Biology - Osmosis and Tonicity

1. Osmosis & Tonicity
Adv. Bio 2016

2. Osmosis
What is it?
Osmosis is the diffusion of water across a membrane; the
movement water molecules from a region of higher water
potential (lower solute concentration) to a region of lower water
potential (higher solute concentration) down a concentration
gradient through a selectively permeable membrane. Osmosis
occurs in cells all the time.

3. Water Potential
high water potential = higher concentration of
water molecules (more dilute)
i.e. a 5% sucrose solution has a higher water
potential than a 10% sucrose solution.

4. Osmosis
Osmosis. Campbell Biology (2010)

5. Tonicity
Tonicity is a term that describes the ability of a solution to cause a cell to gain or
lose water. It mostly depends on the concentration of a solute or salts on both sides
of the membrane.
- Hypotonic
- Isotonic
- Hypertonic
These solutions can only be looked at in comparison; you cannot call one solution a
hypotonic or hypertonic solution. They always work in comparisons.

6. Hypotonic Solution
- A hypotonic solution is one that has a
high water potential as compared to the
other solution.
- The solute concentration is lower
outside the cell, water molecules move
into the cell, and the cell will expand and
may burst.
- This bursting of an animal cell caused
by over stretching of the cell membrane
is called lysis. https://sites.google.com/site/talbaneses1st2013/home/part-1-physical-chemical-
celluar-basis-of-life/19hypotonicsolution

7. Isotonic Solution
- Isotonic solutions have
the same water potential.
- The concentration of
solute is the same on both
sides of a membrane, and
the cell volume will not
change.
https://sites.google.com/site/talbaneses1st2013/home/part-1-physical-chemical-
celluar-basis-of-life/19hypotonicsolution

8. Hypertonic Solution
- A hypertonic solution is one that has
a lower water potential as compared
to the other solution.
- The solute concentration is higher
outside the cell, water molecules
move out of the cell. The cell will
shrink.
- Cell crenation is when an animal cell
loses water and thinks.
https://sites.google.com/site/talbaneses1st2013/home/part-1-physical-chemical-
celluar-basis-of-life/19hypotonicsolution

9. Animal Cell vs Plant Cell
From: http://biology-forums.com/index.php?action=gallery;sa=view;id=307

10. Animal Cell vs Plant Cell
From http://cursa.ihmc.us/rid=1165370189189_2102640856_6267/Cell%20Membrane.cmap:

11. https://www.youtube.com/watch?v=OYoaLzobQmk
Osmosis in Animal Cells

12. Osmosis in Plant Cells
https://www.youtube.com/watch?v=zVvHn6Sj9PQ