Cell Transport (7.3)

Passive Transport Important: Keep the cell’s internal conditions relatively constant Cell needs to be regulate the movement of molecules from one side of the membrane to the other Diffusion the process in which particles move from an area of higher concentration to an area of lower concentration this is the force behind moving particles into and out of the membrane The particles moving from an area of high concentration to an area of lower concentration will occur until the particles reach equilibrium (particles are the same concentration on both sides) After equilibrium: the particles will continue to move back and forth, but will remain of equal concentrations depends on RANDOM MOVEMENT of particles → substances diffuse across the membrane without using additional energy (PASSIVE TRANSPORT)

Passive Transport Most molecules that diffuse through the lipid bilayer easily are small and uncharged Large and charged molecules have the ability to pass through the membrane as well → facilitated diffusion Facilitated Diffusion the process where molecules CANNOT directly diffuse across the membrane but pass through special protein channels hundreds of proteins have been discovered that help in facilitated diffusion Since it is still diffusion, it does not require the cell to use energy to pass the molecules through the membrane Ex: Red blood cells have special proteins that allow glucose into the cell

Osmosis Water needs special channel proteins to move water into and out of the cell → aquaporins Osmosis: the diffusion of water through a selectively permeable membrane molecules still move from an area of higher concentration to an area of lower concentration the semipermeable membrane allows for the water particles to move from one side to the other, but NOT the solute particles (pg 210) Equilibrium: the water and sugar will be equal on both sides of the membrane

Osmosis (pg 211) 1. Isotonic (same strength): the concentration of solutes are the same inside and outside the cell. The water moves back and forth equally. 2. Hypertonic (above strength): the solution has a higher solute concentration than the cell. The movement of water out of the cell causes it to shrink. 3. Hypotonic (below strength): The solution has a lower solute concentration than the cell. The water movement is into the cell causing it to swell.

Osmotic Pressure Osmotic pressure: the movement of water into or out of the cell Cells are almost always hypertonic in fresh water because they contain salts, sugars, and other dissolved proteins → this causes water to move into the cell causing it to swell and burst Cells are mostly surrounded by isotonic solutions (blood) so this is not a reoccurring problem Plant cells Hypertonic and Hypotonic solutions do not interfere with a plant cell’s structure, but they can cause injuries to the cell wall

Active Transport Active transport: the movement of material against a concentration gradient Requires energy Usually small molecules or ions are carried through the membrane using protein pumps that are found in the membrane itself Ions (charged molecule): calcium, potassium, and sodium larger molecules are actively transported through endocytosis or exocytosis → this usually involves changes in shape of the cell membrane considerable amounts of energy are needed for active transport (ATP)

Active Transport (pg 212) Endocytosis: the process of taking material into the cell by means of infoldings (pockets) of the cell membrane → the pocket breaks off and becomes a vesicle in the cytoplasm Phagocytosis (phago = to eat): extensions of cytoplasm surrounding a particle and package it within a food vacuole Requires a considerable amount of ENERGY Ex: White blood cells eat damaged cells Pinocytosis (pino = to drink) : cells take up liquids from the surrounding environments and pinch off to form vacuoles within the cell Exocytosis: the release of large amounts of material from the cell the membrane of the vacuole fuses with the cell membrane and forces the contents out Ex: Removal of water using a contractile vacuole