11th Class Biology Photosynthesis in Higher Plants Bacterial Photosynthesis

Like green plants, some purple and green sulphur bacteria are capable of synthesizing their organic food in presence of light and in absence of \[{{O}_{2}},\]which is known as bacterial photosynthesis.

Van Niel was the first to point out these similarities. Oxygen is not liberated in bacteria during process of photosynthesis. Their photosynthesis is non-oxygenic. Because bacteria use \[{{H}_{2}}S\]in place of water \[({{H}_{2}}O)\] as hydrogen donor. Photosynthetic bacteria are anaerobic. Only one type of pigment system (PSI) is found in bacteria except cyanobacteria which possess both PSI and PSII. Bacteria has two type of photosynthetic pigments. Bacteriochlorophyll and Bacterioviridin.

The photosynthetic bacteria fall under three categories

(1) Green sulphur bacteria : It contains chlorobium chlorophyll, which absorb 720-750nm (far red light) of wavelength of light. e.g., Chlorobium.

(2) Purple sulphur bacteria : e.g., Chromatium.

(3) Purple non-sulphur bacteria : e.g., Rhodospirillum, Rhodopseudomonas.

Characteristics of bacterial photosynthesis are :

(1) No definite chloroplasts but contain simple structures having pigments called chromatophores (term coined by Schmitz).

(2) Contain chlorobium chlorophyll or bacterio-chlorophyll.

(3) Use longer wavelengths of light \[(720-950nm).\]

(4) No utilization of \[{{H}_{2}}O\](but use \[{{H}_{2}}S\]or other reduced organic and inorganic substances).

(5) No evolution of \[{{O}_{2}}.\]

(6) Photoreductant is \[NAD{{H}_{2}}(Not\,\,NADP{{H}_{2}}).\]

(7) Only one photoact and hence one pigment system and thus one reaction centre, i.e., \[{{P}_{890}}.\]

(8) Cyclic photophosphorylation is dominant.

(9) It occurs in presence of light and in absence of \[{{O}_{2}}.\]