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Cell Biology - Cell Division

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The cell cycle consists of Interphase (G1G_{1}, SS, and G2G_{2}) and the M-phase (Mitosis and Cytokinesis).

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During the SS phase (Synthesis), DNA replication occurs, ensuring that each daughter cell receives a complete set of genetic information.

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Mitosis results in two genetically identical diploid daughter cells, represented by the chromosome number 2n2n.

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The four stages of Mitosis are Prophase, Metaphase (chromosomes line up at the equator), Anaphase (sister chromatids separate), and Telophase.

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Meiosis is a reduction division that produces four non-identical haploid (nn) gametes, occurring in two stages: Meiosis I and Meiosis II.

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Genetic variation in Meiosis is achieved through 'Crossing Over' during Prophase I and 'Independent Assortment' during Metaphase I.

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Cytokinesis is the division of the cytoplasm; in animal cells, it occurs via a cleavage furrow, while in plant cells, a cell plate forms.

📐Formulae

2n=Diploid number of chromosomes2n = \text{Diploid number of chromosomes}

n=Haploid number of chromosomesn = \text{Haploid number of chromosomes}

N=2kN = 2^{k}

Mitotic Index=Number of cells in mitosisTotal number of cells×100%\text{Mitotic Index} = \frac{\text{Number of cells in mitosis}}{\text{Total number of cells}} \times 100\%

💡Examples

Problem 1:

A single parent cell undergoes 55 rounds of mitotic division. Calculate the total number of daughter cells produced.

Solution:

Using the formula for exponential growth in mitosis: N=2kN = 2^{k} Given k=5k = 5: N=25=32N = 2^{5} = 32

Explanation:

In mitosis, each division doubles the number of cells. After 55 consecutive divisions, the number of cells is 2×2×2×2×2=322 \times 2 \times 2 \times 2 \times 2 = 32.

Problem 2:

If a horse has a diploid chromosome number of 2n=642n = 64, determine the number of chromosomes found in its gametes and the number of chromatids present during Metaphase of mitosis.

Solution:

  1. For gametes (haploid): n=642=32n = \frac{64}{2} = 32
  2. For Metaphase: Chromatids=2×2n=2×64=128\text{Chromatids} = 2 \times 2n = 2 \times 64 = 128

Explanation:

Gametes are haploid (nn), meaning they contain half the species' diploid number. During Metaphase of mitosis, each of the 6464 chromosomes has been replicated into two sister chromatids, resulting in 128128 chromatids total.