Question

Outline TWO pieces of evidence for the endosymbiotic hypothesis for the origins of chloroplasts and mitochondria in eukaryotic cells. (4 marks)

Answer 1

The endosymbiotic theory was put forward by Lynn Margulis in the year 1967. The theory explains the origin of mitochondria and chloroplast which are found in eukaryotic cells and states that these membrane-bound organelles were developed from free-living prokaryotic microbes. The idea of this theory is that small prokaryotic organisms were engulfed by one another with passing time both of these survived and evolved as eukaryotic cell

The theory proposed that mitochondria were developed from proteobacteria and the chloroplast were developed from blue-green algae cyanobacteria. The anaerobic bacteria engulfed the aerobic bacteria and a symbiotic relationship was maintained.

Evidence

1-These membrane-bound organelles have double-membrane consists of the phospholipid bilayer similar to the purple aerobic bacteria and blue-green bacteria.

2- Both mitochondria and chloroplast have their own DNA and they replicate independently and results in maternal inheritance and maternal effect.

3- Chloroplast and mitochondria replicate by splitting into 2 daughter cells just as the asexual mode of reproduction in prokaryotes(Binary fission).

4- The chloroplast is responsible for the process of photosynthesis in plants and converts the sunlight energy into carbohydrates and the mitochondria use oxygen for the production of ATP by oxidative phosphorylation.