Biology
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What Is a Protist?
The kingdom Protista may include more than
200,000 species.
Most, but not all, protists are unicellular.
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Classification of Protists
One way protists can be classified is by how they obtain nutrition:
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Heterotrophs are called animal-like protists.
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Photosynthesizers are called plantlike protists.
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Decomposers and parasites are called funguslike protists.
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20 –2 Animal-like Protists:
Protozoans
20-2 Animal-like Protists:
There are four phyla of animal-like protists:
• zooflagellates
• sarcodines
• ciliates
• sporozoans
Animal-like protists are classified by their means of movement.
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20 –2 Animal-like Protists:
Protozoans
Zooflagellates
Animal-like protists that swim using flagella are called zooflagellates.
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20 –2 Animal-like Protists:
Protozoans
Sarcodines
Sarcodines are animal-like protists that have pseudopods.
Pseudopods are temporary cytoplasmic projections used for feeding or movement.
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20 –2 Animal-like Protists:
Protozoans
Sarcodines
Amoebas
Amoebas are flexible, active cells with thick pseudopods that extend out of the central mass of the cell.
Cytoplasm streams into the pseudopod, and the rest of the cell follows.
This type of locomotion is known as amoeboid movement .
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20 –2 Animal-like Protists:
Protozoans
Sarcodines
Structures of an Amoeba
Contractile vacuole
Nucleus
Food vacuole
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Pseudopods
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20 –2 Animal-like Protists:
Protozoans
Ciliates
Ciliates use cilia for feeding and movement.
Cilia are short hairlike projections that propel a cell.
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20 –2 Animal-like Protists:
Protozoans
Ciliates
Paramecia
One type of ciliate is a paramecium .
In a paramecium, the cilia are grouped into rows and bundles, and beat in a regular pattern.
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20 –2 Animal-like Protists:
Protozoans
Structures of a Paramecium
Ciliates
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20 –2 Animal-like Protists:
Protozoans
Sporozoans
Sporozoans do not move on their own — they are parasitic.
Sporozoans are parasites of a wide variety of organisms, including worms, fish, birds, and humans.
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20 –2 Animal-like Protists:
Protozoans
Sporozoans
Many sporozoans have complex life cycles that involve more than one host.
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Malaria
Malaria is one of the world’s most serious infectious diseases, killing as many as 2 million people each year.
The sporozoan Plasmodium , which causes malaria, is carried by the female Anopheles mosquito.
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Malarial Infection
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
A female Anopheles mosquito bites a human infected with malaria and picks up Plasmodium gamete cells.
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
The sexual phase of the Plasmodium life cycle takes place inside the mosquito.
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Infected mosquito bites another human, injecting saliva that contains Plasmodium sporozoites .
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Plasmodium sporozoites
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Sporozoites infect liver cells and multiply asexually.
Plasmodium sporozoites
Liver
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Infected liver cells burst, releasing Plasmodium cells called merozoites that infect red blood cells.
Plasmodium sporozoites
Liver
Merozoites
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Liver cells burst
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20 –2 Animal-like Protists:
Protozoans
Animal-like Protists and Disease
Merozoites reproduce asexually inside red blood cells.
Merozoites
Red blood cells
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20 –2 Animal-like Protists:
Protozoans
Ecology of Animal-like Protists
Many animal-like protists are essential to the living world.
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Some live symbiotically within other organisms.
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Some recycle nutrients from dead organic matter.
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Some live in water, where they are eaten by tiny animals, which in turn serve as food for larger animals.
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20 –2 Animal-like Protists:
Protozoans
Ecology of Animal-like Protists
Some animal-like protists are beneficial to other organisms.
The protist Trichonympha lives within the digestive systems of termites.
It breaks down cellulose, allowing termites to digest wood.
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