Diffusion and Concentration

concentration gradients + diffusion

concentration gradient: when the concentration of a dissolved substance is higher on one side of a membrane than the other

• cells naturally want to move from higher to lower concentrations (look to even out)

diffusion: the movement of molecules from a region of higher concentration to a region of lower concentration

cell transport

two types: active + passive

passive transport: the movement of molecules across a cell membrane down their concentration gradient. no energy is expended

• eg. osmosis, diffusion, facilitated diffusion

osmosis: movement of water across a membrane from an area of high water concentration to an area of low water concentration

facilitated diffusion: transport proteins facilitate the passage of molecules that cannot easily pass through on their own

active transport: drives molecules across a membrane from a region of lower concentration to a region of higher concentration

• eg. sodium-potassium pump

transport proteins are used, energy is required

types of solutions

MORE SOLUTE = HYPERTONIC → WATER WANTS TO MOVE FROM HYPO- TO HYPERTONIC

hypertonic solution: has a higher concentration of dissolved particles (solute) than a cell

hypotonic solution: has a lower concentration of solute than a cell

isotonic solution: when the concentrations of dissolved particles is equal between a cell and the solution

• eg. if red blood cells were placed in a hypertonic solution, they would shrink

bulk transport

endocytosis: the process of taking larger molecules into the cell by engulfing them in a membrane (2 types)

1. phagocytosis (cell eating): white blood cells engulf and destroy the "bad guys"

• plays a key role in immune system

2. pinocytosis (cell drinking): cells take in liquid droplets too large to diffuse in naturally

exocytosis: the release of substances out of a cell by the fusion of a vesicle within the membrane