Question

Which process is an example of serial endosymbiosis?

a)endosymbiosis between mitochondria and chloroplasts

b)endosymbiosis between heterotrophic protists and green algae

c)endosymbiosis between heterotrophic protists and cyanobacteria

Answer 1

Answers:

The right answer is option A endosymbiosis between mitochondria and chloroplasts

Explanation:

The most common consequence of serial endosymbiosis is the existence of plastids, in addition to mitochondria, in the cytoplasms of photosynthetic eukaryotes, cellular evolution holds that the cellular evolution of eukaryotes arose through the endosymbiotic union of engulfed bacteria with a precursor eukaryotic cell. The advent of oxygen releasing Cyanobacterial photosynthesis about 3 billion years ago (3 Ga) gradually converted the Earth's atmosphere from its primordial reducing state. Oxygen is toxic to organisms that lack the metabolic machinery to rapidly utilize oxygen, so symbiotic union with bacteria capable of oxidative metabolism would ensure cellular survival in environments with increased oxygen tension (pO₂). This union ultimately resulted in mitochondrial organelles, while a second union with Cyanobacterial cells ultimately resulted in photosynthetic plastids (chloroplasts).

Mitochondria and Chloroplast DNA exists in closed circular form as it does in a prokaryotic cell. This DNA of the chloroplast is very similar to photosynthetic blue-green bacteria, while the mitochondrion DNA is very similar to the aerobic bacteria. Both organelles lack histones and introns like bacteria. Mitochondria and Chloroplast’s ribosome are the 70s in size, the same as those of prokaryotes.

Phylogenetic analyses using the ribosomal RNA sequencing method, convincingly suggested that mitochondria and chloroplast are evolutionarily related to bacteria. The sequence comparison of mitochondria and chloroplast show that mitochondria came from bacterial lines related to alpha-proteobacteria and chloroplast originated from cyanobacteria. Mitochondria and chloroplast are the same in size as bacteria. The size of bacteria is commonly 0.1-10 micrometers, while the size of mitochondria and chloroplast is 0.5-10 micrometers and 1- 10 micrometers respectively.

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