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After reading about osmosis (5.15 and 5.16 in the text), study the diagrams above the chart on page 3 - 11 in the Study Guide.

Here is the background information needed to understand the diagrams.

	A solution consists of two parts : a solute (particles dissolved in a liquid) and a solvent (the liquid portion - in the case of cells, the solvent is water).
	In all 3 diagrams, there is a cell (the big round circle!), surrounded by a solution.
	Some of the material inside the cell is also in solution. Thus, in all three diagrams there are two solutions (the one in the cell and the one outside the cell) separated by a membrane (the cell membrane).
	Water can move freely across the membrane, however, this is generally not the case for the solute.
	The small circles in the diagram refer to the solute or particles NOT to water. The arrows indicate the direction of water movement.

The terms hypotonic and hypertonic are usually the big hang up. The good news is that if you understand one of the terms, you will understand the other since they are opposites! Here goes!

As you probably know, the prefix "hypo" means less than. What does a hypotonic solution have less of ?? If you are thinking particles or solute, you are right!! A solution that is a hypotonic solution has fewer or less PARTICLES than the solution on the other side of the membrane.

Note that in the middle diagram - the hypotonic solution surrounding the cell - there are fewer PARTICLES in the solution surrounding the cell than in the cell ( 2 vs. 3 ). Since the parts of the solution (solute + solvent) must add up to 100%, this means there is more water in the solution surrounding the cell than there is in the solution inside the cell!

A hypotonic solution contains fewer particles ( less solute) but more water (the solvent) than the solution on the other side of the membrane. Since water can move freely across cell membranes, it moves from an area where it is in greater concentration to an area where the concentration is less. . Thus, if a cell is placed in a hypotonic environment, water will move into the cell (from an area of greater concentration to an area of lesser concentration). Note the heavy arrows showing movement of water into the cell in the hypotonic solution - there is a net gain of water into the cell.

Possibly the confusion lies in the fact that the term hypotonic refers to the particle concentration (hypo = less than) whereas the process we are concerned with (water movement) is determined by the water concentration! Look at the diagrams on page 83 (5.16) in your text to see what happens when an animal cell or a plant cell is placed in a hypotonic environment.

Can you explain the term hypertonic and what happens to cells when they are placed in a hypertonic environment?

Why MORE Water in a Hypotonic Solution???