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Secondary Biology: Cell Structure and the Microscope (Paper 4)
Secondary Biology: Cell Structure and the Microscope (Paper 4)
Ten original questions converting between image and actual length, matching the wall, ribosomes and vacuole to their jobs, comparing total magnification after an eyepiece change, and using resolution to explain why viruses are invisible in a light microscope.
Direct answer Actual length is image length divided by magnification, and resolution is not the same thing as magnification.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: Secondary Biology: Cell Structure and the Microscope |
| Level | 4 basic, 3 advanced, 2 challenge and 1 redo question |
02 Questions (10 items)
- FoundationAn image measures 45 mm at a magnification of 500. What is the actual length of the cell in micrometres?
- FoundationWhich substance is the plant cell wall mainly made of?
- FoundationWhich organelle makes proteins?
- FoundationWhat does the large central vacuole mainly store in a plant cell?
- IntermediateAn image is 20 mm long and the specimen is 100 micrometres. What is the magnification?
- IntermediateAt 400×, how long does a specimen of 1/5 mm appear in the image?
- IntermediateThe eyepiece is changed from 10× to 15× while the objective stays at 40×. What is the new total magnification?
- ChallengeThe resolution limit of a light microscope is about 1/5 micrometre. Why can a virus of about 1/10 micrometre not be seen?
- ChallengeThe same specimen looks sharp at 400× and at 600×. What differs at 600×?
- Error redoSeeing an 8 mm image at 400×, a student answers that the cell is 8 mm long. What is the correct answer?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 90 micrometres (45 000 divided by 500). | Convert millimetres to micrometres first, then divide by the magnification to get the real size. |
| 2 | Cellulose. | Cellulose fibres are strong yet let water and solutes through, and animal cells have no wall. |
| 3 | The ribosome. | Ribosomes link amino acids in the order the gene dictates, and they are not membrane-bound. |
| 4 | Water and dissolved substances such as sugars and salts, and it keeps the cell firm. | A full vacuole pushes the cytoplasm against the wall to keep the cell firm, so a plant wilts when it loses water. |
| 5 | 200×. | Magnification is image length divided by actual length, so both must be in the same unit first. |
| 6 | 80 mm. | To go from specimen to image you multiply by the magnification, so the image is far larger than the real object. |
| 7 | 600×, which is 1.5 times the original 400×. | Total magnification is eyepiece times objective; changing the eyepiece only changes the image size. |
| 8 | It is smaller than the resolution limit, so neighbouring points cannot be told apart and blur into a smudge. | Resolution decides whether two points can be told apart, while magnification only makes the image bigger. |
| 9 | The image is 1.5 times bigger, but resolution does not improve and no extra detail appears. | Magnifying beyond the resolution limit only enlarges a blur, which is called empty magnification. |
| 10 | 20 micrometres (8 000 micrometres divided by 400). | This is the classic error of treating image length as real length; always divide by the magnification. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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