The Movement of Molecules

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  • Created by: Freja
  • Created on: 13-04-21 13:26
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  • The Movement of Molecules
    • Active Transport
      • e.g. mineral ions moving into a root hair cell.
      • Movement of molecules from a region of low concentration to a region of high concentration, against the concentration gradient.
      • Uses a carrier protein and ATP. Each carrier protein is specific.
      • A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane releasing it on the other side.
    • Cytosis
      • Endocytosis
        • Bulk transport of materials into the cell
        • Uses ATP as an energy source.
        • 2 types
          • Phagocytosis for solids
          • Pinocytosis for liquids
        • Some molecules are too large to be taken into a cell by carrier proteins. Instead a cell can surround a substance with a section of plasma membrane. The membrane then pinches off to form a vesicle inside the cell containing the ingested substance.
      • Exocytosis
        • Bulk transport of materials out of the cell.
        • Vesicles containing these substances pinch off from the sacs of the Golgi apparatus and move towrds the plasma membrane. The vesicles fuse with  the plasma membrane and release their contents outside the cell.
          • Some substances aren't released outside the scell- instead they are inserted straight into the plasma membrane.
    • Diffusion
      • Rate of Diffusion
        • The higher the concentration gradient, the faster the rate of diffusion.
        • The larger the surface area, the faster the rate of diffusion.
        • The higher the temperature, the faster the rate of diffusion, because the particles have more kinetic energy so they move faster.
        • The thinner the exchange surface (i.e. the shorter the distance the particles have to travel), the faster the rate of diffusion.
      • The net movement of particles from an area of higher concentration to an area of lower concentration.
      • Molecules will diffuse both ways, but the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas.
      • The concentration gradient is the path from an area of higher concentration to an area of lower concentration. Particles diffuse down a concentration gradient.
      • Diffusion is a passive process- no energy is needed for it to happen.
      • Faciliatated Diffusion
        • Some larger molecules, ions and polar molecules don't diffuse directly through the phospholipid bilayer of the cell membrane.
        • They diffuse through carrier proteins or channel proteins in the cell membrane- this is facilitated diffusion.
        • Particles move down a concentration gradient, from a higher to lower concentration.
        • It is a passive process.
        • Carrier proteins- move large molecules into or out of a cell, down the concentration gradient. Different carrier proteins facilitate the diffusion of different molecules.
          • 1) Firstly, a large molecule attaches to a carrier protein in the membrane.  2) Then, the protein changes shape.        3)  This releases the molecule on the opposite side of the membrane.
        • Channel proteins- form pores in the membrane for charged particles to diffuse through (down their concentration gradient). Different channel proteins facilitate the diffusion of different charged particles.

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