People like you and I need a few things to live — we need healthy food, we need water, and we need air. Plants, though, are a little different than you and me. They need food and water, but they also need sunlight to live. Plants use sunlight as a way to make energy to grow.
Plants and animals, including people like you and me, breathe in air. But plants use a different part of the air than you or I do. We breathe in a part of the air called oxygen. We use the oxygen that we breathe in the air to feed the blood in our bodies. Plants use a different part of the air, a gas called carbon dioxide. We breathe in oxygen and breathe out carbon dioxide. Plants do just the opposite — plants breathe in carbon dioxide and breathe out oxygen. So the oxgyen you’re breathing now probably came from a plant. Thanks, plants!
Plants also get food from the soil. To live, they need a certain chemical that you can find in the soil. This chemical is called nitrogen. You have nitrogen in your body, too, but your body can’t use it. So when you get nitrogen in your body, your body gets rid of it. How does it do this? It leaves your body through pee and poo. All the stuff in pee and poo is stuff that your body can’t use. That’s why pee and poo is sometimes called “waste” — because it’s something leftover that you can’t use.
But because pee and poo are full of nitrogen, plants love it! If you’re a tree and a dog pees on you, are you happy or sad? You’re happy, because that pee is full of nitrogen that you can use to eat. The same is true with poo. In fact, farmers take poo from their cows and spread it across their fields to make the plants in their fields grow better. This is called “fertilization” — the farmer is using cow poo to make it easier for plants to grow in the field.