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

✅ Correct answers

• Nucleus → Eukaryotic cells
• Permanent vacuole → Plant cells only
• Plasmid → Prokaryotic cells

Marking point: 1 mark for one or two correct links, 2 marks for all three correct links.

💡 Key knowledge

• Nucleus is found in eukaryotic cells such as plant and animal cells.
• Permanent vacuole is a feature of plant cells.
• Plasmids are small rings of DNA found in bacteria and other prokaryotes.

🧠 Exam technique

• Use cell type clues: plant-only structures vs bacteria-only structures.
• For matching questions, check each item one by one rather than guessing the whole row.

❌ Common errors

• Mixing up plant cells and prokaryotic cells.
• Thinking a nucleus is in bacteria — it is not.
• Forgetting that the permanent vacuole is plant cells only at GCSE level.

✅ Correct answers

Structure A: Vacuole

Structure B: Ribosome

Structure C: Cell wall

The correct row is: Vacuole / Ribosome / Cell wall.

💡 Key knowledge

• The vacuole is the large central space in a plant cell.
• Ribosomes are tiny structures found in the cytoplasm.
• The cell wall is the thick outer layer of a plant cell.

🧠 Exam technique

• Use the diagram first, then check the options in the table.
• The mark scheme says the tick box takes precedence if the answer is shown there.
• If writing is added on the figure and in the table, both must be correct.

❌ Common errors

• Calling the large pale region a nucleus instead of a vacuole.
• Confusing the cell membrane with the cell wall.
• Choosing chloroplasts even though they are not shown in this figure.

✅ Correct answer

Turn the fine focusing knob until the cells are in focus.

Accept “focus it” or equivalent.

💡 Key knowledge

• The fine focus knob sharpens the image.
• At this stage, the cells are not clear because the microscope needs focusing, not more magnification.

🧠 Exam technique

• Use the exact microscope control: fine focus knob.
• The examiner wanted a focus adjustment, not a change in magnification.

❌ Common errors

• Saying “increase magnification” — this does not earn the mark.
• Writing vague answers like “make it clearer” without naming the control.
• Talking about illumination or zoom when the mark scheme does not require it.

✅ Correct answer

Rotate the nosepiece / change the objective lens to a higher power lens.

Two marking points: 1 for changing the lens, 1 for using a higher power lens / increasing magnification.

💡 Key knowledge

• To see a more detailed view, the student needs a higher-power objective lens.
• The nosepiece is the part you rotate to change lenses.

🧠 Exam technique

• Give both parts if possible: what to do and why.
• Good full-mark phrasing: “Rotate the nosepiece to a higher-power objective lens to increase magnification.”

❌ Common errors

• Saying only “change magnification” without stating the lens change.
• Giving an unqualified answer like “use a stronger lens” without linking it to the nosepiece/objective lens.
• Talking about an electron microscope — not needed here.

📐 Calculations — step by step

1. Convert units so they match.
2. 112 mm = 112 000 µm
3. Use the formula: magnification = size of image ÷ size of real object
4. magnification = 112 000 ÷ 280
5. magnification = 400

Answer: ×400

A correct final answer of 400 gains full marks. Units must not be written in the answer.

✅ Correct answer

Magnification = ×400

Mark scheme note: an answer of 400 scores 3 marks.

🧠 Exam technique

• Always check the units before calculating.
• Use the formula in the correct order: image size ÷ real size.
• Write the final answer as ×400 or just 400 if required.

❌ Common errors

• Forgetting to convert mm to µm.
• Doing 280 ÷ 112 instead of image ÷ real object.
• Writing units in the final magnification answer.
• Using a wrong formula triangle without rearranging correctly.

💡 What distinguished top responses

• Accurate knowledge of where cell structures are found.
• Correct microscope terminology: fine focus knob, nosepiece, objective lens.
• A clear magnification calculation with units converted before substitution.

❌ Where students lost marks

• Confusing focusing with magnification.
• Mixing up cell wall, cell membrane, and vacuole.
• Not converting mm to µm in the calculation.

🧠 Quick memory tips

• Plant only: permanent vacuole, cell wall, chloroplasts.
• Bacteria only: plasmids.
• Eukaryotic: nucleus.
• Focus = fine knob. Detail = higher power lens.