Cell Membranes and Cell Transport
Cell Membrane:
All cells have a cell membrane
Helps control what goes in and out of
the cell
Helps regulate homeostasis
Cell membrane structure:
Made of a phospholipid bilayer (2
layers)
Head (polar: molecules have unequal sharing of electrons among
atoms)
Tail (non-polar: molecules have equal sharing of electrons among
atoms)
Simple diffusion:
Some molecules have no problem going through the cell membrane
and go through the phospholipid bilayer
Very small non-polar molecules fit into this category (e.g. oxygen,
carbon dioxide gas)
This is called simple diffusion, a
type of passive transport
High concentration low
concentration
Facilitated diffusion:
Some transport proteins act as
channels
Some change their shape to
get things across
Some open and close
Help molecules that are too big to cross the membrane on their own
(e.g. charged ions, glucose)
Facilitated diffusion: All polar molecules need the help of a
transport protein
High concentration low concentration
Type of passive transport
Osmosis:
For water to travel through the membrane at a fast rate, it goes
through protein channels called aquaporins
Active Transport:
Movement of molecules from low high concentration takes energy
because it’s against the flow
Against the concentration gradient
Through specialised membrane channel
ATP energy: adenosine, triphosphate has 3 phosphates
