Question

The Endosymbiotic Theory was proposed by Lynn Margulis in the 1970s.

Answer 1

The endosymbiont theory explains the origin of the eukaryotic cell organelles where the cells were engulfed but not digested by the larger prokaryotic cells and in the process developed into the chloroplast, mitochondria and other organelles.
(A) The theory was trying to explain the evolutionary origin of the various cell organelles and,
also explains the dependence of cells on one another.
(B) The evidences that supported the Endosymbiotic theory includes;
    -The photosynthetic bacteria; This bacteria utilize the sun's energy to make energy hence the oxygen released from the process accumulated in the atmosphere thereby leading to the death of the anaerobic cells.
    -Organelles have their own DNA and divide independently, therefore Margulis predicted that if the organelles were really prokaryotic symbionts, then they would have their own DNA.
    - The study of fossils showed the aerobic cells in it, therefore the cells  could use the toxic oxygen and convert it into ATP(energy) and water. Organisms that could thrive in aerobic environments were now best suited to the environment.