What is the key difference between mitosis and meiosis?

Mitosis divides once into two 2n cells, while meiosis divides twice into four n cells.

Why does a secondary spermatocyte still have 6 chromosomes?

The first division only separates homologues, so each chromosome still has two chromatids.

S4 Biology Cell Division, Paper 4: mitosis and meiosis side by side

2026-11-02

Paper 4 contrasts where mitosis and meiosis happen and their outcomes, using 2n = 24, 10 and 12 with timing and gamete yield.

Focus　Mitosis keeps 2n for growth and repair, meiosis halves it for gametes, pairing happens in prophase I and one spermatocyte gives four sperm.

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 body cell with 2n = 24 completes mitosis. How many chromosomes per daughter cell?
FoundationWhat is the main purpose of meiosis?
FoundationIn which cells does mitosis mainly happen?
FoundationAt which stage do homologous chromosomes pair up in meiosis?
IntermediateA cell with 2n = 10 finishes meiosis. How many chromosomes per gamete?
IntermediateA cell divides every 30 minutes. How many cells come from one after three hours?
IntermediateAfter the first meiotic division, how many chromosomes does each secondary spermatocyte of a 2n = 12 cell have?
ChallengeA cell cycle lasts 24 hours and mitosis takes 1.5 hours. What percentage of the cycle is mitosis?
ChallengeIf 25 spermatocytes each complete meiosis, how many sperm result?
Error redoError: a student says mitosis turns one cell into four. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	24	Mitosis copies and shares chromosomes equally, so each daughter cell also has 24.
2	To form haploid gametes so that fertilisation restores the diploid number	Gametes carry half the chromosomes so that fusion restores the diploid number.
3	Body cells, for growth, repair and replacing dead cells	Body cells multiply by mitosis, while only germ cells carry out meiosis.
4	Prophase of the first meiotic division	Homologues pair in prophase I before separating to the poles, and crossing over happens then.
5	5	Meiosis halves the number, so 10 divided by 2 gives 5.
6	64	Three hours hold six divisions, and 2 to the power 6 is 64.
7	6, each with two chromatids	The first division separates homologues so the count falls from 12 to 6, still with two chromatids each.
8	6.25 per cent	One and a half divided by 24 times 100 gives 6.25, leaving 22.5 hours in interphase.
9	100	Each spermatocyte yields four sperm, so 25 times 4 gives 100.
10	Two daughter cells with the same chromosome number as the parent	Mitosis divides once, so the cell splits into two with the chromosome number unchanged.

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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