Creeping Water!

It’s a hot day, and you’re feeling thirsty. You poke a straw through a packet of iced lemon tea. As you suck the juice up the straw, it coolly flushes your throat and refreshes your body. Ever wondered how plants and trees drink?

In the stems of plants and the trunks of trees are specialized structures that are called the xylem. This structure acts like a straw in plants, whereby it sucks up the water in the soil and channels it upwards to the leaves where they are needed for food processing. Plants don’t take up water through their leaves, but through their roots which is in the ground.

This action of water travelling upwards against gravity is called capillary action. Water molecules are sometimes attracted to molecules of other materials. This called adhesive forces. As they are attracted to other molecules, for example the molecules of a tissue paper, they will, at the same time, also pull the other water molecules along with them. This attraction of water molecules with themselves is called cohesive forces. Imagine that those water molecules are holding hands with each other. This combination of being attracted to other molecules as well as with themselves is what causes capillary action.

Capillary action is also essential for the drainage of constantly produced tear fluid from the eye. There is a tiny duct at the inner corner of the eye that sucks up excess tear fluid; otherwise your eyes will be overflowing with tears. Another example is the kerosene lamp that we use for ‘Hari Raya’ celebrations. The kerosene in the container travels upwards in the wick to the top where the flame is.