Membrane Transport, Cell Division & Reproduction

12 methods · 25 questions

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Two facts answer almost every division item: mitosis makes two genetically identical cells with the SAME chromosome number, meiosis makes four haploid cells with HALF the number. Use the number change to label a diagram arrow and the counts to tally products.

Trigger: a life-cycle diagram with n and 2n, 'which stage is meiosis', or 'how many cells / chromosomes'.

Instances:
(i) label an arrow: number unchanged (or haploid growing to haploid) is mitosis, number halved (diploid to haploid) is meiosis, number doubled is fertilisation and not a division at all;
(ii) count products: each mitosis multiplies the cell count by two, a final meiosis multiplies by four;
(iii) sanity checks: mitosis never makes three or four cells, and gametes come from diploid stem cells through meiosis, never from haploid ones.

Linked questions (3)

NSAA 2016 Section 1, Part D (Biology questions) · Q67

A diploid cell from a type of fly that contains 8 chromosomes, divides to form sperm cells.

Which row is correct for the number of strands of DNA in each sperm cell and the number of sperm cells produced?

(Each option gives the number of strands of DNA in each sperm cell, then the number of sperm cells produced.)

A4 strands; 2 sperm cells
B4 strands; 4 sperm cells
C8 strands; 2 sperm cells
D8 strands; 4 sperm cells
E16 strands; 2 sperm cells
F16 strands; 4 sperm cells

Worked solution

Answer:D

Sperm cells are produced by meiosis, which makes four haploid cells from one diploid cell. Each sperm therefore contains half the chromosome number,

8 \div 2 = 4

chromosomes.

After meiosis each chromosome consists of a single chromatid, which is one molecule of DNA, and every DNA molecule is a double helix made of two strands. A sperm cell therefore contains

4 \times 2 = 8

strands of DNA. (The value 16 would apply to a diploid cell with 8 chromosomes, and 4 counts molecules rather than strands.)

The answer is D.

NSAA 2017 Section 1, Part D (Biology questions) · Q58

Which of the following statements about stem cells in a healthy human female is/are correct?

1. An adult stem cell contains the same genes as an epithelial cell from that organism.
2. Stem cells from this human will all contain two X chromosomes.
3. When a stem cell divides it produces a new stem cell plus two specialised body cells.

(Assume that no mutations have occurred.)

Anone of them
B1 only
C2 only
D3 only
E1 and 2 only
F1 and 3 only
G2 and 3 only
H1, 2 and 3

Worked solution

Answer:E

Statement 1 is correct: every body cell of an organism, stem cells included, carries the same set of genes; specialised cells differ only in which genes they switch on.

Statement 2 is correct: a healthy human female has two X chromosomes in every body cell, and her stem cells are body cells, so they all contain two X chromosomes.

Statement 3 is wrong: a cell divides by mitosis into two cells, never three. A dividing stem cell produces two cells, of which one may remain a stem cell while the other goes on to specialise.

The answer is E.

NSAA 2017 Section 1, Part D (Biology questions) · Q66

The diagram shows the life cycle of a simple type of plant.

(In the diagram, n is the haploid number of chromosomes and 2n the diploid number.)

At which two of the numbered stages does only mitosis occur?

A cycle of boxes joined by numbered arrows. Adult plant stage P (n) at the top gives, by arrow 1, a female gamete (n) and a male gamete (n) on the right; both gametes lead by arrow 2 to adult plant stage Q (2n) at the bottom; arrow 3 leads from stage Q to spores (n) on the left; arrow 4 leads from the spores back to stage P. A key states that n is the haploid number of chromosomes and 2n the diploid number.

A1 and 2 only
B1 and 3 only
C1 and 4 only
D2 and 3 only
E2 and 4 only
F3 and 4 only

Worked solution

Answer:C

Mitosis produces cells with the same chromosome number as the parent cell; meiosis halves it.

Stage 1 turns the haploid (n) adult stage P into haploid (n) gametes, so it is mitosis. Stage 2 is the fusion of two haploid gametes to form the diploid (2n) stage Q: fertilisation, not a cell division at all. Stage 3 turns the diploid stage Q into haploid spores, so it must be meiosis. Stage 4 turns a haploid spore into the haploid adult stage P by growth, which is mitosis.

Only mitosis occurs at stages 1 and 4.

The answer is C.