AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2022: Question 2

✅ Correct answer

gene → chromosome → nucleus → cell

1 mark for putting all four in the correct order.

💡 Key knowledge

• A gene is a section of DNA on a chromosome.
• A chromosome contains many genes.
• The nucleus contains chromosomes.
• The cell contains a nucleus.

🧠 Exam technique

• Read the size order carefully: smallest to largest.
• For 1 mark, the order must be exact.
• Write the words clearly in a line, not as a list of random facts.

❌ Common errors

• Putting cell before nucleus.
• Mixing up gene and chromosome.
• Writing the right words but in the wrong order.

✅ Correct answer

Differentiation

The mark scheme allows only this word. “Specialisation” is not needed.

💡 Key knowledge

• Embryo cells change to become different specialised cells.
• Examples in the figure: red blood cells, muscle cells, and nerve cells.

🧠 Exam technique

• Use the exact biological term from the specification.
• If a question says “Name the process”, one word is often enough.

❌ Common errors

• Writing specialisation instead of differentiation.
• Describing the cells without naming the process.

📐 Calculations / reasoning

Answer: 4

1. Start with 1 fertilised egg cell.
2. After 1 division → 2 cells
3. After 2 divisions → 4 cells
4. After 3 divisions → 8 cells
5. After 4 divisions → 16 cells
6. After 5 divisions → 32 cells

So to make 18 cells, 4 divisions are needed.

The mark scheme allows 15 too, but the expected answer is 4 because 2⁴ = 16 and 2⁵ = 32.

🧠 Exam technique

• Remember that each mitosis doubles the number of cells.
• Check whether the question asks for the number of cells or the number of divisions.

❌ Common errors

• Answering 18 because you copied the number of cells.
• Using subtraction instead of doubling.
• Forgetting that each division doubles the cell count.

💡 Key knowledge

Embryos grow by repeated cell division. One cell becomes two, then four, then eight, and so on.

✅ Correct answer

46

Allow 23 pairs of chromosomes.

💡 Key knowledge

• Humans have 23 pairs of chromosomes in body cells.
• 23 pairs = 46 chromosomes.
• Mitosis produces cells with the same number of chromosomes as the original cell.

🧠 Exam technique

• Know both ways to write it: 46 or 23 pairs.
• If the question asks “How many chromosomes”, the number alone is usually enough.

❌ Common errors

• Answering 23 without saying “pairs”.
• Thinking chromosome number halves during mitosis.

✅ Correct answers

Stage 1: cell grows, more sub-cellular structures are made, DNA replicates, chromosomes duplicate.

Stage 2: chromosomes are pulled to opposite ends of the cell, or two nuclei form.

Stage 3: the cytoplasm or cell membrane divides, forming two identical cells.

1 mark for one correct change in each stage.

💡 Key knowledge

• Stage 1 = growth and DNA copying.
• Stage 2 = mitosis, where chromosomes separate.
• Stage 3 = cytokinesis, where the cell splits into two.

🧠 Exam technique

• Give one clear change for each stage.
• Short, precise statements score best.
• Use scientific vocabulary: replicate, chromosomes, nuclei, cytoplasm.

❌ Common errors

• Saying “mitosis occurs” for Stage 2 when the question asks for a change.
• Writing the same idea for more than one stage.
• Forgetting that Stage 1 includes DNA replication.

✅ What a top-level answer includes

A strong answer compares both height and rate of growth using data from the graph.

• Boys are slightly taller at birth.
• Up to about age 11, boys are slightly taller, but the difference is small.
• At about age 11, girls and boys are about the same height.
• Between about 11 and 14, girls are taller and grow faster than boys.
• At about age 14, they are about the same height again.
• After 14, boys become taller than girls and keep growing for longer.

💡 Key knowledge

• Girls have an earlier growth spurt.
• Boys grow for longer and end up taller.
• The graph shows rate of growth by the steepness of the line.

🧠 Exam technique

• To get 4–6 marks, make several correct comparisons.
• Use phrases like “whereas”, “compared with”, and “between ages…”.
• Use the graph data to support your points, for example:
  • around age 10–11 the lines are close together
  • girls rise more steeply between 11 and 14
  • boys continue rising after girls level off

❌ Common errors

• Only describing one line.
• Saying “girls are taller” without saying when.
• Not mentioning the growth spurt or the rate of growth.
• Giving vague answers like “boys grow more” with no data.

✅ Correct answer

Repair of tissues or replacement of cells

Either answer gains the mark.

💡 Key knowledge

• Mitosis is used for repair after damage.
• Mitosis replaces worn out or damaged cells.
• In fully grown animals, mitosis is not mainly for growth anymore.

🧠 Exam technique

• Give one clear use of mitosis.
• If you write a longer answer, keep it focused on animals that are already fully grown.

❌ Common errors

• Saying growth for fully grown animals.
• Writing “repair of organs” instead of the simpler accepted wording.
• Giving a general description of mitosis without its purpose.

💡 What distinguished top answers

• They used the exact required term: differentiation.
• They gave the chromosome number as 46 or 23 pairs.
• For the graph question, they made several comparisons and included data.
• They described the cell cycle in the correct order: growth → mitosis → division.

❌ Where students lost marks

• Mixing up the order of gene, chromosome, nucleus, and cell.
• Using vague growth statements without comparing boys and girls directly.
• Not realising that mitosis makes identical cells with the same number of chromosomes.