In the previous chapter, you learned that energy flows through an ecosystem in one direction. In short, the energy moves from the prey to predator, NOT predator to prey.
| This is Energy Flow Through a Food Chain | This is Flo from Progressive |
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Nutrients move through ecosystems too, but they are recycled. For example, your body’s water was once a part of the ocean and may even have once been inside Reinhold. (Water is not a nutrient but is necessary for life.) The amount of water on Earth is finite, so it needs to cycle through the Earth’s systems.
In this chapter, we are going to focus on the carbon cycle and the nitrogen cycle. Carbon and nitrogen are essential elements because they are used to build all the tissues of your body.
The Nitrogen Cycle
We need nitrogen to make proteins and DNA. Luckily, nitrogen is abundant on Earth. Nitrogen gas comprises 78% of the atmosphere and is in the Earth, water, and biosphere. With every breath, you inhale nitrogen, but the nitrogen is unusable. It’s like having a billion dollars, but you are stranded alone on a deserted island. You may be a billionaire, but your money is useless on the island.
So, how does the nitrogen in the nitrogen gas get into the food we eat, and the fertilizer plants use to make proteins and DNA?
I don’t know. Some dude named Bill?
You are correct. Let me introduce you to Bill.
Bill is a nitrogen-fixing bacterium.
A what?
A NITROGEN FIXING BACTERIUM!!!!!
Really? All caps? That is such an old person thing. What I want to know is: what are nitrogen-fixing bacteria?
Bill and his band, The Nitrogen Fixers, can convert nitrogen gas into nitrogen compounds that plants use as fertilizer via a process called nitrogen fixation. The plants take in the fertilizer through their roots and use it to make proteins and DNA. Herbivores or omnivores eat the plants and digest the proteins and DNA into the molecules they use to make their own proteins and DNA. If a predator eats the herbivore, the predator will use the nitrogen compounds to make its own DNA and proteins. When an organism dies, mushrooms and other decomposers convert the proteins and DNA back into fertilizer.
Over time, wouldn’t there be too much nitrogen-based fertilizer in the soil?
Yes, there would be, if it were not for Ted.
Who’s Ted?
Ted and his band, The Denitrification Experience, covert nitrogen fertilizer into nitrogen gas via denitrification, which keeps helps maintain the right amount of nitrogen in the soil and water.
Therefore, nitrogen cycles from the atmosphere to land and water and back with Bill and Ted’s help. The nitrogen cycle truly is an excellent adventure.
Here is the nitrogen cycle:
The Carbon Cycle
All life is carbon-based. Carbon is an element that can form four stable chemical bonds. The proteins, carbohydrates, lipids, and nucleic acids (DNA) that makeup you need to be reasonably stable to keep you intact. That is why you will find carbon in every organic compound in your body and the biosphere.
Like nitrogen, carbon is in the atmosphere, biosphere, lithosphere (ground), and hydrosphere (oceans and freshwater). Carbon cycles through all four of the Earth’s spheres to maintain the optimal amount of carbon in the biotic and abiotic factors within ecosystems.
Our cells produce carbon dioxide as a byproduct of metabolism. However, we cannot use the carbon in carbon dioxide to make our body’s structural carbon molecules. Instead, we exhale the CO2 as a waste product, which plants use as a building block to making sugars and starches. When we or animals eat plants, we obtain carbon that our body uses to make our proteins, lipids, DNA, and carbohydrates.
Like nitrogen, too much or too little carbon can have a drastic effect on the biosphere. Carbon dioxide comprises 0.04% of the atmospheric gases, which seems negligible. However, CO2 is a potent greenhouse gas where a tiny increase or decrease can drastically alter the Earth’s climate. For example, let us look at some lethal toxins. The skin of newts and the harpoon of a cone snail contain tetrodotoxin, a deadly toxin that paralyzes the breathing muscles leading to suffocation. Botulinum is a bacterial toxin that causes muscle paralysis and suffocation too. However, the lethal human dose of tetrodotoxin is 8,000 ng/kg, while the lethal dose of botulinum is 0.03 ng/kg. Both toxins are lethal, but it takes a lot more tetrodotoxin to kill.
This is the carbon cycle:
