Water and its relation to

Diffusion and Osmosis

What is Diffusion?

Diffusion is the natural tendency of molecules to flow from higher concentrations to lower concentrations of solute particles until the concentration is the same on both sides of the membrane.

Diffusion across a Membrane

Semi - Permeable membranes –

Living membranes alter what may pass through at any given time

Kidney Dialysis

Diffusion of CO2 and O2 in the Lung

Diffusion of Liquids

When two fluids mix together without any help from us.

We can explain this using the idea that particles move.

Instead of the particles moving around and mingling with particles of the same material, they move around and mingle with particles of the other material as well

How Diffusion of Liquid in Liquid Works

Add a drop of food coloring in a container of water.

The color will “diffuse” or disperse throughout the entire sample until the sample is a uniform color.

How Diffusion of Solid in Liquids Works

Diffusion of Gases A bottle of perfume opened in one

corner of a room would slowly fill the room

Molecules disperse from a concentrated source, the newly opened bottle, until they are evenly distributed throughout the room

Smell of freshly baked cookies

The solute (solid) dissolving in the solvent is also an example of diffusion.

The water “attacks” the solute which eventually dissolve.

What are ways that this process in increased?

How Diffusion of Solid in Liquid Works

If the concentration of dissolved substances (solutes) is not the same inside and outside the cell –

A process called osmosis occurs

Living cells contain aqueous (water) solution and they are surrounded by aqueous solutions

Osmosis: the diffusion of water molecules from an area

with less solutes (low concentration) to an area with more solutes in the solution (high concentration)

What are semi-permeable membranes?

Those membranes that allow the solvent (liquid), but not the solutes to pass from one side of the membrane to another

EX: egg, cellophane, and cell membranes

In these membranes the pores are large enough for water to pass through but too small for other compounds to pass

Examples

Sailor died from dehydration due to the high concentration of salt in the seawater.

After drinking the seawater the high concentration of salt caused the water to travel out of his cells.

This caused the cells to dehydrate or shrink

How do we get pickles?

If the concentration of solute in the fluid surrounding the cell is higher than inside the cell the solution is hypertonic

Water will travel out of the cell through the membrane - crenation

Red Blood Cells in a Hypertonic Solution

Hypertonic Solution

The word "HYPER" means more, in this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction.

If the concentration of the solute outside the cell is less than inside the cell it is called a hypotonic solution.

Hemolysis will occur – additional water will travel into the cell causing it to swell and rupture.

Red Blood Cells in a Hypotonic Solution

Hypotonic Solution

The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, so water will move into the cell.

When the fluids have the same concentrations they are called isotonic

EX: when fluids are administered to a patient

Red Blood Cells in an Isotonic Solution

Isotonic Solution

If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side.

"ISO" means the same

REVIEW

Diffusion is the natural tendency of molecules to flow from higher concentrations to lower concentrations

Movement may be of molecules or ions across a semi-permeable membrane

Depends on molecular size, ionic charge, and molecular solubility (ability of solute to dissolve in solvent)

ReviewOsmosis: the diffusion of water

molecules from an area of low solute concentration to an area of high solute concentration.

The water diffuses through the semi-permeable membrane until the concentration of the solutes is the same on both sides.

1% salt (low concentration) in the bag

10% salt (high concentration) surrounding the bag

Which way does the water move?

Diffusion or Osmosis?

Starch solution in the bag

Iodine solution surrounding the bag.

What do you predict will happen?

Diffusion or Osmosis?

Lab Set-up