AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2023: Question 6

✅ Correct answer

Any one of:

• blood glucose / sugar concentration
• water content of the body
• pH
• ion / salt levels
• carbon dioxide level
• oxygen level
• blood pressure

🧠 Exam technique

This is a quick recall question. Give one clear condition only. Keep it simple.

❌ Common errors

• Repeating temperature even though the question says not to.
• Giving something vague like health or hormones.

✅ Correct answer

Body temperature is controlled to keep conditions close to the optimum for enzyme action.

This allows cells to function properly and reactions in cells to happen at the right rate.

💡 Key knowledge

• Enzymes control many reactions in cells.
• Enzymes work best at an optimum temperature.
• If body temperature changes too much, enzyme-controlled reactions do not work as well.

🧠 Exam technique

For 2-mark explain questions, make sure you include both the what and the why:

1. State that temperature is kept near the optimum.
2. Link this to enzymes / cell reactions.

❌ Common errors

• Saying only to keep us alive — too vague.
• Not mentioning enzymes at all.

📐 Calculation

1. Starting temperature = 37.0 °C
2. Temperature after 4 hours = 35.5 °C
3. Decrease in temperature = 37.0 − 35.5 = 1.5 °C
4. Mean rate per hour = 1.5 ÷ 4 = 0.375

Rate = 0.375 °C per hour

Accepted: 0.38 °C per hour or 0.4 °C per hour

🧠 Exam technique

Always read the graph carefully:

• Use the value at 0 hours and 4 hours.
• This is a mean rate, so divide by the time interval.
• Include units: °C per hour.

❌ Common calculation traps

• Using the wrong graph reading at 4 hours.
• Forgetting to divide by 4.
• Writing just 1.5 instead of the rate.
• Worrying about the minus sign — the mark scheme ignores it here, but rate of decrease is usually given as a positive value.

📐 Calculation

1. Find 5.5% of 37:
   37 × 5.5 ÷ 100 = 2.035 °C
2. Subtract this decrease from the starting temperature:
   37 − 2.035 = 34.965 °C
3. Round to 2 significant figures:
   35 °C

Body temperature = 35 °C

💡 Key knowledge

You are calculating the temperature after a decrease, not just the amount decreased.

An alternative method is:

1 − 5.5/100 = 0.945

37 × 0.945 = 34.965 °C

Then round to 35 °C.

❌ Common errors

• Giving 2.035 °C as the final answer — that is only the decrease.
• Writing 35.0 °C. This is not accepted because the question asks for 2 significant figures, and 35.0 is 3 significant figures.
• Not rounding at the end.

🧠 Exam technique

For percentage decrease questions:

1. Find the percentage amount.
2. Subtract from the original.
3. Check the required significant figures.

Examiners often see students stop halfway through the method. Full marks come from completing every step.

✅ Correct answer

Pituitary gland

💡 Key knowledge

The pituitary gland is often called the master gland because it releases hormones that act on other glands.

❌ Common errors

Do not answer thyroid gland or adrenal gland here. The question asks which gland stimulates the adrenal glands.

✅ Correct answer

The adrenal glands release adrenaline.

Adrenaline increases heart rate.

This causes faster delivery of oxygen and glucose to the muscles and brain.

More oxygen and glucose are needed for respiration.

This helps muscles to contract / shiver and release heat, increasing body temperature.

💡 Key knowledge

• Adrenaline is a hormone released by the adrenal glands.
• Respiration releases energy.
• In this context, more respiration helps increase movement and heat release.
• Shivering is repeated muscle contractions that help warm the body.

🧠 Exam technique

This is a longer explanation question, so write it as a linked chain.

A strong 5-mark answer sounds like this:

Decrease in temperature → adrenal glands release adrenaline → heart rate increases → oxygen and glucose delivered faster → respiration increases → muscles contract / shiver more → more heat released → body temperature rises

Top answers are logical and linked all the way through, not just a list of facts.

❌ Common errors

• Saying energy is made or created. The mark scheme does not accept that wording. Better: energy is released.
• Talking only about fight or flight without linking to body temperature.
• Not mentioning respiration or how heat is produced.

✅ Correct answer

When body temperature decreases, the thyroid gland releases thyroxine.

Thyroxine increases metabolic rate (or increases metabolism / respiration / reactions in cells).

As body temperature increases again, this reduces the release of thyroxine. That is negative feedback.

💡 Key knowledge

• Negative feedback means a change triggers a response that reverses that change.
• Thyroxine increases metabolic rate.
• A higher metabolic rate means more cell activity and more heat produced.

🧠 Exam technique

To secure all 3 marks, include the feedback loop:

1. Temperature falls.
2. Thyroxine is released and metabolic rate rises.
3. When temperature rises again, less thyroxine is released.

Students often lose the final mark by forgetting to explain the negative feedback part.

❌ Common errors

• Describing only what thyroxine does, but not how the response is switched down again.
• Mixing up the thyroid and pituitary glands.

🧠 How to score highly

• Use exact biology terms: homeostasis, enzyme action, adrenaline, thyroxine, metabolic rate, negative feedback.
• In calculations, show every step clearly.
• Read the command words carefully: give, calculate, explain, determine.
• For longer answers, link ideas in the right order.

❌ Biggest mark-losers

• Not using the graph correctly.
• Stopping percentage calculations too early.
• Using vague phrases instead of precise scientific language.
• Forgetting that negative feedback means the response is reduced once conditions return towards normal.