Transport summary and applications

• In order to survive, cells must exchange substances between themselves and their environment
• Transport processes


  • Diffusion
  • Osmosis
  • Active transport
• Diffusion, osmosis and active transport


  • They are the processes by which substances are transported into and out of cells
• Sports drinks


  • Help replace water, salts (ions/electrolytes) and glucose lost from the body during exercise
• During sport and exercise

  The body's temperature increases, leading to the loss of water and salts through sweat (and water vapour through the lungs from increased breathing rate)
• Physical activity


  Requires greater muscle activity, so the rate of aerobic respiration in muscle cells increases during exercise
• Increased aerobic respiration in muscle cells

  More glucose is used up and must be replaced
• Athletes opt to drink sports drinks over bottled water after competing
• Balance between ions and water


  It is very important that the balance is correct between the cells of the body and the bloodstream
• If there is too little water in the blood or the blood ion concentration is too high


  Cells will lose too much water by osmosis and shrink/dehydrate
• If the concentration of water in the blood is too high or the ion concentration is too low


  Cells will absorb too much water, swelling and possibly bursting
• Isotonic sports drinks


  Contain similar concentrations of salt and sugar (glucose) as the human body and are primarily used for hydration and fluid replacement
• Hypertonic sports drinks


  Contain concentrations of salt and sugar higher than typical blood levels, providing high salt and sugar levels for absorption from the small intestine - these drinks are suitable for supplying glucose in particular during intense physical exercise (eg. during a marathon)
• Hypotonic sports drinks


  Contain concentrations of salt and sugar lower than typical blood levels, creating a concentration gradient between the bloodstream and small intestine with the water potential in the small intestine being higher - these drinks are suitable for rapid rehydration as water is drawn into the bloodstream by osmosis
• Diffusion


  Movement of substances in a fluid down a concentration gradient
• Osmosis


  Special type of diffusion of water; occurs between two solutions separated by a partially permeable membrane down a water potential gradient (or from a dilute to concentrated solution)
• Active transport


  Movement of substances actively across a membrane (usually against a concentration gradient); Energy from respiration required
• Summary


  • Diffusion: No
  • Osmosis: No
  • Active transport: Yes
• Substances moved by osmosis


  • Water
• Substances moved by active transport

  • Glucose
  • Mineral ions (e.g. sodium, potassium, magnesium, nitrates)
• Important places diffusion occurs

  • In the lungs and leaves (gas exchange)
  • In the digestive system between the lumen of the small intestine and intestinal cells
• Important places osmosis occurs

  • Between all cells and their immediate environment (but particularly between cells and the bloodstream)
• Important places active transport occurs

  • Between the lumen of the small intestine and intestinal cells
  • Between roots and the soil