AQA GCSE Biology Biology Paper 2 (Foundation), June 2023: Question 6

12 marks · Standard Demand difficulty · Extended Answer

Answer questions on kidney filtration, reabsorption of water, and an evaluation of treatments for kidney disease including calculating the cost of a kidney transplant.

Practise this question

Question

Question 6 consists of four parts: 06.1 shows Figure 10, a diagram depicting blood plasma being filtered across a porous filter into filtrate. A key identifies water molecules, sodium ions, urea molecules, glucose molecules, and large protein molecules. The question asks candidates to draw one line from each substance ('Glucose' and 'Protein') to the reason for where it is found among three given statements. 06.2 presents Table 4 with water filtered from blood (160.0 dm³) and water lost in urine (1.9 dm³), asking for the volume of water reabsorbed into the blood. 06.3 provides Figure 11 summarizing details of dialysis (3 sessions a week of 8 hours, in hospital, dietary protein/salt limits, cost £35 000/year) and kidney transplant (general anaesthetic risk, immunosuppressants for life, £17 000 first year then £5 000/year, lasts ~10 years). Candidates must evaluate a doctor's statement that a kidney transplant is better than dialysis in a 6-mark response. 06.4 asks candidates to calculate the total cost of kidney transplant treatment over the first 5 years given the costs in the text.
Question text

06 The kidneys filter the blood.

Figure 10 shows filtration in the kidney.

Figure 10

06.1 Glucose molecules are found in the blood plasma and in the filtrate.

Protein molecules are only found in the blood plasma.

Draw one line from each substance to the reason for where the substance is found.

[2 marks]

Substance Reason

The molecules are too large to

pass through the filter

Glucose

The molecules are small enough to

pass through the filter

Protein

The molecules are too small to

27 pass through the filter

06.2 The kidneys control the volume of water in the body.

*26* Table 4 shows information about a person on one day.

Table 4

Volume in dm3

Water filtered from blood 160.0

Water lost in urine 1.9

Calculate the volume of water reabsorbed into the blood.

[1 mark]

28 Volume = dm3

06.3 A person with kidney disease may be treated by dialysis or by having a

kidney transplant.

Figure 11 gives information about dialysis and kidney transplants.

Figure 11

Dialysis

• A person needs 3 dialysis sessions a week, with each session lasting

about 8 hours.

• Most patients have dialysis in hospital.

• Protein and salt levels in food must be kept low.

• Dialysis costs £35 000 per year for each patient.

Kidney transplant

• In a surgical operation the use of a general anaesthetic can occasionally

cause damage to other organs.

• After a transplant the patient must take drugs for the rest of their life to

*27* suppress the immune system.

• A transplant costs £17 000 in the first year and then £5 000 in each of the

following years for drugs.

• The transplanted kidney will work well for about 10 years.29

A doctor states:

‘It is better to treat a person with kidney disease by using

a kidney transplant rather than by dialysis.’

Evaluate the doctor’s statement.

Use information from Figure 11.

[6 marks]

06.4 A kidney transplant costs £17 000 in the first year and then £5 000 in each of the

following years for drugs.

Calculate the total cost of treatment by kidney transplant over the first 5 years.

[3 marks]

*29* Total cost = £

Mark scheme

Show the mark scheme Mark scheme for Question 6: 06.1 awards 1 mark for Glucose linked to 'The molecules are small enough to pass through the filter' and 1 mark for Protein linked to 'The molecules are too large to pass through the filter'. 06.2 awards 1 mark for 158.1 (dm³). 06.3 is a 6-mark level-of-response question. Indicative content includes points for transplant (cheaper overall, less lifestyle and dietary restriction, no dialysis infection/clotting risk, maintains correct blood levels continuously) and points against transplant (surgical and anaesthetic risk, organ rejection, shortage of donors, life-long immunosuppressants increasing infection risk, replacement needed after ~10 years). 06.4 awards 3 marks: 1 mark for 4 × 5 000 = 20 000, 1 mark for 20 000 + 17 000, and 1 mark for 37 000 (also allows 42 000 if 5 × 5 000 was done). Total marks: 12.

Question 6

AO /

Question Answers Mark

Spec Ref.

06.1 AO3

4.5.3.3

do not accept more than one line from a box on the left

AO /

Question Answers Extra information Mark

Spec Ref.

06.2 158.1 (dm3) 1 AO2

4.5.3.3

AO /

Spec Ref.

06.3 Level 3: A judgement, strongly linked and logically supported by a AO3

5–6

sufficient range of correct reasons, is given.

Level 2: Some logically linked reasons are given. There may also 3–4 AO3

be a simple judgement.

Level 1: Relevant points are made. They are not logically linked. 1–2 AO2

No relevant content 0

4.5.3.3

Indicative content

points for transplant:

• transplant is cheaper

• numerical comparison, eg £18 000 cheaper in first year and

£30 000 cheaper in subsequent years

• less / no inconvenience, eg time or cost for hospital visits

• less / no restriction on lifestyle

• less / no restriction on diet or fluid intake

• no danger of infection from eg puncturing skin or blood in

contact with machine

• less / no possibility of blood clots

• no need to take anti-clotting drugs

• transplanted kidney keeps water / urea / ions in blood at correct

level at all times 17

• feel well all the time

points against transplant:

• danger of rejection

• need tissue match for transplant

• donors in short supply

• possibility of organ damage due to anaesthetic

• possibility of infection in surgery

• possibility of damage due to surgery

• need to take immunosuppressant drugs

• may suffer other infections due to suppressed immune system

• may need repeat operation (after about 10 years)

For Level 3 students should refer to both points for and points

against.

AO /

Spec Ref.

