogenic: cardiac muscle contracts on its own without nervous stimulation; the beat starts at the sino-atrial node (SAN).
  • SAN, AVN and Purkyne fibres: the SAN starts a wave of excitation across the atria; the AVN delays it and passes it down the bundle of His to the Purkyne fibres in the ventricle walls.
  • Tachycardia, bradycardia: a resting heart rate faster than 100 beats per minute; a resting heart rate slower than 60 beats per minute.
  • Affinity: how strongly haemoglobin binds oxygen. Fetal haemoglobin has a higher affinity than adult haemoglobin.
  • Bohr effect: more carbon dioxide lowers haemoglobin's affinity for oxygen, shifting the dissociation curve to the right so oxygen is released more readily.

What these questions cover (OCR 3.1.2)

The questions test these learning outcomes from the OCR A Level Biology A specification (H420):

  • (a) the need for transport systems in multicellular animals
  • (b) the different types of circulatory systems (single, double, open and closed)
  • (c) the structure and functions of arteries, arterioles, capillaries, venules and veins
  • (d) the formation of tissue fluid from plasma (hydrostatic and oncotic pressure)
  • (e)(i) the external and internal structure of the mammalian heart
  • (e)(ii) the dissection, examination and drawing of the external and internal structure of the mammalian heart (PAG2)
  • (f) the cardiac cycle (including cardiac output = heart rate × stroke volume)
  • (g) how heart action is initiated and coordinated
  • (h) the use and interpretation of electrocardiogram (ECG) traces (tachycardia, bradycardia, fibrillation and ectopic heartbeat)
  • (i) the role of haemoglobin in transporting oxygen and carbon dioxide (including carbonic anhydrase and the chloride shift)
  • (j) the oxygen dissociation curve for fetal and adult human haemoglobin (including the Bohr effect)

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.2 minutes per mark: the 20 questions are worth 49 marks, so about 59 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.

Recall

Question 1

AS Paper 1 · June 2025 · Q25(a) · 2 marks · Easy

Explain two reasons, other than long diffusion distances, why an Asian elephant needs a transport system.

Question about the Asian elephant, the largest land mammal in Asia, asking for two reasons other than long diffusion distances why it has a transport system.
Show the mark scheme Mark scheme: small or low surface area to volume ratio; high metabolic demand or rate. 'Diffusion rate too slow' and 'use more energy' are ignored.

Tap an image to open it full size.

From the examiners' report: Most students scored both marks, but some wrote that a large animal has a large SA:V. It is small, and pair it with a high metabolic rate.

Question 2

A level Paper 3 · June 2022 · Q4(a)(ii) · 2 marks · Easy

Describe the type of circulatory system shown for the zebra shark.

Fig. 4.2: diagram of the zebra shark's circulation, with blood going from the heart through arteries to the gills, then to the body tissues and back through veins to the heart.
Show the mark scheme Mark scheme: closed (or described); single (or described).

Tap an image to open it full size.

From the examiners' report: Most students described it as single and closed. Give both words: single because blood passes through the heart once per circuit, and closed because it stays in vessels.

Question 3

A level Paper 3 · June 2022 · Q2(d)(i) · 2 marks · Easy

Decide whether vessel L in a stained tissue section is an artery or a vein and give two pieces of evidence.

Fig. 2.2: micrograph of stained tissue showing two blood vessels, L and M, and a substance labelled N.
Show the mark scheme Mark scheme: L is an artery because of a smaller lumen, a thicker layer of smooth muscle or elastic tissue, a more open lumen, or a folded endothelium. No marks if L is called a vein.

Tap an image to open it full size.

From the examiners' report: Say 'a thicker layer of smooth muscle' or 'a thicker wall', not just 'thick smooth muscle', and only use features you can see: valves aren't visible here.

Question 4

AS Paper 2 · June 2024 · Q4(b)(i) · 2 marks · Medium

Explain the role of valves in veins.

Question asking students to explain the role of valves in veins, with answer lines.
Show the mark scheme Mark scheme: valves stop backflow of blood because the pressure in veins is low; they allow one-way flow back to the heart.

Tap an image to open it full size.

From the examiners' report: Don't just state that valves stop backflow. Explain it: blood in veins is at low pressure, so valves keep it flowing one way, back to the heart.

Question 5

AS Paper 1 · June 2022 · Q23(a)(iii) · 1 mark · Medium

Name the vessel labelled W that carries blood into a capillary network.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question asking students to name the structure labelled W on the diagram of a capillary network in muscle tissue.
Show the mark scheme Mark scheme: arteriole. Mark first answer only.

