read this http://www.mercola.com/2002/feb/13/gall_bladder.htm - not very interactive stuff but I liked the anology - but hey , what do I know about biology!! The gallbladder serves an important digestive function. It is required to emulsify fats. What is emulsification? One can easily understand this concept when washing greasy dishes. It is nearly impossible to properly clean greasy dishes without soap as the soap emulsifies the fat so it can be removed.
read this http://www.mercola.com/2002/feb/13/gall_bladder.htm - not very interactive stuff but I liked the anology - but hey , what do I know about biology!! The gallbladder serves an important digestive function. It is required to emulsify fats. What is emulsification? One can easily understand this concept when washing greasy dishes. It is nearly impossible to properly clean greasy dishes without soap as the soap emulsifies the fat so it can be removed. Similarly, the gallbladder stores bile and bile acids, which emulsify the fat one eats so it can be properly transported through the intestine into the blood stream. If you vomit hard enough and long enough you can vomit up bile - it tastes horrible. (I'm told but haven't checked)
I once met someone who in a bike accident had lost most of/all his pancreas, he could not eat much fat at all because of this - he described to me an occasion when he had eaten a cream bun - and his faeces became shiny and slimy with the undigested fat For some reason my pupils like these stories. I normally show pupils emulsification with either washing up liquid on some oil - or we make mayonnaise. The part that seems difficult for them to describe seems to be that it is not an enzyme - and we model this by having a group of pupils together as a lump of fat with lipases 'nibbling' at the edges - but unable to get to the centre until the big blob is broken apart by the bile (or varienats on this)