AQA GCSE Biology Biology Paper 1 (Foundation), June 2025: Question 5

✅ Mark Scheme Matches

• Flexible leaves → Stop seagrass breaking in strong water currents [1 mark]
• Long, deep roots → Keep seagrass in one place on the sea floor [1 mark]

❌ Common Errors & Pitfalls

• Drawing multiple lines from one box: The question states "Draw one line from each adaptation". Drawing two lines from one box forfeits that mark.
• Selecting "Poison animals...": This is a chemical adaptation, not related to roots or flexible leaves.

✅ Correct Answer

Lungs [1 mark]

🧠 Exam Technique: Biological Hierarchy

Read the question carefully: it asks for organs (plural/organ level).

Examiner Guidance: The mark scheme explicitly states "ignore alveoli". While alveoli are the specific tissue structures/air sacs where diffusion occurs, the organ is the lung.

✅ Correct Selections (Tick Two)

• ☑ Gills have a large surface area [1 mark]
• ☑ Gills have thin walls [1 mark]

💡 Fick's Law of Diffusion

Efficient exchange surfaces always share key features:

• Large surface area: More particles can exchange simultaneously.
• Thin walls (short diffusion distance): Rapid movement between water/air and blood.
• Rich blood supply: Gills actually have many capillaries (not few) to maintain a steep concentration gradient.

📐 Step-by-Step Calculation

1. Identify values from Table 4:
   Resting = 484 | Swimming = 944
2. Set up the ratio (swimming ÷ resting):
   944 / 484 [1 mark]
3. Calculate intermediate value:
   1.950413... [1 mark]
4. Round to nearest whole number:
   2 [1 mark]

❌ Common Mistakes to Avoid

• Subtracting instead of dividing: Calculating 944 - 484 = 460 scores 0 marks. "How many times greater" indicates division.
• Dividing upside down: 484 / 944 = 0.51 .
• Failing to round: Leaving your answer as 1.95 loses the final mark because the prompt specifies "nearest whole number".

[1 mark] for oxygen on LHS • [1 mark] for carbon dioxide on RHS • [1 mark] for water on RHS (RHS products accepted in either order). Chemical formulae (O₂, CO₂, H₂O) are also credited.

💡 Chemical vs Word Equation

Aerobic respiration breaks down glucose using oxygen to release cellular energy (ATP), producing carbon dioxide and water as waste products:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

❌ Distractor Words

magnesium and nitrogen are distractors provided in the box to test whether students confuse atmospheric gases or minerals with biological respiration.

✅ 3-Step Scoring Chain

1. The stingray is moving / swimming [1 mark]
2. So muscles contract [1 mark]
3. Which needs / requires energy from respiration [1 mark]

❌ The "Energy Created" Trap

This is one of the most penalised phrases in GCSE Biology:

• NEVER write: "energy is produced", "energy is created", or "energy is made". Energy cannot be created (Law of Conservation of Energy).
• Do NOT write: "energy released for respiration". Respiration releases energy for muscle contraction, not the other way around.
• ALWAYS write: "energy is released by respiration for muscle contraction" or "muscles need energy supplied by respiration".

✅ Correct Products (Tick Two)

• ☑ Carbon dioxide [1 mark]
• ☑ Ethanol [1 mark]

💡 Animal vs Plant Anaerobic Respiration

Organism	Word Equation
Animals	glucose → lactic acid
Plants & Yeast	glucose → ethanol + carbon dioxide

Note: In yeast, this process is also known as fermentation and is used in bread-making and brewing.