5. The Mitotic Cell Cycle

Question 1

Explain why the growth of roots involves mitosis and not meiosis. [3m]

Answer 1

• needs number of chromosomes to remain constant
• needs all daughter cells to be genetically identical
• meiosis halves the number of chromosomes and produces genetic variation

Question 2

Explain why it is important that the daughter cells produced during a mitotic cell cycle in humans are genetically identical. [2m]

Answer 2

• so they have the same number of chromosomes
• cells would be rejected if genetically different
• by immune system

Question 3

Describe the role of mitosis in a growing plant root tip. [2m]

Answer 3

• producing more cells
• GENETICALLY identical
• same number of chromosomes
• repair of root tip / tissue
• mitosis makes cells for differentiation

Question 4

Suggest the differences in the cell cycle of a cancer cell compared with that of a normal cell of the same type. [2m]

Answer 4

• cell cycle shorter
• cell cycle checkpoints not controlled
• uncontrolled (growth/division)
• no differentiation
• no cell death / apoptosis

Question 5

Vinblastine disrupts the formation of the spindle apparatus during mitosis.
Explain how vinblastine has its effect as an anti-cancer drug. [3m]

Answer 5

• growth of tumour involves mitosis
• spindle fibres attach to chromosome at prophase and align chromosome at metaphase
• mitosis stops at metaphase, hence cannot proceed to anaphase and telophase
• no separation of chromatids at centromere
• apoptosis occurs when cell cycle disrupted

Question 6

In many multicellular organisms, the time taken for the mitotic cell cycle varies considerably between tissues, but is very carefully controlled in each cell.

Suggest the importance of this control in mammals. [2m]

Answer 6

• coordination of growth
• minimising exposure to mutations / alteration to DNA during replication
• prevent tumour formation
• tumour invades other tissues/organs
• • timing of cell cycle is linked to cell function

Question 7

Describe how mitosis is involved in an immune response. [3m]

Answer 7

• occurs in both primary AND secondary response
• SPECIFIC B cells and T cells divide by mitosis
• clonal expansion producing clones
• mitosis in memory cells for rapid secondary response

Question 8

Explain why determining the activity of telomerase may be useful in the diagnosis of lung cancer. [2m]

Answer 8

• cancer cells divide uncontrollably
• telomerase required to ensure CHROMOSOMES do not shorten
• high levels of telomerase indicate cells that are cancerous