Organic matter cycle

What do you think of when you hear the term recycling? Chances are, you think of separating waste into different bins, or the recycling of waste products such as plastic bottles or paper. But water, minerals, gases, and other materials on Earth, have been continuously used and reused since long before humans invented recycling! In fact, almost no matter can ever leave Earth, and no new matter can enter Earth. Well — unless it’s on a meteorite.

But otherwise, the same matter, in the same amounts, has been on the planet since long before dinosaurs roamed! But wait a minute. Living organisms use water, minerals, and gases to stay alive. How can these remain in the same amounts? Let’s take a look at how matter cycles on Earth.

A cycle is a continuous process, with no start or finish. But since we have to start our story somewhere, let’s begin here, in the soil of this natural system — a forest. In the soil, we find simple inorganic compounds, such as water, ions, minerals and gases. These compounds are taken up by plants, for example grass, and used to make more complex organic molecules such as sugars, fats and proteins. Now, the compounds have entered the food chain.

When an animal, like a deer, eats the grass, these molecules are transferred from the plant to the animal. When the deer gets eaten by a wolf, the molecules move along the food chain again. When any part of this food chain dies, whether it be the plant at the beginning or the wolf at the end, the complex biological molecules return to their simpler, inorganic forms — through the process of decomposition. Dead organisms are decomposed by organisms known as decomposers. There are many different species of decomposers, from animals like earthworms, to fungi and even bacteria.

Decomposers release enzymes into the soil or directly onto the dead organisms. These enzymes then break down organic material such as sugars, fats and proteins into smaller, simpler compounds. These simpler compounds, like gases and minerals, are then available in the soil for plants to take up again. So in our forest ecosystem, matter is removed from the soil, through the process of plants growing, and returned by the process of decomposition. In a stable ecosystem, these two processes are balanced — materials are removed and returned at the same rate.

What about in an artificial ecosystem, like a community garden? Here, people grow vegetables. When they pick the vegetables to consume them, how do nutrients return to the soil? One way is through composting. Kitchen scraps, twigs, dead plants and weeds from the garden are collected in a wooden crate.

Over time, decomposers, such as beetles, pillbugs and earthworms, enter the crate and break down the plant waste. Just as in nature, complex biological molecules are broken down into water, minerals, and gases. Then, the compost is added to the vegetable patch, and nutrients return to the soil. They are taken up by the plants, and the cycle continues.