Why is the cell membrane said to be selectively permeable
Cell membrane permeability - Animated membrane physiology
with their hydrophobic cores and charged
surfaces cell membranes are very
efficient at blocking passage of many
molecules some molecules such as water
dissolved oxygen and simple alcohols are
able to pass through cell membranes
freely by passive diffusion
however charged molecules and large
molecules cannot pass directly through
cell membranes and hydrophobic molecules
tend to become stuck inside the
hydrophobic interior of cell membranes
in order to allow these complex
molecules to enter and exit the cell
organisms rely on two forms of membrane
transport passive transport and active
transport passive transport occurs along
an electrochemical gradient it does not
require the expenditure of energy in the
form of ATP for transport active
transport requires the expenditure of
ATP in order to transport molecules
across the membrane active transport and
some forms of passive transport require
the use of transport proteins such as
the integral protein seen here
