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TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
Endosymbiotic Theory Notes
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
Is the living cell
simple or complex?
• Cells vary in complexity.
• Most eukaryotic cells are highly specialized and
contain an intricate array of organelles and internal
compartments.
• Many prokaryotic cells lack internal membranes
and organelles except for ribosomes.
• However, even prokaryotic cells are complex in
their own way.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
plant and animal cells contain a variety of organelles. Some structures are
specific to either plant cells or animal cells only.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
How did cellular complexity
come about?
• The fossil record provides few clues about the
history of life at the cellular level.
• Microscopic fossils generally lack internal detail
of cellular structure.
• However, careful studies of living cells have
helped to answer questions about the origins of
cellular complexity.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
What is the
endosymbiotic theory?
• The endosymbiotic theory proposes that
eukaryotic cells formed from symbiotic
relationships among prokaryotes.
• The theory proposes that mitochondria evolved
from free-living aerobic bacteria that began to live
inside anaerobic prokaryotes.
• Chloroplasts evolved from free-living
photosynthetic bacteria paired with the earliest
(contd.)
eukaryotes.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
The endosymbiotic theory is diagramed below.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
What evidence supports the
endosymbiotic theory?
• Mitochondria and chloroplasts are similar in size to
bacteria, have their own genomes, contain
ribosomes similar to those of prokaryotes, and are
formed by division of preexisting mitochondria and
chloroplasts.
• The membrane systems of chloroplasts resemble
those of photosynthetic prokaryotes.
• Some cells today contain endosymbiotic bacteria
and algae.
TEKS 7G: Analyze and evaluate scientific explanations concerning the complexity of the cell.
Do we fully understand the cell?
• No, but evidence suggests that
complex cellular structures and
pathways were produced by the
process of evolution.
• However, there are many uncertainties
in our current understanding of cellular
complexity.