上,中国的
for reduction of CO2,
5. Photosynthetic sulphur bacteria differ from higher plants in
that they do not have the pigment
.-. and they do
not use .............. as electron donor in photosynthesis .
6. When treated with crystal violet and subsequently with
jodine some bacteria remain colourless and these are
called Gram
bacteria
7. During conjugation Ffactor is commonly called 25
8
are short, curved comma-shaped flagellated
bacteria
9. A nitrite oxidising bacterium is
10. The causative organism for tetanus is
tuberculosis
11. The cell wall of Gram -ve bacteria is comparatively less
than Gram+ ve bacteria .
chemical energy
.
-...
Answers
Answer:
Explanation:
Plants, algae, and cyanobacteria perform photosynthesis with the resultant production of oxygen, which supports all organisms that consume it through their respiration. This type of photosynthesis is an indispensable part of the global oxygen flux. However, another type of photochemical reaction, photosynthesis without oxygen production, exists, and has been designated anoxygenic photosynthesis. A number of ecologists regard anoxygenic photosynthesis as a negligible photochemical reaction because it contributes nothing to the reproduction of oxygen. This type of photosynthesis does not appear to have any beneficial function.
The global impact of anoxygenic photosynthesis is considered to be negligible. Nevertheless, organisms in the domain Bacteria perform this type of photosynthesis, with some dilettantes referring to them as anoxygenic phototrophic bacteria. Contrary to all expectations, studies on anoxygenic phototrophic bacteria have a long history in microbiology. Anoxygenic phototrophic bacteria were discovered at the dawn of microbiology more than 100 years ago. The first anoxygenic phototrophic bacterium was identified in 1901 and was subsequently described as Rhodospirillum species by the German botanist, Hans Molisch in 1907 (10). Rhodospirillum species are purple bacteria that belong to the phylum Proteobacteria, and the term “purple bacteria”, which refers to a major group among anoxygenic phototrophic bacteria, was also simultaneously proposed by Molisch. Another major anoxygenic phototrophic group, green sulfur bacteria, which belong to the phylum Chlorobi, was described by the Russian biologist, Georgii A. Nadson in 1906 (13). Martinus W. Beijerinck, a famous microbiologist in the Netherlands, who was a contemporary of Molisch and Nadson, proposed a lactic acid bacterial group, the genus Lactobacillus, in 1901.
None of the anoxygenic phototrophic bacteria have the ability to use water as an electron donor (or cannot oxidize water), and, thus, perform photosynthesis using sulfide, hydrogen or organic substrates. Therefore, photosynthesis by these bacteria does not involve oxygen. In the domain Bacteria, oxygenic photosynthesis is limited to only one phylum, i.e., Cyanobacteria. On the other hand, anoxygenic photosynthesis is widely distributed over several bacterial phyla. Purple bacteria in the phylum Proteobacteria and green sulfur bacteria in the phylum Chlorobi described above inhabit various environments such as soil, ocean, lakes, and rivers. Some species have even been discovered in hot springs (7, 25), and a culture-independent survey revealed that a brackish lake was abundant in a number of green sulfur bacteria (12). In addition to these bacteria, there are two groups, i.e., thermophilic or mesophilic phototrophs showing filamentous morphologies, designated as filamentous anoxygenic phototrophs belonging to the phylum Chloroflexi (4), and spore-forming anoxygenic phototrophs called heliobacteria are included in the phylum Firmicutes (3). Anoxygenic phototrophs have recently been discovered in two phyla Acidobacteria and Gemmatimonadetes, i.e., Chloracidobacterium thermophilum isolated from a hot spring (23) and Gemmatimonas phototrophica from a lake (28), respectively. Therefore, the phylogenetic extent of anoxygenic phototrophic bacteria is larger than expected.
Anoxygenic phototrophic bacteria vary broadly not only in terms of their phylogenetic positions, but also in the compositions of their photosynthetic apparatuses. Organisms performing oxygenic photosynthesis, i.e., cyanobacteria, algae, and plants, basically share a common mechanism for photosynthesis; it is performed in algae and plant chloroplasts, which originated from an ancestor of cyanobacteria. They have chlorophyll a as the essential photo-pigment and two types of photochemical reaction centers called photosystems I and II. However, anoxygenic phototrophic bacteria possess bacteriochlorophyll(s) instead of chlorophyll and contain one of two photosystems because anoxygenic photosynthesis only requires one type of photochemical reaction center. Phototrophs belonging to the phyla Chlorobi (green sulfur bacteria), Firmicutes (Heliobacterium spp.) and Acidobacteria (C. thermophilum) contain photosystem I only (23). On the other hand, those in the phyla Proteobacteria (purple phototrophic bacteria), Chloroflexi (filamentous anoxygenic phototrophic bacteria), and Gemmatimonadetes ( G. phototrophica) have photosystem II (28).