Movement in and out of cells

• Diffusion


  Random movement of molecules, atoms and ions from a region of high concentration to a region of low concentration down a concentration gradient until an equilibrium is achieved
• Molecules have kinetic energy (energy of motion), move randomly and collide with each other
• There are more collisions in a region of high concentration than in a region of low concentration
• Random movement of molecules spread the molecules out, down the concentration gradient
• Some substances will diffuse through the cell membrane
• Concentration gradient


  The difference in concentration of a particular substance in one region compared to another region
• Diffusion is the main way in which substances move over short distances
• Substances that need to move

  • Oxygen
  • Carbon dioxide
  • Urea
  • Steroids
  • Sodium ions
  • Potassium ions
  • Fatty acids
  • Glycerol
• Substances that move in and out of cells by diffusion

  • Gases
  • Food molecules
  • Waste products
• Diffusion is spontaneous and does not require energy
• A small amount of kinetic energy (energy of motion) is involved in diffusion
• The source of energy for simple diffusion comes from the random motion of molecules
• All atoms, ions and molecules at a temperatures above absolute zero have kinetic energy
• Factors influencing diffusion


  • Surface area
  • Temperature
  • Concentration gradient
  • Diffusion distance
• Surface area


  Total area of the surface of an object, total area around the outside of a cell
• Larger surface area


  Quicker rate of diffusion
• Temperature


  As temperature increases, the average kinetic energy of particles increases
• Increased kinetic energy


  Increased speed of movement (velocity)
• Increased velocity


  Greater chance of collisions between particles
• Increased collisions


  Increased rate of diffusion
• Increase in temperature


  Quicker rate of diffusion
• Concentration gradient


  A concentration gradient exists when two or more substances of differing concentrations are in close proximity
• Greater difference in concentration

  Quicker rate of diffusion
• Diffusion distance


  The distance between two objects
• Shorter diffusion distance


  Faster diffusion rates
• Larger diffusion distance


  Slower diffusion rates
• Water potential


  The relative tendency of water molecules to move
• Solution


  A simple solution is basically two or more substances that are mixed. Solute = substance to be dissolved, Solvent = the one doing the dissolving (water).
• Hypotonic solution


  A solution that contains less dissolved substances (solutes) and more water (lots of free water molecules). It has a high water potential and is dilute or weak.
• Hypotonic solution


  When a cell is put in the hypotonic solution, the water moves into the cell through osmosis.
• Hypertonic solution


  A solution that contains more dissolved substances (solutes) and less water (lots of free water molecules). It has a low water potential and is concentrated or strong.
• Hypertonic solution


  When a cell is put in the hypertonic solution, the water moves out of the cell through osmosis.
• Isotonic solution


  A solution having the same water potential, where the two solutions have the same water molecules and the same concentration of solutes.
• Selectively permeable membrane


  Some substances move through the cell membrane while other substances cannot pass through.
• Turgor pressure


  Pressure from fluid within the cell pushing against the cell wall, which gives plants a rigid and sturdy structure.
• Turgor pressure


  Is maintained by osmosis
• Large number of root hair cells give a large surface area to the root, and mitochondria are present to provide energy for active transport.</b>
• Carrier proteins


  Protein molecules that move particles e.g. mineral ions and glucose across a membrane during active transport.
• Experiments to show diffusion
• Potato osmosis experiment