Cell Transport & Cell Division


Cell Membranes

  • Cell membranes act as barriers and can control what passes into and out of cells and organelles
  • It is composed of phospholipids, proteins, glycoproteins, glycolipids and cholesterol
  • Gylcolipids and glycoproteins allow cell adherence, stability and acts as recognition sites
  • Cholesterol has a hydrophillic end and a hydrophobic end & regulates membrane fluidity by interclataing between the phospholipids
  • At high temperatures the phospholipid bilayer increases its fluidity and permeability, increasing the risk of proteins being denatured. 
    • At low temperatures, the phospholipds are compressed, making the membrane stiff
  • Organic solvents disrupt the bilayer and dissolves the membrane

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Passive Transport

  • Involves the exchange of substances without requiring metabolic energy from the cell
  • Diffusion =  the net movement of paricles form an area of higher concentration to an area of lower concentration (down the concentration gradient)
  • Facilitated diffusion = the net movement of particles down their concentration gradient across a partially permeable membrane via channel or carrier proteins
  • Water potential is a measure of the tendency of water molecules to move from one area to another area and describes the pressure created by these water molecules
    • the more dilute a solution the high the water potential
  • Osmosis is the net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane
  • The rate of diffusion can be increased by increasing the number of channel & carrier proteins, the surface area of the cell membrane, reducing the diffusion distance and creating a steeper concentration gradient

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Active Transport

  • Active transport is the movement of particles from an area of low concentration to an area of high concentration (against their concentration gradient) across a cell membrane, using ATP and carrier proteins
  • Bulk transport transports large substances across the cell membrane
  • Endocytosis is the bulk transport of large moleculesinto a cell. The membrane invaginates and encloses the material being taken up into a vesicle, which pinches off
  • Exocytosis is the bulk transport of large molecules out of cell.
    • A vesicle fuses witht he cell membrane, releasing its material

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Mitosis Overview

  • Within multicellular organisms, not all cells retain the ability to divide
  • Mitosis produces genetically identical daughter cells, which is useful for gorwth, repair and asexual reproduction
  • The eukaryotic cell cycle has 3 main stages
    • Interphase consists of two growth phases (G1 and G2), and a DNA synthesis stage (S). 
      • The cell may exit at the G0
    • Mitosis is the cuclear division
    • Cytokinesis is when the cell splits in two forming two identical daughter cells
      • In animal cells, the plasma membrane folds inwards until the two dents meet to separate the two daughter cells
      • In plant cells, cellulose starts to build up at the equator (the end plate). Plasma membrane forms in the middle of the end plate resulting in two fully separated plant cells
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Mitosis Stages

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Cell Cycle

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  • Meiosis produces 4 haploid daughter cells that are genetically different from each other
  • Variation results from independent assortment of chromosomes and crossing over during meiosis 1. Also, random fertilisation of the gametes.

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