Tap an image to open it full size.

From the examiners' report: Few students knew this. The small vessel leading into a capillary bed is an arteriole; 'artery', 'vein' or 'blood vessel' don't score.

Question 6

A level Paper 1 · November 2021 · Q16(a)(i) · 5 marks · Medium

Identify the structures labelled A to E on a drawing of a dissected human heart.

Fig. 16.1: drawing of a dissected human heart with five structures labelled A to E, including a region in the wall of the right atrium, a chamber, a large vein and two valves.
Show the mark scheme Mark scheme: A sinoatrial node (not 'sinoarterial'); B right atrium; C (inferior) vena cava; D semilunar (aortic) valve; E bicuspid, mitral or left atrioventricular valve (not tricuspid).

Tap an image to open it full size.

Question 7

A level Paper 1 · June 2025 · Q20(c) · 4 marks · Medium

Identify the structures labelled J to M on a drawing of a dissected human heart.

Drawing of a dissected human heart with four structures labelled J, K, L and M, from the wall of the right atrium down to the walls of the ventricles.
Show the mark scheme Mark scheme: J is the sino-atrial node; K the atrio-ventricular node; L the septum (bundle of His allowed); M the Purkyne fibres (Purkinje allowed).

Tap an image to open it full size.

From the examiners' report: Most students named all four. Some swapped L and M: the bundle of His runs down the septum, and the Purkyne fibres spread through the ventricle walls.

Question 8

A level Paper 3 · June 2022 · Q6(b) · 3 marks · Medium

Tick which properties apply to hydrogen, hydrogencarbonate and chloride ions in oxygen transport.

Table listing hydrogen, hydrogencarbonate and chloride ions with columns for has a negative charge, binds to haemoglobin, a product of the dissociation of carbonic acid, and involved in the chloride shift.
Show the mark scheme Mark scheme: hydrogen ions bind to haemoglobin and come from carbonic acid; hydrogencarbonate ions are negative, come from carbonic acid and are in the chloride shift; chloride ions are negative and in the chloride shift.

Tap an image to open it full size.

From the examiners' report: Remember that hydrogen ions bind to haemoglobin, and that hydrogencarbonate ions leaving the red blood cell are half of the chloride shift.

Applying what you know

Question 9

A level Paper 1 · June 2025 · Q21(a)(ii) · 3 marks · Medium

Explain why insects can function with open circulatory systems.

Question asking students to explain why insects can function with open circulatory systems, with answer lines.
Show the mark scheme Mark scheme: tracheae or tracheoles supply oxygen directly to tissues; the haemolymph does not transport oxygen; small size and short distances mean high flow rate or pressure is not needed. Low metabolic rate is ignored.

Tap an image to open it full size.

From the examiners' report: The key idea is that insects get oxygen through their tracheal system, so their blood doesn't carry it. Don't say insects have a low metabolic rate: in flight it can be very high.

Question 10

AS Paper 1 · June 2022 · Q23(b) · 3 marks · Hard

Describe how oncotic pressure is established.

Question asking students to describe how oncotic pressure is established, with answer lines.
Show the mark scheme Mark scheme: plasma proteins are too large to leave the capillary; this creates a lower water potential in the capillary than in the tissue fluid; water moves into the capillary by osmosis.

Tap an image to open it full size.

From the examiners' report: Very few students could explain oncotic pressure. Build it in steps: large plasma proteins stay in the blood, so the blood has a lower water potential than the tissue fluid, so water moves back in by osmosis.

Question 11

AS Paper 2 · June 2018 · Q4(a)(ii) · 2 marks · Medium

Use hydrostatic and oncotic pressure values to explain fluid movement in and out of a capillary.

Question giving net hydrostatic pressure of 4.6 kPa at the arterial end, net oncotic pressure of −3.0 kPa, and net hydrostatic pressure of 2.3 kPa at the venous end, asking students to explain fluid movement.
Show the mark scheme Mark scheme: at the arterial end hydrostatic (4.6) is greater than oncotic (−3), so fluid moves out; at the venous end hydrostatic (2.3) is lower than oncotic, so fluid moves in. Each statement must name the end, compare the pressures and give the direction.

Tap an image to open it full size.

From the examiners' report: Use the numbers. For each end of the capillary, compare hydrostatic with oncotic pressure and say which way the fluid moves; ignoring oncotic pressure scored nothing.

