MOVEMENT OF MATERIALS

PASSIVE TRANSPORT
1. Process does not require Energy
2. Diffusion
  1. random movement of particles from an area of high concentration to an area of low concentration
  2. higher the concentration gradient
    1. higher the rate of diffusion
  3. factors affecting rate of diffusion
    1. size
      1. small particles diffuse faster than larger paticles
    2. temperature
      1. particles diffuse faster at high temps than low temps due to more kineticE
    3. state
      1. gas>liquid>solid
        gas particles have highest kineticE, then liquids, then solids
  4. small molecules diffuse freely across membranes along the concentration gradient
    1. however, large molecules are prevented from diffusing through membrane
3. Facilitated Diffusion
  1. special trasport/carrier proteins in the membrane provide channels for the process
    1. carrier proteins are specific
      1. i.e. only carry 1 type of molecule
  2. e.g. both oxygen and glucose are facilitated
    1. due to high demand for oxygen and glucose in cells
  3. passive process
    1. molecules can only diffuse from high conc -> low conc across membrane
4. Osmosis
  1. movement of water from an area of high water potential to an area of low water potential across a semi-permeable membrane until water potentials are equal
  2. few solutes dissolves
    1. high water potential
  3. weak/dilute solution
    1. hypotonic
  4. strong/ concentrated solution
    1. hypertonic
  5. 2 solutions with equal water potential
    1. isotonic solutions
  6. particles move in both directions across membrane,
    1. however, net movement is towards area of lower water potential
  7. Osmoregulation
    1. control of water inside a cell or organism
    2. both plant and animal cells
    3. no net loss or gain of water in an isotonic solution
    4. net loss of water in a hypertonic solution
    5. net gain of water in a hypotonic solution
    6. animal cells in:
      1. isotonic
        no change. normal
      2. hypertonic
        dehydrated- shrivels. net loss of water
      3. hypotonic
        burst. excessive net gain of water
    7. plant cells in:
      1. isotonic
        no change. no net gain / loss of water
      2. hypertonic
        plasmolysed- membrane pulls away from cell wall and cell becomes flaccid
      3. hypotonic
        turgid. firm. cell wall prevents cell from bursting- high turgor pressure
ACTIVE TRANSPORT
1. Process requires energy
2. moves substances across membrane against concentration gradient
  1. i.e. from low conc -> high conc
3. e.g reabsorption of glucose by kidney tubule cells by active transport
4. e.g. uptake of nitrates by root hairs
5. carrier protein combines with substance
  1. carrier protein changes shape
    1. substance is released to the other side of the membrane
  2. carrier proteins= specific to which particular protein they carry
6. Cytosis
  1. movement of large amounts of substances into/out of the cells by folding of membranes
  2. Endocytosis
    1. taking substances into cell by infolding of cell membrane
      1. for large molecules that cant fit through protein carriers or lots of molecules
    2. removes part of cell membrane
    3. Pinocytosis
      1. takes in fluids
      2. cell membrane invaginates and fluid droplets enter
        membrane pinches off droplets
        becomes a vesicle inside the cell
    4. Phagocytosis
      1. takes in large particles (food)
      2. cell membrane flows out and around food particle
        membrane outflowings (pseudopodia) meet and fuse, engulfing the food partiicle
        becomes a food vacuole in cytoplasm
  3. Exocytosis
    1. removal of substances from cell
    2. reverse of endocytosis
    3. occurs when cells need to secrete a substance
    4. adds to cell membrane
    5. e.g. a hormone or salivary glands secreting amylase
CELL SIZE SHAPE AND DIFFUSION
1. cells have a dependency on diffusion for getting materials in/out of cell
  1. therefore cells are tiny
2. as a cell grows, ratio b/w S.A : Vol decreases
  1. i.e. less membrane for substances to diffuse through
    1. diffusion gets less efficient
      1. beyond a certain size, centre of cell doesnt recieve required substances
        cell stops growing and divides to form 2 new smaller cells
3. cells increase S.A:Vol ratio by:
  1. having an elongated shape
    1. e.g. nerve cells, root hair cells
  2. having a biconcave shape
    1. e.g. RBC for efficient diffusion of oxygen
  3. folding of cell membrane
    1. e.g. microvilli- cells lining small intestine
4. greater rate of activity with high S.A : Vol ratio

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MOVEMENT OF MATERIALS

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	Created by CChristine about 10 years ago