The Experiment Of Osmosis Through Potato Slices

Have you ever cut open apples or potato slices to see how they discolor and are no longer as fresh as they could be? What can you do to protect these fruits and vegetables and prevent this from happening? What keeps potatoes (or other vegetables) fresher: soaking them in normal water or salt water?

I will explain this question using the concept of osmosis. Osmosis is a property of matter that has to do with diffusion, i.e. the spreading of particles from high concentration to low concentration. More matter equals less matter. For example, if you spray a bunch of perfume in one place, you notice how it spreads around the room.

However, instead of substances in the air, osmosis describes the movement of water passing through something. I'll show you the experiment and then we'll talk about exactly how this water movement happens.

You will immediately notice some differences in the potato slices. The color of the potato slice in salt water is dark brown; this is not a nice picture of how you want to preserve your potatoes! The potato slice in normal water looks like a nice white, freshly cut piece of potato. When bent, the potato in normal water feels firm and crunchy again (try to break the piece, it will break!). The saltwater potato is pliable and does not break at all.

Osmosis is the key to understanding this problem. Osmosis is the diffusion of water through a semipermeable membrane (yikes!) from an area of high water concentration to an area of low concentration.

Salt is the key here. Water moves from an area with less salt to more salt (more water to less water), and when the potato is placed in the salt water, all the water inside the potato (yes, plants have a lot of water in them, that's what gives a plant its structure) moves out by osmosis. This makes the potato very limp and no longer crunchy. It's a bit like watering all your houseplants with salt water. They would all go limp and then die, and your parents would be upset, so please don't try this at home.