Osmosis is the passive movement of water from a higher concentration to a lower concentration through a semi-permeable membrane. This happens all the time in cells.
Osmosis can be quite tough to understand for some people. So here is a demonstration you can do at home to learn about osmosis and how it works.
What you’ll need:
Gummy sweets
Water
A container
Pencil
Paper
Clock or watch
How to do it:
Fill a container with water.
Measure the dimensions of the sweets so you can watch how they change over time.
Place a gummy sweet or two inside the container and note the time.
Leave the sweets in the water for at least a few hours, or even overnight.
Remove them from the water, note the time, and measure their dimensions again. How much have they grown in the time you’ve left them in the water?
Before osmosis After four hours of osmosis
How it works:
Imagine the gummy sweets as living cells.The outside surface area of the sweet is the semi-permeable membrane.
When the sweet is put into the water, there's an uneven concentration gradient - this means that water isn't evenly spread. That's because there isn't as much water inside the sweet as their is outside of it.
This unevenness causes water to move from areas with lots of it, into areas with not as much of it. This is known as osmosis. Water moves from a higher concentration to a lower concentration, through a semi-permeable membrane.
The whole deal with a semi-permeable membrane, like that of the gummy sweets, is that only certain molecules can pass. In this case, the sugar molecules of the sweet are too big to cross the membrane, while water molecules are small enough to do so. So when the sweet is put into water, it swells up and gets bigger as the water moves into it.
Osmosis doesn't just happen in one direction, though. You can watch how the water moves back out by placing the gummies in salty water! This works because the salinity of the water throws the concentration gradient out of balance, so water wants to move out of the sweet and into the water to balance it all out. For this reason, marine organisms have evolved special mechanisms to stay hydrated while living in their salty environment.
These are the basics of osmosis. Isn't it cool to think that your cells do this all the time?