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Protist Kingdom - Ch. 15 p. 311-316
• Droplets of pond water are filled with Protists!
• Protists are the first eukaryotes to evolve from prokaryote (bacteria)
ancestors. They are much more complex than prokaryotes.
• Protists are the ancestors to all other eukaryotes – plants, fungi, and
• The fossil record indicates that eukaryotes evolved from prokaryotes
(bacteria) more than 1.7 billion years ago.
• How did eukaryotic cells evolve, and
how did their membrane-enclosed organelles evolve?
• A widely accepted theory is that eukaryotic cells evolved through a
combination of two processes:
#1: All organelles (except mitochondria and chloroplasts) evolved
from inward folds of the plasma membrane of a prokaryotic cell.
# 2: Endosymbiosis
The Endosymbiosis Theory was largely developed
by Lynn Margulis of the University of
“Chloroplasts and mitochondria evolved from
small prokaryotes that established residence
within other, larger host prokaryotes.”
Ex : mitochondria ancestors may have been
aerobic bacteria that were able to use oxygen to
release large amounts of energy from organic
molecules by cellular respiration.
The host cell may have injested these for food; if
they remained alive, they continued to perform
respiration within the cell.
Ex: Similarly, chloroplasts may have come to live
inside a larger host cell.
Because almost all eukaryotes have mitochondria
but only some have chloroplasts, it is likely that
mitochondria evolved first.
Endosymbiosis eventually became mutually
beneficial. How? ____________________
The Diversity of Protists
Vary in structure and function more than any other group or
• Most are unicellular, but some are colonial or multicellular.
• Each cell must carry out all the basic functions of an entire
• Four major categories of protists: (are grouped more by their
lifestyle than by their evolutionary relationships)
• 1. Protozoans
• 2. Slime molds
• 3. Unicellular Algae
• 4. Seaweeds
1. Protozoans
Ingest food and thrive in all types of aquatic
environments, including wet soil and the watery
environment inside animals.
1) Flagellates: move by means of one or more flagella.
Most free-living, but some are parasitic: cause diarrhea
(infected drinking water) or sleeping sickness from the
tsetse fly.
2) Amoebas: move by means of pseudopodia
3) Forams: move with pseudopodia; flexible
4) Apicomplexans: are all parasitic and are named for an
apparatus at their apex which is specialized for
penetrating host cells. Plasmodium -malaria.
5) Ciliates: use cilia to move and feed.
Ciliate: Paramecium