The plasma membrane is made up of a lipid bilayer and some proteins. The transmembrane proteins are the structures which are involved in the transport of molecules in or through the cell.
Carrier proteins facilitate passive transport of molecules across a membrane by changing its shape, by using ATP, to allow a substance to pass through the membrane.
Transport mechanisms
Water molecules freely diffuse across a semipermeable membrane.
they pass through channels in the cell membrane.
Glucose is too big to pass through.
they pass through channels in the cell membrane
Osmosis
Yes, in an isotonic solution the movement of molecules across the membrane will stop.
when proteins help molecules move across the membrane, it it called Facilitated Diffusion
Carbon dioxide moves out of the cells from a higher to lower concentration across the cell membrane. Then the CO2 moves through the capillary wall across the diffusion gradient. The diffusion process is repeated at the capillary/alveolar junction.
Lipid-soluble molecules such as O2 and CO2 diffuse freely through the plasma membrane.
A process known as passive transport helps molecules to diffuse across a membrane. Passive transport does not involve the use of chemical energy, unlike active transport does.