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Amoeba Protist: Type & Description

Instructor: Sarah Phenix
In this lesson we will explore what makes a protist a protist and an amoeba an amoeba. We will also look at some unique characteristics of these organisms, such as their movement and their method of food consumption.

What is a Protist?

Can you think of a living organism that is neither plant, animal, bacteria, nor fungus? You might think that those categories explain all the groups of living organisms but you'd be wrong. There is still one very important little group of organisms (whose impact is not so small as their size) known as protists.

A protist is any single-celled eukaryotic organism (meaning it has membrane bound organelles, such as a nucleus) that can't be classified as plant, animal, bacteria, nor fungus. Protists are sort of leftover category because they don't universally possess any of the unique features that we use to define say, a plant as a plant (a multicellular photosynthetic organisms with cell walls), or an animal as an animal. Therefore biologists designated protists as their very own kingdom.

Alright, so now that we know what a protist is (or is not) let's take a look at one specific type of protist known as an amoeba.

What is an Amoeba?

An amoeba (pronounced a-meeba) is a classification of protist that are amorphous in shape, meaning their body has no fixed structures. That's right, these little critters have no distinct head or tail regions, meaning they don't need to turn around to change directions, they can just start oozing in a different direction!

There are actually quite a few different species of amoeba, but since they have no fixed shape, they can be really difficult to tell apart. Some of the more common species are

  • Amoeba proteus - named after Proteus, a Greek god who could shape-shift and change the nature of the seas,
  • Chaos species - giant amoebas that range from 1-5mm but are not dangerous to humans,
  • Naegleria fowleri, (cue sinister music) - these can lead to deadly infections of the human brain.

Now, being amorphous doesn't mean that they amoebas are 'shape-shifters' like Mystique from the X-Men, who could mold her body into the shape of anything, all it means is that their body isn't fixed or rigid. So, why is this important other than the fact that it's really cool? Well, it's this very ability to alter the shape of their body that enables them to freely move throughout their environment.

These Boots Were Made for Walking

Okay, so amoeba don't actually wear boots but they are known for their ability to move via psuedopodia, or 'fake feet'. Amoeba can essentially change their internal cytoplasmic viscosity (or thickness) so that they ooze in a specific direction, forming little finger-like pseudopodia, which they then solidify and pull their rear towards.

What's more is that these pseudopods aren't just reserved for movement, amoeba use them to eat too. Amoeba's engage in a form of cell consumption called phagocytosis (literally meaning 'to eat cells'). Essentially amoeba extend their little fake feet around an item that they intend to consume and encase it in a packet of their own cell membrane that they then engulf into their body, forming a vacuole (or a storage bubble) called a phagosome.

This phagosome then fuses with another vacuole, called a lysosome (containing enzymes that breakdown and digest the food item), forming a new vacuole called a phagolysosome, or an enzyme and food containing vacuole.

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