CELL BOUNDARIES Chapter 7, Section 3 Pgs 182-189

The Cell Membrane Regulates what goes in an what goes out, like a bouncer at a club Made up of a lipid bilayer (A fluid, flexible barrier) and proteins The typical model of a cell membrane is called a Fluid Mosaic Model

Quick Stuff Plants have Cell Walls in addition to cell membranes Walls are made mostly of cellulose Provide support and protection Concentration: Cells contain lots of substances in water The amount of any given substance (IE: NaCl or KCl) is called the concentration Diffusion is the process of substance particles moving from areas of high concentration to areas of low concentration

Diffusion Diffusion is the process of substance particles moving from areas of high concentration to low concentration. When the concentration is equal throughout, equilibrium has been reached Diffusion across a cell membrane does NOT require energy!

Osmosis: The Diffusion of Water The diffusion of water across a semi-permeable membrane is osmosis Water moves from areas of high concentration to low concentration just like substances! Hypotonic  Hypertonic until the solutions are Isotonic Hypotonic = “under-stuffed” Hypertonic = “over-stuffed” Isotonic = Equally stuffed

Osmotic Pressure Cells have lots of salts and substances in them If animal cells come in contact with fresh water, they will expand until they explode, if they come in contact with very salty water, they will shrivel Animal cells never come in contact with fresh water Cell walls prevent plant cells from exploding The pressure water can create in cells is called Osmotic Pressure

Passive Transport vs. Active Transport Facilitated Diffusion occurs when substances cross a cell membrane without using energy. Often through a tubular membrane protein than never closes Active Transport uses energy to move membrane proteins so substances can move (usually) from areas of low concentration to high concentration

Endocytosis vs. Exocytosis When cells move very large molecules into the cell body, it’s called Endocytosis Endo- into, cyto- cell Cells perform endocytosis in two ways Phagocytosis Pinocytosis Exocytosis occurs when cells release molecules out of their cell body Exo- out of, cyto- cell Ex: Contractile vacuoles release water out of a single-cell organism

Endocytosis: Both forms in one image

Endocytosis: Phagocytosis Cell membrane expands and surrounds the particle being eaten Engulfs it creating a food vacuole Used to eat large particles Requires energy, therefore active transport

Endocytosis: Pinocytosis Similar to phagocytosis but used to ingest small particles Small pockets form in the cell membrane, fill with fluid and pinch off into the cytoplasm around the particle

Transport Videos Lipid Bilayer 3D view of organelles http://www.youtube.com/watch?v=owEgqrq51zY&feature=fvsr 3D view of organelles http://www.youtube.com/watch?v=f1dp7tSC3Wg&feature=related Active vs. Passive Transport and cell eating http://www.youtube.com/watch?v=j5Qway4LAkk&feature=related http://www.youtube.com/watch?v=kfy92hdaAH0 http://www.youtube.com/watch?v=JShwXBWGMyY&feature=related Osmosis http://www.youtube.com/watch?v=AYNwynwaALo Some cell structures (WAY more info than you need, but cool nonetheless) http://www.youtube.com/watch?v=nKgINP5QDIg&feature=fvwrel