AQA GCSE Biology Biology Paper 2 (Higher), June 2023: Question 5

9 marks · Standard Demand difficulty · Short Answer

Explain negative feedback control of substance Q, how thyroxine increases body temperature, and the effect of decreased ADH concentration on urine production.

Practise this question

Question

Question 5 contains three parts. Part 05.1 shows Figure 8, a flow diagram representing negative feedback: 'Ideal concentration of substance Q' leads via 'Increase of substance Q' to 'Concentration of substance Q too high', then via 'Hormone A' back to ideal; or via 'Decrease of substance Q' to 'Concentration of substance Q too low', then via 'Hormone B' back to ideal. Part 05.2 asks to explain how thyroxine increases body temperature. Part 05.3 provides Table 2 showing blood ADH concentration (0.0 to 5.00 nanograms/dm³), concentration of dissolved substances in urine (50 to 1170 arbitrary units), and rate of urine production (20.0 down to 0.9 cm³/minute), asking to explain the effect of a decrease in ADH from 3.75 to 1.25 nanograms/dm³.
Question text

05 Homeostasis is the regulation of the body’s internal conditions.

Many internal conditions are controlled by hormones.

Homeostasis works by negative feedback control.

05.1 Figure 8 shows how the concentration of substance Q in the blood is controlled by

negative feedback.

Figure 8

Explain how the concentration of substance Q in the blood is controlled by

negative feedback.

Use information from Figure 8.

[3 marks]

05.2 Thyroxine is a hormone produced by the thyroid gland.

A decrease in body temperature causes an increase in thyroxine production.

Explain how the production of thyroxine causes an increase in body temperature.

[2 marks]

05.3 ADH is a hormone made by the pituitary gland.

ADH controls how much water is reabsorbed from the kidney tubules.

Table 2 shows effects of ADH.

Table 2

Concentration of

Concentration of ADH Rate of urine

dissolved substances

in the blood in production in

3 in urine in arbitrary 3

nanograms/dm cm /minute

units

0.0 50 20.0

1.25 700 8.8

2.50 980 3.9

3.75 1110 1.8

5.00 1170 0.9

The concentration of ADH in a man’s blood was 3.75 nanograms/dm3.

The concentration of ADH in his blood decreased to 1.25 nanograms/dm3.

Explain how the decrease in the concentration of ADH would cause the changes to

the urine shown in Table 2.

[4 marks]

Mark scheme

Show the mark scheme Mark scheme for Question 5: 05.1 awards 3 marks for stating that if substance Q is high, hormone A is released, if low, hormone B is released, and these return Q to normal. 05.2 awards 2 marks for stating thyroxine increases metabolic rate and respiration releases energy or heat. 05.3 awards 4 marks for: kidney tubules become less permeable to water, less water is reabsorbed, leading to more water in urine causing increased urine production rate, and more water causing lower concentration of dissolved substances (more dilute urine).

Question 5

AO /

Question Answers Extra information Mark

Spec Ref.

05.1 allow answers in terms of insulin AO3

for hormone A and / or glucagon 4.5.3.7

4.5.3.2

for hormone B

4.5.3.1

allow answers in terms of blood

glucose (concentration) for

substance Q

if (concentration of substance) 1

Q becomes high (hormone) A is

released / used

if (concentration of substance) 1

Q becomes low (hormone) B is

released / used

hormone(s) / A / B brings 1

(concentration of) substance Q

back to ideal / normal

AO /

Spec Ref.

05.2 (thyroxine) increases (basal) allow (thyroxine) increases 1 AO1

metabolic rate metabolism 4.5.3.7

4.4.2.1

allow (thyroxine) increases

4.4.2.3

respiration

allow (thyroxine) increases

reactions in cells

respiration releases energy allow respiration releases heat 1

do not accept energy being

produced / made / created

allow respiration is exothermic

AO /

Spec Ref.

