The Mudcat Café TM
Thread #151975 Message #3703028
Posted By: Steve Shaw
19-Apr-15 - 06:14 PM
Thread Name: BS: Where Have All the Dandelions Gone?
Subject: RE: BS: Where Have All the Dandelions Gone?
Before you get rid of your dandelions, try this elegant, beautiful and simple experiment. Take two small glasses of water. Leave one as it is, but dissolve a tablespoon of salt in the other. Pick one dandelion flower head with at least two inches of stalk. Discard the flower head but keep the hollow stalk. Very carefully, cut a piece of stalk about two inches long. With a sharp knife, cut two strips along its length that are no more than about a millimetre wide but about two inches long. They mustn't be too wide, or else the experiment won't work very well. Before proceeding further, have a very close look at the strips to discern which side was the outside of the stem (usually darker in colour).
Drop one strip into the pure water and one strip into the saltwater. Watch and wait for two or three minutes.
Now normally I would ask you to tell me what you see, but in this instance I shall issue a spoiler alert right now.....then tell you what you might see.
Both strips should curl up quite tightly. But take a closer look. The strip in salt water will have the outside bit of the stem on the outer side of the curve, whereas the strip in the pure water will have the outside bit of the stem on the inside of the curve.
The inner cells of the stem have thin walls that allow water to diffuse through. The outer layer is impervious to water. In the strong salt solution the inner cells lose water via osmosis as water passes through the semi-permeable cell membrane into the solution. Therefore the cells on the inside collectively shrink, so the strip curls up with the inner cells on the inside of the curve. In the pure water, on the other hand, those inside cells take up water by osmosis and collectively swell up. Therefore the swollen cells cause the strip to curve with the impervious outer layer to the inside. Cheap, cheerful and with plenty of explanatory bang for its bucks. You can eat 'em, compost 'em, admire 'em, give your pollinators a boost with 'em and do amazing science with 'em. Yet some of you buggers want to get rid of 'em!