Cell cycle and cell division: NEET short notes
Cell Cycle and Cell Division is a short Class 11 chapter that NEET asks from almost line by line. These notes keep NCERT's terms, put the stages in order, and give you two memory tricks for the parts students mix up most: the phases of mitosis and the five sub-stages of prophase I.
Short notes
- A typical human cell in culture divides about once every 24 hours; the M phase lasts only about 1 hour.
- Interphase (G1, S, G2) takes more than 95% of the cycle. It's called the resting phase, but the cell is very active.
- G1: the cell grows; no DNA replication. S: DNA replicates, from 2C to 4C, but the chromosome number stays 2n. G2: proteins are made for mitosis.
- In animal cells the centriole duplicates in the cytoplasm during the S phase.
- Cells that stop dividing (for example, heart cells) leave G1 for a quiescent stage, G0, and stay metabolically active.
- Mitosis is equational (2n → 2n): prophase, metaphase, anaphase, telophase.
- Metaphase is the best stage to study the shape (morphology) of chromosomes: they line up at the metaphase plate, spindle fibres attached at the kinetochores.
- Anaphase: centromeres split and sister chromatids move to opposite poles.
- Cytokinesis: a furrow in animal cells; a cell plate in plant cells, which becomes the middle lamella.
- Karyokinesis without cytokinesis gives a multinucleate cell (syncytium), as in the liquid endosperm of coconut.
- Meiosis is reductional (2n → n): one DNA replication, two divisions, four haploid cells.
- Prophase I: leptotene, zygotene (synapsis; synaptonemal complex), pachytene (crossing over, by the enzyme recombinase), diplotene (chiasmata appear), diakinesis (terminalisation of chiasmata).
- Anaphase I separates homologous chromosomes; sister chromatids separate only in anaphase II.
At a glance
| Mitosis | Meiosis | |
|---|---|---|
| Type | Equational: 2n → 2n | Reductional: 2n → n |
| Divisions | One | Two (Meiosis I and II) |
| Daughter cells | Two, identical | Four, haploid, varied |
| Crossing over | No | Yes, in pachytene |
| Purpose | Growth, repair, replacing cells | Gametes; keeps chromosome number constant across generations |
Memory tricks
Mitosis in order: PMAT
Prophase, Metaphase, Anaphase, Telophase. Read it as "Please Make A Tea".
Prophase I in order
"Lazy Zebras Pass Dark Doors": Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.
What happens where
Zygotene Zips (synapsis), Pachytene Packs a swap (crossing over), Diplotene Displays the X (chiasmata).
Practice questions
In which stage of prophase I does crossing over take place?
Show answer
Pachytene. Crossing over between non-sister chromatids happens in pachytene, helped by recombinase.
During the S phase, the DNA content and the chromosome number change as:
Show answer
2C → 4C; stays 2n. DNA doubles, but the number of chromosomes doesn't change.
The best stage to study the morphology of chromosomes is:
Show answer
Metaphase. In metaphase the chromosomes are most condensed and lined up at the metaphase plate.
Which statement about anaphase I is correct?
Show answer
Homologous chromosomes separate. Homologues separate in anaphase I; sister chromatids separate in anaphase II.
The liquid endosperm of coconut is an example of:
Show answer
Karyokinesis without cytokinesis. The nucleus divides many times without the cytoplasm dividing, giving a multinucleate syncytium.
Questions
How many questions come from cell cycle in NEET?
It varies by year. The chapter is short and NEET often uses NCERT's own lines from it, so it's worth revising fully, especially the stages and the mitosis-meiosis differences.
What is the easiest way to remember the stages of prophase I?
Use "Lazy Zebras Pass Dark Doors": Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis. Then attach one event to each: synapsis in zygotene, crossing over in pachytene, chiasmata in diplotene.
Can I make notes like these from my own chapter PDF?
Yes. Add your chapter PDF or photos of the pages to TellBrief, choose NEET UG once, and you get short notes, memory tricks and NEET-style MCQs, every point linked to its page.