How is the idea of equilibrium related to the cell membrane?

Cell Membrane Function The cell membrane is the boundary that separates the living cell from its surroundings Membrane allows some molecules to pass while keeping others out. This is called selective permeability. Molecules will move in a particular direction until dynamic equilibrium is reached.

Two Categories of Transport Passive Doesn’t require energy Substances move from high to low concentration. Active Requires energy Substances are transported from low to high concentration

Concentration Gradient? Substances always try to move down their own concentration gradient. (No energy required to do this) What direction will the water move? What direction does the sugar what to move?

Types of Passive Transport Diffusion Osmosis Facilitated Diffusion

Diffusion Movement of a substance from high to low concentration

What kind of substances can diffuse through the cell membrane? Some very small substances like oxygen and carbon dioxide can pass directly through the bilayer by diffusion

Osmosis Movement of water across a semipermeable membrane from high to low concentration

How to other molecules get in and out of the cell? Substances (including water) that cannot pass directly through the membrane require some type of protein to help. This is called Facilitated Diffusion Each protein is specific for the molecule it will transport.

Facilitated Diffusion

Active Transport (Requires Energy) Moves substances against the concentration gradient

Review

Another Way In and Out Fold the Membrane! Endocytosis-Brings large molecules inside in bulk Exocytosis-Molecules are transported out in vesicles