All cells arise from other cells

Question 1

What happens during Interphase

Answer 1

-S phase – DNA replicates semi-conservatively leading to two sister chromatids

-G1 and G2 – Number of organelles and volume of cytoplasm increases; protein synthesis; ATP content increased

Question 2

Explain what happens during mitosis

Answer 2

Parent cell divides = two genetically identical daughter cells, containing identical copies of DNA of the parent cell.

Question 3

Prophase

Answer 3

Chromosomes condense, becoming shorter and thicker = appear as two sister chromatids joined by a
centromere

• Nuclear envelope breaks down and centrioles move to opposite poles forming spindle network

Question 4

Metaphase

Answer 4

Chromosomes align along equator

Spindle fibres attach to chromosomes by centromeres

Question 5

Anaphase

Answer 5

Spindle fibres contract, pulling sister chromatids to opposite poles of the cell

Centromere divides

Question 6

Telophase

Answer 6

Chromosomes uncoil, becoming longer and thinner

Nuclear envelope reforms = two nuclei

Spindle fibres and centrioles break down

Question 7

Cytokinesis(not a stage of mitosis)

Answer 7

The division of the cytoplasm, usually occurs, producing two new cells

Question 8

Importance of mitosis

Answer 8

Growth of multicellular organisms by increasing cell number

Repairing damaged tissues / replacing cells

Asexual reproduction

Question 9

two types of tumours

Answer 9

Malignant tumour – cancer – spreads and affects other tissues / organs

Benign tumour – non-cancerous

Question 10

Explain how cancer treatments are directed at controlling the rate of cell division

Answer 10

It disrupts the cell cycle as mitosis is slowed so tumour growth also slowed.
Does this by:
Prevent DNA replication → prevent / slows down mitosis
Disrupts spindle activity / formation → chromosomes can’t attach to spindle by their centromere → sister chromatids can’t be pulled to opposite poles of the cells→ prevent/slow mitosis

Question 11

give one advantage and one disadvantage of these drugs used to treat cancer

Answer 11

☺ Drugs more effective against cancer cells because dividing uncontrollably / rapidly

☹ Disrupt cell cycle of normal cells too, especially rapidly dividing ones e.g. cells in
hair follicles

Question 12

Describe how prokaryotic cells replicate

Answer 12

Binary fission:
-Circular DNA and plasmids replicate
-Cytoplasm expands as each DNA molecule moves to opposite poles of the cell
- Cytoplasm divides
- 2 daughter cells, each with a single copy of DNA and a variable number
of plasmids

Question 13

Describe how viruses replicate

Answer 13

Viruses don’t undergo cell division because they are non-living

1. Attachment protein binds to complementary receptor protein on surface of host cell
2. Inject nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates the virus particles