Cell Cycle and Cell Division is an important chapter in Class 11 Biology that explains how cells grow, replicate their genetic material, and divide to form new cells. The chapter covers the stages of the cell cycle, including interphase (G₁, S, and G₂ phases) and the M phase. It also explains the processes of mitosis and meiosis, their stages, and their significance in growth, repair, and reproduction. In addition, it discusses key events such as DNA replication, chromosome behavior, and cytokinesis.
These revision notes on Cell Cycle and Cell Division, prepared by ALLEN’s expert faculty, provide a clear overview of the chapter’s key concepts, stages, and important mechanisms involved in cell division. Designed for quick and effective revision, they help students strengthen conceptual understanding, remember important processes and stages, and prepare efficiently for board and competitive exams.
1. What is cell division and why is it important?
Growth and reproduction are fundamental characteristics of cells and all living organisms. Cells reproduce by dividing into two, where each parental cell forms two daughter cells.
These daughter cells can grow and divide repeatedly, forming a large population of cells from a single parental cell. Thus, cycles of growth and division allow a single cell to develop into structures containing millions of cells.
The term mitosis was proposed by Flemming. Mitosis produces genetically identical daughter cells that are similar to the mother cell.
2. What are the causes of mitosis?
Two main explanations are given for the occurrence of mitosis.
a. Kern-Plasm Theory (Hertwig)
According to this theory, mitosis occurs due to disturbance in the karyoplasmic index (KI) or nucleocytoplasmic ratio.
Karyoplasmic Index:
KI = Vn / (Vc − Vn)
Where
Key idea:
b. Surface-Volume Ratio
As a cell grows:
To increase the surface-volume ratio, the cell divides.
3. What is the cell cycle?
The cell cycle is the sequence of events through which a cell passes from one division to the next.
It includes:
These processes occur in a coordinated manner to ensure correct division and formation of daughter cells containing complete genomes.
Although cytoplasmic growth is continuous, DNA synthesis occurs only during one specific stage of the cycle.
Also Read: Cell Cycle and Cell Division
4. What are the phases of the cell cycle?
A typical eukaryotic cell divides once in about 24 hours, while yeast may complete the cycle in 90 minutes.
The cell cycle has two major phases.
Interphase
Interphase occurs between two successive M phases and consists of three stages:
M Phase (Mitotic Phase)
The M phase lasts about one hour in the human cell cycle.
Key events:
Because chromosome number remains unchanged in daughter cells, mitosis is called equational division.
5. What is mitosis and what are its stages?
Mitosis is an equational division in which daughter cells receive the same chromosome number as the parent cell.
It occurs mainly in diploid somatic cells in animals, while in plants it may occur in both haploid and diploid cells.
Mitosis consists of four stages of nuclear division (karyokinesis):
Cytokinesis follows nuclear division.
6. Explain the stages of mitosis.
Prophase
Metaphase
This stage is ideal for studying chromosome morphology.
Anaphase
Telophase
Telophase is often called reverse prophase.
7. What is cytokinesis and how does it occur in animal and plant cells?
Cytokinesis is the division of cytoplasm following nuclear division.
Steps:
This occurs in centripetal order (outside to inside).
Plant cells have a rigid cell wall, so cytokinesis occurs differently.
Steps:
This occurs in centrifugal order.
Also Read: Plant cell and animal cell
8. What is a special case in mitosis?
In some organisms, karyokinesis occurs without cytokinesis, producing a multinucleate cell called syncytium.
Example: Liquid endosperm in coconut.
9. What is the significance of mitosis?
Mitosis plays several important roles:
10. What is meiosis and what are its key features?
Meiosis is a special type of cell division that reduces the chromosome number by half and produces haploid daughter cells.
Key features:
Meiosis maintains the haploid phase, while fertilisation restores the diploid phase.
11. Explain the stages of Meiosis I.
Meiosis I is called reduction division because chromosome number is reduced.
Prophase I
Metaphase I
Anaphase I
Telophase I
12. What is interkinesis?
Interkinesis is the short interval between Meiosis I and Meiosis II.
Characteristics:
13. Explain the stages of Meiosis II.
Meiosis II resembles mitosis and is called equational division.
Prophase II
Metaphase II
Anaphase II
Telophase II
14. What is the significance of meiosis?
Meiosis has two major roles:
Stages of Mitosis : “PMAT = Please Make A Table”
P → Prophase
M → Metaphase
A → Anaphase
T → Telophase
Cell Cycle Phases: Trick: “Grow – Synthesize – Get Ready – Multiply”
G1 → Grow (cell increases in size)
S → Synthesize DNA
G2 → Get ready for division
M → Multiply (mitosis occurs)
Question: Which of the following stages of meiosis involves division of centromere?
Answer: Anaphase II
Question: The process of appearance of recombination nodules occurs during which substage of prophase I?
Answer: Pachytene
Question: Among eukaryotes, replication of DNA takes place in:
Answer: S phase
(Session 2026 - 27)