Diffusion & Osmosis

Define Diffusion The movement of molecules from a area in which they are highly concentrated to a area in which they are less concentrated. Particles naturally travel from an area where they are crowded to an area where they are less crowded. http://lewis.eeb.uconn.edu/lewishome/applets/Diffusion/diffusion.html

An example of diffusion from class.

An amoeba (image courtesy of BIODIDAC) Diffusion of Water All organisms need water to live. The cells of living organisms are surrounded by and filled with fluids that are mostly water. An amoeba (image courtesy of BIODIDAC)

Cell Membrane All cells are surrounded by a cell membrane made of phospholipids. This membrane acts as a barrier between the inside of the cell and the cell’s environment. It also controls the passage of materials into and out of the cell.

Selectively Permeable Membrane a membrane that permits the passage of only certain molecules Many particles can slip through the pores in the membrane because of their small size. Not all particles that a cell needs can pass through the membrane in this way.

Define osmosis The diffusion of water across a selectively permeable membrane.

Osmosis   Water moves from a high concentration of water (less salt or sugar dissolved in it) to a low concentration of water (more salt or sugar dissolved in it).  http://www.usd.edu/~bgoodman/Osmos.htm

Osmosis demo http://www.usd.edu/~bgoodman/Osmos.htm

Osmosis in our body In this picture a red blood cell is put in a glass of distilled water (all water with no salt or sugar in it).  Because there is a higher concentration of water outside the cell, water enters the cell by OSMOSIS.  In this case too much water enters and the cell swells to the point of bursting open.  In the end pieces of cell membrane are left in the water. http://www.usd.edu/~bgoodman/Osmos.htm

See an animation of osmosis here: http://hydrodictyon.eeb.uconn.edu/people/plewis/applets/Osmosis/osmosis.html

Why are osmosis & diffusion important?

Why are osmosis & diffusion important? All living things have certain requirements they must satisfy in order to remain alive – maintain homeostasis These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes. These tasks happen at the cellular level. Molecules move through the cell membrane by diffusion

Passive Transport Passive transport is the movement of molecules into or out of a cell by the processes of diffusion and osmosis (from an area of high concentration to an area of low concentration). Since the cell does no work, the cell is passive.

Active Transport Active transport is when the cell moves molecules against the normal direction of diffusion (from low concentration to high concentration). Since the cell must do work and use energy the cell is active.