Question

Which one of the following is used by purple sulfur bacteria for the reduction of CO$_2$ to CH$_2$O?
A. H$_2$S
B. H$_2$O
C. CH$_4$
D. NH$_4$

Answer 1

Hint: Purple sulphur bacteria are a large group of bacteria that are known as proteobacteria capable of doing photosynthesis. These bacteria are anaerobic and grow in anoxic conditions. The sulphur bacteria are mainly divided into two main groups which are chromatiaceae producing internal sulphur granules and ectothiorhodospiraceae which have external sulphur granules.

Complete answer: Sulphur bacteria, unlike any plant, algae or cyanobacteria, do not use water as their reducing agent, and therefore they do not produce oxygen as a result of the photosynthetic products. The process of photosynthesis is anoxygenic. The sulphur bacteria are known to use sulphur which is in the form of thiosulphate or sulphide as well as some other species that may use hydrogen, iron, or nitrous oxide. These all are used as electron donors in the process of photosynthesis. Sulphur is known to be oxidized to produce elemental sulphur granules which may, in turn, produce sulphuric acid via. oxidation. They have two major photosynthetic pigments which are bacteriochlorophylls a or b. The location of these pigments being the plasma membrane and chromophore. Purple sulfur bacteria are mainly found in lakes having illuminated anoxic zones. They are also found in some other habitats where mostly hydrogen sulfide is accumulated and they are known as hot springs. Most favorable lakes being meromictic lakes that are known to be permanently stratified for the development of these bacteria.
So, the correct answer to this question is the option"A".

Note: Purple sulphur bacteria are known to have their effect on the environment by giving a contribution to nutrient cycling and by using their metabolism they alter the surroundings. They are also known to fix the carbon cycle by the fixation of carbon dioxide. They are also known to contribute to the sulphur and iron cycle to their habitat.