All Cells Arise From Other Cells Test Q/A

Question 1

Colchicine is a substance that prevents the formation of the spindle in mitosis. Dividing cells were treated with colchicine. This stopped them dividing. After a few hours, the colchicine was removed and the cells began to divide again. The diagram shows the chromosomes from one of the treated cells at stage B after the cell began dividing again.

What has happened to the chromosome number?

Answer 1

Doubled

Question 2

Colchicine is a substance that prevents the formation of the spindle in mitosis. Dividing cells were treated with colchicine. This stopped them dividing. After a few hours, the colchicine was removed and the cells began to divide again. The diagram shows the chromosomes from one of the treated cells at stage B after the cell began dividing again.

Suggest an explanation for the change in chromosome number

Answer 2

The cell has replicated the chromosomes again but spindle fibres hasn’t separated so 4 more “x” shaped chromosomes are not present

Question 3

Explain why the bacteria are cultured before the plant tissue is added

Answer 3

The bacteria grow producing many copies of the desired gene

Question 4

Explain why the growth medium contains an antibiotic

Answer 4

Plant tissue that has antibiotic resistance survives. Identifies plant tissue which has desired gene

Question 5

Interphase has 90% in the stage of cell cycle. In this tissue one complete cycle took 20 hours. Calculate the mean time for these cells to complete mitosis

Answer 5

90% interphase
10% mitosis

100-90= 10% for mitosis

10% of 20hours is 2 hours

Question 6

When giving evidence for phrophase what do you say?

Answer 6

Chromosomes condense

And get smaller

Question 7

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 7

Temperature
Water availability
Chance

Question 8

Describe the behavior of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.

Answer 8

❤️chromosomes shorten/thicken
❤️chromosomes (each) two identical
❤️chromatids (due to replication)
❤️chromosomes move to equator attach to individual spindle fibres
❤️spindle fibres contract
❤️sister chromatids separate move to opposite poles
❤️each poles receives all genetic information
❤️nuclear envelope forms around each group of chromosomes