Cell Cycle and Cell Division mind map

Cell Cycle and Cell Division: what the chapter covers

The main idea of each topic with its first key points. Open a branch above for everything, or read the full notes.

1. 1Chapter Overview

   Cell Cycle and Cell Division explains how cells grow, duplicate their DNA and divide to form new cells. NCERT divides the chapter into the cell cycle, mitosis, meiosis and the significance of division. The cell cycle has interphase, where the cell grows and replicates DNA, and M phase, where nuclear and cytoplasmic division occur. Mitosis produces two genetically identical diploid daughter cells and is important for growth, repair and asexual reproduction. Meiosis produces haploid gametes by two successive divisions and creates genetic variation through crossing over and independent assortment. For NEET, the most important areas are phase sequence, chromosome and DNA content changes, differences between mitosis and meiosis, crossing over, chiasmata, synapsis and biological significance.

   • A typical eukaryotic cell cycle is divided into a long interphase and a short M phase.
   • DNA replication occurs only during S phase, not during G₁ or G₂.
   • M phase includes karyokinesis followed by cytokinesis.
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2. 2Cell Cycle

   The cell cycle is the ordered sequence of events by which a cell duplicates its contents and divides into daughter cells. In eukaryotes, it has two major parts: interphase and M phase. Interphase occupies most of the cycle and includes G₁, S and G₂ phases. During G₁, the cell grows and synthesizes RNA and proteins. During S phase, DNA replication occurs and each chromosome becomes two sister chromatids. During G₂, the cell prepares for mitosis by making proteins needed for spindle formation. M phase includes nuclear division and cytokinesis. Cell cycle regulation ensures DNA is copied accurately and division occurs only when conditions are suitable. NEET questions often focus on phase order, DNA content and G₀ phase.

   • A human cell cycle is often described as approximately 24 hours, with M phase lasting about 1 hour in many dividing cells.
   • Chromosome number remains constant during S phase, but DNA amount doubles.
   • Centrioles duplicate during S phase in animal cells.
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3. 3Mitosis

   Mitosis is the type of cell division in which one parent cell produces two genetically identical daughter cells with the same chromosome number as the parent. It is called equational division because sister chromatids separate and chromosome number is maintained. Mitosis includes prophase, metaphase, anaphase and telophase, followed by cytokinesis. In prophase, chromatin condenses into visible chromosomes and spindle formation begins. In metaphase, chromosomes align at the equatorial plate. In anaphase, sister chromatids separate and move to opposite poles. In telophase, chromosomes decondense and nuclear envelopes re-form. Cytokinesis divides the cytoplasm. Mitosis is essential for growth, repair, regeneration and asexual reproduction. NEET often asks stage identification, cytokinesis differences and chromosome behavior.

   • Each metaphase chromosome has two sister chromatids joined at the centromere.
   • Spindle fibres attach to kinetochores of chromosomes.
   • Anaphase begins when centromeres split longitudinally.
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4. 4Meiosis

   Meiosis is a specialized cell division that produces haploid cells from diploid germ cells. It includes two successive divisions, meiosis I and meiosis II, after only one round of DNA replication. Meiosis I is reductional because homologous chromosomes separate and chromosome number becomes half. Meiosis II is equational because sister chromatids separate, similar to mitosis. The most important stage is prophase I, divided into leptotene, zygotene, pachytene, diplotene and diakinesis. Synapsis occurs in zygotene, crossing over occurs in pachytene, and chiasmata are visible in diplotene. Meiosis generates genetic variation through crossing over and independent assortment. It is essential for sexual reproduction and maintenance of chromosome number across generations. NEET frequently tests prophase I events and mitosis-meiosis differences.

   • Homologous chromosomes pair during synapsis to form bivalents.
   • A bivalent has two homologous chromosomes and four chromatids, also called a tetrad.
   • Crossing over occurs between non-sister chromatids of homologous chromosomes.
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5. 5Significance of Cell Division

   Cell division is essential for life because it connects cellular continuity with growth, repair, reproduction and evolution. Mitosis increases cell number while maintaining chromosome number and genetic identity. This makes it vital for embryonic development, growth of multicellular organisms, replacement of worn-out cells, wound healing, regeneration and asexual reproduction. Meiosis has a different significance: it produces haploid gametes or spores, maintains chromosome number across sexually reproducing generations and creates genetic diversity. Without meiosis, fertilisation would double the chromosome number every generation. Without mitosis, a zygote could not develop into a multicellular organism. Genetic diversity produced during meiosis provides raw material for natural selection and adaptation. NEET questions often ask which type of division is responsible for growth, repair, gamete formation or chromosome number maintenance.

   • Mitosis preserves genetic stability by producing identical cells.
   • Meiosis prevents chromosome number doubling in every generation.
   • Asexual reproduction usually depends on mitotic division, producing clones.
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