Osmosis & TonicityAdv. Bio 2016

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.

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.

OsmosisOsmosis. Campbell Biology (2010)

TonicityTonicity 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.

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

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

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

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

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

https://www.youtube.com/watch?v=OYoaLzobQmk

Osmosis in Animal Cells (Video)

Osmosis in Plant Cells (Video)

https://www.youtube.com/watch?v=zVvHn6Sj9PQ