When solutes are in water, they like to be evenly spread out. This is pretty easy if you just have a glass of water with salt in it. But let’s say you put a membrane in this glass that allows water, but not salts, to pass through it. Now if you put saltier water on one side of the membrane and less salty water on the other side, what do you think would happen? If the salt can’t cross to the less salty side, then the water will cross to the more salty side.
If a membrane holds more salt (pink dots) on one side than the other, the water will move to the side with more salt so that the salt and water can be evenly spaced out. |
A freshwater ramshorn snail has nightmares about kids with salt-shakers. Image by Alan R Walker at Wikimedia. |
Very interesting.
ReplyDeleteWhy do we get wrinkles in our finger tips when we have been for a long time in water?
Thank you!
Great question! Our fingers and toes wrinkle in the bathtub for the opposite reason to why snails melt in salt. Our cells contain more solutes than the freshwater of a bath, so our cells are prone to absorbing water. The cells that make up the outermost layers of our palms and bottoms of our feet have properties that cause them to absorb and retain water even more than other cells do. Because they are connected to the cells underneath, their swelling causes the skin to pucker unevenly, creating the pruny-fingers/toes effect.
DeletePlus, wrinkly fingertips give us better grip in wet situations, which means the reaction is an evolutionary benefit.
DeleteWhen i provided a similar answer to why our fingers get pruney in my 300-level Animal Physiology class, one of my students mentioned the following study published in Nature in June 2011:
ReplyDeletehttp://www.nature.com/news/2011/110628/full/news.2011.388.html
Interesting food for thought ...
--Erick
Fascinating theory Erick. Thanks for the link!
Delete