AQA GCSE Biology Biology Paper 1 (Higher), June 2023: Question 5

✅ Correct Answer

Vector

💡 Key Knowledge

A vector is an organism that carries and transmits an infectious pathogen into another living organism without being the primary disease cause itself (e.g. female Anopheles mosquitos passing the malaria protist).

✅ Any Three Differences (Protist vs Prokaryote)

• The protist has mitochondria (prokaryotes do not).
• The protist has a nucleus / its genetic material is inside a nucleus (not free in the cytoplasm).
• The protist does not have a single circular loop of DNA.
• The protist does not have plasmids.
• The protist does not have a cell wall (or slime capsule).

🧠 Exam Technique

Read instructions carefully: "Do not refer to size in your answer." Any mention of size or magnification scores zero.

Always state which cell you are referring to, or write direct comparisons using clear comparative language (e.g., "The protist has a nucleus, whereas prokaryotes have free DNA").

❌ Common Errors

• Writing "eukaryotes do not have a cell wall" — plant and fungal cells are eukaryotic and do have cell walls! You must refer specifically to the protist shown.
• Vague statements like "different genetic material" without specifying the nucleus, loop, or plasmids.
• Mentioning ribosomes (both cell types have ribosomes).

✅ Model Answer

• Fewer red blood cells mean less oxygen carried in the blood (or delivered to body cells). [1 mark]
• Therefore, less energy is released by (aerobic) respiration. [1 mark]

💡 The Respiration Link

Red blood cells contain haemoglobin which transports O₂. Oxygen is essential for aerobic respiration:

Glucose + Oxygen → Carbon Dioxide + Water (+ Energy Released)

Less oxygen directly lowers the rate of aerobic respiration, depriving muscle and nerve cells of available energy, leading to extreme fatigue.

❌ The #1 Biological Error

NEVER say "less energy is produced / created / made". Energy cannot be created or destroyed (First Law of Thermodynamics). Examiners will immediately reject "energy produced". Always say energy released or transferred.

Do not write "no oxygen carried" — there is still oxygen, just less of it.

🧠 Exam Technique

Make sure your answers across a row are directly paired opposites. For example, don't contrast "produces variation" with "is faster" — keep them aligned by category (e.g. genetics with genetics, speed with speed).

❌ Common Errors

• Writing "clones" without explaining that the offspring are genetically identical.
• Confusing mitosis (asexual reproduction/growth) with meiosis (gamete formation for sexual reproduction).

✅ Correct Answer

DNA replication cannot occur (or DNA cannot be copied / duplicated / doubled).

💡 Scientific Reason

DNA bases (A, T, C, G) are the essential building blocks needed to synthesise new complementary strands of DNA. Without free bases, the cell cannot replicate its genetic material during interphase, preventing the chromosomes from duplicating before mitosis begins.

❌ Examiner Warning

Writing simply "it cannot make DNA" is too vague and will not gain credit. You must use terms like replication, copying, duplicating, or doubling of DNA.

✅ 3-Step Model Answer

1. Chromosome Separation: One set of chromosomes is pulled to each end (pole) of the cell. [1 mark]
2. Nuclear Division: The nucleus divides (or two new nuclei form). [1 mark]
3. Cell Division (Cytokinesis): The cytoplasm and cell membrane divide to form two identical cells. [1 mark]

🧠 Chronological Precision

Mitosis descriptions must follow the proper sequence:

Chromosomes pull apart → Nucleus divides → Cytoplasm/membrane divides.

Notice the question starts after DNA replication has already taken place in interphase.

❌ Common Errors

• Saying "half the chromosomes are pulled to each end" — this is incorrect (that happens in meiosis). In mitosis, a full set / chromatids go to each pole.
• Forgetting to mention the division of the nucleus as a distinct stage before cytoplasmic division.

✅ Model Answer (2 Distinct Points)

• Overall effect: Having disorder S reduces the incidence of malaria (it provides protection / lowers risk). [1 mark]
• Age trend: As age increases, the incidence decreases / protection increases up to age 10, and then increases / protection decreases after age 10. [1 mark]

❌ Common Errors

• Only describing one part of the trend (e.g. "it goes down" while ignoring that it rises back up after age 10).
• Failing to recognise that values below 100% mean lower incidence compared to the baseline group.
• Not stating the turning point at age 10 (or 45%) clearly.