shell-less egg osmoregulation demo

Discussion in 'Supporting Biology' started by Peter Sigsworth, Nov 15, 2019.

  1. Has anyone had a go at this?
    Basically you immerse a whole uncooked egg in vinegar for 24 hrs, change the vinegar and leave for a further 24 hrs. The egg should have it's shell now removed leaving it in tact inside its membrane.
    If such an egg is placed in distilled water it will swell up as the water enters through the membrane by osmosis. If it is placed in strong sugar solution it will shrink as water leaves by osmosis.
    I tried this and got the shells removed no problem but the eggs hardly changed in the water or the sugar solution. Left them for two or three days (supposed to work in 24 hrs).
    What went wrong? Has the vinegar damaged the membrane if left too long in it?
    The solutions were ok as the egg in water sank and the egg in sugar floated - but no much change in size.
    Any tips/ideas?
  2. Can't help you i'm afraid, but i am definitely trying it!
  3. I had to do it over the weekend because the teacher wanted it for Monday morning - so I fear that I should have removed it from the vinegar as soon as the shell had been removed instead of following the instructions religiously and leaving the egg in for 48 hrs
  4. This went out a few times for me last year, but instead of vinegar we left the eggs overnight in a large beaker of hydrochloric acid (1.5M -2M)
  5. Did the eggs change size much once in the water/sugar solution?
  6. Gummy bears/Jelly babies do.
  7. I was able to see quite a difference between them, I just can't remember how long it took! The teacher weighed them before and after to record the difference so I'm thinking there must have been a change in the lesson (1 hour)
  8. Did you do anything to the egg after it's vinegar bath but before the osmo-potential bit?

    It's been a while but iirc I had to gently abrade the goop that used to be the shell away by VERY gently rubbing it with my thumb
  9. I tested this recently and did the following:
    • egg in vinegar for ~24 hours with periodic rinses with water to remove the shell gunk
    • egg in treacle for ~6 hours - the egg shrunk quite a large amount (< half size from before) and also turned dark brown.
    • egg in tap water for ~8 hours - the egg greatly increased in size so that it was firm again (and could be bounced) and a little bit bigger than the original shell-less egg
    There was a lot of waiting around for osmosis to do its thing, but I managed to get some good results doing this. Hope that helps!
    Shannon likes this.
  10. Thanks
  11. I just washed it gently with tap water - appeared just to be the membrane left, but the contents had gone a bit cloudy
  12. weighing - I hadn't thought of that seems a good idea
  13. We have used this for a couple of years now for a demo of osmosis for KS3 & 4. I leave 3 eggs in 1.5-2M HCl, usually takes a whole day (froths up quite badly so I sit the whole beaker in a tray) but it's OK to leave them overnight. I left ours in acid over the weekend this time because they were needed last lesson on Monday, and it was fine) We then put one de-shelled egg in honey (smaller beaker on top to hold it underneath the liquid), one in very strong salt solution and the other in distilled water. By the end pf the day they were ready and the differences were clear. The honey one will shrunk significantly, the water one swell, and the one in salt solution shrinks a bit and is quite heavier than at the start. We put them out in petri dishes with an unshelled egg for comparison. I have also discovered this week that the eggs will keep in their solutions for at least 3 days, as we needed them on Monday and Thursday and I didn't want to make it twice.
    Peter Sigsworth likes this.
  14. Fantastic, thanks, Helen

  15. I'm just doing this demo too. The last stage of rehydrating (is that the right description?) the egg that has been in the syrup/honey/liquid glucose with coloured water looks interesting so I'm going to give it a go.
    Shannon likes this.
  16. I normally have previously used ethanoic acid but having chatted to another tech this is why i end up with more breakages as it makes the membrain brittle but just normal vinegar give a lot more flexibility to the membrane.
    and golden syrup gets great visual results of loss, you can visually see the water leaving once you put it in and it really goes down in size, but once the water is in the syrup you have to boil it off again to be able to reuse it.
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  17. Thank you all for your contributions
  18. is ethanoic acid and vinegar not the same thing?
  19. it dose have other things in it, its not pure. not sure the science behind it, its why I had used it rather than buying in vinegar - but going to buy in vinegar now
  20. wine, malt or the white polish stuff?