05.3 (kidney) tubules less permeable 1 AO1

to water

(so) less water is reabsorbed allow (so) less water taken back 1 AO1

into the blood

(so) more water in urine causing allow (so) more water in urine 1 AO2

increased rate of production (of causing increased volume (of

urine) urine)

(so) more water in urine causing (so) more water in urine causing 1 AO2

lower concentration of dissolved more dilute urine

substances (in urine) 4.5.3.3

Total Question 5 9

How to answer it

Homeostasis: Negative Feedback, Thyroxine & ADH

Topic Overview

What this question tests

This question assesses your understanding of hormonal coordination and homeostasis in humans (AQA Biology Specification 4.5.3):

  • Negative feedback mechanisms: How hormones respond to deviations from a set normal/ideal level.
  • Thyroxine function: How thyroxine controls basal metabolic rate and thermoregulation via exothermic respiration.
  • Water balance & ADH: Explaining data to show how changing ADH levels alters kidney tubule permeability, water reabsorption, and resulting urine concentration and volume.
Question 05.1

Negative Feedback Control of Substance Q

Explain how the concentration of substance Q in the blood is controlled by negative feedback. Use information from Figure 8. [3 marks]

✅ Mark Scheme Model Answer

  • Mark 1: If the concentration of substance Q becomes high, hormone A is released.
  • Mark 2: If the concentration of substance Q becomes low, hormone B is released.
  • Mark 3: The hormones / hormone A / hormone B return the concentration of substance Q back to the ideal / normal level.

💡 Key Knowledge

A negative feedback loop acts like a biological thermostat:

  • A change away from the set point is detected.
  • A response is triggered to counteract or reverse that change.
  • The system is restored to its optimum / ideal value.

🧠 Exam Technique

Always state the starting condition, the hormone released, and the end result. Use the letters provided in the diagram (substance Q, hormone A, hormone B). Although examiners allow referencing insulin/glucagon, sticking to the diagram avoids confusion!

❌ Common Errors

  • Forgetting to state that the concentration returns to ideal / normal (losing the 3rd mark).
  • Mixing up hormone A and B (e.g. stating B lowers the concentration).
Examiner Insight: To get full marks, candidates must address both sides of the feedback cycle (high and low) and clearly conclude that the deviation is reversed back to baseline.
Question 05.2

Thyroxine and Thermoregulation

Explain how the production of thyroxine causes an increase in body temperature. [2 marks]

✅ Mark Scheme Model Answer

  • Mark 1: (Thyroxine) increases the (basal) metabolic rate (or increases respiration / rate of chemical reactions in cells).
  • Mark 2: Respiration releases energy / heat (or respiration is exothermic).

💡 Key Knowledge

Thyroxine is secreted by the thyroid gland:

  • It regulates the basal metabolic rate (BMR) — the speed at which chemical reactions happen in resting cells.
  • Cellular respiration is an exothermic reaction, meaning thermal energy is transferred to the surroundings, warming the blood and body tissues.

🧠 Exam Technique

Connect the hormone to the cellular process, then to the thermal outcome:

Thyroxine → Faster Metabolism / Respiration → Releases Heat

❌ Fatal Error: "Energy is Made"

DO NOT write that energy is "produced", "made", or "created". The law of conservation of energy applies in biology exams too! Always say energy is released or transferred.

Examiner Insight: Many students knew that thyroxine warmed the body, but failed to credit the biological mechanism: identifying respiration as an exothermic reaction that transfers heat.
Question 05.3

Effect of ADH on Kidney Function & Urine

Explain how the decrease in the concentration of ADH would cause the changes to the urine shown in Table 2. [4 marks]

📐 Interpreting the Table 2 Data

When ADH drops from 3.75 to 1.25 nanograms/dm³ :

  • Solute concentration: decreases from 1110 to 700 arbitrary units .
  • Rate of urine production: increases dramatically from 1.8 to 8.8 cm³/minute .

✅ Mark Scheme Model Answer

Write a clear, sequential 4-step explanation:

  1. Mark 1: (Kidney) tubules become less permeable to water.
  2. Mark 2: (So) less water is reabsorbed back into the blood.
  3. Mark 3: (So) more water remains in the urine, causing an increased rate of urine production / higher volume of urine.
  4. Mark 4: (So) more water in the urine causes a lower concentration of dissolved substances / more dilute urine.

💡 The Biological Mechanism

  • More ADH = High permeability → High reabsorption → Small volume of concentrated urine.
  • Less ADH = Low permeability → Low reabsorption → Large volume of dilute urine.

❌ Common Errors

  • Confusing the destination: Saying water is reabsorbed into the urine instead of into the blood.
  • Omitting permeability: Forgetting to mention the specific effect of ADH on the walls/tubules of the kidney nephron.
  • Ignoring one of the data columns: Addressing only the volume/rate and forgetting to explain the change in dissolved solute concentration.
Examiner Insight: Top responses systematically linked each change in Table 2 (both urine rate AND solute concentration) directly back to reduced water reabsorption caused by lower tubule permeability.

Topics

Biology · B4: Bioenergetics · B5: Homeostasis and Response

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