Chloroplasts and mitochondria

Question

Which of the following DOES NOT support the endosymbiotic theory?


Chloroplasts and mitochondria contain bacteria-like ribosomes.

 

Chloroplasts and mitochondria are both double-membrane bound.

Chloroplasts and mitochondria have the same sizes.

Chloroplasts and mitochondria contain their own DNA.

Answer 1

Hi Symmeatra,

 

I'd like to help you with this question. Let's take a look at the question and all of the available answers, and then we can discuss which of the answers best suits the question.

 

 

Which of the following DOES NOT support the endosymbiotic theory?

     The endosymbiotic theory states that cellular organelles (such as the mitochondria or chloroplast) in eukaryotes evolved from bacterial symbionts that were able to survive and thrive inside of their host cell's cytoplasm, and that both the host cell and the endosymbiont eventually evolved to become "specialized" in performing certain functions  that are necessary for the other's survival. A simpler way to look at this question, then, is to just ask yourself "Which of these statements does not show evidence that bacteria and mitochondria/chloroplasts are closely related?"

 

Chloroplasts and mitochondria contain bacteria-like ribosomes:

     This claimsmitochondrial ribosomes are more similar to bacterial ribosomes than those found in the cytoplasm of eukaryotic cells. Both mitochondria and chloroplasts contain genes that encode for ribosomes that are smaller and more similar to those of bacteria than the ribosomes coded in nuclear DNA. This is pretty good evidence that mitochondria/chloroplasts most likely have a close evolutionary relationship with bacteria, and that supports endosymbiotic theory.

 

Chloroplasts and mitochondria are both double-membrane bound:

     This statement highlights the fact that the membranes of mitochondria and chloroplasts resemble the membranes which surround free-living cells. This is can be considered evidence that mitochondria and chloroplasts evolved from former free-living organisms, and therefore supports the endosymbiotic theory.

Chloroplasts and mitochondria have the same sizes:

     This statement claims that chloroplasts and mitochondria are similar in size. Although this may show an evolutionary relationship between the two organelles, it would be weak evidence for the link between these organelles and their bacterial ancestors. Furthermore, bacteria can come in many different sizes, so size alone doesn't indicate relationship.

 

Chloroplasts and mitochondria contain their own DNA:

     Mitochondria and chloroplasts are different from other cellular organelles because they have their own special DNA. This supports endosymbiotic theory, because the bacterial ancestors of mitochondria and chloroplasts would have required their own DNA in order to survive and reproduce.

 

After looking through each statement, it appears that the answer to the question "Which of the following DOES NOT support the endosymbiotic theory?" is "Chloroplasts and mitochondria have the same sizes," because this statement would only offer weak evidence at best to an evolutionary link between mitochondria/chloroplasts and their bacterial ancestors.

I hope that helps, and let me know if you have any other questions!

 

 

 

Answer 2

Chloroplast and mitochondria contain their own DNA does not support this theory.  This is because DNA is only associated with the nucleus of a cell.  Mitochondria is responsible for the energy and chemical reactions in the cell and chloroplast is where the food-making process (photosynthesis) takes place.