AQA GCSE Biology Biology Paper 2 (Higher), June 2024: Question 9

✅ Model 6-Mark Answer (Level 3)

"Glyphosate is a herbicide that kills weeds but does not harm the GM soya beans because they carry a gene for resistance.

Because weeds are eliminated, there is significantly less competition between weeds and soya plants for light, water, space, and mineral ions.

As a result, soya bean plants absorb more light and water, which increases the rate of photosynthesis, producing more glucose.

This extra glucose is used in respiration to release energy for growth, and converted into cellulose for strong cell walls. Soya plants also take up more nitrates from the soil to combine with glucose derivatives to produce amino acids and proteins, and more magnesium to make chlorophyll.

More starch, protein, and oils are stored in the developing seeds, directly increasing the total crop yield."

🧠 Level Breakdown & Examiner Insight

• Level 3 (5–6 marks): Must give reasons in detail and logically link weed removal → reduced competition → specific resource uptake → named metabolic uses for growth/yield.
• Level 2 (3–4 marks): Mentions killing weeds and less competition for light/water, but fails to fully explain how this results in increased yield (misses glucose uses/protein synthesis).
• Level 1 (1–2 marks): Isolated statements such as "weeds die so soya grows bigger". No logical link.
• Top Tip: Always name the specific mineral ions and their exact roles: nitrates for proteins, magnesium for chlorophyll.

❌ Common Errors to Avoid

• Vague "nutrients": Simply stating "less competition for nutrients" earns limited credit. Say mineral ions or name them (nitrates, magnesium, phosphates).
• Stopping at photosynthesis: Many students write "more photosynthesis happens" and stop there. To get Level 3, explain what happens to the glucose (respiration, cellulose, storage as starch/protein in beans).
• Confusing fertiliser and herbicide: Glyphosate is an weedkiller (herbicide), not a plant food or fertiliser. It does not provide nutrients to the crop.

📐 Quick Checklist: Did You Include...?

• [   ] Resistant soya survives; weeds die.
• [   ] Name 2+ competition factors: light, water, minerals, space.
• [   ] Photosynthesis → glucose.
• [   ] Glucose → cellulose (walls) or respiration (energy).
• [   ] Nitrates → amino acids / proteins for growth.

✅ Acceptable Answers (Any TWO for 1 mark each)

• Unknown health effects: Possible long-term health effects or unknown side effects on humans/animals when consumed.
• Gene transfer to wild plants: The resistance gene/allele could be transferred to wild relatives or weeds via cross-pollination (creating "superweeds").
• Loss of biodiversity: Spraying broad-spectrum herbicide kills all wild field plants, reducing food sources and habitats for insects and birds.
• Increased costs: High cost of buying patented GM seeds each year for farmers (or increased costs passed to consumers).
• Altered taste / characteristics: GM food products may have altered flavor or texture.

❌ Disallowed Points & Traps

• Ethics & Religion: The question explicitly says: "Do not refer to ethical concerns or religion". Mentioning "playing God" or "morally wrong" scores 0 marks.
• Unqualified "cost": Writing just "it costs a lot" or "expensive" is ignored. You must specify: increased cost of seed for farmers or cost to consumers.
• Vague danger: "It is dangerous" or "it causes cancer" without qualified scientific context receives no credit.