The Evolution of Protists: Importance & Evolutionary History

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  • 0:05 Characteristics of Protists
  • 0:51 Types of Protists
  • 1:56 Endosymbiosis in Protists
  • 2:54 Examples and…
  • 4:18 Lesson Summary
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Lesson Transcript
Instructor: Danielle Weber

Danielle teaches high school science and has an master's degree in science education.

Some organisms are very familiar. However, there are some that play vital roles in our lives that we don't even think about. We will look at a group of one of these unfamiliar kingdoms - protists.

Characteristics of Protists

The cellular structure of protists
Protist Cell Structure

You know the basics of what plants, animals, and fungi are, but what about those eukaryotic organisms that don't quite fit within these groups? Within our system of classification, these organisms fall into the Protista kingdom. Protists are eukaryotic, mostly unicellular, and mostly aquatic. 'Eukaryotic' means that they have cells with a nucleus and membrane-bound organelles and are similar to the cells that make up our bodies. Because they are eukaryotic, protists fall within the domain Eukarya. Most protists are unicellular, meaning they are only made of one cell. However, some protists are multicellular and are made of more than one cell. Most are aquatic, meaning that they live in the water.

Types of Protists

Protists are broken up into three main groups based on how similar they are to other eukaryotic kingdoms. The three groups are animal-like, plant-like, and fungus-like protists.

Animal-like protists are heterotrophs and get their nutrients by ingesting food, which is how animals, who are also heterotrophs, get their nutrients and energy. Animal-like protists are also called 'protozoa,' which means 'first animals.'

Plant-like protists are autotrophs and get their nutrients by performing photosynthesis, which is a process that uses sunlight to make sugars and oxygen and is also performed by plants to make nutrients and energy. Plant-like protists are also called 'protophyta,' which means 'first plants.'

The third group, the fungus-like protists, are also heterotrophs and get their nutrients by absorbing food. Now, this may seem a bit unusual, but this is how fungi get their nutrients and energy. Rather than eating food and then digesting it like animals and protozoa, fungus and fungus-like protists externally digest food and then absorb the nutrients.

Endosymbiosis in Protists

You may remember that endosymbiosis is basically the idea that one cell engulfs another cell. The endosymbiosis theory used this idea to explain the evolution of eukaryotic cells - and specifically, the presence of chloroplasts and mitochondria in cells.

Within the Protista kingdom, there is evidence to help support this theory. Remember that the endosymbiosis theory proposed that the mitochondria was engulfed first. Later, a cell that was capable of photosynthesis, most likely cyanobacteria, was then engulfed and became the chloroplast. Red and green algae, while you may think of them as plants, are actually protists. These simple plant-like protists have DNA that is very similar to the genetic material of cyanobacteria. This similarity helps show the evolutionary connection between cyanobacteria and algae - the more simple cyanobacteria is an evolutionary ancestor of both red and green algae.

Examples and Importance of Protists

Unicellular diatoms are used in nanotechnology
Diatom Image

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