Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
DIFFUSION, OSMOSIS, and OSMOREGULATION
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
DIFFUSION
* All molecules are in constant random motion (Brownian Motion).
* The rate of this motion increases with increasing temperature and decreases with
decreasing temperature.
* Diffusion - the directional movement of molecules from and area of high concentration of
that molecule to an area of lower concentration of that molecule.
* Molecules moving from high to low concentration are said to be moving "with the
concentration gradient".
* No energy is required.
* Diffusion occurs in the air and in water.
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
OSMOSIS
* A specialized type of diffusion.
Osmosis - the diffusion of water through a membrane.
* No energy is required
* In Biology, osmosis will always deal with the movement of water into cells or out of cells.
= water molecule
Diffusion, Osmosis, and Osmoregulation NOTES
What's wrong with this picture?????
Jim Davis didn't study his Biology.
January 23, 2012
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
Passive vs. Active Transport
Passive Transport - the movement of molecules, into or out of cells, with the concentration
gradient.
* No energy required by the cell.
* Examples: diffusion and osmosis
*Active Transport - the movement of molecules, into or out of cells, against the concentration
gradient. (from low to high concentration)
* This requires the cell to expend energy (ATP's).
* Specialized proteins in cell membranes, called carrier proteins, pump the molecules against
the concentration gradient.
PASSIVE TRANSPORT
ACTIVE TRANSPORT
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
Movement Into/Out of Cells
* All cells are surrounded by a cell membrane.
* Composition?
* Cell membranes are selectively permeable; they discriminate based on the size of the
molecule.
Cell's environment
Cell
Cell
Membrane
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
Osmoregulation
* Organisms that live in water must regulate the water concentration inside their
cells to maintain homeostasis.
* The osmosis problem is different for fresh water and salt water organisms. Fresh
water is a hypotonic solution, while salt water is a hypertonic solution.
FRESH WATER FISH
SALT WATER FISH
Diffusion, Osmosis, and Osmoregulation NOTES
Different evolutionary strategies have evolved to osmoregulate.
Osmoconformers:
-Don't actively maintain internal salt and water balance. Their internal
concentrations change as salinity changes.
- Unable to control the flooding of tissues at low salinity.
- Often stay in a salinity that matches body fluids. They don't expend
energy to maintain levels but, if they get outside this range, they
have a problem. Many conformers are found in areas of the
ocean with stable salinity.
- Most marine invertebrates. Ex: Starfish, Jellyfish, Squid
January 23, 2012
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
Osmoregulators:
-Actively maintain internal salt and water balance regardless of external conditions.
-Most marine vertebrates are osmoregulators. Ex: Tuna, Sharks, Salmon
Two regulation strategies:
1. Sharks will actively maintain a high level of the solute urea, in their tissues to
match the water's solute concentration. In this way, their internal solute/water
concentrations match their environment's. Not many shark species in/near fresh water.
The plant Dunaliella can concentrate glycerol
to regulate from fresh to 9x saltier.
2. Marine fish, use active transport to move solutes out of the cells and use their
kidneys to conserve water. In addition, many marine fish will drink the salt water to replace
the water lost by osmosis.
Some species, like salmon, are able
to go from salt to fresh water.
Diffusion, Osmosis, and Osmoregulation NOTES
January 23, 2012
In marine fish, what cells must be in direct and constant contact with the
surrounding water?
Ways to "shield" cells from direct contact with the watery environment: