Cell Cycle AND Cell Division flash cards

1. 1.What is the cell cycle?

   The sequence of events by which a cell duplicates its genome, synthesises its cell constituents and eventually divides into two daughter cells.

   Hint: Duplicate then divide.

2. 2.Name the two basic phases of the cell cycle.

   Interphase and M phase (mitosis phase / dividing phase).

   Hint: Resting vs dividing.

3. 3.In a typical human cell dividing in ~24 hours, how long does the cell cycle take and how is it split?

   About 24 hours; cell division (M phase) lasts only about 1 hour, and interphase takes the remaining ~23 hours.

   Hint: M phase is short.

4. 4.What was the human cell type and duration used as the representative example in NCERT for the 24-hour cell cycle?

   Human cells in culture divide once in approximately 24 hours.

   Hint: Cells in culture.

5. 5.What is interphase often called and why?

   The 'resting phase' — because there is no apparent cell division, but the cell is actually very active, preparing for division by growth and DNA replication.

   Hint: Resting only in appearance.

6. 6.Name the three sub-phases of interphase in order.

   G1 phase (Gap 1), S phase (Synthesis) and G2 phase (Gap 2).

   Hint: Gap–Synthesis–Gap.

7. 7.What happens during the G1 phase?

   The cell is metabolically active and continuously grows, but does not replicate its DNA.

   Hint: Growth, no DNA copying.

8. 8.What key event occurs during the S phase?

   DNA replication (synthesis) — the amount of DNA per cell doubles.

   Hint: S for Synthesis of DNA.

9. 9.If DNA content at G1 is 2C, what is it at the end of S phase?

   4C — the DNA doubles from 2C to 4C, though the number of chromosomes (ploidy, 2n) stays the same.

   Hint: DNA doubles, chromosome number unchanged.

10. 10.During S phase, does the chromosome number change?

    No. DNA amount doubles but the number of chromosomes does not increase; each chromosome now has two sister chromatids.

    Hint: 2n stays 2n.

11. 11.In animal cells, when does centriole duplication occur?

    In the S phase, in the cytoplasm the centriole duplicates.

    Hint: Along with DNA synthesis.

12. 12.What happens during the G2 phase?

    Proteins are synthesised and the cell continues to grow in preparation for mitosis; the cell prepares for division.

    Hint: Grow and make proteins before M.

13. 13.What is the G0 (quiescent) stage?

    A stage where cells that do not divide further exit the G1 phase and stay metabolically active but do not proliferate unless required.

    Hint: Exit from G1, no division.

14. 14.Give an example of cells that remain in the G0 (quiescent) stage.

    Heart cells (and many highly differentiated cells such as neurons) do not divide and stay in G0.

    Hint: Non-dividing differentiated cells.

15. 15.How often do most plant and animal cells (e.g. meristem) vs some organisms differ in cycle timing? Give the yeast example.

    Different cells take different times; e.g. yeast can progress through the cell cycle in only about 90 minutes.

    Hint: Yeast is fast.

16. 16.What are the two stages that make up the M phase (mitosis)?

    Karyokinesis (division of the nucleus) and cytokinesis (division of the cytoplasm).

    Hint: Nucleus first, then cytoplasm.

17. 17.What does mitosis produce and why is it called equational division?

    It produces two daughter cells with the same number of chromosomes as the parent cell — hence 'equational division'.

    Hint: Same chromosome number as parent.

18. 18.Name the four stages of karyokinesis (mitosis) in order.

    Prophase, Metaphase, Anaphase and Telophase.

    Hint: PMAT.

19. 19.What happens to chromosomes during prophase?

    Chromosomal material condenses to form compact mitotic chromosomes; each chromosome is seen to be made of two sister chromatids joined at the centromere.

    Hint: Condensation begins.

20. 20.What happens to the centrosome during prophase?

    The centrosome, which had duplicated in S phase, begins to move towards opposite poles; each centriole radiates out microtubules forming the spindle fibres.

    Hint: Centrosomes migrate to poles.

21. 21.Which cell structures are NOT seen (disappear) at the end of prophase?

    The Golgi complex, endoplasmic reticulum, nucleolus and the nuclear envelope are no longer visible.

    Hint: ER, Golgi, nucleolus, nuclear membrane gone.

22. 22.What is the defining feature of metaphase regarding chromosome position?

    All chromosomes line up (align) at the metaphase plate (equator) of the cell.

    Hint: Chromosomes at the equator.

23. 23.What is a metaphasic chromosome made of and where is the kinetochore?

    Two sister chromatids held together at the centromere; small disc-shaped kinetochores are present at the surface of the centromere.

    Hint: Kinetochore on centromere.

24. 24.What is the role of the kinetochore in metaphase?

    Spindle fibres attach to the kinetochores of chromosomes, which are aligned at the metaphase plate.

    Hint: Spindle attachment site.

25. 25.List the events used to characterise metaphase.

    Spindle fibres attach to kinetochores; chromosomes are moved to the spindle equator and get aligned along the metaphase plate through spindle fibres.

    Hint: Attach and align at equator.

26. 26.What key event marks anaphase?

    The centromeres split and the two sister chromatids separate; each chromatid becomes a daughter chromosome that moves towards opposite poles.

    Hint: Sister chromatids pulled apart.

27. 27.During anaphase, how do the daughter chromosomes move?

    They move towards opposite poles, with the centromere leading (at the leading edge) and the arms trailing behind.

    Hint: Centromere goes first.

28. 28.What happens to chromosomes during telophase?

    Chromosomes cluster at opposite poles, decondense (lose individuality) into chromatin, and the nuclear envelope reassembles around each cluster.

    Hint: Reverse of prophase.

29. 29.Which organelles reappear/reform during telophase?

    The nuclear envelope, nucleolus, Golgi complex and endoplasmic reticulum reform.

    Hint: Everything that vanished in prophase returns.

30. 30.What is cytokinesis?

    Division of the cytoplasm that follows karyokinesis, completing cell division into two daughter cells.

    Hint: Cytoplasm splits.

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