Download Diffusion and Osmosis

• Solution - a homogeneous mixture of 2
substances
• Solute - the dissolved substance
• Solvent - the dissolving agent
Diffusion
• Random movement of molecules from an area
of their higher concentration to an area of
their lower concentration.
• Lighter molecules diffuse faster than heavier
molecules
Diffusion occurs in both liquids and gases.
Examples: sugar in water; perfume in air.
Osmosis
• Diffusion of water molecules through a semipermeable membrane from an area of higher
water concentration to an area of lower water
concentration
• (An area of high water concentration has a
low solute concentration, and visa versa)
Figure 3.7 Generation of osmotic pressure by osmosis.
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The plasma membrane is a semi-permeable membrane.
The cytoplasm is completely enclosed.
Solute concentrations of outside solutions
relative to the inside of a cell:
• Isotonic: the same solute concentration
• Hypertonic: higher solute concentration
• Hypotonic: Lower solute concentration
Osmosis and Cells
Osmosis and cells
• In hypertonic environment, the cell
shrinks. In a plant cell, this is called
plasmolysis: the cell shrinks inside the
cell wall.
• In hypotonic environment, the cell swells.
An animal cell will burst, which is called
lysis.
Differences between dialysis tubing and the cell
membrane (both are selectively permeable):
1. Dialysis tubing has pores. Whether or not a
molecule can cross depends only on its size.
2. The cell membrane is made of a lipid bilayer.
Whether or not a molecules can cross
depends on its chemical properties.
3. Proteins are embedded in the membrane,
and regulate the passage of most molecules
across the membrane.
Membrane Lipids: basic structure
head
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tails
The plasma membrane. (DON’T NEED TO KNOW THE DETAILS)
Copyright © 2009 Pearson Education, Inc.