Crash Course Membranes and Transport-CrashCourse (Resources Page)

Solute and Solvent A solute is something that is dissolved into a solution. The solvent is the solution the solute dissolves in. Water is our universal solvent because it can dissolve many things.

Passive Transport Passive transport is when no energy (ATP) is required to move the molecules from one side of the membrane to the other. This happens along the concentration gradient, going from and area of high concentration to and area of low concentration.

Diffusion Diffusion is the tendency for molecules to spread evenly into available space. Example of Passive Transport The movement of each molecule is random, but the movement of the population of molecules may be directional. At equilibrium, molecules cross the membrane equally in each direction.

Facilitated Diffusion Facilitated diffusion must occur when the molecule crossing the membrane is not able to cross because it is large or charged. This requires the use of a carrier protein or a channel protein to make this possible. This still requires no energy and the molecules are moving from an area of high concentration to an are of low concentration.

Facilitated Diffusion In facilitated diffusion, transport proteins speed the passive movement of molecules across the membrane.

Active Transport Active transport requires energy to move solutes against their concentration gradient. Low concentrations to high concentrations. Requires energy which is usually in the form of ATP. Performed by specific proteins embedded in the membranes. Ex. Sodium-Potassium pump

Endocytosis is Active Transport Endocytosis requires energy and is the movement of larger particles into the cell by use of a membrane vesicle. Examples are: Phagocytosis- larger molecules are brought into the cell by engulfing them in a vesicle Pinocytosis- Dissolved molecules are brought in by using a vesicle. Receptor Mediated Endocytosis- receptors outside the membrane allow molecules to attach then get engulfed using a vesicle.

Exocytosis is Also Active Transport Exocytosis is the opposite of endocytosis because the molecules are going out of the cell rather than into the cell. The Golgi Apparatus is involved and packaging and sorting these items. They then get sent out of the cell using a vesicle. Example: Proteins made by the ribosomes that are not used in the cell.

Osmosis Osmosis is the diffusion of water across a membrane. Passive transport but travels using Aquaporins. Water will diffuse from lower solute concentration to higher solute concentration until the concentrations are equal on both sides. In other words, water is moving to dilute the solution with the higher concentration of solute.

Water Balance of Cells Without Walls Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water

Blue dots do not represent water molecules, they are solute molecules

Osmosis in Plant and Animal Cells