What happens to nutrients when organisms die?

In following energy through a food chain, food web, or energy pyramid, only 10% of the energy is passed from one organism to the next. This means producers receive the most energy from the sun, while top predators receive the least.

But what happens to all of that energy when organisms die? Does it go into the air? The soil? The answer is actually both. As organisms die, they are broken down into organic material (carbon and nitrogen), which are then returned to the soil and air. This is done with the help of decomposers such as bacteria, protists, and fungi. These decomposers are the main driving force behind the Carbon and Nitrogen Cycles, and without them, we would not be able to recycle organic material or nutrients.

Remember: all living things are made of carbon and nitrogen. Carbon makes up the deoxyribose sugar in DNA, while nitrogen makes up the nucleic acids. Humans inhale oxygen and breathe out carbon dioxide. Though Earth's atmosphere is 78% nitrogen gas, we do not breathe it in. Instead, we get nitrogen through the things we eat.

Your goal today is to describe how nutrients move through the Carbon and Nitrogen cycles and recognize how various human activities can affect these cycles.

Carbon is one of the building blocks of life. All living things are made with carbon, so we call them organic.

In cellular respiration, plants and animals take in oxygen and release carbon dioxide into the atmosphere.

When living things die, their bodies decompose. Over millions of years, the carbon that made them becomes crude oil, coal, and gas (fossil fuels) which we use to create power and electricity. Every time you drive in a vehicle, it burns gasoline, which releases carbon dioxide back into the atmosphere.

The only thing that can remove carbon dioxide from the atmosphere is photosynthesis, where plants take in CO₂ in order to create glucose.

Why should we care about CO₂ in the atmosphere?

Carbon Dioxide acts as an insulator in Earth's atmosphere, meaning it traps heat and prevents it from escaping. This contributes to the greenhouse effect, where heat collects in Earth's atmosphere, which causes the planet to warm.

Every time you breathe, ride in a vehicle that runs on gasoline, or use natural gas, you are releasing more carbon dioxide into the atmosphere. As the human population continues to grow and we continue to cut down trees, we are adding more and more CO₂ to the atmosphere without creating more ways to remove it.

We said earlier that nitrogen is an important element that helps make up proteins and nucleic acids and is another key component of DNA. All living things need nitrogen to survive. Animals cannot breathe in nitrogen, so we get it by eating plants and other animals.

The real MVP in the nitrogen cycle is actually NOT plants, but bacteria and decomposers! Plants rely on bacteria in the soil to take in nitrogen from the air and convert it into nutrients that the plant can use. These special bacteria are found in the roots of plants.

We also see bacteria in the soil two more times. Certain bacteria will break down dead organisms into another form of nitrogen, and other bacteria will return nitrogen in the soil back to the atmosphere.

Without bacteria to help convert and recycle nitrogen, plants would not be able to get the nutrients they need to grow. In fact, nitrogen is so essential to plant growth that many of the fertilizers we use today are full of nitrogen.