1. A symbiotic relationship is one in which both partner organisms benefit... Fi

Question

1. A symbiotic relationship is one in which both partner organisms benefit...

First, specifically describe a way that humans help our resident microbes to perform their necessary life processes:

Second, describe a specific way that the microbiome aids humans to perform our necessary life processes.

2. There are no fossils of early prokaryotes, nor of the first eukaryotes. No one was present to observe events first-hand, yet we know that eukaryotes arose from endosymbiosis of two prokaryotic organisms. Describe a piece of evidence that strongly supports the endosymbiotic origin of eukaryotic life.

Explanation / Answer

1)

Symbiosis is the mutual beneficial relationship between two organisms. On human body several microbiota reside and they obtain the necessary growth conditions on the human skin. The body temperature of humans supports the growth of several mesophilic bacteria. The salts excreted along with sweat provide the required nutrients for the microbial growth. The sebum and lysozyme in sweat and tears promote the growth of acidophilic bacteria.

The microbes living on humans skin competitively inhibit the pathogens. The bacteria also produce the substances like lactic acid and bacteriocins that inhibit the pathogenic species. The bacterial enzymes produced protect the skin surface and some fatty acids produced by bacteria contribute to soft texture of skin and mucous membranes of the human body.

2)

The prokaryotic cells evolved earlier were started to develop internal membranes some 2 billion years ago, due to which the evolution of eukaryotic cells had took place. The eukaryotic organelles like mitochondria and chloroplast resemble the prokaryotic cells. This has happened due to establishment of symbiotic relationship between prokaryotes that entered the eukaryotic cells. Thus, endosymbiotic theory states that the eukaryotic cells are produced from living communities formed by prokaryotic organisms.

The endosymbiotic hypothesis emphasizes that the mitochondria arose from the stable incorporation of aerobic bacterium in to other cells and the chloroplasts arose from incorporation of a cyanobacterium like organism performing the oxygenic phtosynthesis. Thus, the physiology and metabolism of mitochondria and chloroplast along with their structure and sequence of genomes support the endosymbiotic hypothesis. The prokaryotic organisms, the mitochondria and the chloroplast contain 70S type of ribosomes and their 16S ribosomal RNA sequence is similar and characteristic to bacteria.

The phylogenetic trees constructed from gene sequences of 16S rRNA of mitochondria place their ancestor in the phylum alphaproteobacteria and that of chloroplast place their ancestor in the phylum cyanobacteria. Therefore, the major events like establishments of endosymbiotic relationship of prokaryotes in other organisms had lead to the evolution of eukaryotic cells that contain membrane bound nucleus.

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