Movement Across Membrane

Diffusion Osmosis Active transport

. This means that they allow certain substances to pass through them freely, but they prevent other substances from passing through. Substances are allowe to apss through based on there chemical nature and size

. Diffusion is the movement of molecules from a region of high concentration of molecules to a region of low concentration of molecules until the concentration is the same in both regions

No there is no barrier and no energy

Osmosis is the moevment of water from a high water potential to a low Water potential across a Selectively permeable membrane until dynamic equilibrium is reached

Water potential is the ability of water, due to its “free” kinetic energy, to move from a region where there is relatively a larger number of water molecules (e.g. pure water), to a region where there is a lower number of water molecules (e.g. a solution).

Solutes reduce the free energy of water molecules, so a solution has a lower potential than pure water.

N.B.: Active transport involves the absorption of substances across a DPM, against a concentration gradient. Energy is required for active transport to take place.

Some organic molecules, such as amino acids and glucose, are too large to pass through the cell membrane . Proteins in the membrane can actively carry these large molecules through the membrane.. The proteins select which molecules they will carry through the membrane and use energy produced by the mitochondria in the cell to move these molecules through the membrane.