Chapter 16, Problem 7STP

Summary Introduction

Introduction:

Scientists speculate that prokaryotes were involved in evolution of eukaryotes as prokaryotes are much simple organisms. The endosymbiont theory which states that bacteria might have lived inside prokaryotes and eventually became organelles was proposed by Lynn Margulis. In 1966, Margulis proposed that the ancestors of eukaryotic cells lived in association with prokaryotic cells. In some cases prokaryotes might have lived inside eukaryotes. Prokaryotes might have entered as undigested prey or could have been internal parasites. Eventually the relationship became mutually beneficial and prokaryotic symbionts became organelles in eukaryotic cells.

Answer to Problem 7STP

Correct answer :

The correct answer is option A. Mitochondria and chloroplasts are found living outside eukaryotic cells

Explanation of Solution

Explanation/justification for the correct answer:

Option A. Mitochondria and chloroplasts are found living outside eukaryotic cells- There is evidence that chloroplasts and mitochondria might have evolved by endosymbiosis. Both the organelles have their own genetic material and ribosomes which resemble the DNA and ribosomes of prokaryotes. Both reproduce independently from the rest of the cell by binary fission just like the prokaryotic cells. Both have similar size and structure as prokaryotic cells. They are found living outside the eukaryotic cells; this was not the reason scientists supported the endosymbiont theory. Hence this is the correct option.

Explanation for incorrect answer:

Option B. - Mitochondria and chloroplasts reproduce by fission- Both the organelles reproduce independently from the rest of the cell by binary fission just like the prokaryotic cells. This reason supported the endosymbiont theory.

Hence this is not the correct option.

Option C. The size and structure of mitochondria and chloroplasts is similar to prokaryotic cells- Both the organelles have similar size and structure as prokaryotic cells. Both are enclosed within a double membrane and their inner membranes resemble bacterial membranes. This reason supported the endosymbiont theory.

Hence this is not the correct option.

Option D. The genetic material in mitochondria and chloroplasts is circular- Both the organelles have their own genetic material (DNA) which resemble the circular DNA of prokaryotes. This reason supported the endosymbiont theory.

Hence this is not the correct option.