AQA AS Level Biology Paper 1, November 2021: Question 6
9 marks · Medium difficulty · Short Answer
Describe the pathway of a red blood cell from the kidney to the lungs, identify blood vessel M and explain its structure, and explain how water from tissue fluid is returned to the circulatory system.
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Question text
06.1 Give the pathway a red blood cell takes when travelling in the human circulatory
system from a kidney to the lungs.
Do not include descriptions of pressure changes in the heart or the role of heart
valves in your answer.
[3 marks]
Figure 6 shows a section through two types of blood vessels observed using an
optical microscope.
Figure 6
06.2 Identify the type of blood vessel labelled M in Figure 6.
Explain your answer.
[2 marks]
Type of blood vessel
Explanation
06.3 Tissue fluid is formed from blood at the arteriole end of a capillary bed.
Explain how water from tissue fluid is returned to the circulatory system.
[4 marks]
Mark scheme
Show the mark scheme
Question Marking Guidance Mark Comments
06.1 1. Renal vein;
2. Vena cava to right atrium; 3
3. Right ventricle to pulmonary artery;
06.2 1. Vein;
2. Wide(r) lumen
OR
Thinner wall;
06.3 1. (Plasma) proteins remain;
1. Accept
albumin/globulins/fibrinogen
2. (Creates) water potential gradient for (plasma) protein
OR
Reduces water potential (of blood);
3. Water moves (to blood) by osmosis;
4. Returns (to blood) by lymphatic system;
TOTAL 9
How to answer it
Transport Systems in Humans Study Guide
What this question tests
This assessment evaluates your knowledge of the mammalian circulatory system pathway, your ability to identify histological features of blood vessels under a light microscope, and your understanding of mass transport and water potential dynamics involved in the formation and return of tissue fluid.
Pathway of a Red Blood Cell (Kidney to Lungs)
✅ Correct Answer
- Renal vein
- Vena cava to right atrium
- Right ventricle to pulmonary artery
🧠 Exam Technique
Read the negative constraint carefully: "Do not include descriptions of pressure changes in the heart or the role of heart valves." Including extraneous anatomical details wastes time and can introduce contradictory statements that lose marks.
❌ Common Errors
- Forgetting the vena cava connects the veins of the lower body directly to the right atrium.
- Misrouting blood directly from the lungs or left side of the heart by confusing systemic and pulmonary circuits.
Identification of Blood Vessel M
✅ Correct Answer
Type of blood vessel: Vein
Explanation: Wide(r) lumen OR thinner wall (compared to the adjacent artery).
💡 Key Knowledge
Veins have a significantly wider lumen and thinner walls with less muscle and elastic tissue compared to arteries, reflecting their role in returning blood under lower pressure.
❌ Common Errors
Giving vague descriptions such as "it looks rounder" or failing to link the histological feature directly to the identification of the vessel.
Return of Water from Tissue Fluid
✅ Correct Answer
- (Plasma) proteins remain in the blood (and cannot leave through capillary endothelium).
- This creates a water potential gradient / reduces the water potential of the blood.
- Water moves from tissue fluid into the blood by osmosis.
- Any remaining fluid is returned to the circulatory system via the lymphatic system.
💡 Key Knowledge
Starling's hypothesis: Hydrostatic pressure forces fluid out at the arteriole end, but towards the venule end, the low water potential caused by retained plasma proteins pulls water back in via osmosis.
🧠 Exam Technique
Use precise biological terminology: always refer to water potential rather than "concentration" or "amount of water". Mentioning osmosis explicitly is often a required marking point.
Topics
Biology · 3.3 Organisms exchange substances with their environment
Question and mark scheme from the AQA AS Level Biology examination, Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.