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 2)

2026-10-31

Ten original questions on multiplying eyepiece and objective powers, converting between image and actual length, cells across the field of view, chloroplasts against mitochondria and the limit of magnification.

Direct answer　Multiply eyepiece by objective for magnification and divide image length by it for actual length. Detail depends on resolution, not magnification alone.

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)

FoundationA 15x eyepiece is used with a 10x objective. What is the total magnification?
FoundationAt 150x a cell measures 6 mm in the image. What is its actual length?
FoundationTo reach 600x with the same 15x eyepiece, which objective is needed?
FoundationWhat is the main function of the nucleus?
IntermediateThe field of view is 500 micrometres wide and a cell is 50 micrometres across. How many fit across?
IntermediateA specimen is 30 micrometres long. How long is its image at 400x?
IntermediateHow is the cell membrane described in the current model, and what property does it have?
ChallengeWhy can electron microscopes usually not be used on living cells?
ChallengeHow do chloroplasts and mitochondria differ in function, and which cells contain them?
Error redoA pupil says the highest magnification always shows every structure clearly. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	150x (15 times 10 = 150).	Total magnification is the product of the eyepiece and objective powers, not the sum.
2	40 micrometres (6 mm = 6 000 micrometres, divided by 150).	Convert to one unit first, then divide the image length by the magnification.
3	40x (600 divided by 15 = 40).	The eyepiece is usually fixed, so magnification is changed on the nosepiece.
4	It stores DNA and controls the activities of the cell.	The DNA in the nucleus carries the instructions for making proteins.
5	10 cells (500 divided by 50).	Both lengths must be in the same unit before dividing.
6	12 mm (30 times 400 = 12 000 micrometres).	This one works the other way: multiply instead of divide.
7	A phospholipid bilayer with proteins embedded in it; it is selectively permeable and controls what enters and leaves.	Selective permeability means some substances pass while others do not; the membrane is not a solid seal.
8	Samples must be fixed, dehydrated and placed in a vacuum, so living cells cannot survive.	Resolution depends on wavelength, and electrons have a far shorter wavelength than visible light.
9	Chloroplasts carry out photosynthesis and occur in green plant parts; mitochondria release energy by aerobic respiration and occur in both plant and animal cells.	Both involve energy, but one stores it in food while the other releases it.
10	Higher power narrows the field and dims the image; beyond the resolution limit the image is only blurred, not clearer.	Seeing detail depends on resolution, not magnification alone.

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.

Book a Secondary Biology tutor

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.