AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2019: Question 3

💡 Key focus

• Vectors are not enzymes.
• Vectors carry genes into cells.
• Herbicide-resistant crops reduce competition from weeds.
• Genetic engineering is used in medicine and agriculture.
• The Human Genome Project helps find genes linked to disease.

🧠 Exam technique

• Tick only statements that are definitely correct.
• In explain questions, write a chain: feature → effect → result.
• For “give two examples”, any two valid examples score 2 marks.

✅ Correct answers

• Vectors are used to insert genes into cells.
• Vectors are usually plasmids or viruses.

💡 Key knowledge

• A vector is a delivery system for a gene.
• Common vectors include plasmids and viruses.
• Restriction enzymes are the ones that cut DNA, not vectors.

❌ Common errors

• Thinking vectors are enzymes that “cut open” DNA.
• Ticking “isolate the required gene” — this is not the role of a vector.
• Ticking “stimulate cell division” — also not the role of a vector.

✅ Correct answer

The wheat is not affected by the herbicide, so the weeds are killed. This means the wheat has less competition for light, water, nitrates/minerals, so it can carry out more photosynthesis and make more glucose/proteins, giving a higher yield.

💡 Key knowledge

• Herbicides kill weeds.
• If weeds are removed, crop plants get more of the limiting factors needed for photosynthesis.
• More photosynthesis means more biomass, which usually means higher yield.

🧠 Exam technique

• Use cause and effect: spraying kills weeds → less competition → more crop growth.
• For full marks, include at least one resource the plant gets more of: light, water, nitrates, ions/minerals.
• It is fine to say the crop gets more glucose or proteins from increased photosynthesis.

❌ Common errors

• Saying “the wheat gets more carbon dioxide” was not credited in the mark scheme.
• Forgetting to explain why yield increases.
• Only saying “the weeds die” without linking to less competition or more photosynthesis.

✅ Any two valid examples

• Production of human insulin / medicines
• Crops resistant to diseases / pests
• Crops resistant to frost
• Crops resistant to drought
• Crops / foods with added nutrients
• Plants / crops with more fruit or higher yield
• Crops with improved taste
• Crops with improved shelf life

💡 Key knowledge

The mark scheme accepts examples such as golden rice with vitamin A or potatoes resistant to blight. These are good concrete examples if you know them.

❌ Common errors

• Repeating the same idea twice in different words.
• Giving herbicide resistance here, which the question says not to use.
• Writing descriptions instead of examples, e.g. “better crops” with no specific use.

✅ Correct answers

One good answer is: It identifies genes linked to a disease, so scientists can prevent or treat that disease better.

Another valid route is: It identifies genes causing inherited disorders, so children may be prevented from being born with the disorder by using IVF or gene therapy.

Another valid idea is: It helps trace human migration patterns and human evolution, so we understand ancient human history better.

💡 Key knowledge

• Genome mapping shows the location of genes.
• This can help find genes linked to disease such as cancer or diabetes.
• It can also help with inherited disorders and human ancestry.

🧠 Exam technique

• To reach 2 marks, avoid single vague statements like “it helps medicine”.
• Be specific: name the disease, treatment, or benefit.
• Use “so that…” or “therefore…” to show the link.

❌ Common errors

• Saying only “it tells us all the genes” without explaining the benefit.
• Writing about evolution with no link to human history or migration.
• Mixing up the Human Genome Project with genetic modification.

🧠 What top answers do

• They use correct biology terms: vector, plasmid, herbicide, yield, genome.
• They explain the chain of events, not just the final result.
• They answer exactly what the question asks and avoid extra irrelevant detail.

❌ Big mark-losing traps

• Confusing a vector with a restriction enzyme.
• Giving a list without enough valid examples.
• Writing general statements without a cause-effect link.

✅ Quick revision recap

• Vectors carry genes into cells.
• Herbicide-resistant crops reduce weed competition and improve yield.
• Genetic engineering can make useful products and improved crops.
• Genome projects help identify disease genes and understand human history.