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Protist Kingdom

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Protist Kingdom

Prokaryote or eukaryote?

This organism consists of a single cell with several flagella. Is it a prokaryote, such as a bacterium? Actually, it’s larger than a prokaryotic cell, and it also has a nucleus. Therefore, this organism belongs to the domain Eukarya, the domain that includes humans. This particular eukaryote is one of the smallest, simplest organisms in the domain, called a protist. It’s scientific name is Giardia lamblia. As a human parasite, it can make us sick.

Kingdom Protista

Protists are a group of all the eukaryotes that are not fungi, animals, or plants. As a result, it is a very diverse group of organisms. The eukaryotes that make up this kingdom, Kingdom Protista , do not have much in common besides a relatively simple organization. Protists can look very different from each other. Some are tiny and unicellular, like an amoeba , and some are large and multicellular, like seaweed . However, multicellular protists do not have highly specialized tissues or organs. This simple cellular-level organization distinguishes protists from other eukaryotes, such as fungi, animals, and plants. There are thought to be between 60,000 and 200,000 protist species, and many have yet to be identified. Protists live in almost any environment that contains liquid water. Many protists, such as the algae , are photosynthetic and are vital primary producers in ecosystems. Other protists are responsible for a range of serious human diseases, such as malaria and sleeping sickness.

The term protista was first used by Ernst Haeckel in 1866. Protists were traditionally placed into one of several groups based on similarities to a plant, animal, or fungus: the animal-like protozoa , the plant-like protophyta (mostly algae), and the fungus-like slime molds and water molds . These traditional subdivisions, which were largely based on non-scientific characteristics, have been replaced by classifications based on phylogenetics (evolutionary relatedness among organisms). However, the older terms are still used as informal names to describe the general characteristics of various protists.

Diversity of protists

Protists range from single-celled amoebas to multicellular seaweed. Protists may be similar to animals, plants, or fungi.

Summary

  • Kingdom Protista includes all eukaryotes that are not animals, plants, or fungi.
  • Kingdom Protista is very diverse. It consists of both single-celled and multicellular organisms.

Explore More

Use this resource to answer the questions that follow.

  1. List three characteristics of protists.
  2. How are protists classified?
  3. What is another name for animal-like protists and plant-like protists?
  4. Complete this statement: Any eukaryote that is not a plant, animal or fungus is a __________.

Review

  1. What are protists?
  2. How are unicellular protists and multicellular protists similar?
  3. How are protists classified? What are the main categories of protists?

Vocabulary

alga

alga

(plural, algae): A plant-like protist, such as diatom and seaweed.
amoeba

amoeba

Unicellular protist.
malaria

malaria

Disease caused by Plasmodium protozoa; transmitted by mosquitoes in tropical and subtropical regions of the world.
phylogenetics

phylogenetics

Evolutionary relatedness among organisms; based on molecular sequence information.
Protista

Protista

Eukaryotic kingdom; comprised of eukaryotes that are not fungi, animals, or plants.
protophyta

protophyta

Plant-like protists, such as algae.
protozoa

protozoa

(singular, protozoan): Animal-like protists, such as Amoeba and Paramecium.
seaweed

seaweed

A large multicellular photosynthetic protist.
slime mold

slime mold

Fungus-like protist; commonly found on rotting logs and other decaying organic matter.
water mold

water mold

Fungus-like protist; commonly found in moist soil and surface water.

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