06.4 4 × 5 000 = 20 000 1

AO2

20 000 + 17 000 allow 25 000 + 17 000 1 4.5.3.3

(£) 37 000 allow 1

(25 000 + 17 000) = (£) 42 000

Total Question 6 12

How to answer it

Kidney Filtration, Water Reabsorption & Treatments for Kidney Failure

WHAT THIS QUESTION TESTS

This question assesses core understanding from Homeostasis and Response (AQA Specification 4.5.3.3):

  • Ultrafiltration in the kidney: Why certain molecules (like glucose, water, ions, urea) pass into the filtrate while others (large proteins) remain in the blood.
  • Quantitative reasoning: Simple subtraction of fluid volumes to deduce water reabsorption.
  • Extended evaluation (6 marks): Comparing the advantages and disadvantages of kidney dialysis versus kidney transplants using stem data and scientific knowledge.
  • Multi-step financial calculations: Calculating cumulative medical costs over a 5-year period.
QUESTION 06.1 • 2 MARKS

Molecular Size and Kidney Filtration

Linking molecular identity to why substances enter the filtrate or remain in the plasma

✅ Correct Matches

  • Glucose → The molecules are small enough to pass through the filter [1 mark]
  • Protein → The molecules are too large to pass through the filter [1 mark]

💡 Key Knowledge

  • Capillary filter pores: The membranes of the glomerulus and Bowman's capsule act as a sieve.
  • Small molecules: Water, glucose, urea, and mineral ions easily fit through the microscopic pores.
  • Large molecules: Blood cells and large plasma proteins are far too large to pass through and must stay in the capillary.

❌ Common Errors

  • Drawing multiple lines from one box on the left (the question states "Draw one line from each substance"; extra lines cancel marks).
  • Selecting the distractor: "The molecules are too small to pass through the filter" (biologically nonsensical).
Examiner Insight: Read the reason boxes carefully. Candidates often rush and confuse "too large" with "too small" because the wording looks similar at a glance.
QUESTION 06.2 • 1 MARK

Calculating Water Reabsorption

Deducing reabsorbed volume from filtered volume and excreted urine

📐 Step-by-Step Calculation

  1. Identify total volume filtered: 160.0 dm³
  2. Identify volume lost in urine: 1.9 dm³
  3. Subtract excreted volume from filtered volume:
    160.0 − 1.9 = 158.1 dm³

Answer: 158.1 dm³

🧠 Exam Technique

  • If 160.0 dm³ is removed from the blood into the nephron, and only 1.9 dm³ leaves the body as urine, the rest must have been reabsorbed back into the bloodstream.
  • Keep the answer to 1 decimal place to match the precision of the raw data given in Table 4.
QUESTION 06.3 • 6 MARKS

Evaluating Dialysis vs. Kidney Transplant

6-Mark Extended Response: Evaluating the doctor's statement using Figure 11

✅ Arguments For Kidney Transplant

  • Financial: Significantly cheaper long-term (£17 000 year 1 then £5 000/yr vs. £35 000 every single year for dialysis).
  • Time & Convenience: Dialysis takes 3 sessions of 8 hours a week (24 hours/week) in a hospital; transplants restore normal daily routine.
  • Dietary freedom: Dialysis requires strict limits on protein and salt intake; transplant patients have fewer dietary restrictions.
  • Constant regulation: A working kidney maintains correct blood ion and urea levels continuously, so patients feel healthier overall.

❌ Arguments Against Transplant (For Dialysis)

  • Surgical/Anaesthetic risks: General anaesthetic can damage other organs, plus surgical risks (infection, blood clots).
  • Organ rejection: The recipient's immune system may attack the donor kidney.
  • Immunosuppressant drugs: Must be taken daily for life, leaving the patient vulnerable to other infectious diseases.
  • Limited lifespan: Transplants typically last only ~10 years, requiring another operation or a return to dialysis.
  • Availability: Shortage of kidney donors.

🧠 How to Secure Level 3 (5–6 Marks)

To reach Level 3, you must include a balanced evaluation with reasons for and against, followed by a justified conclusion/judgement:

Mark Range Requirement
Level 3 (5–6 marks) Balanced comparison (points for AND against transplant) with logical links, clear scientific justification, and a final conclusion.
Level 2 (3–4 marks) Gives arguments on both sides or detailed arguments on one side, but links are weak or lacks a supported judgement.
Level 1 (1–2 marks) Simple recall of isolated points copied directly from Figure 11 without evaluation or comparison.

Example Conclusion: "In conclusion, the doctor is largely correct because a transplant offers a vastly superior quality of life without weekly hospital visits and saves thousands of pounds. However, it carries significant risks of surgical complications and lifelong immunosuppression."

QUESTION 06.4 • 3 MARKS

Calculating Treatment Costs Over 5 Years

Multi-step calculation for the financial cost of a transplant

📐 Step-by-Step Calculation

  1. Calculate cost of drugs for the remaining years:
    The question specifies the first 5 years total. Year 1 has already passed, leaving 4 remaining years:
    5 − 1 = 4 years
    4 × £5 000 = £20 000 [1 mark]
  2. Add Year 1 upfront cost:
    £20 000 + £17 000 [1 mark]
  3. Final total cost:
    £37 000 [1 mark]

❌ Common Trap & Mark Scheme Allowance

  • The Trap: Multiplying £5 000 by 5 years instead of 4 (giving £25 000 + £17 000 = £42 000).
  • Mark Scheme Note: The exam board allowed 25 000 + 17 000 = £42 000 for candidates who misread "following years" as 5 full drug years, but calculating 4 following years ( £37 000 ) is the primary intended answer.

Topics

Biology · B5: Homeostasis and Response

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Foundation), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.