A cell must exchange its materials with its surroundings a process controlled by
The plasma membrane
Plasma membranes are selectively permeable regulating what?
the cell's molecular traffic
What can dissolve in the lipid bilayer and pass through the membrane rapidly
hydrophobic (non polar) molecules, such as hydro carbons
What does not pass through the membrane easily?
Polar molecules such as sugars
transport proteins allow passage of hydrophilic substances where?
Across the membrane
What are aquaporins?
Channel proteins that facilitate the passage of water
These transport proteins bind to molecules and change shape to shuttle them across the membrane
Carrier proteins
a transport protein is specific for?
the substance it moves
what is diffusion?
The tendency for molecules to spread out evenly in the available space.
Transport proteins allow what?
passage of hydrophilic substances across the membrane
Although each molecule moves randomly, diffusion of a population of molecules may be what?
directional
as many molecules cross the membrane in one direction as in the other
dynamic equilibrium
The region along which the density of a chemical substance increases or decreases?
concentration gradient, where substances diffuse
How much work must be down to move substances down there concentration gradient?
none