As I fished out a shriveled mango from the jar of brine, I marvel at the nature of science and its application in day-to-day life. Thanks to our understanding of this, I am able to enjoy a dish of raw mango much past the peak mango season. All I had to do is to drop it in a concentrated solution of salt. The raw mango very soon shrivels up but stays edible and scrumptious for a very long time.
An opposite phenomenon is what would happen if you were to drop a raisin into a bowl of water. The water molecules enter the raisin and make it more rounded and fuller than before. What do you think has happened in both these cases? What happened is a carefully orchestrated movement of water molecules in a phenomenon called ‘osmosis’.
So by definition, osmosis is the movement of water molecules (remember that water is a solvent) from one side of a partially permeable membrane to the other side. This movement is not random from one side to another but it goes from the side which has a higher concentration of water molecules (the dilute side) to the one with a lower concentration. These sides can be referred to as the ‘hypotonic’ (more water/solvent molecules) and hypertonic (less water/solvent molecules).
The membrane in the case of the examples above would be that of the cells in the mango and that of the raisin. So here you see that in the case of the mango in brine, there was more water in the mango than in the concentrated salt solution which is what brine is. So these water molecules moved from the mango to the solution thereby resulting in a wrinkled pickled mango. The water molecules move from the hypotonic solution to the hypertonic solution till it reaches a kind of balance with an equal number of water molecules on either side (a condition called an ‘isotonic’ state).
In the case of the raisin which is nothing but a dried grape, there is more water in the bowl of water than inside the raisin and hence it gladly moves across the membrane of the raisin to make it rounder. As you may have noticed food preservation uses a lot of this principle to store food material from spoiling.
Osmosis is what is responsible for a wide variety of processes in biology including root cells absorbing water from the soil and nourishing the plant. It is also the reason why slugs die when you sprinkle salt on them. There are many such examples in day-to-day life involving this phenomenon. See how many you can spot around you. Drop your answers in the comment box.
To read more:
https://www.britannica.com/science/osmosis
https://en.wikipedia.org/wiki/Osmosis
