Eli5: What differentiates animals from other living things?
In: Biology
Animals are any multi cellular life that moves around on its own at some point in its life and eats stuff.
Plants are multi cellular life that photosynthesizes, and has a cell wall. They also dont move.
Fungi (mushrooms) are multi(ish) cellar life eat other stuff, has a differenter cell wall, and doesnt move about.
Turns out their isnt any species with multiple that moves and has cell walls or moves and photosynthesizes, so thats fine. Turns out moving takes a lot of energy and photosynthesis doesnt make much
Then there are a bunch of single celled stuff that just breaks all the rules, but its single celled so its fine.
There is only 3 types of living things that we know about: plants, fungi and animals.
Plants have cell walls and do photosynthesis, fungi are mushrooms and animals. Animals is just anything that is multicellular and not a plant or mushroom.
“Animal” is one specific type of organism. All animals share certain biological characteristics, which no other kinds of creatures have.
The two main other options are called “fungi” and “plants.” Plants do photosynthesis, and have “cell walls” made of cellulose. Animals don’t have cell walls, but they do have other things that plants don’t. Fungi also have cell walls, but theirs are made differently using a different material, chitin.
There are also other kinds of organism, but most of them are single-celled beings. Scientists don’t entirely agree on how these should be split up. One common classification says there are three additional kinds of living things: “bacteria,” “archaea” (ancient and very primitive cousins of “true” bacteria), and “protists” (things like amoebas, but also kelp). In most cases, these kinds of organism don’t really matter for ordinary people, except in how they can contaminate water or food, which is why it is very important to only drink clean water and to always cook meat thoroughly.
Strictly speaking, a term like ‘animal’ or ‘plant’ really means it belongs to a particular branch of the tree of life. Animals are all the organisms that descend from one particular common ancestor.
They have features in common, like they are multicellular, have cells without cell walls and complex nuclei, they tend to move around actively. All these things are inherited and shared from their common ancestor. But the thing that makes an ‘animal’ an ‘animal’ scientifically, is its descent. An organism would still be an animal even if it lost some of the typical animal-y features through evolution.
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