Question 12

A level Paper 1 · June 2018 · Q21(a)(iii) · 3 marks · Medium

Suggest and explain the effect on heart rate of slower conduction in the Purkyne fibres.

Question stating that TTX reduces the speed of conduction in the Purkyne fibres and asking students to suggest and explain the effect on heart rate.
Show the mark scheme Mark scheme: heart rate decreases; impulse from the AVN to the ventricles is slowed; ventricular systole is slowed or delayed; more time in diastole. 'Ventricular' must appear once.

Tap an image to open it full size.

From the examiners' report: Say the heart rate falls, then explain it in terms of the ventricles: the impulse reaches them more slowly, so there is a longer delay before ventricular systole.

Question 13

AS Paper 2 · June 2022 · Q3(c) · 3 marks · Medium

Identify and correct three errors in a student's description of a pressure graph for the cardiac cycle.

Fig. 3.4: pressure in the aorta, left ventricle and left atrium during one cardiac cycle, with points A, B and C, followed by a student's description of the events at A, B and C.
Show the mark scheme Mark scheme: the wave starts at the SAN, not the AVN; the atrioventricular valve closes, not opens; aortic pressure rises, not falls; the semilunar valve closes, not opens. Max 1 for errors without corrections.

Tap an image to open it full size.

From the examiners' report: Set each answer out as 'Error: … Correction: …'. Long quotes from the description without saying what is wrong, or a correction with no error, lost marks.

Question 14

A level Paper 1 · June 2025 · Q20(e)(i) · 1 mark · Medium

Identify the abnormality shown on an ECG trace and give a reason.

Fig. 20.1: a normal ECG trace, and Fig. 20.2: an ECG trace from a patient with abnormal heart activity, with lines for the abnormality and the reason.
Show the mark scheme Mark scheme: bradycardia, because the T wave and the next P wave are further apart than normal (or heart rate slower). Both needed; 'brachycardia' not allowed.

Tap an image to open it full size.

From the examiners' report: Spell it bradycardia ('brady' means slow; 'brachy' means short), and give a reason from the trace, such as the beats being further apart.

Question 15

A level Paper 1 · June 2025 · Q20(e)(ii) · 1 mark · Medium

Identify a second ECG abnormality and give a reason from the trace.

Fig. 20.3: an ECG trace from another patient with abnormal heart activity, with lines for the abnormality and the reason.
Show the mark scheme Mark scheme: ectopic heartbeat, because the gap between the 4th and 5th beats is shorter than normal (one beat is early); or fibrillation, because there are no distinct P waves. Both needed.

Tap an image to open it full size.

From the examiners' report: Look at the whole pattern of beats, not one wave. Many students named the abnormality but gave a wrong reason, such as too many beats or a missing T wave.

Question 16

AS Paper 2 · June 2022 · Q4(d)(ii) · 2 marks · Medium

Explain why the Bohr effect is important during exercise, using dissociation curves at rest and during exercise.

Fig. 4.2: oxygen dissociation curves for haemoglobin at rest and during exercise, with the exercise curve shifted to the right.
Show the mark scheme Mark scheme: more CO2 during exercise shifts the curve to the right; at the same pO2 haemoglobin is less saturated; oxygen dissociates more readily; more oxygen for aerobic respiration in muscles.

Tap an image to open it full size.

From the examiners' report: Read the graph carefully: during exercise the curve moves right, so haemoglobin's affinity for oxygen decreases, not increases, and it releases oxygen more readily to respiring muscles.

Practical, maths and data

Question 17

AS Paper 1 · June 2023 · Q26(a) · 3 marks · Hard

Draw a simple diagram of the front half of a dissected heart and label the left ventricle.

Fig. 26.1: photograph of a human heart cut into a back (dorsal) half and a front (ventral) half, with a space to draw the front half.
Show the mark scheme Mark scheme: simple line drawing with continuous, non-overlapping lines; no shading and covering at least half the box; left ventricle labelled (left bottom chamber). Label lines must be ruled with no arrowheads.

Tap an image to open it full size.

From the examiners' report: Draw clean, continuous lines with no shading, rule the label line without an arrowhead, and work out the left side from the specimen: it isn't always on the right of the page.

Question 18

A level Paper 1 · June 2023 · Q16(a)(i) · 3 marks · Hard

Use graphs of stroke volume and heart rate in pregnancy to calculate cardiac output at week 20.

