S1 Science: Microscope Skills And Cell Observation (Paper 4: Mistake Clinic)

S1 Science: Microscope Skills and Cell Observation (Paper 4: mistake clinic)

2026-11-12

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S1 Science: Microscope Skills and Cell Observation (Paper 4: mistake clinic)

This last paper revisits the high frequency errors from the earlier three: adding magnifications, reversing the slide direction, swapping micrometres and millimetres, and forgetting to square for area. Check those four points after every question.

Direct answers　If one cause appears twice, write it on the first page of your notes and read only that page before the exam.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S1 Science: Microscope Skills and Cell Observation
Level	S1 Science

02　Questions (10 items)

FoundationIs total magnification added or multiplied? Work it out with 10x and 40x.
FoundationThe image sits at the lower left of the field. Which way do you move the slide to centre it?
FoundationHow many millimetres are there in 1 micrometre?
IntermediateWith a 10x eyepiece and 10x objective a cell image is 15 mm across. What is the real diameter in micrometres?
IntermediateAt 40x the field diameter is 2.4 mm. What is it at 400x?
IntermediateAt 100x a cell image is 4 mm long. What is the real length in micrometres?
Challenge400 evenly spread cells are visible at 100x. How many are visible at 400x?
ChallengeA cell is 80 micrometres across. What is the diameter of its image at 400x in millimetres?
ChallengeThe field diameter is 0.6 mm and cells are 30 micrometres across. How many fit across the diameter?
Error redoWhat is wrong with saying every plant cell has chloroplasts?

03　Answers and one-line notes

#	Answer	One-line note
1	Multiplied: 10 x 40 = 400x.	Adding gives only 50x, eight times too small, and that is the commonest careless error.
2	Towards the lower left.	The slide moves towards the side where the image appears; that single rule prevents reversing the direction.
3	0.001 mm	Going from micrometres to millimetres means dividing by 1 000, the reverse of the other direction.
4	150 micrometres	Total magnification is 100x, so 15 / 100 = 0.15 mm and 0.15 x 1 000 = 150 micrometres.
5	0.24 mm	Magnification rises ten times, so 2.4 / 10 = 0.24 mm.
6	40 micrometres	4 / 100 = 0.04 mm and 0.04 x 1 000 = 40 micrometres.
7	25 cells	The area becomes one sixteenth, so 400 / 16 = 25 cells.
8	32 mm	80 micrometres = 0.08 mm and 0.08 x 400 = 32 mm.
9	20 cells	0.6 mm = 600 micrometres and 600 / 30 = 20.
10	Only cells in green parts such as leaves have chloroplasts; onion epidermal cells and root cells have none.	Onion epidermal cells are colourless precisely because they lack chloroplasts, which is why a stain is needed.

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.

Use three columns in the error log: question, cause, corrected working. The three commonest causes are adding instead of multiplying magnifications, moving the slide the same way as the image seems to move, and treating the field diameter as shrinking by the square of the magnification.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.