Fourth Exam Overview

  • Schedule: The fourth exam is scheduled for the day after Easter in April.
  • Chapters Covered: This exam will cover Chapters 9 and 10.
  • Key Topics:
    • Mitosis
    • Meiosis
    • The Cell Cycle
    • Asexual Cell Division
    • Reproduction (both asexual and sexual)

Mitosis and Meiosis

  • Mitosis: A form of asexual cell division critical for growth and development in multicellular organisms and for reproduction in unicellular organisms.
    • Used for growth, tissue renewal, and repair.
    • Important for eukaryotic organisms that grow and need to produce more cells.
    • Notably slower than binary fission due to the complexity of eukaryotic cells.

Asexual Reproduction

  • Binary Fission: Method of asexual reproduction in unicellular prokaryotes.
    • Simple and quick process without a nucleus.
    • Nutrient availability influences division frequency.
  • Fragmentation and Regeneration: Some organisms regain lost parts, a form of asexual reproduction.
    • Examples include sea stars and lizards that can regenerate their limbs or tails, but the new limb does not grow into a new organism.
    • Vertebrate organisms have limited regenerative abilities compared to invertebrates.

Cell Cycle Explained

  • The cell cycle comprises the stages that a cell goes through to grow and divide.
  • Stages of the Cell Cycle:
    1. Interphase: The non-dividing phase where the cell prepares for division.
    2. M Phase: The actual division occurs (mitosis and cytokinesis).
  • Checkpoints in the Cell Cycle:
    • G1 Checkpoint: Checks for DNA damage before moving to S phase.
    • G2 Checkpoint: Checks that DNA has been replicated correctly before mitosis.
    • M Phase Checkpoint: Ensures proper separation of chromosomes.

Mitosis Process

  • Phases of Mitosis: Prophase, metaphase, anaphase, and telophase.
  • Cytokinesis: The physical splitting of the cytoplasm, resulting in two separate daughter cells.
    • Animal cells use microfilaments for division.
    • Plant cells form a cell plate to separate the new cells.

Genetic Terminology

  • Diploid (2n): Refers to cells containing two complete sets of chromosomes.
  • Haploid (n): Cells containing one set of chromosomes, as seen in gametes (sperm and eggs).
  • Example Calculation:
    • If diploid number is 18, then haploid number is 9.

Meiosis and Sexual Reproduction

  • Meiosis: Sexual cell division occurring in gametes, creating genetic variation.
    • Unlike mitosis, meiosis results in genetically different cells.
  • Importance of Genetic Variation: Vital for evolution and adaptability of species.

Cancer and Cell Cycle

  • Role of G0 Phase: Non-dividing state, can be temporary or permanent, particularly in mature cells like neurons.
    • Cancer treatments often aim to push cells into G0 to stop division.

Error Consequences

  • If Cytokinesis Fails: Can result in multinucleated cells, which typically cannot divide further.
    • Errors in division can lead to developmental issues or diseases.