Diffusion & Osmosis

What is Diffusion? The movement of molecules from a area in which they are highly concentrated to a area in which they are less concentrated. The movement of molecules from a area in which they are highly concentrated to a area in which they are less concentrated.

What do we mean by concentration? The amount of a particular substance in a given amount of another substance

So let’s look at a diagram of an example of diffusion.

Notice how the molecules of food coloring changes from an area of high concentration to spread out in solution to a lower concentration of food coloring.

See an animation of diffusion here: u/lewishome/applets/Diffu sion/diffusion.html u/lewishome/applets/Diffu sion/diffusion.html

So…what is osmosis?

Osmosis The diffusion of water molecules across a selectively permeable membrane.

How does osmosis work? Water moves through a semi- permeable membrane. The molecules go from a high concentration of water to a low concentration of water until the number of molecules are balanced on both sides of the membrane. Then the water has reached equilibrium

How water molecules move during osmosis…

Which way would the water molecules move?

335% water inside cell 78% water outside the cell This cell has a concentration of 35% water inside and is in a solution that contains 78% water. How will the water molecules move? Will the cell get bigger, get smaller, or stay the same size? The cell will get bigger.

335% water inside cell 12% water outside the cell This cell has a concentration of 35% water inside and is in a solution that contains 12% water. How will the water molecules move? Will the cell swell, shrink, or stay the same? The cell will shrink.

335% water inside cell 35% water outside the cell This cell has a concentration of 35% water inside and is in a solution that contains 35% water. How will the water molecules move? Will the cell swell, shrink, or stay the same? The cell will remain the same size.

See an animation of osmosis here: u/lewishome/applets/Osm osis/osmosis.html u/lewishome/applets/Osm osis/osmosis.html

What is a selectively permeable membrane? (also known as semi-permeable)

So….what is a selectively permeable membrane?  A membrane that allows only certain materials to cross it  Materials pass through pores in the membrane

For more information on diffusion & osmosis, click here: tutorial/default.html tutorial/default.html

Why are osmosis & diffusion important?

 All living things have certain requirements they must satisfy in order to remain alive.  These include exchanging gases (usually CO 2 and O 2 ), taking in water, minerals, and food, and eliminating wastes.

Why are osmosis & diffusion important?  All living things must maintain homeostasis  These tasks happen at the cellular level.  Molecules move through the cell membrane by diffusion.  The diffusion of water through the membrane is known as osmosis.

Why is the cell membrane important? It is a complex structure that is responsible for separating the contents of the cell from its surroundings and for controlling the movement of materials into and out of the cell.

Passive Transport vs. Active Transport

Passive Transport Movement of materials in and out of the cell Movement of materials in and out of the cell Requires no energy to happen Requires no energy to happen Only happens with small molecules that fit through pores Only happens with small molecules that fit through pores

Two types of Passive Transport 1. Diffusion: When small molecules that are dissolved in water move 1. Osmosis: When water moves across the cell membrane

Active Transport When substances are too large to pass through the pores in the cell membrane When substances are too large to pass through the pores in the cell membrane Requires cell to use energy for molecules to move in or outRequires cell to use energy for molecules to move in or out Does not follow the same rules as diffusion. Goes OPPOSITE of the concentration levels. (Molecules travel the other way.) Does not follow the same rules as diffusion. Goes OPPOSITE of the concentration levels. (Molecules travel the other way.)

Passive and Active Transport How are they the same? Both involve the transport of a substance across a membraneBoth involve the transport of a substance across a membrane Both change the concentrations on different sides of a membrane.Both change the concentrations on different sides of a membrane. Both are also important for the cell to functionBoth are also important for the cell to function

Passive and Active Transport How are they different? Active transport requires energy but passive transport requires none. Passive transport moves molecules from higher to lower concentrations; active transport moves the opposite..