Unit-4

Photosynthesis - it refers to a process in which light energy is converted into chemical energy. It is an important and primary C assimilation process operating in any base level food chain

Oxygenic photosynthesis - Is kind of photosynthesis in which water acts as electron donor resulting in formation of oxygen during the process of photosynthesis, commonly takes place in plants and cyanobacteria.

Anoxygenic photosynthesis - Is a kind of photosynthesis, in which reduced inorganic compounds like H2S acts as source of electron donor for the process of carbon fixation during photosynthesis, as a result oxygen will not be formed at the end, and the process is referred as anoxygenic photosynthesis.

Sulfur oxidizers - refers to phylogenetically different group of bacteria that are capable of oxidizing reduced sulfur compounds and using them as energy and electron donor molecules concomitantly fixing the atmospheric CO2 into cell carbon.

Methanogens - they are anaerobic, chemolithotrophic group of Archaea that are capable of converting CO2 or methyl or acetate to methane with the help of several co-enzymes that acts in tandem.  

Hydrogen bacteria - they are also called as hydrogen oxidizing bacteria or knallgas bacteria that are capable of oxidizing hydrogen to obtain energy for their growth. e.g. members belong to Aquificales  

Nitrifying bacteria - Group of bacteria that can able to use reduced inorganic nitrogen compounds like NH3 and NO2 as energy and electron donor source and fixes atmospheric CO2 into cell carbon.

Iron bacteria – they are the bacteria that are capable of obtaining energy by oxidizing iron, bacteria carrying out this process lives in the low pH or at very low O2 concentration. E.g. Thiobacillus ferroxidans.

Chemolithotrophs - The term chemolithotrophy denotes energy metabolism of bacteria in which inorganic substances are oxidized, mainly in the absence of light, and used as a source of energy for cell biosynthesis and maintenance. The term was coined by Winogradsky.

Carotenoids - they are referred as accessory pigments, typically in yellow, red, brown or green colour absorb the light in the blue region of the spectrum and transfer the energy absorbed to the chlorophyll of the reaction center. They primarily function as photoprotective pigments  

Phycoerythrin and phycocyanin – Refers to a group of phycobiliproteins that absorbs light at 550 nm (phycoerythrin) and 620 nm (phycocyanin), these phycobiliproteins associates with another phycobiliproteins called allophycocyanin and forms into aggregated and assembled structure called phycobilisomes.

Phycobilisomes – refers to aggregated and assembled phycobiliproteins (phycoerythrin and phycocyanin), a kind of carotenoid pigments commonly present in cyanobacteria and red algae, they absorb light a shorter wavelength and transfer to the primary chlorophyll molecules.

Geosmin - Organic compounds of earthy flavor and aroma produced by certain groups of cyanobacteria and actinobacteria.

Chlorophyll – refers to green photosynthetic pigment present in plant, cyanobacteria and algae involved in carbon fixation. They commonly absorb light at red and blue wavelength of electromagnetic spectrum and essential component of photosynthesis process.