Q. Which one of the following categories of organisms do not evolve oxygen during photosynthesis :
(a) Photosynthetic red algae
(b) Photosynthetic green algae
(c) Photosynthetic blue-green algae
(d) Photosynthetic bacteria
Solution :
Correct option : D Photosynthetic bacteria are capable of entrapping solar energy and utilizing it for the synthesis of complex food materials due to the presence of pigments like bacteriochlorophyll (bacteriopurpurin) and bacterioviridin. Bacterial photosynthesis is also known as anoxygenic photosynthesis. In bacterial photosynthesis, water is not the source of electron that acts as reducing agent to convert CO2 into glucose. The bacteria obtain reducing power from various compounds such as hydrogen sulphide, thiosulphate or even some organic compounds. No oxygen is evolved as it does not involve splitting of water. Hydrogen released by various compounds is picked up by NAD+ which gets reduced to NADH2 acting as reducing power. NADH2 along with ATP, produced generally by entrapping solar energy are used to reduce CO2 to glucose. The byproduct of bacterial photosynthesis is sulphur (S).
