Protists are grouped together because they share

Protists are a unique group of organisms because they don’t quite fit the mold. And while some protists prefer to live as individuals, other prefers to work together for the greatest benefit. These colonial protists are the topic of this lesson.

What are Protists?

When we classify living things we tend to group them together based on evolutionary relationships.

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In other words, animals, plants, and other organisms are grouped together because they share common ancestors. For example, mammals are more closely related to each other than they are to birds or fish.But one group of organisms doesn’t really follow this convention. In fact, they are grouped together because they simply don’t fall into other categories. And that’s what makes the protists so special! These eukaryotes don’t fit into one of the other kingdoms, such as plant, animal, or fungi, so they get put into their own kingdom called Protista.

But this is about the only commonality they have.Most do not share any evolutionary relationships, and they often don’t even look the same. They come in all shapes and sizes, ranging from the microscopic to the very large, living in all different kinds of environments, and offering a multitude of different functions to life on Earth.

Kelp is a multicellular protist.
kelp forest

You’re likely already familiar with some well-known protists. Yeasts, algae (such as kelp and seaweed), and amoebas are just a few examples. Most protists are unicellular, but some like kelp are multicellular organisms. Some, known as the plant-like protists photosynthesize, while others that do not photosynthesize are called animal-like protists. Others still are called fungi-like or slime molds because they somewhat resemble fungi, though again there is no evolutionary relationship.

Colonial Protists Live Together

Just like people, some protists prefer to live individually while others prefer to live in large groups. Colonial protists are individual protists that form a colony and act as a larger, multicellular organism. This colony may consist of many individual protists of the same species, but what’s really cool about them is that instead of acting as individuals they work together to function as one large group, benefiting from each other.But be careful, because this is not the same as symbiosis which is when two or more organisms of different species live together and mutually benefit from one another.

Colonial protists aggregate together to form a larger group.
Volvox aureus is a colonial protist that is also quite beautiful.
volvox
  • Species in the genus Codosiga are another example of colonial protists. The colonies formed by these guys may be attached to a substrate or they may be swimming around as a group, often looking very similar to the Volvox algae!
  • Species in the genus Dictyostelium are slime molds (fungi-like protists) that also form colonies of multiple individual protists.

    You’ll likely find these guys in soil feeding on bacteria. But what’s really cool about these guys is how well they work together. When food is abundant they will typically be found as individual single-celled organisms.

    But when food is scarce they will band together to form a larger organism that can reach out to find a better environment. And some of the individuals even sacrifice themselves so that others can be successful in this endeavor. Now that’s teamwork!

Dictyostelium discoideum may be found as individuals, or when conditions demand it as an aggregate group.

Dictyostelium

Lesson Summary

Protists don’t quite fit the mold, so they get lumped together in their own group of ‘unclassifiable’ organisms. They come in all shapes, sizes, and colors, and live in just about every environment you can imagine. Some are unicellular while others are multicellular; some are photosynthetic while others are not. Some are the plant-like protists like algae that photosynthesize, while others that do not photosynthesize are called animal-like protists.

Others still are called fungi-like or slime molds because they somewhat resemble fungi.But what’s really cool about protists is when they work together. Colonial protists are individual protists that form a colony and act as a larger, multicellular organism.

This is different than symbiosis in which two or more organisms of different species live together and mutually benefit.Examples include

  • golden and green algae (such as from the genus Volvox),
  • protists belonging to the genus Codosiga and can cling to substrate in water or swim together alone,
  • slime mold protists from the genus Dictyostelium, who come together when food is scarce and sometimes sacrifice their own lives for the best interest of the group as a whole.
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