Why cannot the magnification be used for area directly?

It describes length, so area scales with its square: ten times means a hundred times the area.

How do I tell a plant cell from an animal cell?

Look for a cell wall, chloroplasts and one large central vacuole.

S4 Biology Cells, Paper 1: microscopy arithmetic and cell structure

2026-11-02

Tutor Prep Guide · Primary English

Paper 1 begins with magnification and real-size arithmetic, then separates plant and animal cell structures.

Focus　Find the total magnification before the real size, and square the factor for area.

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: S4 Biology: Cells and Microscopy
Level	S4

02　Questions (10 items)

FoundationA specimen is viewed with a 10× eyepiece and a 40× objective. What is the total magnification?
FoundationAn image measures 20 mm at 400×. What is the real length in micrometres?
FoundationWhich organelle releases most of the ATP by aerobic respiration?
FoundationName three structures found in plant cells but not in animal cells.
IntermediateChanging the objective from 10× to 40× reduces the field diameter from 1.6 mm to what?
IntermediateFor a cube-shaped cell of side 20 micrometres, what is the surface area to volume ratio?
IntermediateA human body cell has 46 chromosomes. How many pairs is that?
ChallengeThe light microscope resolves about 200 nm and the electron microscope about 0.1 nm. How many times larger is the first figure?
ChallengeSpecimen A is 12 mm long at 400× and specimen B is 15 mm long at 1000×. Which is really longer?
Error redoError: a student says 400× means the area is 400 times larger. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	400×	Total magnification is the eyepiece power times the objective power, so 10 times 40 gives 400.
2	50 micrometres	Dividing 20 mm by 400 gives 0.05 mm, which is 50 micrometres.
3	Mitochondria	Mitochondria carry out aerobic respiration, so busy cells contain more of them.
4	Cell wall, chloroplast and a large central vacuole	These three features separate plant cells from animal cells most quickly.
5	0.4 mm	Quadrupling the magnification cuts the field diameter to a quarter, so 1.6 becomes 0.4.
6	0.3 per micrometre	Surface area is 2400 and volume is 8000 square micrometres units, so the ratio is 0.3.
7	23 pairs	Homologous chromosomes pair up, so 46 divided by 2 gives 23 pairs.
8	2000 times	Dividing 200 by 0.1 gives 2000, and a larger figure means coarser detail is resolvable.
9	A, at 30 micrometres against 15	Twelve divided by 400 is 30 micrometres while 15 divided by 1000 is 15 micrometres.
10	Length is 400 times, area 160000 times	Magnification describes length, so area is squared and 400 squared is 160000.

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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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.