LOST AT SEA

[candice]

WHY CAN YOU NOT DRINK SEA WATER IF YOU ARE STRANDED? THE SALT MAY MAKE YOU RETAIN WATER, BUT AT LEAST YOU WON'T DEHYDRATE...

JUST WONDERING

[shijun]

Candice,

I found an article on this page that answers your question: http://www.madsci.org/posts/archives/oc ... .Me.r.html

Biological Applications Of Osmosis

Osmosis displays itself in most biological systems that are cellular. The cell
wall is a semi-permeable membrane. So is the cell nuclear wall 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.