AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2018: Question 6

✅ Correct answers

• meristem(s)
• tip of shoot
• tip of root

1 mark for any one correct location.

💡 Key knowledge

• Plant stem cells are found in meristems.
• Meristems are regions of active growth at the shoot tip and root tip.

🧠 Exam technique

• Give one clear location only.
• If you write “stem” or “embryo”, this does not gain the mark for plant stem cells.

❌ Common errors

• Writing just “stem cells” instead of where they are found.
• Confusing plant stem cells with animal stem cells.
• Giving a general plant part without a specific location.

✅ Correct answer

To produce large numbers of identical plants

1 mark for this exact idea.

💡 Key knowledge

• Plant stem cells can be cloned to make many genetically identical plants.
• This is useful for agriculture because a successful crop plant can be copied quickly.

🧠 Exam technique

• The key phrase is large numbers and identical plants.
• “To create genetically modified crops” is not the answer here.

❌ Common errors

• Choosing “to increase variation in plants” — cloning does the opposite.
• Thinking stem cells are mainly used to make new species.

📐 Calculations — step by step

1. 1 picogram = 10⁻¹² grams
2. 6 picograms = 6 × 10⁻¹² grams

Mass = 6 × 10⁻¹² g

1 mark for the correct conversion in standard form.

💡 Key knowledge

• “Pico” means 10⁻¹².
• Standard form should be written clearly as a × 10ⁿ .

🧠 Exam technique

• Include the unit: grams, not just a number.
• Use the correct power of 10.

❌ Common errors

• Writing 6 × 10⁻¹² mg or another unit.
• Forgetting that pico = 10⁻¹².
• Writing the answer in ordinary form when the question asks for standard form.

📐 Calculations — step by step

1. The mitosis sector is 28°.
2. A full circle is 360°.
3. Fraction of cycle in mitosis = 28/360.
4. Time in mitosis = 28/360 × 15
5. = 1.1666... hours
6. Rounded to 3 significant figures = 1.17 hours

Time spent in mitosis = 1.17 hours

2 marks: one for the correct method, one for the correct answer.

💡 Key knowledge

• Pie charts show proportion of time.
• Use the angle to find the fraction of the full cycle.

🧠 Exam technique

• Set up the ratio correctly: 28/360 × 15
• Give the answer with units.
• Round to 3 significant figures because the question asks for it.

❌ Common errors

• Using 28/15 or 15/28 instead of part ÷ whole × total.
• Forgetting to multiply by the total cycle time.
• Giving an answer without units, or rounding too early.
• Writing 1 hour 10 minutes without clear units if not asked that way.

✅ Correct answers: the marking points

• Stage 1: cell growth or increase in number of organelles.
• Stage 1: DNA replicates / doubles / two copies of each chromosome form.
• Stage 2 (mitosis): one set of chromosomes moves to each end of the cell.
• Stage 2: nucleus divides.
• Stage 3: cytoplasm / cell membrane divides to form two genetically identical cells.

Up to 5 marks available. Correct sequence matters for full credit.

💡 Key knowledge

• The cell cycle is: growth → DNA replication → mitosis → cell division.
• Mitosis produces genetically identical daughter cells.
• The stage labels in the diagram help you match each process to the correct stage.

🧠 Exam technique

• Use the three stages in order.
• Names like “interphase” are not needed here; the mark scheme wants the described events.
• Marks can be gained from a labelled diagram if you cannot write lots of words.
• To get the top marks, include the idea that the cells formed are identical.

❌ Common errors

• Mixing up the order of DNA replication and mitosis.
• Saying only “the cell divides” without describing what happens to the nucleus or chromosomes.
• Forgetting to mention that the final two cells are identical.
• Using stage numbers wrongly or not referring to the stages at all.

✅ Correct answers — advantages

• May be used to cure/treat diseases or medical conditions.
• Can produce replacement cells / tissues / organs.
• Cells/tissues of any type could be produced.
• Cells are unlikely to be rejected by the patient.
• May reduce waiting time for organ transplants.
• Cells could be used for research.

✅ Correct answers — disadvantages

• Potential life is killed / destroyed (embryo destroyed).
• Shortage of donors / eggs.
• Egg donation / collection has risks.
• Do not yet know risks / side effects for the patient.
• May transfer viral infection.
• Poor success rate to produce viable eggs / embryo.

🧠 Exam technique

• You need any two advantages and any two disadvantages.
• Use short, distinct points to avoid repeating the same idea.
• For full marks, make the answer clearly about therapeutic cloning in medicine.
• Examples like diabetes or paralysis can help, but are not required.

❌ Common errors

• Writing about cost — ignore cost references here.
• Giving ethical points in vague terms only; the mark scheme wants specific biological or medical disadvantages.
• Saying “identical cells are produced” as a disadvantage — that is not credited.
• Repeating the same point twice, which only counts once.

06.1 model answer

Tip of root.

06.2 model answer

To produce large numbers of identical plants.

06.3 model answer

6 × 10⁻¹² g

06.4 model answer

1.17 hours