- 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:
- 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
Glucose is broken down in aerobic respiration to release cellular energy which can be used for muscle contraction. Never, ever say that glucose allows energy to be produced or that it provides energy for respiration. Energy cannot be created or destroyed.
Expect to see tables of sports drinks with different concentrations of nutrients and ions in them in the exam. You may be asked to decide which drink is the best or worst option for an athlete to consume during recovery.
Also, be conscious that sports drinks are often high in sugar (for obvious reasons!) but that for individuals with diabetes or other health problems they can be unhealthy and make them ill.