AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2024: Question 5

✅ Correct answers

carbon dioxide + water light → glucose + oxygen

Accept H₂O for water and O₂ for oxygen.

💡 Key knowledge

• Photosynthesis needs carbon dioxide and water.
• It happens in the presence of light.
• The products are glucose and oxygen.

🧠 Exam technique

• Use the word equation exactly as learned.
• Make sure you put the reactant on the left and the product on the right.
• This is 1 mark for each missing substance.

❌ Common errors

• Writing oxygen as a reactant instead of a product.
• Confusing water with ethanol or nitrogen.
• Leaving out the light arrow or putting light in the wrong place.

✅ Correct answer

C₆H₁₂O₆

💡 Key knowledge

Glucose is a simple sugar made in photosynthesis. Its formula must be memorised.

🧠 Exam technique

In a multiple-choice question, tick only the exact formula C₆H₁₂O₆.

❌ Common errors

• Choosing CO₂, H₂O, or O₂ instead of glucose.
• Misspelling the formula or changing the numbers.

✅ Correct answers

Any two of:

• used in respiration
• converted to / stored as starch
• used to make / store fat or oil
• used to make cellulose
• used to make amino acids or protein

💡 Key knowledge

Plants do not just “use glucose for growth” in a vague way. They use it for specific processes:

• Respiration releases energy.
• Starch is a storage molecule.
• Cellulose makes cell walls.
• Amino acids/protein are needed to build tissues.

🧠 Exam technique

• Give two different uses for full marks.
• Short answers are fine if they are exact.
• If you write “used for growth”, that is too vague unless explained with a specific product like cellulose or protein.

❌ Common errors

• Saying glucose is “used to make energy” without mentioning respiration.
• Writing “used for growth” as a standalone answer.
• Confusing starch with cellulose.

✅ Correct answer

Burning the logs releases carbon dioxide into greenhouse B and also raises the temperature. This increases the rate of photosynthesis, so more glucose is made. More glucose can then be used to make protein and cellulose, so the plants grow faster.

💡 Key knowledge

• Photosynthesis rate increases if conditions improve.
• Extra carbon dioxide is a reactant, so more is available for photosynthesis.
• Higher temperature can increase enzyme activity up to the optimum.
• More photosynthesis means more glucose production.
• Glucose is used to make materials needed for growth, especially cellulose and protein.

🧠 Exam technique

To get all 4 marks, build a chain of explanation:

1. Burning logs → more carbon dioxide / higher temperature
2. More carbon dioxide / warmer conditions → faster photosynthesis
3. Faster photosynthesis → more glucose made
4. More glucose → more protein/cellulose made → faster growth

❌ Common errors

• Saying “the fire gives plants energy” — plants do not use heat from the fire as food.
• Writing only “more carbon dioxide” without explaining the result.
• Stopping at “more photosynthesis” without linking to glucose and growth.
• Using vague phrasing like “they grow better” with no biology explanation.

💡 Core facts

• carbon dioxide + water → glucose + oxygen
• glucose formula = C₆H₁₂O₆
• glucose can be used for respiration, starch, cellulose, fat/oil, protein

🧠 Best exam habit

When asked to explain plant growth, always link the idea to photosynthesis, then glucose, then the substance needed for growth.