3.2.2 - CELL CYCLE + MITOSIS

Question 1

describe binary fission in bacteria (3)

Answer 1

1. replication of circular DNA
2. replication of plasmids
3. division of cytoplasm to produce daughter cells

Question 2

state the process by which bacteria divide (1)

Answer 2

binary fission

Question 3

suggest and explain how two environmental variables could be changed to increase the growth rate of cells (4)

Answer 3

any two pairs:

1. increased concentration of glucose
2. increased respiration

OR

3. increased concentration of oxygen
4. increased respiration

OR

5. increased temperature
6. increased enzyme activity

OR

7. increased concentration of phosphate
8. increased ATP/DNA/RNA

OR

9. increased concentration of nucleotides
10. increased DNA synthesis

Question 4

describe the role of spindle fibres and the behaviour of the chromosomes during prophase, metaphase and anaphase (4)

Answer 4

1. in prophase, chromosomes condense (shorten and thicken)
2. in prophase/metaphase, centromeres of chromosomes attach to the spindle fibres
3. in metaphase, chromosomes line up at the equator/centre of the cell
4. in anaphase, centromeres divide

Question 5

what name is given to the division of the cytoplasm during the cell cycle (1)

Answer 5

cytokinesis

Question 6

the dark stain used on the chromosomes bind more to some areas of the chromosomes than others, giving the chromosomes a striped experience.

suggest one way the structure of the chromosomes could differ along its length to result in the stain binding more in some areas. (1)

Answer 6

any one:

1. differences in base sequences
2. differences in histones/interactions with histones
3. differences in condensation

Question 7

what is a homologous pair of chromosomes? (1)

Answer 7

two chromosomes that carry the same genes/same loci/genes for the same characteristics

Question 8

a microbiologist investigated the ability of different plant oils to kill the bacterium Listeria monocytogenes. she cultured the bacteria on agar plates. she obtained the bacteria from a broth culture.

describe two aseptic techniques she would have used when transferring a same of broth culture onto an agar plate. explain why each was important (4)

Answer 8

any two pairs:

1. keep lid on Petri dish
2. to prevent unwanted bacteria from contaminating the dish/L monocytogenes may get out

OR

3. wear gloves/mask/wash hands
4. to prevent contamination from bacteria on hands/to prevent spread of bacteria outside the lab

OR

5. use sterile pipette
6. to maintain a pure culture of bacteria

Question 9

describe the appearance and behaviour of chromosomes during mitosis (5)

Answer 9

during prophase:
1. chromosomes condense (shorten and thicken), and become visible
2. chromosomes appear as two sister chromatids joined at the centromere

during metaphase:
3. chromosomes line up on the equator of the cell
4. chromosomes attach to the spindle fibres
5. by their centromere

during anaphase:
6. the centromere splits
7. sister chromatids separate and are pulled to opposite poles of the cell

during telophase:
8. chromosomes become longer and thinner

Question 10

chemotherapy is the use of a drug to treat cancer. the drug kills dividing cells.

more cancer cells could be destroyed if the drug was given more frequently.

suggest why the drug was not given more frequently (2)

Answer 10

1. so that more healthy cells would not be killed
2. because it would take time to replace these cells

Question 11

the events that take place during interphase and mitosis lead to the production of two genetically identical cells. explain how (4)

Answer 11

1. DNA is replicated
2. involving complementary base-pairing
3. sister chromatids are identical
4. each chromatid is separated to opposite poles of a cell.

Question 12

bacteria are often used in industry as a source of enzymes. one reason is because bacteria divide rapidly, producing a large number of them in a short time.

describe how bacteria divide (2)

Answer 12

1. binary fission
2. replication of circular DNA
3. division of cytoplasm to produce 2 daughter cells
4. each with a single copy of DNA

Question 13

what is a tumour? (2)

Answer 13

1. abnormal cells
2. due to uncontrolled cell division/mitosis

Question 14

describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope (3)

do not include details of how you would prepare the tissue observed with an optical microscope

Answer 14

1. count cells in mitosis in field of view
2. divide this by the total number of cells in field of view
3. repeat this many times

Question 15

suggest why preventing the formation of spindle fibres stops the cell cycle (2)

Answer 15

1. chromosomes cannot attach to the spindle
2. so metaphase cannot occur

Question 16

suggest and explain why ABZ could be used as a treatment for cancer even though it affects some healthy cells (1)

Answer 16

cancer cells divide more rapidly than healthy cells