Mitosisi

Question 1

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 1

During prophase)

1. Chromosomes

coil / condense / shorten / thicken / become visible;

2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;

(During metaphase)

3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;

(During anaphase)

6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;

(During telophase)

8. Chromatids / chromosomes

uncoil / unwind / become longer / thinner.

Question 2

A student investigated mitosis in the tissue from an onion root tip.

(a) The student prepared a temporary mount of the onion tissue on a glass slide. She covered the tissue with a cover slip. She was then given the following instruction.

“Push down hard on the cover slip, but do not push the cover slip sideways.”

Explain why she was given this instruction.

Answer 2

Push hard – spread / squash tissue;

2. Not push sideways – avoid rolling cells together / breaking chromosomes

Question 3

a stain was used;

______________________________________________________________

______________________________________________________________

(1)

(iii) the root tip was firmly squashed.

Answer 3

to distinguish chromosomes / chromosomes not visible
without stain;

1

(iii) to let light through / thin layer;

Question 4

A different set of results was obtained when the count was repeated on another occasion with a different garlic root tip. Give two reasons for the difference in results.

Answer 4

genetic differences / different types of garlic;
time of day;
chance;
age of root tip;
water availability;
temperature;
nutrient availability

Question 5

A cancerous tumour is formed by uncontrolled mitotic division. This results in a mass of cells with an inadequate blood supply. Drugs are being developed which only kill cells in a low oxygen environment. Suggest how these drugs could be useful in the treatment of cancer.

Answer 5

cancer cells killed, normal body cells survive;

cancer cells low oxygen (as blood supply cannot satisfy demand);