Solutions, and Movement of Molecules Therein

Isotonic, Hypotonic and Hypertonic Solutions A description of the concentrations of a solute or solvent in a solution on either side of a membrane.

Isotonic Solutions "ISO" means the same When the concentration of the solute is equal on both sides of the membrane, movement of water across the membrane won't have any affect on the concentrations on either side of the membrane.

Hypotonic Solutions "HYPO" means less Here, there are less solute molecules outside the cell membrane, so it has a lower concentration. Water will move into the cell to help balance the number of water molecules out.

Hypertonic "HYPER" means more There are more solute molecules outside the cell, which causes the water leave the cell.

Blood Cell Example

Concentration Gradient DOWN Concentration Gradient- molecules move from areas of High concentration to areas of Low concentration. UP Concentration Gradient- molecules move from areas of Low concentration to areas of High concentration. UP DOWN

Diffusion The net movement of molecules from an area of high concentration to an area of lower concentration (down the gradient!) due to random motion of molecules. NO ENERGY NEEDED

Diffusion Movement of the molecules continues, until the rate is constant and the concentration uniform. This is called Equilibrium.

Osmosis The movement of water (solvent!) from an area of high concentration to an area of low concentration.

Osmosis Adding sugar to water decreases the water concentration because the sugar molecules displace the water. 31 Water Molecules *More molecules means more concentrated. 20 Water Molecules *Less molecules means less concentrated.

Osmosis If the two beakers were connected by a tube that contained a semi-permeable membrane, the water molecules would flow from a high concentration to a lower concentration. High Concentration Of Water Low Concentration of Water 

Osmosis This flow of water, results in a change in volume of both sides. The side that has sugar now has a larger volume. Water moved from the side with the higher concentration to the side with the lower concentration. Now there is more water on this side! 

Osmosis If there was a membrane with twice as many water molecules on one side as there were on the other (and remember, water can move through the membrane), what do you think would happen?

Osmosis More water would move in one direction than the other. More water would flow from a higher concentration to a lower concentration of water.

Osmosis Eventually, the concentration of water on each side of the membrane would be equal and the flow of water would be diffusing through the membrane in both directions at the same rate – ie. Equilibrium.