Scientists Say: Excretion

This is how an organism gets rid of waste

a photo of a white and brown dog pooping on grass

No one ever said excretion was a pretty process, but every living thing needs to get rid of its waste.

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Excretion (noun, “ex-KREE-shun”, verb, “excrete,” “ex-KREET”)

This is how an organism gets rid of waste products.

Every living thing makes waste, or material the body no longer needs or cannot use. As our bodies use the oxygen we inhale, for example, we produce waste carbon dioxide. When we breathe out that carbon dioxide, we are excreting it. We also produce waste from food particles we can’t digest. Our bodies excrete this solid waste as poop, and liquid waste as pee. We can even excrete waste products through the skin in our sweat.

Waste products can harm organisms if they aren’t excreted. If we did not get rid of extra carbon dioxide, for example, we would get tired and confused. We can even faint or die. Animals have different body systems that separate waste. Human excretions, as well as those from other animals, usually leave the body after passing through the lungs, kidneys and skin. But single-celled organisms such as bacteria produce waste, too. They excrete their chemical waste through the membrane that separates them from their environment.

One organism’s trash is another one’s treasure, though. Bacteria live on our skin, and eagerly dine on our sweat. Plants excrete oxygen as their waste product — and we can’t live without it.

In a sentence

As if they weren’t bad enough, bed bugs excrete a chemical in their poop that can make people itch.

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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