AQA GCSE Biology Biology Paper 2 (Higher), June 2024: Question 8
10 marks · Standard Demand difficulty · Short Answer
Define homeostasis, describe the handling of glucose, protein, and urea by the kidneys, and explain how ADH affects urine production and concentration.
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Question text
08 Conditions inside and outside of the human body often change.
Homeostasis helps the human body to survive changing conditions.
08.1 Explain what is meant by the term ‘homeostasis’.
[2 marks]
The kidneys have an important role in homeostasis.
08.2 Describe what happens to glucose, protein and urea in the kidneys.
[4 marks]
08.3 Explain how ADH affects the production and concentration of urine by the kidneys.
[4 marks]
Mark scheme
Show the mark scheme
Question 8
AO /
Question Answers Extra information Mark
Spec Ref.
08.1 regulation / control / allow keeping internal conditions 1 AO1
maintenance of internal the same 4.5.1
conditions
for optimum conditions for cell(s) allow a description of optimum 1
/ enzyme(s) (activity) functioning of cell / body
AO /
Spec Ref.
08.2 glucose and urea are filtered allow a description of filtration of 1 AO1
(out of the blood) glucose and urea (out of the 4.5.1
blood) 4.5.3.3
protein is not filtered (out of the 1
blood)
all glucose reabsorbed allow all glucose absorbed back 1
into the blood
urea (mostly) not reabsorbed allow urea not absorbed back 1
or into the blood
urea passes out in urine – – –
AO /
Spec Ref.
08.3 allow converse for decreased /
low / no ADH
AO1
(increased / high) ADH 1
increases water reabsorption
or
(increased / high) ADH
increases permeability to water
AO1
(water reabsorption) from kidney 1
tubules
AO1
(so) ADH increases the 1
concentration (of urine)
AO2
(so) ADH decreases the volume 1
(of urine)
4.5.1
4.5.3.3
Total Question 8 10
How to answer it
Homeostasis & Kidney Function Guide
What this question tests
This question tests your understanding of the principles of homeostasis (specification reference 4.5.1) and the specific role of the urinary system in excretion and osmoregulation (specification reference 4.5.3.3). Specifically, you need to know:
- The formal definition of homeostasis and why optimum internal conditions are necessary.
- How the kidneys filter blood and selectively reabsorb molecules (glucose, protein, urea).
- The negative feedback mechanism of Anti-Diuretic Hormone (ADH) in controlling urine volume and concentration.
Definition of Homeostasis
Explaining what is meant by the term 'homeostasis'
✅ Model Answer (Full Marks)
Homeostasis is:
- The regulation, control, or maintenance of internal conditions [1 mark]
- To provide optimum conditions for enzyme action or cellular function [1 mark]
🧠 Exam Technique
Always state what it is and why it matters:
- Part 1 (What): Say "internal conditions"—do not just say "keeping the body the same".
- Part 2 (Why): Link directly to enzymes or cells working at their best (optimum).
❌ Common Errors
- Vaguely answering "keeping conditions constant" without stating internal conditions.
- Forgetting to explain why it is important (leaving out enzymes or cellular functioning loses the 2nd mark).
💡 Key Knowledge
Internal conditions controlled include:
- Blood glucose concentration
- Body temperature
- Water levels
• Mark 1: regulation / control / maintenance of internal conditions (allow: keeping internal conditions the same)
• Mark 2: for optimum conditions for cell(s) / enzyme(s) (activity) (allow: optimum functioning of cell / body)
Fate of Substances in the Kidney
Describing what happens to glucose, protein, and urea
✅ Model Answer (Full Marks)
- Filtration: Glucose and urea are filtered out of the blood into the kidney tubule [1 mark].
- Protein: Protein is not filtered (remains in the blood) [1 mark].
- Glucose: All glucose is reabsorbed back into the blood [1 mark].
- Urea: Urea is not reabsorbed (or only partially) and passes out in the urine [1 mark].
💡 Why does this happen?
| Substance | Filtered? | Reabsorbed? |
|---|---|---|
| Protein | ❌ No (molecules are too large to pass through capillary walls) | N/A |
| Glucose | ✅ Yes (small molecule) | ✅ All reabsorbed by active transport |
| Urea | ✅ Yes (small waste molecule) | ❌ Not reabsorbed (excreted in urine) |
🧠 Exam Technique
The prompt highlights three words: glucose, protein, and urea. Structure your answer by addressing both the filtering stage and the reabsorption stage for each substance to guarantee all 4 marks.
❌ Common Errors
- Saying protein is "excreted" or "filtered out and reabsorbed". Protein is never filtered because it is too large.
- Saying "some" glucose is reabsorbed. In a healthy person, all glucose is selectively reabsorbed.
- Confusing urea with urine. Urea is a specific toxic chemical formed in the liver from excess amino acids.
• Mark 1: glucose and urea are filtered (out of the blood)
• Mark 2: protein is not filtered (out of the blood)
• Mark 3: all glucose reabsorbed (allow: all glucose absorbed back into the blood)
• Mark 4: urea (mostly) not reabsorbed OR urea passes out in urine
Role of ADH in Osmoregulation
Explaining how ADH affects urine production and concentration
✅ Model Answer (Full Marks)
When ADH levels increase:
- ADH increases the permeability of the kidney tubule walls to water (or increases water reabsorption) [1 mark].
- More water is reabsorbed from the kidney tubules back into the blood [1 mark].
- This causes the concentration of urine to increase [1 mark].
- This causes the volume of urine produced to decrease [1 mark].
🧠 Exam Technique: Follow the Flow
Read the question carefully: it asks for both production (volume) and concentration. If you only explain concentration, you miss a mark.
Use a clear cause-and-effect chain:
Higher ADH → Tubules more permeable → More water reabsorbed → Lower volume & Higher concentration of urine.
📐 Converse Answer is Allowed!
You can also answer by describing what happens when ADH is low / decreased:
- Lower permeability to water in the kidney tubules [1 mark].
- Less water reabsorbed from the tubules into blood [1 mark].
- Urine is more dilute / lower concentration [1 mark].
- A larger volume of urine is produced [1 mark].
❌ Common Errors
- Failing to mention the specific location: water is reabsorbed from the kidney tubules.
- Confusing concentration and volume (e.g. stating high ADH makes more urine).
- Not stating which direction water moves (water moves into the blood, leaving solutes behind).
• Mark 1: (increased / high) ADH increases water reabsorption OR increases permeability to water
• Mark 2: (water reabsorption) from kidney tubules
• Mark 3: (so) ADH increases the concentration (of urine)
• Mark 4: (so) ADH decreases the volume (of urine)
Note: Converse points accepted for low/decreased ADH.
Topics
Biology · B5: Homeostasis and Response
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Higher), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.