Osmosis – Science Experiment

Q: My daughter is doing an experiment with carrots, leaving one in water, another in salt water, another in a dry bowl. Her question is, does water leave plant cells? These were her results:

Cup – no water: carrot drying out
Cup – with plain water: carrots swelled
Cup – with 2 tbs. salt: carrots shrank.

We aren’t quite certain of the process. We have read alot about osmosis and transpiration, but now we are becoming totally confused.

A: Osmosis is the phenomenon of water flow through a semi-permeable membrane (like a plant or animal skin) that incompletely blocks the transport of salts through it. When two water volumes are separated by a semi-permeable membrane (carrot skin), water will flow from the side of low salt concentration, to the side of high salt concentration.

Just like your daughter, water molecules like to hang out with their friends. Best of all, they like hanging out where a bit of chemical (usually called a salt) is mixed in.

When the carrot had no water, it dried because of low humidity in the air around it.

In plain water, the water molecules outside the carrot wanted to be with their friends inside the carrot which had some salt around them. That’s why the carrot swelled.

In salt water, the water inside the carrot saw that its friends outside the skin had more salt to play with so the water inside the carrot left it – causing it to shrink.

This also explains why your fingers wrinkle when you soak them in soapy water.