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Lesson OverviewLesson Overview21.1 Protist Classification 21.1 Protist Classification

—The Saga Continues—The Saga Continues

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THINK ABOUT IT Blendspace Video #10

Some of the organisms we call “protists” live quietly on the bottom of shallow ponds, soaking up the energy of sunlight. Others swim vigorously in search of tiny prey. Some, such as diatoms, sparkle in coastal waters. Still others drift in the human bloodstream, destroying blood cells and killing nearly a million people a year.

What kind of life is this, capable of such beauty and such destruction?

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The First EukaryotesWhat are protists?

Protists are eukaryotes (cells have a

nucleus) that are not members of the

plant, animal, or fungi kingdoms.

(Blendspace video #11)

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The First Eukaryotes

• Appeared on earth millions of years ago- the first eukaryotes

• “Protist” means “first”• Members of Kingdom Protista• Most are single-celled• Some are multi-celled (example: brown algae

called kelp; largest protist)

**Fun fact- Otters wrap themselves in giant kelp to keep from drifting out to sea while they sleep.

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The “Protist” Dilemma

• More diverse than any other eukaryotic kingdomEuglena, brown algae, diatoms, and slime molds are examples

of protists.

• Many “protists” are far more closely related to members of other eukaryotic kingdoms than they are to other “protists”

• By definition, the members of a living kingdom should be more like one another than like members of other kingdoms. This is not true of protists, which means that reclassification is necessary.

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The “Protist” Dilemma

Classification (in the past) (Blendspace video #19)

1. plant-like protists

2. animal-like protists

3. fungu-slike protists

4. other?

Biologists also discovered that many of the animal-like and fungus-like protists are so similar that they belong in a single group, not two.

Some protists have characteristics of more than one group!

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Multiple Kingdoms?

The most recent studies of protists divide them into six major clades, each of which could be considered a kingdom.

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Multiple Kingdoms? This cladogram represents an understanding of protist relationships supported by current research.

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Multiple Kingdoms?

Surprisingly, the plant, animal, and fungi kingdoms fit right into these six clades. Animals and fungi actually emerge from the same protist ancestors.

Protists were the first eukaryotes, and evolution has had far more time to develop differences among protists than among more recently evolved eukaryotes like plants and animals.

By finding the fundamental divisions among protists, we also identify the most basic differences among all eukaryotes.

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What “Protist” Means Today Even though the biologist building the Tree of Life prefer a different classification, the word “protist” remains in common usage, even among scientists.

Bear in mind that “protists” are not a single kingdom but a collection of organisms that includes several distinct clades.

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Protists—Ancestors and Descendants How are protists related to other eukaryotes?

Today’s protists include groups whose multicellular ancestors were among the very last to split from the organisms that gave rise to plants, animals, and fungi.

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Protists—Ancestors and DescendantsMicroscopic fossils of eukaryotic cells, like Tappania plana shown, have been found in rocks as old as 1.5 billion years.

Genetic and fossil evidence indicates that eukaryotes evolved from prokaryotes and are more closely related to present-day Archaea than to Bacteria.

The split between Archaea and Eukarya may have come as early as 2.5 billion years ago. Since that time, protists have diversified into as many as 300,000 species.

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Protists—Ancestors and Descendants

Most of the major protist groups have remained unicellular, but two have produced multicellular organisms. Plants, animals, and fungi arose from the ancestors of these multicellular groups.

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Protists—Ancestors and Descendants

The roots of all eukaryotic diversity, from plants to animals, are found among the ancestors of protists.