AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), June 2025: Question 5

✅ Correct Options

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

💡 Key Knowledge

The word equation for anaerobic respiration in plant cells and yeast is:

glucose → ethanol + carbon dioxide

In yeast cells, this process is known as fermentation and is economically important in bread-making and alcohol production.

❌ Common Errors

• Selecting "Lactic acid": Lactic acid is produced during anaerobic respiration in animal muscles, not in plants or yeast.
• Selecting "Water": Water is a product of aerobic respiration, not anaerobic respiration.
• Selecting "Glucose": Glucose is the reactant, not a product.

🧠 Exam Technique

Notice the prompt explicitly says "Tick (✓) two boxes". If you tick more than two, examiners subtract incorrect marks from correct ones, reducing your score.

✅ Correct Answer

Palisade mesophyll (or palisade layer) [1 mark]

💡 Key Knowledge: Leaf Cross-Section

From top to bottom, a leaf is organised into:

1. Waxy cuticle & Upper epidermis: Transparent to let light through.
2. Palisade mesophyll (Tissue A): Column-shaped cells packed with chloroplasts near the top surface.
3. Spongy mesophyll: Rounded cells with large air spaces for gas exchange.
4. Lower epidermis: Contains stomata guarded by guard cells.

❌ Common Errors

Confusing tissues with cells or organelles. Saying just "chloroplast" or "epidermis" receives 0 marks. The mark scheme notes: ignore reference to cells, but the correct tissue name is required.

🧠 Exam Technique

Look at the orientation of the cells in the diagram: Tissue A consists of regularly arranged, elongated columnar cells packed closely at the top of the leaf slice.

✅ Correct Answer (Mark Scheme Breakdown)

• Feature: (Contains) many chloroplasts / a lot of chlorophyll / cells are closely packed together [1 mark]
• Function/Reason: To absorb more light for photosynthesis [1 mark]

🧠 Exam Technique: Feature + Reason

Whenever an exam asks you to explain an adaptation, always structure your answer in two parts:

1. Structural feature: What does it look like / contain?
2. Functional benefit: Why does that feature help the plant?

❌ Common Errors

• Saying only "it carries out photosynthesis" without stating the structural adaptation (chloroplasts / chlorophyll).
• Saying "absorbs sunlight" without linking it to the process of photosynthesis.

💡 Top Tip

Chloroplasts are the organelles; chlorophyll is the green pigment inside them that absorbs light. Both terms are accepted by the mark scheme.

💡 The Transpiration Stream

Think of water movement as a continuous unbroken column pulled by evaporation:

Soil → Root hair → Xylem → Mesophyll → Stomata → Air

Evaporation from leaves creates tension (transpiration pull), drawing water up through xylem vessels.

❌ Critical Examiner Traps

• Xylem vs Phloem: The mark scheme explicitly states: do NOT accept water travels up through the phloem . Phloem transports dissolved sugars (translocation).
• Transpiration vs Translocation: The mark scheme explicitly states: do NOT accept translocation for water loss.
• Vague water loss: Stating water is "lost from the plant" is not enough; you must specify stomata and evaporation/transpiration.

🧠 Exam Strategy for 5-Mark Process Questions

• Follow chronological order from the start point (soil) to the end point (atmosphere).
• Always name both the tissue/structure (root hair cell, xylem, stomata) and the transport mechanism (osmosis, evaporation, transpiration).
• Safety net mark: If a student fails to score other marks, writing "transpiration stream" awards 1 consolatory mark.

📐 Keyword Checklist for Full Marks

• Root hair cells (absorption from soil)
• Osmosis (movement across cell membranes)
• Xylem (transport up stem to leaf)
• Spongy mesophyll (movement inside leaf)
• Stomata (exit pores)
• Evaporation / Transpiration (loss to atmosphere)