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.