20-1 The Kingdom Protista
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20-1 The Kingdom Protista
What Is a Protist?
What Is a Protist?
Protists are eukaryotes that are not members of the
Plant, Animal, or Fungi kingdoms.
The kingdom Protista may include more than 200,000
species.
Most, but not all, protists are unicellular. Some
consist of hundreds or thousands of cells but are still
protists.
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20-1 The Kingdom Protista
Evolution of Protists
Evolution of Protists
The first eukaryotic organisms on Earth were
protists, and appeared 1.5 billion years ago.
They belong to the kingdom Protista, which come
from Greek meaning “the very first.”
Mitochondria and chloroplasts in eukaryotic cells
may have descended from aerobic and
photosynthetic prokaryotes that lived inside larger
cells.
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20-1 The Kingdom Protista
Classification of Protists
Classification of Protists
It is suggested that protists be divided into multiple
kingdoms because DNA evidence indicates that
different groups of protists evolved independently
from archaebacteria.
Scientists cannot agree on how to divide them
currently.
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20-1 The Kingdom Protista
Classification of Protists
One way protists can be classified is by how they
obtain nutrition:
• Heterotrophs are called animal-like protists.
• Photosynthesizers are called plantlike protists.
• Decomposers and parasites are called
funguslike protists.
These are an artificial way to organize an
extremely diverese group.
They do NOT reflect the evolutionary history of the
protists in each group.
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