OCR Biology A-level - Cell Division: Well Defined
Terms with Certified Solutions 2023-2024
Interphase
The stage in which normal growth and working take place e.g. producing
enzymes or hormones and preparing for division, no active division takes place.
During interphase
DNA replicated + checked. Protein synthesis. Mitochondria grow + divide )in
plant and algal cells). Chloroplasts grow + divide. Normal metabolic processes
occur
Mitotic phase
The period of cell division
Stages of cell division
1. Mitosis 2. Cytokinesis
Mitosis
The nucleus divides
Cytokinesis
The cytoplasm divides and two cells are produced
Stages of interphase
G1 = 1st growth = proteins are synthesised, organelles replicate = cell increases
in size.
S = synthesis = DNA replicates
G2 = 2nd growth = cell grows more, energy stores increase, duplicated DNA is
checked for errors
, OCR Biology A-level - Cell Division: Well Defined
Terms with Certified Solutions 2023-2024
G0
The phase when the cell leaves the cycle, either temporarily or permanently.
Differentiation
A cell that becomes specialised to carry out a particular function is no longer able
to divide. It will carry out the function indefinitely and not enter the cell cycle
Why might a cell leave a cycle (temporarily or permanently)
Differentiation, damaged DNA = cell arrest, get older = more cells
How is the cell cycle controlled?
Checkpoints = monitor and verify whether each stage has been accurately
completed before the cell goes in to the next phase.
Checkpoints
Monitor and verify whether each stage has been accurately completed before the
cell goes in to the next phase. G1, G2 and metaphase checkpoints
G1 checkpoint
After the G1 phase, before the S phase.
If the requirements are met then the checkpoint triggers the DNA replication, if
not it enters resting state
G2 checkpoint
At the end of G2 phase, before the mitotic phase. DNA is checked. If it passes
the cell initiates the molecular process that signifies the beginning of mitosis
Terms with Certified Solutions 2023-2024
Interphase
The stage in which normal growth and working take place e.g. producing
enzymes or hormones and preparing for division, no active division takes place.
During interphase
DNA replicated + checked. Protein synthesis. Mitochondria grow + divide )in
plant and algal cells). Chloroplasts grow + divide. Normal metabolic processes
occur
Mitotic phase
The period of cell division
Stages of cell division
1. Mitosis 2. Cytokinesis
Mitosis
The nucleus divides
Cytokinesis
The cytoplasm divides and two cells are produced
Stages of interphase
G1 = 1st growth = proteins are synthesised, organelles replicate = cell increases
in size.
S = synthesis = DNA replicates
G2 = 2nd growth = cell grows more, energy stores increase, duplicated DNA is
checked for errors
, OCR Biology A-level - Cell Division: Well Defined
Terms with Certified Solutions 2023-2024
G0
The phase when the cell leaves the cycle, either temporarily or permanently.
Differentiation
A cell that becomes specialised to carry out a particular function is no longer able
to divide. It will carry out the function indefinitely and not enter the cell cycle
Why might a cell leave a cycle (temporarily or permanently)
Differentiation, damaged DNA = cell arrest, get older = more cells
How is the cell cycle controlled?
Checkpoints = monitor and verify whether each stage has been accurately
completed before the cell goes in to the next phase.
Checkpoints
Monitor and verify whether each stage has been accurately completed before the
cell goes in to the next phase. G1, G2 and metaphase checkpoints
G1 checkpoint
After the G1 phase, before the S phase.
If the requirements are met then the checkpoint triggers the DNA replication, if
not it enters resting state
G2 checkpoint
At the end of G2 phase, before the mitotic phase. DNA is checked. If it passes
the cell initiates the molecular process that signifies the beginning of mitosis
