Carbon is an element that is present in all living things, and is a part of carbohydrates, proteins, and fats. It is constantly recycled on our planet, moving from the atmosphere to living things and back to the atmosphere as carbon dioxide. Carbon can also be passed between living things when one organism eats another. Known as the Carbon Cycle, this recycling process is composed of a number of steps that cycle carbon through the biosphere, atmosphere, hydrosphere, and geosphere.
Comprised of four major processes (combustion, photosynthesis, respiration, and decomposition), the carbon cycle is essential for the existence of all living beings.
Combustion is commonly known as burning. It is a chemical reaction that requires oxygen and produces heat. The equation of this reaction is fuel + oxygen → carbon dioxide + water. Combustion is used for many different things in modern society. It is used to generate electricity for our homes and offices, and it is used to move the cars, trains, and airplanes that people rely on to travel. Fossil fuels, like coal and gasoline, are made of the remains of once-living organisms from millions of years ago. When they are burned, the carbon inside them is released into the atmosphere as carbon dioxide.
Photosynthesis is the process that plants use to create glucose. Unlike humans, plants are autotrophic, meaning they create their own food. Photosynthesis is a chemical reaction which takes place in all green parts of the plant, but especially in the leaves. The reaction takes place in a part of a plant cell called chloroplasts. Plants use sunlight, carbon dioxide, and water to produce oxygen and glucose. The world equation is carbon dioxide + water → oxygen + glucose. The plants get water from the roots and water travels up the stem through tubes called xylem. The plant gets the carbon dioxide from the air that enters the leaves through holes called stomata.
Cellular Respiration is a process that living things use to produce energy. Respiration takes place inside the mitochondria in the cells of living things. Respiration doesn’t just occur in animals, it also occurs in plants and single-celled organisms. The word equation for this reaction is glucose + oxygen → carbon dioxide + water.
Decomposition is the process where dead organisms and waste products are broken down by organisms known as decomposers. The organisms release the carbon into the atmosphere through cellular respiration. Decomposers are essential for recycling the carbon inside dead organisms.
The oceans are also an important part of the carbon cycle. There is a large amount of carbon dioxide dissolved in the seas and oceans all over our planet. Some of the dissolved carbon dioxide is converted into biological carbon through photosynthesis. This is then exchanged from organism to organism through food chains. Some of the carbon is turned into calcium carbonate and used by some organisms to make their shells. When these organisms die, they fall to the ocean floor. Over time, they build up and form limestone. Sometimes this limestone can be exposed due to movements in the Earth. Exposed limestone can be weathered, which releases carbon back into the atmosphere.
Carbon dioxide is a greenhouse gas. Increased levels of carbon dioxide, among other gases, in our atmosphere are what experts think is causing our planet to heat up. This effect is called the greenhouse effect. Governments around the world are calling on people to reduce the amount of carbon dioxide they are releasing into the atmosphere. For more activities, check out our Greenhouse Effect lesson plan.