Question

How would you define the endosymbiotic theory?

Answer 1

Hint: The endosymbiotic theory is responsible for explaining the origin of some of the cell organelles found in eukaryotic cells such as mitochondria and chloroplasts. It is an example of a symbiotic relationship.

Complete Answer:
The endosymbiotic theory states that some cell organelles such as mitochondria and chloroplast found in eukaryotic cells were free-living prokaryotic organisms that started living in a symbiotic relationship within the eukaryotic organism after being engulfed by it. The proof that mitochondria and chloroplasts were prokaryotic organisms lies in the fact that both of them contain their own DNA which is circular in nature, their own ribosomes, and are covered by double membranes. The ribosomes found in them are of 70S type which is the same as that found in prokaryotes.
-Mitochondria and chloroplast are said to be semi-autonomous organelles because they can function on their own and require less amount of command from the nucleus.
-The mitochondria is believed to be an aerobic prokaryotic organism that started living inside a eukaryotic cell and performed the function of aerobic respiration for that cell.
-Similarly, the chloroplast is believed to be a prokaryotic organism that performed photosynthesis that started living inside a eukaryotic cell to perform photosynthesis for that cell in return for nutrients.
-The mitochondria consist of enzymes present on their outer and inner membrane which are responsible for the process of aerobic respiration.
-Chloroplasts contain enzymes in the stroma required for the synthesis of carbohydrates during the process of photosynthesis.

Note:
-Both mitochondria and chloroplast divide through the process of binary fission which is seen in prokaryotes.
-The innermost part of mitochondria is known as the matrix whereas, in the case of chloroplasts, it is known as the stroma.
-The unit used to represent ribosomes is known as Svedberg (S) and it represents the sedimentation rates of different ribosomes during centrifugation.