Question

Prokaryotic origin if mitochondria were proposed by
(a) Rabinowitch
(b) Altmann and Schimper
(c ) Salton
(d) Morrison

Answer 1

Hint: Mitochondria and prokaryotes share some similarities and thus it is considered that mitochondria have a prokaryotic origin. The scientist who proposed this studied pathology in Germany where he observed the similarities between bacteria and cell organelles like mitochondria.

Complete answer:
Altmann and Schimper in 1890 proposed that mitochondria and chloroplasts were once a free-living prokaryote. These were engulfed by a eukaryotic cell where these prokaryotes developed a symbiotic relationship with them. Mitochondria were formed by an aerobic bacteria that was ingested while chloroplasts were developed when a photosynthetic bacteria was ingested.

Additional Information:
-The DNA molecules found in mitochondria and chloroplasts are small and circular, similar to the DNA of prokaryotes. Also, the presence of 70S ribosomes in chloroplast and mitochondria is similar to prokaryotes. These support the origin of these cell organelles as a free-living prokaryotic cell.
-Mitochondria produce cellular energy in the form of ATP by aerobic respiration, hence, commonly known as ‘powerhouses of the cell’. It is a double membrane-bound organelle with a highly convoluted inner membrane forming characteristic folds known as cristae.
-It houses an enzyme complex known as ATP synthase or oxysome. The number of mitochondria correlates with the metabolic activity of cells. The active cell has more mitochondria compared to the less active.
-Chloroplast is a double-membrane organelle found exclusively in plants. Pigments such as chlorophyll and carotenoid pigments are located in the chloroplast. They play a vital role in photosynthesis. The matrix of chloroplasts bears closed flat bags of membranes known as thylakoids bearing pigments.

So, the correct answer is ‘Altmann and Schimper.’

Note: Chloroplast and Mitochondria are also known as semi-autonomous organelles as they contain circular DNA, mRNA, and tRNAs. The electron microscopy and various other studies show that new chloroplast and mitochondria originate from the growth and division of pre-existing organelles.