AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2022: Question 1

✅ Correct answer

Aerobic respiration

💡 Key knowledge

• Aerobic respiration uses oxygen and produces carbon dioxide and water.
• Photosynthesis uses water, but it does not produce water.
• Anaerobic respiration does not produce water as the main product.

🧠 Exam technique

• For tick-box questions, read every option carefully before choosing.
• Look for the word produces — this is asking for a product of the reaction.

❌ Common errors

• Ticking photosynthesis because it involves water.
• Confusing aerobic and anaerobic respiration.

✅ Correct answers

1. Evaporation
2. Condensation
3. Precipitation
4. Draining / drainage
5. Transpiration

💡 Key knowledge

• Evaporation = liquid water changes into water vapour because of the Sun’s heat.
• Condensation = water vapour cools and forms tiny droplets in clouds.
• Precipitation = water falls from clouds as rain, snow, etc.
• Drainage = water flows over or through land into rivers, lakes, or seas.
• Transpiration = water vapour leaves plant leaves through stomata.

🧠 Exam technique

• Match the arrow direction to the process shown in the diagram.
• Use the exact scientific term, but some alternative wording is allowed.
• For example, rainfall is allowed for precipitation, and run-off is allowed for drainage.

❌ Common errors

• Writing respiration instead of transpiration.
• Mixing up evaporation and condensation.
• Forgetting that water can move underground as drainage / groundwater flow.

📐 Calculations — step by step

1. Find 4.5% of 6 000 000 000.
2. Convert 4.5% to a decimal: 4.5 ÷ 100 = 0.045
3. Multiply: 6 000 000 000 × 0.045 = 270 000 000
4. Write in standard form: 2.7 × 10⁸

Answer: 2.7 × 10⁸

💡 Key knowledge

• Standard form is written as a × 10ⁿ , where 1 ≤ a < 10 .
• Percent means “out of 100”.
• Keep track of large numbers carefully.

🧠 Exam technique

• Show the percentage conversion and the multiplication to gain method marks.
• Even if your first answer is not exact, you can still gain the final mark if your standard form is correct.
• Always check the power of 10 and that the number is between 1 and 10.

❌ Common calculation traps

• Using 4.5 instead of 0.045.
• Forgetting to convert the final answer into standard form.
• Writing 27 × 10⁷ or 0.27 × 10⁹ — these are not standard form.

✅ Correct answers

• Climate change has increased the area of deserts.
• More water is used to grow crops.

💡 Key knowledge

• Desert areas increase when climates become hotter and drier.
• More farming means more freshwater is needed for irrigation.
• Water demand rises as populations grow.

🧠 Exam technique

• Only tick statements that directly explain water shortage.
• Think: does the statement reduce supply or increase demand?

❌ Common errors

• Ticking Each person drinks less water — this does not explain global shortage well.
• Ticking Sea levels have risen... — this may be true, but it does not directly explain more people having shortage.
• Ticking Some countries have built de-salting factories — this is a solution, not a cause.

✅ Correct answer

Fallen leaves are decayed / decomposed by microorganisms such as decomposers. The microorganisms respire, releasing carbon dioxide. The carbon dioxide is then used in photosynthesis for new plant growth.

💡 Key knowledge

• Decomposers break down dead organic matter.
• As they respire, they release carbon dioxide into the atmosphere or soil air.
• Plants take in carbon dioxide for photosynthesis to make new biomass.

🧠 Exam technique

• To get full marks, give the process in the correct order.
• Use the key words: decay, respiration, carbon dioxide, photosynthesis.
• The mark scheme rewards the chain of explanation, not just one fact.

❌ Common errors

• Saying carbon is “absorbed by roots” — this is not the correct route for carbon dioxide.
• Leaving out respiration, which is essential to explain how CO₂ is released.
• Writing only “the leaves rot” without explaining what happens to the carbon.

✅ Correct answer

Nitrates are released into the soil.

💡 Key knowledge

• As leaves decay, decomposers break them down.
• This releases useful mineral ions, including nitrates, into the soil.
• Plants need nitrates to make proteins and grow well.

🧠 Exam technique

• Look for the option that directly benefits plant growth.
• In GCSE Biology, nitrates in soil is a common answer linked to decomposition.

❌ Common errors

• Choosing energy is released for living plants — this is too vague and not the expected answer.
• Choosing oxygen is supplied to root cells — roots mainly need water and mineral ions, not this as the key benefit.

💡 Top-level responses

• Used the exact scientific terms from the water cycle.
• Linked decomposers to respiration and carbon dioxide release.
• Showed the calculation clearly, then wrote the answer in standard form.

❌ Where students lost marks

• Mixing up condensation and evaporation.
• Not giving the full carbon cycle explanation in 01.5.
• Forgetting to convert the final number into standard form in 01.3.

🧠 Quick revision summary

• Water cycle: evaporation → condensation → precipitation → drainage → transpiration
• Carbon cycle: decomposition + respiration releases CO₂ → photosynthesis uses CO₂
• Calculations: percentage of a number = multiply by decimal