AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2020: Question 1

✅ Correct answer

Tick the middle diagram. It shows the double helix shape of DNA.

💡 Key knowledge

• DNA is shaped like a twisted ladder.
• This structure is called a double helix.
• It consists of two strands coiled around each other.

🧠 Exam technique

For a 1-mark image question, choose the diagram that matches the standard textbook model of DNA. You do not need extra explanation unless asked.

❌ Common errors

• Picking the wrong shape because it “looks scientific”.
• Confusing DNA with a cell, chromosome, or molecule diagram that is not the double helix.

✅ Correct answer

DNA is made of two strands twisted/coiled around each other to form a double helix.

💡 Key knowledge

• Accept: two strands, twisted, coiled, or spiralled.
• You could also mention DNA is a long polymer.
• Examiner note: references to cross-links between the two strands are allowed.

🧠 Exam technique

For 1 mark, one accurate statement is enough. The safest answer is to say “two strands twisted into a double helix”.

❌ Common errors

• Writing only “a helix” without saying it has two strands.
• Confusing DNA structure with the idea of genes or chromosomes.
• Giving very vague answers like “it is shaped like a ladder” without showing twisting.

✅ Correct answers

A gene codes for a particular sequence of amino acids .

This sequence makes a specific protein .

💡 Key knowledge

• Genes are sections of DNA that contain instructions.
• The order is important: DNA → amino acids → protein.
• Accept polypeptide for protein.

🧠 Exam technique

Marks are awarded in the correct order. Even if you know the ideas, the answer must fit each blank properly.

❌ Common errors

• Writing “protein” in the first blank.
• Putting the words in the wrong order.
• Saying “a gene codes for a trait” instead of the required biological sequence.

✅ Correct answer

The genome is all the genetic material of an organism.

💡 Key knowledge

• You may also see: all the DNA or all the genes.
• It refers to the complete set of genetic information.

🧠 Exam technique

Use the exact idea of whole genetic material. This is a definition question, so keep it precise.

❌ Common errors

• Saying chromosomes alone is enough.
• Giving a description of one gene instead of the whole organism’s genetic material.

✅ Correct answer

Tracing how Aboriginal people spread across Australia

💡 Key knowledge

• Genome information can be used to study ancestry and population movement.
• This question expects the example from the mark scheme, not a random use of genome data.

🧠 Exam technique

When a question asks for one correct example, choose the option that directly uses DNA/genome comparisons for human history.

❌ Common errors

• Choosing an answer that sounds scientific but is unrelated to the genome.
• Thinking the human genome is mainly used for food, weather, or climate questions.

✅ Correct answer

Variation

💡 Key knowledge

• Variation means individuals in a species are not all exactly the same.
• Differences can be inherited or caused by the environment.

🧠 Exam technique

This is a straight recall term. Give the exact scientific word.

❌ Common errors

• Writing a full explanation instead of the key term.
• Confusing variation with evolution or adaptation.

✅ Correct answer

Snail P may have a stronger/larger shell, so it is more likely to survive and breed.

Alternatively, it may be better camouflaged, so it is less likely to be eaten and will breed more.

💡 Key knowledge

• Useful traits help an organism survive.
• Organisms that survive are more likely to reproduce.
• They pass the helpful genes to their offspring.

🧠 Exam technique

To get both marks, link the feature of snail P to survival and then to breeding/passing on genes. This is the full explanation the examiner wants.

❌ Common errors

• Only describing snail P as different, without explaining why it becomes more common.
• Missing the key idea of survive → reproduce → pass on genes.
• Using vague language like “it is better” without saying why that helps.

💡 What the examiner rewards

• Accurate key terms: double helix, amino acids, protein, genome, variation.
• Clear links in explanations, especially in the snail question.
• Using the exact order required in fill-in-the-blank questions.

🧠 Best revision takeaway

Learn the simple chain:

DNA → gene → amino acid sequence → protein → characteristic

And for evolution questions:

variation → survival advantage → breeding → genes passed on