This is a work in progress... please bear with me, come back and watch it grow? Send constructive suggestions?
What you see below might be seen as an outline for what will eventually be spread across multiple pages.
No squirming... no giggling, please....
When you sit and put brown stuff ("polite" name: "feces"... pronounced "FEE- seas") in the toilet, you are (mostly) not excreting!
When you exhale (breath out), you are excreting
Is nothing as it seems? Well, actually, when you pass a yellow liquid into the toilet, that is excreting. At least something is what you would expect.
But did you know that when you walk across a lawn on a sunny day you are breathing in things the lawn has excreted?
For your studies into biology, it is most helpful if you think of "excreting" as the process of getting excess chemicals out of the organism.
If you suck on your pencil, is it "inside" your body? Your lips and mouth may be around it, but the pencil isn't really "inside" you. Not like, say, your blood is inside you. The pencil is merely in "a cave". And if you swallow a penny, it will pass right through, as if it were traveling through a tunnel leading from your mouth to your anus. Hence the idea that the elimination (note the word) of feces is not "excretion". Since the stuff coming out wasn't "really" "inside" you, you can't talk of it as being got out of you. Much of what comes out is parts of your food that your body didn't digest, particularly plant materials. Some is dead (or living) bacteria from the large colonies that live in the "tunnel" that passes though you. (Small amounts of things that were inside you pass out along with the feces, and that material is being excreted. The brown color comes largely from "bits" left over after old red blood cells are broken down during the quite normal, process of blood cell replacement that goes on all the time. The brown color of a scab and the brown color of feces are directly connected.)
When you exhale, the air you breath out has much more carbon dioxide in it than the air you breathed in. All over your body, you are constantly making carbon dioxide. It must not build up in your system, or you will feel various types of discomfort. (When your muscles get "weak" after violent use, it is connected with carbon dioxide not being excreted fast enough.) Happily, your blood moves carbon dioxide...
Lawns excrete gasses?
During a sunny day, a lawn will make more oxygen than it needs, and so the chemical will be excreted into the air. Lucky for us! We need that oxygen. Plants do, too... but they make more than they need.
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