Osmosis - I know the basics, bu I need more information (Nov/17/2005 )
I may be doing a school science fair project on osmosis, and the kit is at https://www2.carolina.com/webapp/wcs/stores...6%7C1737%7C1744 . I hope this will work, but I need to know a little more about osmosis, so if you could tell me that'd be great.
I was going to write out an explanation but found the quote below, have a read. Put simply a higher concentration of salt on the outside of the cell causes water to flow out to fast and the cell shrinks, conversely a lower concentration of salt on the outside of the cell causes the water to flow into the cell to fast and the cell swells. If the cell shrinks it becomes desiccated and if it swells it can burst.
Osmosis displays itself in most biological systems that are cellular. The cell membrane is a semi-permeable membrane. So is the cell nuclear membrane which keeps DNA molecules inside the nucleus while allowing the transfer RNA molecules to pass through in and out of the nucleus. Nutrients,oxygen, water, and waste gases can pass in or out of the cell through the semi-permeable cell membrane. Cells in which water passes out of the cell faster than can get in are said to shrink and undergo crenation. This happens when cells are placed in an extracellular fluid of more than .9% salt solution. The extracellular solution is concentrated enough to allow water molecules to osmotically pass to the outside of the cell faster than water can pass into the cell. As a result the cells dehydrate and shrink. This is what happens if a person dying of thirst on a raft in the middle of the ocean decides to drink sea water. The sea water increases the salinity of the extracellular fluids, and a condition arises where more water osmotically leaves the cells than can get out. The cells dehydrate, and ironically, the person suffers from cellular dehydration which becomes more severe as the person takes in more sea water. Such an extracellular solution is called a hypertonic solution.
On the other hand if cells are placed in a salt solution of less than .9% then the water on the outside of the cell in the extracellular fluid can pass into the cell faster than water can get out. The result is that the cells swell with the excess water and eventually burst open. When red blood cells do this it is referred to as hemolysis. The extracellular fluid itself is said to be hypotonic. A condition known as water intoxication results in too much water being ingested where the Sodium/Potassium ion pump can't control the water intake into the cells and the cells rupture due to this intoxication.
Pysiological saline (salt) solution is 0.9% and results in an equilibrium between osmosis into the cell and out of the cell. This kind of solution is the extracellular fluid that our cells respond most positively to. The solution is said to be isotonic. This intricate balance in osmosis in and out of the cells needs to be maintained at all times. The controller of this process is the kidneys themselves which filters out waste products and recycles needed nutrients while maintaining this isotonic condition in the extracellular fluids.
Another example of osmosis is found in the plant kingdom. Plants through their leaves, stems, stalks and root systems take in needed CO2 and water during their photosynthetic process and takes in Oxygen during the respiration cycle of the plant. It is important that water be allowed to enter and leave in a balanced way just as in the animal kingdom. If the roots of plants are placed in soil that is too saline (salty), then a condition of hypertonicity occurs, and the cells in the roots will shrink and dehydrate. That is why plants shrivel up and die in a soil that is too salty. Have you ever wondered how large tall trees can receive the necessary nutrients that only come from the soil? The total osmotic pressure of a large tree with an extensive network of roots can generate an osmotic pressure of several atmospheres enough to overcome the gravity pull downward.