Step-by-step NCERT solutions for Cell Cycle and Cell Division (Chapter 10, NCERT Class 11 Biology) — every question and answer worked out in full, not just the final result. You can also read the Cell Cycle and Cell Division textbook chapter.
All 16 questions in Cell Cycle and Cell Division are solved in the PDF. Here's what's inside, exercise by exercise:
3 questions from Cell Cycle and Cell Division, solved step by step.
Exercises
The average duration of the cell cycle for a typical mammalian cell grown in culture is approximately 24 hours.
Of this total, the M phase (actual cell division) lasts only about 1 hour, while the interphase occupies more than 95% of the cycle — roughly 23 hours.
Answer: Approximately 24 hours for a typical mammalian cell in culture, with interphase occupying more than 95% of that time.
Exercises
Karyokinesis:
1. It is the division of the nucleus.
2. It involves the separation and distribution of duplicated chromosomes (DNA) into two daughter nuclei.
3. It encompasses the four stages: prophase, metaphase, anaphase, and telophase.
4. It precedes cytokinesis.
Cytokinesis:
1. It is the division of the cytoplasm.
2. It results in the physical splitting of one parental cell into two daughter cells.
3. In animal cells, it occurs by cleavage furrow formation (inward pinching of the plasma membrane).
4. In plant cells, it occurs by cell-plate formation that grows outward from the centre to meet the lateral walls.
5. It follows karyokinesis to complete cell division.
Note: In some organisms karyokinesis occurs without cytokinesis, producing multinucleate cells called syncytia (e.g., liquid endosperm of coconut).
Answer: Karyokinesis = nuclear division (segregation of chromosomes into two nuclei); cytokinesis = cytoplasmic division that physically separates the two daughter cells. Cytokinesis follows karyokinesis.
Exercises
Interphase is the preparatory phase between two successive M phases. Though called the 'resting phase', the cell is highly metabolically active. It comprises three sub-phases:
G1 phase (Gap 1 / First Growth phase):
- Corresponds to the interval between the end of the previous M phase and the start of DNA replication.
- The cell grows in size; metabolic activity is high.
- Organelle duplication (other than centrioles) occurs.
- DNA is NOT yet replicated.
- Cells that exit the cycle permanently enter the G0 (quiescent) stage from here.
S phase (Synthesis phase):
- DNA replication (synthesis) takes place; the amount of DNA per cell doubles from 2C to 4C.
- Chromosome number remains the same (2n — no new chromosomes are added; each chromosome now consists of two identical sister chromatids).
- In animal cells, centrioles also duplicate during this phase.
G2 phase (Gap 2 / Second Growth phase):
- DNA replication is complete; the cell checks for errors.
- Proteins required for mitosis (e.g., tubulin for spindle fibres) are synthesised.
- Cell growth continues in preparation for division.
Answer: Interphase has three phases — G1 (cell growth, no DNA replication), S (DNA replication, DNA doubles from 2C to 4C, centriole duplication in animal cells), and G2 (protein synthesis for mitosis, further cell growth). The cell prepares for division throughout.
All 16 questions in Cell Cycle and Cell Division are solved step by step in the Solutions PDF above.
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