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Diffusion, Osmosis and the SF Bay
Solutions
1. Define solution
•
A homogeneous mixture in which
one substance is dissolved in another.
•
Ex. Kool-aid, saltwater
2. Define solute
•
The substance in a solution that is
dissolved.
•
Ex. Sugar, salt
3. Define solvent
•
The substance in a solution that does
the dissolving.
•
Ex. water
Diffusion
2. Define diffusion
•
The process by which molecules of a substance move across a
concentration gradient, from areas of higher concentration of
that substance to areas of lower concentration
3. Define concentration gradient
•
The distinguishing line between higher and lower concentrations
4. Define selectively permeable membrane
•
A biological membrane that allows some substances to pass
through, but not others
Selectively Permeable Membrane
Diffusion
5. Factors that determine whether diffusion
occurs across a membrane include:
•
Unequal concentration of substances
on either side of a membrane
•
Membrane permeability
If molecules can penetrate a
membrane, diffusion will continue
until equilibrium is reached!
Osmosis
6. Define osmosis
•
The diffusion of water through a selectively permeable
membrane from an area of greater water concentration to an area
of lesser water concentration.
Osmosis
9. Problems
•
Cell cytoplasm is filled with solute particles (sugars, salts,
proteins etc.)
•
Water concentration is lower inside the cell than in fresh water
•
Cell membrane is permeable to water, but not to solutes
•
If water moves in, the cell will expand and burst!
10. Solutions
•
Some cells do not come into contact with fresh water
•
Plants cells and bacteria have cell walls to prevent cells from
expanding
•
Some unicellular organisms pump excess water out of cell
Passive Transport
11. Define passive transport
•
The transport of molecules, down a concentration gradient, from a
region of higher concentration to a region of lower concentration
•
Energy is NOT required for this process to occur
•
Ex. diffusion, osmosis and facilitated diffusion
Facilitated Diffusion
12. Define facilitated diffusion
•
The transport of molecules across a membrane in the direction of
lowest concentration by a carrier protein
Explanation:
•
Some molecules are too big or have to wrong charge to be
permitted to freely pass through a cell membrane
The molecules move down a
concentration gradient, so energy is
NOT required!
Active Transport
13. Define active transport
•
The transport of molecules against a concentration gradient,
from a region of low concentration to a region of high
concentration
Examples:
•
Molecules are carried through membrane-associated pumps
•
Endocytosis
The molecules move against a
concentration gradient, so
energy IS required!
Applying the Concepts-Hypotonic Solution
1. Hypotonic solution-a solution with a lesser concentration of
solute compared to the concentration of solute inside the cell
•
Example: a single celled salt water organism is
placed in brackish water
brackish water
b.
Direction of water flow?
c.
Direction of solute flow?
d.
What will happen to the cell?
b.
Water flows into the cell.
c.
The solute does not move because of
the selectively permeable membrane.
d.
The cell will expand and could burst!
Applying the Concepts-Hypertonic Solution
2. Hypertonic solution-a solution with a greater concentration of
solute compared to the concentration of solute inside the cell
•
Example: a single celled fresh water organism is
placed in salt water
salt water
b.
Direction of water flow?
c.
Direction of solute flow?
d.
What will happen to the cell?
b.
Water flows out of the cell.
c.
The solute does not move because of
the selectively permeable membrane.
d.
The cell will shrink!
Applying the Concepts-Isotonic Solution
3. Isotonic solution-a solution with an equal concentration of
solute compared to the concentration of solute inside the cell
•
Example: a single human red blood cell is placed
in a 0.9% saline (salt) solution
0.9% saline
b.
Direction of water flow?
c.
Direction of solute flow?
d.
What will happen to the cell?
b.
There is no net movement of water in
a particular direction.
c.
The solute does not move because of
the selectively permeable membrane.
d.
The cell size stays the same!
Osmosis Animation
Diffusion Demonstration
Set-up #1
•
The cornstarch represents the living cell. The iodine solution represents the
environment.
•
Example: a single celled salt water organism placed in brackish water.
•There is a lower concentration of iodine
inside the cell, so the iodine moves in.
Iodine solution
Cornstarch
solution
•There is no net movement of cornstarch
because of the selectively permeable
membrane.
•This causes the liquid inside the plastic bag
to change color and the plastic bag to
expand.
hypotonic
•This is an example of a_____________
environment.
Diffusion Demonstration
Set-up #2
•
The cornstarch represents the environment. Iodine represents the living cell.
•
Example: a single celled fresh water organism placed in salt water.
•There is greater concentration of iodine inside
the cell, so iodine moves out.
Cornstarch solution
Iodine
solution
•There is no net movement of cornstarch
because of the selectively permeable
membrane.
•This causes the liquid outside the plastic bag
to change color and the plastic bag to shrink.
hypertonic
•This is an example of a _______________
environment.