Cell divisionOxford AQA IGCSE Biology: Flashcards

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Define mitosis.

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Define mitosis.: Mitosis is a form of cell division that produces two genetically identical daughter cells. It occurs during growth, repair and asexual reproduction in organisms.
What are the three main stages of the cell cycle?: The three main stages of the cell cycle are: growth (G1 and G2 phases), DNA replication (S phase), and mitosis (M phase).
Describe what happens during the growth phase of the cell cycle.: During the growth phase (G1 and G2), the cell increases in size, accumulates nutrients and energy, and synthesises proteins and organelles needed for division.
What occurs during DNA replication in the cell cycle?: During DNA replication (S phase), the DNA content of the cell doubles as each chromosome is copied to produce identical copies. This ensures each daughter cell receives a complete set of genetic information.
Define meiosis.: Meiosis is a form of cell division that produces four genetically different haploid cells called gametes. It involves two consecutive divisions (meiosis I and meiosis II).
What is a haploid cell?: A haploid cell is a cell that contains half the number of chromosomes as the parent cell. Gametes (sex cells) are haploid cells, containing n chromosomes.
Explain why the daughter cells produced by mitosis are genetically identical.: The daughter cells produced by mitosis are genetically identical because DNA replication during the S phase produces exact copies of each chromosome, and these copies are distributed equally to each daughter cell during mitosis.
Name two reasons why mitosis is significant in organisms.: Mitosis is significant because it: (1) allows growth by increasing cell numbers whilst maintaining genetic information, and (2) enables repair of damaged tissues through replacement of worn-out cells.
What is independent assortment in meiosis? (HT): Independent assortment is the random distribution of homologous chromosome pairs to daughter cells during meiosis I. Each gamete receives a random combination of maternal and paternal chromosomes, creating genetic variation.
What is crossing over in meiosis? (HT): Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis. Non-sister chromatids swap sections of DNA, creating new combinations of alleles and increasing genetic variation.
Explain why meiosis produces genetic variation. (HT): Meiosis produces genetic variation through two mechanisms: independent assortment (random distribution of homologous chromosomes) and crossing over (exchange of genetic material between homologous chromosomes). These processes ensure each gamete is genetically unique.
What is the significance of meiosis in terms of chromosome number?: Meiosis halves the chromosome number, producing four haploid cells (n) from one diploid cell (2n). This is significant because when gametes fuse during fertilisation, the diploid number is restored in the offspring.
Compare the chromosome number in daughter cells produced by mitosis and meiosis.: Mitosis produces two daughter cells, each with the same chromosome number as the parent cell (2n). Meiosis produces four daughter cells, each with half the chromosome number of the parent cell (n).
What is the role of meiosis in sexual reproduction?: Meiosis produces gametes (sex cells) with half the chromosome number. When two gametes fuse during fertilisation, the full chromosome number is restored in the zygote, allowing sexual reproduction.
Explain the significance of mitosis and meiosis in maintaining chromosome numbers across generations.: Mitosis maintains chromosome numbers in somatic (body) cells for growth and repair. Meiosis halves chromosome numbers in gametes. When gametes fuse during fertilisation, the diploid number is restored, ensuring chromosome numbers remain constant across generations.