ICSE Class 10 Biology Chapter 2: Cell Cycle and Division

ICSE Class 10 Biology Revision Notes

• Class 10 Biology Chapter 2 covers Cell Cycle, Cell Division, and Structure Of Chromosomes
• Revision Notes and Short Key-notes are prepared by expert Biology teachers as per ICSE guidelines
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Importance of ICSE Class 10 Exam

• Considered the first milestone in a student's educational journey
• Marks obtained in the exam are considered by schools, colleges, and universities for admission
• Reflects a student's educational excellence and basic academic skills

Cell Cycle and Division

• Cell division is essential for growth, replacement of old cells, repair of injury, and reproduction of living organisms.
• The cell cycle consists of two phases: Interphase and Mitotic phase (M-phase).

Interphase

• Interphase is the interval between two successive cell divisions.
• It is divided into three stages: G1 phase, S-phase, and G2 phase.

Cell Division

• Cell division involves three major steps: replication of DNA, division of nucleus (karyokinesis), and division of cytoplasm (cytokinesis).
• There are two types of cell division: Mitosis and Meiosis.

Mitosis

• Mitosis is the cell division that occurs in four phases: prophase, metaphase, anaphase, and telophase.
• Prophase: chromosomes become short and thick, move towards the equator of the cell, and duplicate to form two chromatids attached to each other at the centromere.
• Metaphase: chromosomes arrange themselves on the equatorial plane, each attached to a spindle fibre at its centromere.
• Anaphase: centromere divides, and two sister chromatids of each chromosome separate and move towards opposite poles.
• Telophase: chromatids become thinner, and nuclear membrane reappears; nucleolus also reappears in each daughter nucleus.
• Mitosis is followed by cytokinesis, which divides the cytoplasm into two, producing two new cells.

Meiosis

• Meiosis is the type of cell division that produces sex cells or gametes.
• It involves two divisions: meiosis I (reduction division) and meiosis II (equational division).
• Meiosis reduces the number of chromosomes in the cells by half.

Significance of Mitosis

• Mitosis plays an important role in vegetative growth, wound healing, repair, and regeneration.
• It maintains the same chromosome number in the daughter cells as the mother cell.
• It maintains the proper size of a cell.
• It helps in asexual reproduction, e.g., binary fission in Amoeba.

Significance of Meiosis

• Meiosis plays an important role in sexual reproduction, i.e., in the formation of gametes (sperms and ova).
• It maintains the constant number of chromosomes in a species.
• It brings about recombination between maternal and paternal genes, thereby bringing in genetic variations responsible for evolution.

Chromosomes and DNA

• Chromosomes are long thread-like structures made of DNA and proteins.
• DNA molecule is made up of a double chain of nucleotides in the form of a helix.
• A nucleotide is a sugar molecule joined to a phosphate group and an organic base.

Differences between Mitosis and Meiosis

• Mitosis occurs in vegetative cells, whereas meiosis occurs in reproductive cells.
• Mitosis involves one cell division, whereas meiosis involves two successive divisions.
• Mitosis produces two daughter cells, whereas meiosis produces four daughter cells.
• Mitosis produces genetically similar daughter cells, whereas meiosis produces genetically different daughter cells.
• Mitosis maintains the same number of chromosomes in the daughter cells as the parent cell, whereas meiosis reduces the number of chromosomes by half.