Fig. 16.1: two graphs against length of pregnancy in weeks: stroke volume (cm3) rising from 65 to a peak of 85 at weeks 20 to 24, and heart rate (bpm) rising from 75 to about 88.
Show the mark scheme Mark scheme: stroke volume 85 cm3 and heart rate 82.5 bpm read from the graphs; cardiac output = heart rate × stroke volume = 7012.5; unit cm3 min−1.

Tap an image to open it full size.

From the examiners' report: Multiply, don't divide: cardiac output = heart rate × stroke volume. Give the unit as cm3 min−1, not cm3/bpm.

Question 19

A level Paper 1 · June 2023 · Q16(c)(i) · 1 mark · Medium

Sketch the oxygen dissociation curve for fetal haemoglobin on the mother's curve.

Fig. 16.3: oxygen dissociation curve for the mother's haemoglobin, percentage saturation against partial pressure of oxygen from 0 to 13 kPa.
Show the mark scheme Mark scheme: a sigmoid curve sketched to the left of the adult curve, starting and finishing at the same percentage and not exceeding 96%.

Tap an image to open it full size.

From the examiners' report: Draw an S-shaped curve to the left of the mother's curve, and level it off at the same saturation: going above it was the common error.

Question 20

A level Paper 1 · June 2023 · Q16(c)(ii) · 3 marks · Easy

Explain how the different affinities of maternal and fetal haemoglobin let oxygen pass to the fetus.

Question asking students to explain how the different affinities of maternal and fetal haemoglobin enable transfer of oxygen from the maternal circulation to the fetus.
Show the mark scheme Mark scheme: fetal haemoglobin has a higher affinity at the same pO2; pO2 in the placenta is low; oxygen dissociates from maternal haemoglobin; oxygen diffuses from maternal to fetal blood; fetal haemoglobin becomes more saturated at low pO2.

Tap an image to open it full size.

From the examiners' report: Most students said fetal haemoglobin has a higher affinity but few mentioned the low pO2 in the placenta. Say that at this low pO2 oxygen dissociates from maternal haemoglobin and fetal haemoglobin picks it up.

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

Each point below is followed by wording that gained marks.

  • Elephants have a small SA:V: Explaining why a large mammal needs a transport system, some students wrote that large organisms have a large surface area to volume ratio, so lost the mark.

    ✔ Gains credit: "It has a smaller surface area to volume ratio" and "it has a higher metabolic demand".

  • Insects breathe through tracheae, not blood: Many answers said insects can manage with an open system because they have a low metabolic rate; low metabolic rate was ignored, and few said the haemolymph doesn't carry oxygen.

    ✔ Gains credit: "Tracheoles supply oxygen directly to the tissues, so the circulatory system does not transport oxygen".

  • A thicker layer of muscle: Giving evidence that L was an artery, phrases such as 'thick smooth muscle' or 'thick elastic fibres' scored nothing without 'layer' or 'wall', and valves couldn't be seen in the image.

    ✔ Gains credit: "L is an artery: it has a smaller lumen and a thicker layer of smooth muscle and elastic tissue".

  • Oncotic pressure starts with plasma proteins: Most students left this blank or described oncotic pressure as blood pressure or hydrostatic pressure, with no mention of plasma proteins or water potential.

    ✔ Gains credit: "Plasma proteins are too large to leave the capillary, so they create a lower water potential in the blood than in the tissue fluid, and water moves into the capillary by osmosis".

  • Label each error and each fix: In the cardiac cycle question, answers copied long parts of the student's description without saying what was wrong, or gave corrections without the error; this capped the mark at 1.

    ✔ Gains credit: "Error: the wave starts at the AVN. Correction: it starts at the SAN" and "Error: the atrioventricular valve opens. Correction: it closes".

  • Brady means slow: The slow heart rhythm was often spelt 'brachycardia', which was not allowed, and the abnormality needed a reason from the trace as well.

    ✔ Gains credit: "Bradycardia, because the T wave and the next P wave are further apart than normal".

  • Bohr shift lowers affinity: Misreading the axes, some students concluded that haemoglobin's affinity for oxygen increases during exercise, when the graph shows it decreases.

    ✔ Gains credit: "More CO2 during exercise shifts the curve to the right, so at the same pO2 haemoglobin is less saturated and releases oxygen more readily to the muscles".

  • Cardiac output is per minute: Some students divided heart rate by stroke volume instead of multiplying, and many gave the unit as cm3/bpm.

    ✔ Gains credit: "Cardiac output = 82.5 × 85 = 7012.5 cm3 min−1".

Download the questions

Download the PDF pack (20 questions, mark schemes at the end)

Keep practising

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

Tom Whitburn
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