MOVEMENT OF MATERIALS THROUGH THE CELL MEMBRANE

Background Info… Every living cell contains a liquid interior and is surrounded by a liquid One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other

Background Info… Carbohydrates act like chemical identification cards for other cells The core of nearly all cell membranes is a LIPID BILAYER which is a tough flexible structure Protein channels pumps help move materials across

PASSIVE TRANSPORT No energy needed because movement occurs down the concentration gradient (from high concentration to low concent.) There are 3 types of passive transport: 1. Diffusion 2. Osmosis 3. Facilitated Diffusion

1. Diffusion Movement of molecules from an area of greater concentration to an area of lesser concentration *continues until equilibrium is reached; molecules will continue to move in both directions at the same rate

2. Osmosis Diffusion of water across a selectively permeable membrane Some substances can pass through the membrane & others cannot Ex: carrot in salt water; water can pass through the carrot cell membrane but salt cannot

OUTSIDE THE CELL INSIDE THE CELL

Osmotic Pressure Pressure created by osmosis Cells are filled with sugars, salts, proteins, and other molecules If a cell is placed in fresh water, which way will the water move? INTO THE CELL!! Which will cause the cell to swell and burst Why doesn’t this happen in your body? Blood has same amount of solutes as cells Plant cells are surrounded by tough cell walls

ISOTONIC solution: Concentration of water & sugar same on both sides of membrane. Molecules will continue to move in both directions at the same rate (Osmosis continues until equilibrium is reached) HYPERTONIC solution: Higher concentration of solutes outside the cell than inside the cell itself, water leaves the cell through osmosis. (Lower solute concentration inside cell) HYPOTONIC solution: Lower concentration of solute outside the cell than inside the cell, water will enter it through osmosis. (Higher solute concentration inside cell)

3. Facilitated Diffusion involves the use of protein channels located in the cell membrane protein channels help material across *glucose transported across this way

ACTIVE TRANSPORT requires energy because material is moved across the membrane against the concentration gradient (from low concentration to high concent.) Compared to a pump!

WHY DO WE NEED THIS PROCESS?:

We need active transport in order to… 1. Transport (or pump) macromolecules across the cell membrane Ex: Na+/ K+ pump; Ca+2 ions (responsible for nerve impulses) Cell uses energy to force ions across the membrane, like you would use energy to force a boulder up a hill

Na/K Pump Video Examples Dying from drinking to much water Wii http://www.biology4all.com/resources_library/source/63.swf Examples Dying from drinking to much water Wii Chico 2005

We need active transport for… 2. Endocytosis- taking materials into a cell (forms a vacuole within the cytoplasm) ex: phagocytosis: large particles are engulfed

We need active transport for… Exocytosis- bulk passage out of the cell