Lesson 4 ·Class 10 · Structure of Chromosomes, Cell Cycle and Cell Division · Flow Lab
Why Cells Divide — The Cell Cycle
And why interphase is not a rest.
A cell does not divide the moment it is born. Follow the cycle it goes through first.
→ → → → →
❓ Step 1 of 6 · Why divide at all?
For growth, for the repair and replacement of worn-out cells, and for reproduction. A cell also cannot grow indefinitely — as it enlarges, its surface falls behind its volume.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Interphase takes up most of the cell cycle. Division is the short, dramatic part at the end of a long period of preparation.
What this lesson covers
Challenges to clear
- Advance to the phase where the DNA is actually copied.
- Reach the correction about the so-called resting phase.
- Step through the whole cycle.
The task
A cell does not divide the moment it is born. Follow the cycle it goes through first.
What this lesson covers
- Why divide at all? — For growth, for the repair and replacement of worn-out cells, and for reproduction. A cell also cannot grow indefinitely — as it enlarges, its surface falls behind its volume.
- G₁ — First Growth Phase — RNA and proteins are synthesised and the volume of cytoplasm increases. The cell is growing and preparing.
- S — Synthesis Phase — DNA is synthesised and the chromosomes are duplicated. This — not prophase — is where copying happens.
- G₂ — Second Growth Phase — A shorter phase in which the RNA and proteins needed for division itself are made. Absent in meiosis.
- M — the dividing phase — Karyokinesis, the division of the nucleus in four phases, followed by cytokinesis, the division of the cytoplasm.
- Not a resting phase — Interphase was once called the resting phase because nothing visibly changes. Selina corrects this directly: in reality the cell is quite active during interphase in synthesising more DNA. Cells that genuinely withdraw from the cycle are said to enter a resting state in late G₁.
Hint
Interphase takes up most of the cell cycle. Division is the short, dramatic part at the end of a long period of preparation.