Chapter 10: Cell Cycle and Cell Division – Case-Based / Source-Based Questions with Answers

CBSE Class 11 Biology Case-Based / Source-Based Questions – Cell Cycle and Cell Division (Chapter 10 | NCERT)

Course & Examination Details (Systematic Format)

Course: CBSE Class 11 Biology
Unit: III – Cell Structure and Function
Chapter: 10 – Cell Cycle and Cell Division
Based on: NCERT Textbook
Examination: CBSE Board Examination (Class XI)
Assessment Focus: Flowcharts, stage identification, comparison of mitosis and meiosis, application-based understanding

Section A: Cell Cycle and Its Phases (Case-Based Q1–Q6)

Case 1:

A population of cells is observed under a microscope. Most cells are found synthesizing proteins and replicating DNA, while very few are dividing.

Q1. Which phase of the cell cycle do most cells belong to?
Answer:
Most cells belong to interphase, which is the longest and most metabolically active phase of the cell cycle.

Q2. Why are fewer cells observed in the dividing stage?
Answer:
Cell division occurs in a shorter duration compared to interphase, so fewer cells are observed in the M phase.

Case 2:

A cell fails to enter the S phase due to unfavorable environmental conditions.

Q3. Which checkpoint prevents the cell from progressing further?
Answer:
The G₁ checkpoint prevents the cell from entering the S phase under unfavorable conditions.

Q4. What is the fate of such a cell if conditions remain unsuitable?
Answer:
The cell may enter the G₀ phase, where it stops dividing but remains metabolically active.

Case 3:

During an experiment, DNA content of a cell is found to be doubled, but chromosome number remains unchanged.

Q5. Identify the phase of the cell cycle.
Answer:
The cell is in the S phase of interphase.

Q6. Why does chromosome number remain unchanged despite DNA duplication?
Answer:
Because each chromosome duplicates into sister chromatids joined at the centromere, maintaining chromosome number.

Section B: Mitosis (Case-Based Q7–Q12)

Case 4:

A cell shows condensed chromosomes, disappearance of nuclear membrane, and spindle formation.

Q7. Identify the stage of mitosis.
Answer:
The stage is prophase.

Q8. State one major event that follows this stage.
Answer:
Chromosomes align at the equatorial plane during metaphase.

Case 5:

Chromosomes are clearly visible and arranged at the equator of the cell.

Q9. Name the stage of mitosis shown.
Answer:
The stage is metaphase.

Q10. Why is this stage suitable for karyotyping?
Answer:
Chromosomes are maximally condensed and clearly distinguishable in size and shape.

Case 6:

During division, sister chromatids move toward opposite poles after centromere division.

Q11. Identify the stage of mitosis.
Answer:
The stage is anaphase.

Q12. What ensures equal distribution of chromosomes during this stage?
Answer:
Splitting of centromeres and spindle fiber action ensure equal distribution.

Section C: Meiosis (Case-Based Q13–Q19)

Case 7:

Homologous chromosomes pair and exchange genetic material.

Q13. Name the process occurring here.
Answer:
The process is crossing over.

Q14. During which stage of meiosis does this occur?
Answer:
Crossing over occurs during the pachytene stage of prophase I.

Case 8:

Two homologous chromosomes remain attached at certain points after crossing over.

Q15. What are these attachment points called?
Answer:
They are called chiasmata.

Q16. What is the significance of chiasmata?
Answer:
They indicate sites of genetic recombination and help in proper separation of homologous chromosomes.

Case 9:

A cell division results in two cells with half the chromosome number of the parent cell.

Q17. Which division is responsible for this reduction?
Answer:
Meiosis I is responsible for reduction in chromosome number.

Q18. Which stage leads to this reduction?
Answer:
Anaphase I, where homologous chromosomes separate.

Case 10:

A division resembles mitosis but occurs in haploid cells.

Q19. Identify this division.
Answer:
The division is meiosis II.

Section D: Comparison of Mitosis and Meiosis (Case-Based Q20–Q23)

Case 11:

A tissue shows rapid cell multiplication for growth, while another tissue produces gametes.

Q20. Which type of division occurs in the growing tissue?
Answer:
Mitosis occurs in growing somatic tissues.

Q21. Which type of division occurs during gamete formation?
Answer:
Meiosis occurs during gamete formation.

Case 12:

Cells produced after a division are genetically identical.

Q22. Identify the type of cell division.
Answer:
The division is mitosis.

Q23. Why is genetic identity maintained in this division?
Answer:
Because there is no crossing over and chromosome number remains unchanged.

Section E: Significance of Cell Division (Case-Based Q24–Q25)

Case 13:

A wound heals due to formation of new skin cells.

Q24. Which type of cell division helps in this process?
Answer:
Mitosis helps in wound healing by replacing damaged cells.

Case 14:

A species shows variation among offspring even with same parents.

Q25. Which process during cell division is responsible for this variation?
Answer:
Crossing over and independent assortment during meiosis are responsible for variation.

✅ Academic Relevance

✔ Fully aligned with NCERT Class 11 Biology
✔ Ideal for CBSE competency-based & case-based questions
✔ Strong focus on application, reasoning, and stage identification