osmosis

tivol at tethys.ph.albany.edu tivol at tethys.ph.albany.edu
Fri Feb 3 17:12:58 EST 1995


In article <3gpala$8ia at Owl.nstn.ca>,
cquinn at fox.nstn.ca (Cam Quinn) writes:
>Hi!  My name is Erin Quinn and I am doing a Grade 8 science project on 
>osmosis.  I put celery in glasses of baking soda, cornstarch, salt and 
>sugar.
>I observed that the salt dried it up, baking soda one was dying slowly, 
>cornstarch just sank to the bottom and didn't do anything and sugar was 
>really healthy BUT I DON'T KNOW WHY!
>I've tried to get information from the library but don't know where to 
>look and can't get any information.
>
>Can anyone help me by explaining what happened or tell me where to look 
>for an explanation?

Dear Cam,
	Here's a start.  Probably salt dried the celery by withdrawing water
to match osmotic pressures; however, since salt in high concentrations is
toxic (there are special adaptations for plants growing in briny areas), it 
may simply have disrupted the metabolism of the celery so that it lost water
by transpiration to the atmosphere.  The fact that baking soda works the same,
but slower, may indicate that HCO3- and Cl- have different transport properties
or that there were fewer ions (and a lower osmotic difference).  Both these
results can be complicated because of transport across membranes.  The sugar
was probably taken up as a nutrient, accounting for the health of the celery
in that experiment.  Since cornstarch consists of large, insoluble molecules,
the fact that it didn't do anything is no surprise.  The bottom line here is
that you do not have a simple osmosis experiment, and the other features of
the experiment (common with living systems--that's why physics is simple [but
not necessarily easy] and biology is complicated) make interpretations diffi-
cult.  Keep up your interest--it's great to see people your age both interested
in science and computer-literate and courageous enough to ask such questions.
				Yours,
				Bill Tivol



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