Biology module 2.6

• Mitosis


  A form of cell division that produces identical cells, there are four stages: prophase, metaphase, anaphase and telophase
• Cell cycle


  1. Cell forms

  2. Cell grows

  3. Cell divides to form daughter cells
• Cell cycle


  • Controlled by checkpoints
• Cytokinesis


  1. Parent and replicated organelles move to opposite sides of the cell

  2. Cytoplasm divides to produce two daughter cells
• Interphase


  1. Cell grows

  2. Chromosomes and some organelles are replicated

  3. Chromosomes begin to condense
• Prophase


  1. Nuclear envelope breaks down and disappears

  2. Chromosomes condense

  3. Centrioles move to opposite poles for spindle formation
• Metaphase


  Chromosomes move to the equator and attach to spindle fibres via centromeres
• Anaphase


  Sister chromatids are separated
• Telophase


  1. Nuclear envelope reforms

  2. Spindle is broken down and disappears

  3. Chromosomes uncoil
• Meiosis


  A form of cell division that gives rise to genetic variation, produces haploid gametes
• Genetic variation in meiosis

  • Crossing over of chromatids
  • Independent assortment of chromosomes
• Meiosis I


  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I
• Meiosis II


  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II
• Tissue


  Cells grouped together to perform a common function
• Xylem


  • Transport water and minerals
  • Provide structural support
  • Made of dead tissue with open ends
  • Thickened with lignin
  • Consist of parenchyma, fibres and vessels
• Phloem


  • Tubes made of living cells
  • Involved in translocation of food substances and nutrients
  • Meristem tissue produces cells that elongate and line up end-to-end
  • Have perforated sieve plates
  • Have metabolically active companion cells
• Epithelial tissue


  • Sheet of cells that serves as a lining/cover a surface
  • Squamous type is smooth, flat and very thin
  • Ciliated type has column shaped cells with cilia
• Stem cells


  Undifferentiated cells with ability to develop into any cell type
• Differentiation


  Process by which a cell specialises to carry out a particular function
• Specialised cells


  • Sperm cells
  • Palisade cells
  • Root hair cells
  • Guard cells
• Plants retain ability to differentiate into different cell types throughout their life
• The Cell Cycle


  1. Interphase

  2. Nuclear division (mitosis)

  3. Cytokinesis

  
• Interphase


  The cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)

  
• Phases of Interphase


  • G1 phase
  • S phase
  • G2 phase
• S phase


  DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids)
• G1 phase


  The gap between the previous cell division and the S phase, cells make the RNA, enzymes and other proteins required for growth
• G2 phase


  The gap between the S phase and next cell division event, the cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired

  
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Mitosis


  • Nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent cell nucleus
• Prophase


  Chromosomes condense and are now visible when stained, the two centrosomes move towards opposite poles, spindle fibres begin to emerge, the nuclear envelope breaks down, the nucleolus disappears
• Metaphase


  Centrosomes reach opposite poles, spindle fibres continue to extend, chromosomes line up at the equator of the spindle (metaphase plate), spindle fibres attach to the centromeres of the chromosomes
• Anaphase


  The sister chromatids separate at the centromere, the separated sister chromatids (now called chromosomes) are pulled to opposite poles by the shortening spindle fibres
• Telophase


  Chromosomes arrive at opposite poles and begin to decondense, nuclear envelopes begin to reform around each set of chromosomes, the spindle fibres break down, new nucleoli form within each nucleus
• Mitosis is essential for growth, repair and asexual reproduction in multicellular organisms

  
• Mitosis ensures that the daughter cells are genetically identical to the parent cell
• Mitosis is tightly regulated by checkpoints to ensure accurate DNA replication and chromosome segregation

  
• Prophase


  Stage of cell division where DNA condenses and becomes visible as chromosomes

  
• Telophase


  Stage of cell division where nuclear membranes form around the chromosomes at opposite poles and the spindle breaks down
• Number of nuclei within one cell


  Can help identify if the cell is in telophase (multiple nuclei)
• The size of cells or structures of tissues may appear inconsistent in different specimen slides