Mitosis

Question 1

Explain what happens during Interphase (2)

Answer 1

1. DNA is replicated

2. Two copies of DNA join at the centromere

Question 2

Explain what happens during Prophase (3)

Answer 2

1. Chromosomes condense and become visible
2. Centrioles migrate to opposite poles and spindle fibres develop
3. Nucleolus disappears and nuclear envelope breaks down

Question 3

Explain what happens during Metaphase (2)

Answer 3

1. Chromosomes are seen to be made up of 2 chromatids. Each is an identical copy of DNA to the parent cell
2. Microtubules attached to centromere pull chromosomes along spindle apparatus so that they aline across the equator of the cell

Question 4

Explain what happens during Anaphase (4)

Answer 4

1. Centromere divides in 2 and spindle fibres pull individual chromatids of the chromosome apart
2. Chromatids move to opposite poles of cell
3. Energy is provided by mitochondria, that gather around spindle fibres
4. If chemicals destroy the spindle, chromosomes remain at the equator

Question 5

Explain what happens during Telophase (4)

Answer 5

1. Chromosomes spread-out to form chromatin, disappearing
2. Spindle fibres disintegrate
3. Nuclear envelope and nucleolus re-form
4. Cytoplasm divides (Cytokinesis)

Question 6

Explain what happens during Binary Fission (4)

Answer 6

1. Circular DNA molecule replicates and both copies attach to cell membrane
2. Plasmids replicate
3. Cell membrane grows between the 2 DNA molecules and pinches inwards, dividing cytoplasm in two.
4. New cell wall forms between two molecules of DNA dividing into 2 daughter cells each with a single copy of circular DNA and variable copies of plasmids

Question 7

Explain the importance of mitosis (3)

Answer 7

1. Growth - cells used in growth are genetically identical
2. Repair - New cells must be identical to replace damaged and dead cells
3. Asexual reproduction - division by mitosis to give two new offspring, each offspring genetically identical to the parent

Question 8

Explain what happens during Cancer treatment (3)

Answer 8

1. Drugs use to treat cancer (Chemotherapy) disrupt the cell cycle by inhibiting DNA replication
2. Inhibiting the metaphase stage by disrupting spindle formation
3. Drugs also disrupt cell cycle of normal cells although cancerous cells are affected more as they divide rapidly.

Question 9

Describe the cell cycle (3)

Answer 9

1. Interphase - occupies most of cell cycle, no division takes place
2. Nuclear division - Nucleus divides into two or four
3. Cytokinesis - Cytoplasm divides to produce two or four cells