What is the commonest genetics mistake?

Applying the 3:1 ratio before writing the parental genotypes; test crosses and homozygous parents then break it.

Do units matter in magnification questions?

Yes: mm and micrometres differ by a factor of 1000, so a missed conversion is out by three orders of magnitude.

Secondary Biology: Cell Structure and the Microscope (Paper 1)

2026-10-31

Ten original questions cover the roles of the membrane, nucleus and mitochondria, then total magnification and the conversion between image and actual length.

Direct answer　Compare plant and animal cells through the wall, chloroplasts and large vacuole. Multiply eyepiece by objective for magnification, and divide image length by it for actual length.

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)

FoundationWhich part of a cell controls the movement of substances into and out of the cell?
FoundationAn eyepiece of 10x is used with an objective of 40x. What is the total magnification?
FoundationName three structures found in plant cells but not in animal cells.
FoundationWhich molecule stores genetic information inside the nucleus?
IntermediateA cell measures 8 mm in a drawing at 400x. What is its actual length?
IntermediateWhat is the main function of mitochondria?
IntermediateWhy is onion epidermis used instead of leaf mesophyll to observe the cell wall?
ChallengeA specimen is 50 micrometres long. How long will it appear at 400x?
ChallengeTo reach a total of 1000x with a 10x eyepiece, which objective is needed?
Error redoA pupil claims animal cells have no cell wall and therefore no membrane. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	The cell membrane.	The cell membrane is selectively permeable and decides what may pass.
2	400 times (10 x 40 = 400).	Total magnification multiplies the two lens powers; it is not their sum.
3	Cell wall, chloroplast and a large vacuole.	These three features separate plant cells from animal cells most quickly.
4	DNA (deoxyribonucleic acid).	The nucleus is the control centre and DNA holds the coded instructions.
5	20 micrometres (8 mm divided by 400 gives 0.02 mm).	Divide the image length by the magnification, and convert mm to micrometres by multiplying 1000.
6	Aerobic respiration, releasing energy as ATP.	Cells with high energy demand, such as muscle cells, contain more mitochondria.
7	Epidermal cells have no chloroplasts, so the green colour does not hide the wall.	Choose material that removes colour and structural interference.
8	20 mm (50 micrometres times 400 = 20 000 micrometres).	Image length equals actual length times magnification, the reverse of the earlier question.
9	100x (1000 divided by 10 = 100).	When more magnification is needed, change the objective as the eyepiece is usually fixed.
10	Animal cells do have a membrane; only the wall is missing. The two lie close but differ in composition.	The membrane is made of phospholipids and protein; the wall is mainly cellulose.

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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