Adaptations for rapid transport across membranes

what does the rate of transport depend on

• temperature

• surface area of the exchange surface

• concentration gradient across the membrane

• thickness (or diffusion distance) of the exchange surface

• number of protein channels or carrier proteins

• availability of ATP (for active transport)

how does increased surface area increase transport

more membrane surface allows more substances to cross simultaneously

e.g. microvilli on epithelial cells in the small intestine

how deos more channel proteins increase transport

Allows faster facilitated diffusion of specific ions or polar molecules

how does more carrier proteins increase transport

Speeds up facilitated diffusion and active transport of larger molecules

e.g. glucose carriers in kidney tubules and intestinal epithelium

how does thin exchange surface increase transport

Reduces diffusion distance, speeding up the rate of diffusion

e.g. alveolar and capillary walls are 1 cell thick

how does rich blood supply increase rate

Maintains a steep concentration gradient by constantly removing or supplying substances

e.g. capillary networks in alveoli and villi

how does ventilation or flow of the surrounding medium increase rate

Replaces substances to maintain high/low external concentrations, sustaining a gradient

e.g. ventilation in lungs maintains oxygen/carbon dioxide gradients

how does many mitochondria increase rate

Provides more ATP for active transport, supporting uptake against a concentration gradient

e.g. root hair cells for ion uptake from the soil