Aprimary difference between cyanobacteria and purple and green phototrophic bacteria is a) energy source. b) cell wall type. c) electron donor for co2 reduction. d) cell type. e) color.

The right answer is C.

Sulfur purple bacteria (also called sulfooxidative phototrophic bacteria) are part of the family of photosynthetic bacteria with green sulfur bacteria and cyanobacteria. However, unlike cyanobacteria, purple bacteria such as sulfurous green bacteria do not produce oxygen during photosynthesis. In the sulfur oxidation-reduction process, these bacteria oxidize sulfide (H2SO3) to elemental sulfur (S).

im not intirely sure but i think the anwser is d relative humidity