Biology
Morphology of Flowering Plants Solutions
Mitochondrial Relatives
“Well that's weird,” Ivy said, thinking out loud. “Mitochondria look like little bacteria and even have some of their
genes! It seems like mitochondria were once bacteria that infected another cell and then they just stayed
together. I'm going to look into why this might have occurred. It doesn't make sense to say that mitochondria are
pathogens since the cell is not harmed. It benefits from the association."
Ali cut her off. “But, could they have once been a pathogen? Or, what if they weren't bacteria, to begin with?
Listen to what I found. There are some small, simple eukaryotes called protists that do not have mitochondria
like the rest of eukaryotic cells. Instead, they have a mitochondria-like organelle called a mitosome that does not
produce ATP, but aids in the formation of iron-sulfur clusters that are incorporated into proteins. Some other
protists have a mitochondria-like organelle called a hydrogenosome, which does produce ATP and hydrogen gas
but does not use oxygen. If that's the case, then which came first? I think that the eukaryotic cell may already
have had other organelles, possibly mitosomes or hydrogenosomes, that evolved into mitochondria.”
Ivy wasn't convinced. “Or did a bacterium infect a cell, which later evolved into mitochondria, mitosomes, or
hydrogenosomes?"
Guide Questions:
1. Based on the information above and other information you've learned in class, select the hypothesis you
think is most likely:
a. Mitochondria evolved from an engulfed bacterial cell that lost its complex, free-living lifestyle.
b. Mitochondria evolved energy-producing capabilities from simpler organelles that gained new functions.
