Transport Summary & Applications (AQA GCSE Biology)

• In order to survive, cells must exchange substances between themselves and their environment
• In summary, the transport of substances occurs into and out of cells by diffusion, osmosis and active transport
• The table below describes some of the differences between the three processes:

Transport summary & applications table

• During sport and exercise, the body’s temperature increases and this leads to the loss of water and salts through sweat (and water vapour through the lungs from increased breathing rate)
  • See The Nervous System: Control of Body Temperature

• Physical activity also requires greater muscle activity, so the rate of aerobic respiration in muscle cells increases during exercise
• As a result, more glucose is used up in muscle cells and must be replaced

• Athletes opt to drink sports drinks over bottled water after competing
• These drinks are designed to help replace water, salts (ions/electrolytes) and glucose lost from the body during exercise
• It is very important that the balance between ions and water is correct between the cells of the body and the bloodstream
• If there is an imbalance then there could be negative effects on the body’s cells leading to them working inefficiently:
  • 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
  • This provides 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
  • Drinking this type of drink creates 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