Osmosis Diffusion Active Transport Diffusion Osmosis and Concentration

Osmosis, Diffusion, Active Transport

Diffusion, Osmosis and Concentration Gradient n n n Diffusion – the movement of a substance from a high concentration to a low concentration Osmosis – the movement of WATER from a high concentration to a low concentration. Concentration Gradient – the difference in concentration between a region of high concentration and a region of lower concentration

Passive or Active Transport: n Passive Transport - does not require cell energy n n Examples: Diffusion, Facilitated diffusion and Osmosis Active Transport Requires cell energy (ATP) n Examples: Carrier mediated active transport, Endocytosis and Exocytosis

Methods of Transport: n 1. Diffusion: the random movement of particles of a solute from an area of higher concentration to an area of lower concentration. Particles always move with (down) a concentration gradient (the difference in concentrations across a membrane). n Passive transport. n

Equilibrium n n n Diffusion stops at equilibrium (when the concentrations across a membrane are equal). The movement of molecules continues at equilibrium but the # of molecules moving across the membrane remains the same. The rate of transport is dependent on: n n 1) if the material is solid, liquid or gas. 2) the size of the molecules. 3) temperature Examples of molecules that can diffuse through the bilayer: carbon dioxide, oxygen, water but very, very slowly.

Diffusion through a Plasma Membrane

Osmosis n Osmosis: the diffusion of water through a selectively permeable membrane. Passive transport n Water molecules move from a higher concentration OF WATER to a lower concentration OF WATER. n Water will move to where there is a greater amount of solute because there is less water there n

Isotonic Solution n Isotonic solutions: the concentration of solute inside and outside of the cell is the same. n Isotonic: Water in = Water out No net movement of water. Molecules in equilibrium. Normal state for animal cells. Cell in homeostasis. n n n

Hypotonic Solution n Hypotonic solutions: the concentration of solute is lower outside the cell than inside the cell. n n n Have more water outside the cell so water moves into the cell Causes an increase in pressure inside the cell: called turgor pressure (plants) or osmotic pressure (animals). Increase in pressure in animal cells causes them to swell or even burst; gives plant cells shape and support.

Example Hypotonic n n Hypotonic: Water enters cell. Cell swells and bursts (cytolysis). Give plant cells shape and support.

Hypertonic Solution n Hypertonic solutions: the concentration of solute is higher outside the cell than inside the cell. Have more water inside the cell so water moves out of the cell n Causes a drop in turgor or osmotic pressure: called plasmolysis. n Plasmolysis causes animal cells to shrivel up and plants to wilt. n

Hypertonic Example n n n Hypertonic: Water exits cell. Cell shrinks (plasmolysis) due to water loss.

The effects of osmotic pressure

Hypo, Iso, Hyper

The effects of osmotic pressure in a plant cell

Facilitated Diffusion n n Particles always move with (down) a concentration gradient. Uses transport/channel proteins. Passive transport. Usually for specific molecules such as glucose. Facilitated diffusion stops at equilibrium.

Active transport n Active Transport: requires energy in the form of ATP. Capable of moving solute particles against the conc. gradient (from low conc. to high conc. ) n Uses transport/carrier proteins (protein pumps) embedded in the plasma membrane. n Carrier proteins are specific for the molecules that they allow through. The carrier protein changes shape which requires energy (ATP). n

Active Transport against the concentration gradient

Active Transport n Endocytosis: a process of taking material into the cell by means of infoldings, or pockets, of the cell membrane (usually putting them into a vacuole). n Phagocytosis -“Cell eating” n Nonspecific molecules n Intake of solids n Pinocytosis –”Cell Drinking” n Nonspecific molecules n Intake of small droplets of liquid

Active Transport n Exocytosis (reverse endocytosis): a process in which the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

EXO and ENDO