2.1.6 Cell division, cell diversity and cellular
organisation
(a) the cell cycle
The cell cycle is the process by which all body cells grow and
divide.
A cell spends the majority of its time in interphase, consisting of G1,
S and G2. There are two stages of the mitotic phase: mitosis and
cytokinesis.
Mitosis: the nucleus divides
Cytokinesis: the cytoplasm divides and two cells are produced.
Phase Events
M phase Cell growth stops
Mitosis Nuclear division (4 stages)
Cytokinesis
G0 phase Cells may undergo apoptosis, differentiation or senescence
Gap Some remain in this phase for a very long time/indefinitely (neurones)
G1 phase Cell growth
Growth Transcription of genes to make RNA
Organelles duplicate
Protein synthesis (e.g. enzymes needed for DNA replication in S)
S phase DNA replicates – each chromosome has 2 sister chromatids
Synthesis Very fast as exposed DNA is susceptible to mutations
G2 phase Cell grows
Growth Energy stores increased
Duplicated DNA checked for errors
(b) how the cell cycle is regulated
Checkpoints:
Checkpoints monitor and verify whether the processes at each phase have been accurately
completed before the cell can progress onto the next phase. Checkpoints prevent uncontrolled
division that would lead to tumours. They detect and repair damage to DNA.
Checkpoint Details
M checkpoint Checkpoint chemical triggers condensation of chromatin
Metaphase checkpoint ensures chromosomes are attached to the spindles
Early G1 Triggers cell to enter G0 (resting phase)
G1 checkpoint G1 checkpoint control mechanism ensures cell is ready to enter S phase
Checks chemicals needed for replication are present
Checks for DNA damage
G2 checkpoint Checks for cell size, DNA damage, DNA replication
(c) the main stages of mitosis
(d) sections of plant tissue showing the cell cycle and stages of mitosis
organisation
(a) the cell cycle
The cell cycle is the process by which all body cells grow and
divide.
A cell spends the majority of its time in interphase, consisting of G1,
S and G2. There are two stages of the mitotic phase: mitosis and
cytokinesis.
Mitosis: the nucleus divides
Cytokinesis: the cytoplasm divides and two cells are produced.
Phase Events
M phase Cell growth stops
Mitosis Nuclear division (4 stages)
Cytokinesis
G0 phase Cells may undergo apoptosis, differentiation or senescence
Gap Some remain in this phase for a very long time/indefinitely (neurones)
G1 phase Cell growth
Growth Transcription of genes to make RNA
Organelles duplicate
Protein synthesis (e.g. enzymes needed for DNA replication in S)
S phase DNA replicates – each chromosome has 2 sister chromatids
Synthesis Very fast as exposed DNA is susceptible to mutations
G2 phase Cell grows
Growth Energy stores increased
Duplicated DNA checked for errors
(b) how the cell cycle is regulated
Checkpoints:
Checkpoints monitor and verify whether the processes at each phase have been accurately
completed before the cell can progress onto the next phase. Checkpoints prevent uncontrolled
division that would lead to tumours. They detect and repair damage to DNA.
Checkpoint Details
M checkpoint Checkpoint chemical triggers condensation of chromatin
Metaphase checkpoint ensures chromosomes are attached to the spindles
Early G1 Triggers cell to enter G0 (resting phase)
G1 checkpoint G1 checkpoint control mechanism ensures cell is ready to enter S phase
Checks chemicals needed for replication are present
Checks for DNA damage
G2 checkpoint Checks for cell size, DNA damage, DNA replication
(c) the main stages of mitosis
(d) sections of plant tissue showing the cell cycle and stages of mitosis
