2.2 all cells arise from other cells

Question 1

what are the 3 stages of the cell cycle in eukaryotic cells

Answer 1

1. interphase
2. mitosis
3. cytokinesis

Question 2

what happens during interphase

Answer 2

• S phase: DNA replicates semi conservatively leading to 2 chromatids joined at the centromere
• G1/2: number of organelles and volume of cytoplasm increases, protein synthesis

Question 3

what happens during mitosis

Answer 3

nucleus divides to produce 2 nuclei with identical copies of DNA produced by parent cell

Question 4

what happens during cytokinesis

Answer 4

cytoplasm and cell membrane divide to form 2 new genetically identical daughter cells

Question 5

what are the 4 stages of mitosis

Answer 5

1. prophase
2. metaphase
3. anaphase
4. telophase

Question 6

describe the behaviour of chromosomes and role of spindle fibres during prophase

Answer 6

• chromosomes condense becoming shorter/thicker which appears as 2 sister chromatids joined by a centromere
• nuclear envelope breaks down
• centrioles move to opposite poles forming spindle network

Question 7

describe the behaviour of chromosomes and role spindle fibres during metaphase

Answer 7

• spindle fibres attach to chromosomes by their centromeres
• chromosomes align along the equator

Question 8

describe the behaviour of chromosomes and role of spindle fibres during anaphase

Answer 8

• spindle fibres shorten/contract
• centromere divides pulling chromatids from each pair to opposite poles of the cell

Question 9

describe the behaviour of chromosomes and role of spindle fibres during telophase

Answer 9

• chromosomes uncoil becoming larger and thinner
• nuclear envelope reforms = 2 nuclei
• spindle fibres and centrioles break down

Question 10

why do some eukaryotic cells not undergo the cell cycle

Answer 10

• within multicellular organisms not all cells retain the ability to divide
• only cells that retain this ability go through the cell cycle

Question 11

explain the importance of mitosis in the life of an organism

Answer 11

parent cells divide to produce 2 genetically identical daughter cells for:
- growth if multicellular organisms by increasing cell number
- replacing cells to repair damaged tissues
- asexual reproduction

Question 12

describe how tumours and cancers form

Answer 12

mitosis which is a controlled process:
- mutations in DNA controlling mitosis can lead to uncontrolled cell division
- tumours form if this results in a mass of abnormal cells

Question 13

what are malignant tumours

Answer 13

cancerous tumours which can spread

Question 14

what are benign tumours

Answer 14

non cancerous tumours

Question 15

how do cancer treatments that disrupt spindle fibre activity and formation control the rate of cell division

Answer 15

• chromosomes cannot attach to spindles by their centromere
• so chromatids cannot be separated to opposite poles ( no anaphase )
• preventing/slowing down mitosis

Question 16

how to cancer treatments that prevent DNA replication during interphase control the rate of cell division

Answer 16

2 copies of each chromosome cannot be made preventing/slowing down mitosis

Question 17

what are the weaknesses of cancer treatments

Answer 17

disrupts the cell cycle of rapidly dividing healthy cells

Question 18

how do prokaryotic cells replicate

Answer 18

binary fission:
1. replication of circular DNA
2. replication of plasmids
3. division of cytoplasm to produce 2 daughter cells which have a single copy of circular DNA and a variable number of copies of plasmids

Question 19

how do viruses replicate

Answer 19

1. attachment proteins attach to complementary receptors on host cell
2. inject viral nucleic acid into host cell
3. infected host cell replicates virus particles:
   - nucleic acid replicated
   - cell produces viral protein, capsid and enzyme
   - virus is assembled and then released