Module 2 - cell division

Question 1

Describe the stages of the cell cycle.
(4 marks)

Answer 1

• G1 phase- cells grow, organelles and protein synthesis are synthesised.
• S phase- DNA is replicated and chromatid sisters are formed
• G2 phase - cell continues to grow, checks for DNA errors and prepares for mitosis.
• M phase- nuclear division followed by cytokinesis to form two identical daughter cells

Question 2

Explain the importance of checkpoints in the cell cycle. (3 marks)

(THIS ANSWER ONLY FOR 3-4 MARKERS)

Answer 2

Checkpoints are control mechanisms in cell cycles that ensure cells progress to the next stage when the conditions are correct. They check for DNA damage, successful DNA replication and correct the chromosomes attached to the spindle fibre before anaphase. If any errors are detected, the cell cycle stops and repairs the error before proceeding to the next stage. This prevents damaged DNA from dividing and helps maintain genetic stability.

Question 3

Explain the importance of checkpoints in the cell cycle. (6-8 markers)

Answer 3

Checkpoints are control mechanisms in the cell cycle that ensure the cell proceeds to the stage when the condition is right. There are checkpoints for each stage in the cell cycle:
- G1 checkpoint Checks for environmental conditions suitable for cell division, assessing cell size and nutrients. If the conditions are not favorable, the cell will not proceed to DNA replication.
- S checkpoint Monitors DNA replication for errors during synthesis.
- G2 checkpoint Ensures that all DNA has been replicated correctly before the cell enters mitosis.
- M checkpoint Spindle assembly checkpoint ensures chromosomes are properly attached to the spindle before anaphase.

Question 4

Describe what happens during interphase.
(4 marks)

Answer 4

• Cell grows and carries out normal metabolic functions.
• DNA is replicated during the S phase.
• Organelles are synthesized and proteins needed for mitosis are produced.
• The cell checks for DNA damage and prepares for mitosis.