Download 3.4 Diffusion and Osmosis - Greenall

3.4 Diffusion and Osmosis
Cells are constantly taking in and sending out substances. If they had
to use energy to move every molecule, it would require a massive
amount of energy. Some molecules do not have to use energy to move.
3.4 Diffusion and Osmosis
Passive transport does not require energy input from a
cell.
• Molecules can move across the cell membrane
through passive transport.
• There are two types of
passive transport.
• diffusion
• osmosis
3.4 Diffusion and Osmosis
Diffusion is the movement of molecules from a place of higher
concentration to a place of lower concentration. It is a natural
motion of particles.
• Molecules diffuse down a
concentration gradient, meaning they
move from a higher concentration
area, to a lower concentration area.
High
concentration
Low
concentration
3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive transport.
• The diffusion of water molecules is called osmosis. The
process of osmosis is exactly the same as diffusion but
refers only to water molecules. Water molecules diffuse
across a semipermeable membrane from a place of
higher water concentration to a place of lower water
concentration.
3.4 Diffusion and Osmosis
A Dynamic equilibrium is reached when the
concentration is the same throughout the
solution.
3.4 Diffusion and Osmosis
In cells, small lipids, and other nonpolar
molecules, such as carbon dioxide and
oxygen, easily diffuse across the membrane
3.4 Diffusion and Osmosis
Water is the solvent in our cells, the other molecules
are the solute.
There are three types of solutions.
•
isotonic
•
hypertonic
•
hypotonic
3.4 Diffusion and Osmosis
• A solution is isotonic if it has the same concentration of
solutes that the cell has. Equal amount of water enter and
exit a cell so size remains constant.
• A solution is hypertonic if it has a higher concentration of
solutes than a cell. More water diffuses out of the cell, and
the cell shrivels.
• A solution is hypotonic if it has a lower concentration of
solutes than a cell. More water diffuses into the cell, and
the cell grows larger.
3.4 Diffusion and Osmosis
Some molecules can not diffuse through cells on their
own, they need the help of transport proteins to diffuse.
• Some molecules cannot easily diffuse across the cell
membrane.
• Facilitated diffusion is diffusion
through transport proteins.
• Some transport proteins are
simple channels, or tunnels,
through with particles such as ions
can pass. Others act more like
enzymes. When bound, the
protein changes shape, allowing
the molecule to travel the rest of
the way into the cell.