Hour long argument with biology professor about OSMOSIS

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mercanucaribe

Banned
Oct 20, 2004
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I've been arguing with my biology teacher (I'm taking the intro Bio at the community college for my minor). We did the egg experiment, in which you put the eggs, that have had their shells dissolved by vinegar, in deionized water, saltwater, and karo syrup. The problem is that our egg in the saltwater supposedly became larger and the one in the deionized water supposedly stayed the same. The one in the karo syrup shrivelled like it was supposed to. According to what I know about osmosis, water potential, etc, the egg in the distilled water should have been larger. Either there's an error in the experiment or I don't know how osmosis works.

I tried to argue that if an egg has higher salt concentration than saltwater, it has to have a higher salt concentration than deionized water. I even drew a diagram. Am I missing something??

Cliff notes: Egg in distilled water stayed the same, egg in saltwater swelled, egg in karo syrup shrivelled. Professor says it's because of osmosis.
 
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iluvtruenos

Banned
Apr 14, 2005
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Egg has less salt than saltwater hence the water comes from the salt water to the egg.

The egg has more salt than deionized water, hence the water comes out from the egg to the deionized water.

That's why what happened happened.




(If I'm wrong, take into account the fact that I just started saucing up.)
 
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mercanucaribe

Banned
Oct 20, 2004
9,763
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Originally posted by: iluvtruenos
Egg has less salt than saltwater hence the water comes from the salt water to the egg.

The egg has more salt than deionized water, hence the water comes out from the egg to the deionized water.

That's why what happened happened.




(If I'm wrong, take into account the fact that I just started saucing up.)
Click to expand...

No, that's backwards. But even if it were right, the prof would be contradicting himself.
 
A

akubi

Diamond Member
Apr 19, 2005
4,392
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I'm assuming that the salt water solution has a concentration such that it's isotonic to the egg?

in that case it's correct to assume the distilled water is hypotonic, syrup is hypertonic, and the (slightly) salt water is isotonic.

so the correct result should be:

distilled water => swell
salt water => same
syrup => shrink.
 
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mordantmonkey

Diamond Member
Dec 23, 2004
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first year lab experiments suck. always take your answers and fill in the data your supposed to get. :p
you guys probably screwed something up, so either do the experiment again on your own time, or "fix" your data and move on.
 
C

cjgallen

Diamond Member
Jan 20, 2003
6,419
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Originally posted by: mercanucaribe
I've been arguing with my biology teacher (I'm taking the intro Bio at the community college for my minor).
Click to expand...

Let's see, INTRO Biology, and how long has your professor been doing this Biology stuff?

him > you
 
9

91TTZ

Lifer
Jan 31, 2005
14,374
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Originally posted by: mercanucaribe

Cliff notes: Egg in distilled water stayed the same, egg in saltwater swelled, egg in karo syrup shrivelled. Professor says it's because of osmosis.
Click to expand...

The salt shouldn't have been able to pass through the membrane. I think you're right. But I don't see how the teacher would be wrong. Probably just a misunderstanding on your part.
 
C

chowderhead

Platinum Member
Dec 7, 1999
2,633
263
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Originally posted by: mercanucaribe
I've been arguing with my biology teacher (I'm taking the intro Bio at the community college for my minor). We did the egg experiment, in which you put the eggs, that have had their shells dissolved by vinegar, in deionized water, saltwater, and karo syrup. The problem is that our egg in the saltwater supposedly became larger and the one in the deionized water supposedly stayed the same. The one in the karo syrup shrivelled like it was supposed to. According to what I know about osmosis, water potential, etc, the egg in the distilled water should have been larger. Either there's an error in the experiment or I don't know how osmosis works.

I tried to argue that if an egg has higher salt concentration than saltwater, it has to have a higher salt concentration than deionized water. I even drew a diagram. Am I missing something??

Cliff notes: Egg in distilled water stayed the same, egg in saltwater swelled, egg in karo syrup shrivelled. Professor says it's because of osmosis.
Click to expand...

water flows from low concentration to high concentration (of solute)

I think you mixed up the two saltwater and the distilled water. If the distilled water egg remained the same, that means the egg and the water would have the same osmotic pressure (i.e. a net flow of water that is zero). In the second result, if the salt water egg became bigger, that would mean more water flowed into it. How can the egg have more salts in it in result two when it did not in example 1?

What makes more sense is that you switched the two trials. You may expect the salt water one to balance with the egg leaving no change in size. But with distilled water, more water will flow into the egg because it is saltier than the water.
 
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mercanucaribe

Banned
Oct 20, 2004
9,763
1
0
Originally posted by: chowderhead
Originally posted by: mercanucaribe
I've been arguing with my biology teacher (I'm taking the intro Bio at the community college for my minor). We did the egg experiment, in which you put the eggs, that have had their shells dissolved by vinegar, in deionized water, saltwater, and karo syrup. The problem is that our egg in the saltwater supposedly became larger and the one in the deionized water supposedly stayed the same. The one in the karo syrup shrivelled like it was supposed to. According to what I know about osmosis, water potential, etc, the egg in the distilled water should have been larger. Either there's an error in the experiment or I don't know how osmosis works.

I tried to argue that if an egg has higher salt concentration than saltwater, it has to have a higher salt concentration than deionized water. I even drew a diagram. Am I missing something??

Cliff notes: Egg in distilled water stayed the same, egg in saltwater swelled, egg in karo syrup shrivelled. Professor says it's because of osmosis.
Click to expand...

water flows from low concentration to high concentration (of solute)

I think you mixed up the two saltwater and the distilled water. If the distilled water egg remained the same, that means the egg and the water would have the same osmotic pressure (i.e. a net flow of water that is zero). In the second result, if the salt water egg became bigger, that would mean more water flowed into it. How can the egg have more salts in it in result two when it did not in example 1?

What makes more sense is that you switched the two trials. You may expect the salt water one to balance with the egg leaving no change in size. But with distilled water, more water will flow into the egg because it is saltier than the water.
Click to expand...

I should have tasted the water but I was afraid of salmonella.
 
2

2cpuminimum

Senior member
Jun 1, 2005
578
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0
The egg experiments don't always work very well because things other than water can permeate the membrane. Remember, Osmosis is defined as the diffusion of water down its concentration gradient.

Concentration of water in salt water should be lower than the concentration in the egg, causing water to move from the egg.
Same for any syrup.

Distilled water will always have the highest concentration of water, and will result in water flowing into the egg.
 
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