AQA GCSE Biology Biology Paper 1 (Higher), June 2022: Question 4

✅ Correct Answer

💡 Key Knowledge

• Physical defences: Structural barriers that physically prevent pathogens or pests from entering (e.g. waxy cuticle, cellulose cell walls, layers of dead cells/bark).
• Chemical defences: Substances produced by the plant that poison, deter, or kill pests and pathogens (e.g. antibacterial chemicals, poisons).

❌ Common Errors

Confusing bark falling off with a chemical process. The bark is a dead outer protective layer (physical); shed layers take pathogens away physically.

🧠 Exam Technique

Follow the prompt closely: "Tick (✓) one box in each row." Never tick both columns in the same row, or that row is marked wrong.

✅ Correct Answer

Any one of the following linked explanations:

• Predators / animals are tricked or deceived (by its appearance/colouring) and avoid eating it / attack it less.
• Predators believe it can sting (like a hornet) and are deterred from attacking it.

🧠 Exam Technique

Notice the two parts required for full credit: perception (predators think it's a hornet / dangerous) + outcome (so they don't eat it). Simply writing "it looks like a hornet" is not enough on its own to explain how it helps it survive.

🧠 Level of Response Mark Scheme

• Level 3 (5–6 marks): Multiple relevant causes identified and detailed with clear logical links (Cause → Mechanism → Effect on Tree).
• Level 2 (3–4 marks): Relevant points identified with attempted logical links, though some explanations may be incomplete.
• Level 1 (1–2 marks): Isolated points stated simply with no logical linkage.

💡 Indicative Science Content to Link

• Water absorption: Less water absorbed → reduced photosynthesis → less glucose for cellular respiration / energy release; cells lose turgidity (wilting).
• Nitrate ions: Fewer nitrates absorbed → fewer amino acids formed → less protein synthesis for growth and repair.
• Magnesium ions: Less magnesium absorbed → less chlorophyll produced → lower rate of photosynthesis.
• Vascular damage: Damaged xylem (reduced transport of water & minerals up to leaves) or damaged phloem (less translocation of sugars to roots for respiration).
• Anchorage: Less root stability → tree can fall over.

✅ Model 6-Mark Answer

"Damaged roots absorb less water from the soil. Since water is a reactant in photosynthesis, less water reduces the rate of photosynthesis, meaning less glucose is produced for respiration to release energy for growth. Furthermore, less water causes cells to lose turgor pressure, leading to wilting.

Additionally, damaged roots take up fewer mineral ions. A deficiency in nitrates means the tree cannot synthesise enough amino acids to make proteins needed for growth and repair. A lack of magnesium ions prevents the plant from making chlorophyll; without chlorophyll, light cannot be effectively absorbed, further decreasing photosynthesis. Finally, if the phloem or xylem vessels in the roots are destroyed, transport of sugars and water throughout the tree fails, eventually causing the tree to die."

❌ Common Errors & Lost Marks

• Saying "energy is produced": Always state "energy is released during respiration."
• Vague mineral references: Saying "no nutrients" without naming specific ions (nitrates or magnesium) and their specific functions.
• Unlinked statements: Just listing "less water, less minerals, tree falls" without connecting them to cellular processes like photosynthesis and protein synthesis.

✅ Correct Answer (4 Marks)

1. Genetic material / DNA / chromosomes are doubled / replicated / copied. [1]
2. The (replicated) chromosomes are pulled / separated apart to opposite ends of the cell. [1]
3. The cytoplasm / cell membrane divides (or two new nuclei form) to form two cells. [1]
4. Each new cell contains an identical set of chromosomes / DNA. [1]

💡 Key Knowledge

Remember the 3 key phases of the cell cycle:

• Interphase: Cell grows, organelles increase in number, DNA replicates.
• Mitosis: One set of chromosomes pulled to each pole of the cell; nucleus divides.
• Cytokinesis: Cytoplasm and cell membranes divide to yield two daughter cells.

❌ Common Errors

• Confusing mitosis (produces 2 genetically identical diploid cells) with meiosis (produces 4 genetically diverse haploid gametes).
• Forgetting to mention that the DNA / chromosomes must replicate first before splitting.

🧠 Exam Technique

Treat 4-mark "describe a process" questions chronologically: Start (DNA copies) → Middle (chromosomes pull apart) → End (cytoplasm divides) → Result (genetically identical).

✅ Correct Answer

differentiation [1 mark]

❌ Common Errors

Writing "specialisation". The question asks: "Name the process by which these stem cells then form specialised cells." Using the root word from the question (specialisation) is ignored by the mark scheme!

💡 Definition Recall

Differentiation is the process by which an unspecialised cell changes to become specialised for a specific structure and function.