Which of the following observations are inconsistent with the endosymbiosis theory

There is compelling evidence that mitochondria and chloroplasts were once primitive bacterial cells. This evidence is described in the endosymbiotic theory. How did this theory get its name? Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.

It's Just a Theory

In everyday speech, people use the word theory to mean an opinion or speculation not necessarily based on facts. But in the field of science, a theory is a well established explanation based on extensive experimentation and observation. Scientific theories are developed and verified by the scientific community and are generally accepted as fact.

Mitochondria Have DNA

Mitochondria and chloroplasts have striking similarities to bacteria cells. They have their own DNA, which is separate from the DNA found in the nucleus of the cell. And both organelles use their DNA to produce many proteins and enzymes required for their function. A double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested by a primitive host. The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division.

Abstract

In comparison to other theories put forward so far, the Serial Endosymbiosis Theory appears to be the most critically favoured as an explanation for the origin of mitochondria and chloroplasts. For this reason some of its implications are drawn attention to. In particular it is shown that present hierarchical concepts and terminology based on the classical cell theory are inadequate to cope with the S.E.T. (as the theory is abbreviated here). It is shown that the topological relations of mitochondria and chloroplasts to the cell suggest that they are topologically "outside" it, "embraced" rather than lying truly within it. This position is consistent with the S.E.T. On the other hand microtubule-organising-centres are truly within the cell. An autogenous origin for the latter seems to be more likely than the endosymbiotic proposal of Margulis. In addition to the primary origin of organelles by the transformation of entire prokaryotic endosymbionts, the possibility of the maintenance of eukaryotic organelles produced by one cell, taken into another, is discussed. Examples of some recently discovered, unusual photosynthetic states in ciliates, brought about by temporary foreign chloroplast maintenance, and possibly degeneration of endosymbiotic photosynthetic flagellates, are discussed in this context. The existence of some contemporary examples of photosynthetic bodies which seem to be intermediate between endosymbiotic blue-green algae and chloroplasts, suggests that some organelles may have had a more recent origin than the Precambrian Era, the process being a continuous one. Some of the difficulties inherent in alternative theories for the origin of eukaryotes are discussed. It is stressed that alternative proposals have not yet received intensive exposition and comparisons with the S.E.T. are thus difficult. Attempts to use single criteria (particularly biochemical) as phylogenetic "markers" should be made with due consideration of the S.E.T. Finally, it has bearing on the recognition of kingdoms, for it widens the already acknowledged chasm between prokaryotes and eukaryotes, intermediates between the two types of organisation being impossible (as stressed by Margulis).

Journal Information

TAXON is the leading international journal devoted to systematics, phylogeny and taxonomy of algae, fungi, and plants. It also publishes papers on methodology, botanical history, biography, bibliography and related subjects, opinion pieces, commentaries and new perspectives, and publishes a number of regular columns including Plant Systematics World. TAXON is the only place to publish proposals to amend the International Code of Nomenclature for algae, fungi and plants (except Chapter F - fungi) or nomenclatural proposals.

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