Transport Across Cell
Membranes
The lipid bilayer is only permeable to small and nonpolar substances.
Oxygen and carbon dioxide are nonpolar gases that freely diffuse from their areas of higher
concentration to areas of lower concentration.
Steroid hormones have a cholesterol-based structure and are able to pass through cell membranes,
although more recent discoveries have demonstrated that even steroid hormones often make use of
a variety of protein channels and transporters.
Membranes
The lipid bilayer is only permeable to small and nonpolar substances.
Oxygen and carbon dioxide are nonpolar gases that freely diffuse from their areas of higher
concentration to areas of lower concentration.
Steroid hormones have a cholesterol-based structure and are able to pass through cell membranes,
although more recent discoveries have demonstrated that even steroid hormones often make use of
a variety of protein channels and transporters.
