How does stuff get in and out of cells? Active and passive transport across the Plasma Membrane (PM) Diffusion and Osmosis

2 categories of transport across PM 1.passive transport: no cell energy required. Moves along a concentration gradient from areas of high concentration to areas of lower concentration. diffusion osmosis 2.active transport: requires cell energy because molecules are transported against a concentration gradient

Passive Transport 1.Diffusion 1.Diffusion : net movement of particles from an area of high concentration (overcrowding) to an area of lesser concentration. 2.Osmosis: 2.Osmosis: the diffusion of H 2 O molecules through the PM.

Diffusion (in detail) All objects in motion have kinetic energy & move in straight line until they collide w/ something else. 1827: Robert Brown (Scotland) –Studied pollen under microscope –Observed random movements of grains –Called it “Brownian motion” What happens when you put a drop of food coloring in water?

Diffusion (cont.) The goal is to get as far away from other molecules as possible  –From area of “high concentration” to area of “low concentration.” –Eventually the particles will be as far apart from each other as possible Fig 2

Key terms –Concentration gradient: –Concentration gradient: diffusion cannot occur unless there’s an area of high concentration (overcrowding). –Selective permeability –Selective permeability: The phospholipid bilayer of the PM is selective about what passes through by diffusion.

OSMOSIS WHAT: Diffusion of H 2 O molecules from higher concentration to lower concentration. PM lets water pass through. concentration of H 2 O is higher OUTSIDE the cell than inside the cell so H 2 O molecules move IN increases pressure in the cell and cell may burst concentration of H 2 O is higher INSIDE the cell than outside so H 2 O molecules move OUT Turgor pressure decreases and cell may shrivel up concentration of H 2 Ois THE SAME inside & outside the cell so there is No Gain or Loss of H 2 O molecules Turgor pressure stays the same & cell maintains homeostasis

Passive Transport (in detail) Substances can pass through PM because it is permeable. They move WITH a concentration gradient They do this via diffusion, osmosis, etc Facilitated Diffusion Carrier (Transport) Proteins Membrane protein