Download Notes: Osmosis

OSMOSIS: The diffusion of water
Diffusion of
from areas of
concentration to areas of
concentration
across a selectively permeable membrane.
Types of Solutions
Solution = Solvent (water) + Solute
Hyper means “
”: Hypertonic solutions have MORE solute.
Cells placed in a
of the cell.
solution will
because water diffuses
Saltwater has
solute (salt) that freshwater, so saltwater is
compared to freshwater.
Examples:
: Shrinking of red blood cells.
: Loss of
in plant cells
due to water diffusing out of the cell, causing the plant to wilt.
Hypo means “
”: Hypotonic solutions have LESS solute.
Cells placed in a
the cell.
Freshwater has
compared to saltwater.
solution will
because water diffuses
solute than saltwater (3% salt), so freshwater is
Examples:
: Red blood cells burst in a hypotonic solution.
vacuole: Freshwater protozoa have to continually pump water
of the cell. (see animation)
: Turgor pressure increases in plant cells due to the diffusion of
water
to the cell.
Iso means “
”: Isotonic solutions have the SAME amount of solute as the cells.
When cells are placed in a hypertonic or hypotonic solution, water will diffuse out or into the cell in an
attempt to reach
.
Once equilibrium has been reached, osmosis does
at the
rate to maintain osmotic balance.
stop, water will diffuse
and
Osmosis in plant cells
Osmosis in animal cells
Cells must maintain osmotic balance
Describe what happens to each cell in the different solutions.
When cells are placed in a hypotonic solution,
water will diffuse
the cell,
causing the cell
to
.
When cells are placed in a hypertonic solution,
water will diffuse
of the cell,
causing the cell
to
.
When cells are placed in an isotonic solution, water
diffuses
and
at the same
rate.
Maintaining balance in freshwater

Freshwater
 is
to cells.
 high concentration of water around cell
 Water diffuses
the cell.
 example:
 problem: cells
water, swell & can
 water continually enters Paramecium cell
 solution:
 pumps water out of cell
Maintaining balance in saltwater

Saltwater
 Is
to cells.
 low concentration of water around cell

cell
water
 example: shellfish
 problem: cell

in plants:
water
.

in animals: shrinking cell
 solution: take up water
Cells at equilibrium

Isotonic solutions

in concentration of water between cell & environment
 Cell in
with the environment.
 Example: blood
 Problem:
 Water flows across membrane
, in both directions volume of cell
change
Review
1. If a cell contains 85% water and is placed into a environment which is 50% water. Is the cell hypotonic or hypertonic?
In which direction will the water diffuse, into the cell or out of the cell?
2. A cell contains 95% water, the environment outside the cell contains 45% solutes. Is the cell in a hypotonic or
hypertonic environment?
3. A plant cell containing 95% water is placed into a 10% salt solution. Is the salt solution hypotonic or hypertonic?
Which direction will the water diffuse, in or out of the cell?
Active transport

Cells may need molecules to move
 need to pump “uphill”

from
the concentration gradient.
to
using energy
 protein pump
 Requires energy that is supplied by
.
How about large molecules?

Moving large molecules into & out of cell
 through
&

: bulk transport
a cell.

: bulk transport
of a cell.

(waste)

saliva
mucous
Types of Endocytosis

: Cellular eating

: Cellular drinking
 Receptor-mediated endocytosis
Draw a series of three pictures to represent illustrate the processes of phagocytosis and pinocytosis.
1
2
3
1
2
3
Phagocytosis
Pinocytosis
Read the following questions carefully. Be sure to answer all parts of each question.
6. If a cell contains 85% water and is placed into a environment which is 50% water. Is the cell hypotonic or
hypertonic? In which direction will the water move, into the cell or out of the cell?
7. A cell contains 85% water and is placed into a solution which contains 90% water. Is the solution in the
environment hypotonic or hypertonic? In which direction will the water move?
8. If a cell which contains 90% water is placed into an isotonic solution, what percentage of the solution is
water?
9. A cell contains 95% water, the environment outside the cell contains 45% solutes. Is the cell in a hypotonic
or hypertonic environment?
10. A cell containing 25% solutes is placed into a solution which contains 35% solutes. Which direction will the
water move, into the cell or out of the cell?
11. A plant cell containing 95% water is placed into a 10% salt solution. Is the salt solution hypotonic or
hypertonic? Which direction will the water move?
12. If water leaves a cell when placed into a solution, is the cell hypotonic or hypertonic