• Key definitions

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Adaptations of exchange surfaces:

• Large surface area
• Thin membranes to provide a short diffusion distance
• Efficient blood supply for a high concentration gradient
• Ventilation for gas exchange in animals </aside>

Single-celled organisms: Relatively large surface area to volume ratio → allows sufficient transport of molecules into and out of the cell to meet the needs of the organism.

Multicellular organisms: Small surface area to volume ratio → diffusion distance is too large → gas exchange doesn’t meet the needs of the organism → needs exchange surfaces and a transport system

Energy/isotonic drinks

During sport and exercise:

• Body temperature increases → loss of water and salts through sweat (and water vapour through the lungs from increased breathing rate)
• Greater muscle activity → rate of aerobic respiration in muscle cells increases during exercise → more glucose is used up in muscle cells

Isotonic sports drinks contain similar concentrations of salt and sugar as the human body used for hydration and water replacement

Hypertonic/energy sports drinks contain concentrations of salt and sugar higher than typical blood levels → provides high sugar levels for absorption from the small intestine → more glucose for respiration to release energy