Osmosis

Do you know why raisins swell when soaked in water or plants stand tall after watering? It’s all because of osmosis!

It is the diffusion of water molecules across a membrane, flowing from a less concentrated solution to a more concentrated one.

In a hypotonic solution, like plain water, there is less dissolved material outside the raisin than inside, which makes water flow into the raisin and causes it to swell.

In contrast, in a hypertonic solution, like concentrated sugar or salt water, there is more dissolved material outside the raisin than inside. This causes water to flow out of the raisin, making it shrink and shrivel.

Meanwhile, in an isotonic solution, where the dissolved material is equal inside and outside the raisin, water moves in and out evenly, and the raisin stays the same size.

Osmosis is also essential for living things. For example, red blood cells in your body need a balanced solution to stay healthy. In a hypertonic solution, they shrink, while in pure water, they swell and can burst.