Question

In hospitals patients sometimes receive l uids
by intravenous injection. Doctors choose a
salt solution and never plain water to inject
into humans. You know that blood is
composed mainly of red blood cells. Use your
knowledge of osmosis to explain why doctors
make this choice

Answer 1

This is a fun case and is used all the time almost everwhere.
Now we remember that osmosis is the pasive diffusion of water involving a membrane.
In the body we have a natural salt concentation, we usualy call the human salt concentration. Now what would happen if the concentration of water was higher outside the cells than inside, by using pure water?

Answer 2

In addition we work with 3 key words:
Hypotonic solution: The hypertonic solution, is a solution with the result that water leaves the cell.
Isotonic solution: The isotonic solution is a solution with the result that the net movement equals 0. (Delta G=0)
Hypertonic solution: The hypertonic solution is a solution with the result that water will enter the site, that may couse the cell to lysis (lysis from Greek to dissolve, in other words the cell may burst).

Answer 3

@Frostbite you kind of messed up your labels :-(

Hypertonic and hypotonic refer to the level of solutes in the solution. Diffusion through a semi-permeable membrane (such as a cell wall) will always attempt to equalize the concentrations on both sides. A hypertonic solution has a greater concentration of solutes, so a cell immersed in a hypertonic solution will lose water as it attempts to lower the solute concentration of the surrounding fluid, and the cell will shrink. A hypotonic solution has a lower concentration of solutes, so a cell immersed in a hypotonic solution will gain water as it attempts to increase the solute concentration of the surrounding fluid, and the cell will swell, possibly bursting. Isotonic solutions have equal solute concentrates to that found in the cell, so the net movement of water is 0.

If you like pictures, see https://en.wikipedia.org/wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg

If you like animations, see http://www.phschool.com/science/biology_place/biocoach/biomembrane1/hypotonic.html

Answer 4

Woops. my bad.

Answer 5

Think I left my head on the table while writing it, sense I did not notice.