Milestones in Biology 1 Test Your Knowledge
What is the function of mitochondria? Of chloroplasts?
a: Mitochondria are cellular “power plants.” They carry out the reactions of cellular respiration to generate usable energy. b: Chloroplasts are the photosynthetic organelles in plant cells. They convert atmospheric carbon dioxide to organic carbohydrates (sugars).
What evidence did Margulis present to support her hypothesis that organelles had once been free-living prokaryotic organisms?
Chloroplasts have their own DNA; they have their own ribosomes; they are about the same size as bacteria and replicate in the same way as bacteria; and mitochondria share these traits with chloroplasts.
On the basis of DNA sequence analysis,
a. which bacteria are likely the closest relatives of the chloroplast?
b. which bacteria are likely the closest relatives of the mitochondria?
a: cyanobacteria; b: Rickettsia
The endosymbiosis in human cells involves
a. a mutually beneficial relationship.
b. the growth of bacteria in our gut.
c. an organelle derived from a photosynthetic bacterium.
d. a parasitic bacterium infecting our cells during embryonic development.
e. all of the above
a
From what you have read here about endosymbiosis:
a. Could you live without your endosymbiotic organelles? Why or why not?
b. Could you live if plants did not have their endosymbiotic organelles? Explain your answer.
a: You could not live without your mitochondrial symbionts. Humans require ongoing cellular respiration to sustain life. b: If plants did not have mitochondria, they would die (much as humans would without mitochondria). That would reduce the food supply for humans (directly or indirectly because of the animals that many humans eat that in turn in eat plants). Furthermore, if plants lacked chloroplasts, they would not be able to carry out photosynthesis. They would die (which would be very bad for humans). Additionally, when plants carry out photosynthesis, oxygen is released, and humans rely on this oxygen.