Why does the chromosome count double in anaphase?

Centromeres split so each chromatid counts as a chromosome, doubling the number briefly.

Why does one oocyte give only one egg?

Both divisions share cytoplasm unequally, so only one cell keeps enough nutrients.

S4 Biology Cell Division, Paper 3: cell cycle and gamete formation

2026-11-02

Paper 3 works from human 2n = 46 and 2n = 8 through chromosome numbers, anaphase counts, the share of mitosis and egg formation.

Focus　Mitosis keeps 2n while meiosis halves it, anaphase doubles the count briefly, and one oocyte yields one egg.

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: Cell Division
Level	S4

02　Questions (10 items)

FoundationA human body cell with 2n = 46 completes mitosis. How many chromosomes per daughter cell?
FoundationHow many chromosomes does a human gamete carry after meiosis?
FoundationIn which part of the cell cycle does chromosome replication happen?
FoundationA cell with 2n = 8 finishes meiosis. How many chromosomes in each of the four daughter cells?
IntermediateA cell divides every 20 minutes. How many cells come from one after two hours?
IntermediateA cell with 2n = 6 is in anaphase of mitosis. How many chromosomes are present in the cell?
IntermediateHow many eggs does one primary oocyte finally produce?
ChallengeA cell cycle lasts 20 hours and mitosis takes 1 hour. What percentage of the cycle is mitosis?
ChallengeIf 40 spermatogonia each divide once by mitosis, how many cells result?
Error redoError: a student says meiosis turns one cell into two haploid cells. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	46	Mitosis copies and shares chromosomes equally, so each daughter cell keeps 46.
2	23	Meiosis halves 46, so each gamete carries 23 chromosomes.
3	Interphase, in the S phase	DNA is copied in the S phase of interphase before the cell enters mitosis.
4	4	Meiosis halves the number, so 8 becomes 4 in each of the four cells.
5	64	Two hours hold six divisions, and 2 to the power 6 is 64.
6	12	At anaphase the centromeres split, so the count temporarily doubles to 12.
7	One egg plus three polar bodies	Cytoplasm is shared unequally, so only one cell becomes the egg and three become polar bodies.
8	5 per cent	One divided by 20 times 100 gives 5 per cent, with the other 19 hours in interphase.
9	80	Mitosis doubles the count, so 40 times 2 gives 80 with the chromosome number unchanged.
10	Four haploid cells, because meiosis has two divisions	Meiosis halves the number first and then separates sister chromatids, giving four cells in all.

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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