Question

Phototrophic microorganisms (A: 2pts; B: 4pts)

• Cyanobacteria
• Algae
• Green-sulfur bacteria
• Purple-sulfur bacteria

A. Big picture: What are similarities between all these microorganisms?

B. Choose one of the oxygenic phototrophs and one of the anoxygenic phototrophs and contrast and compare them focusing on: (You can present the answers in a table.)

1. phylogenetic affiliation
2. energy generation (photosystems, e-donor and acceptor, carbon source)
3. metabolism is they don’t do photosynthesis
4. relationship to oxygen
5. preferred habitats
6. other specific characteristics

Answer 1

Part - A

Ans : Basic similarities between all photrophic microorganism mentioned here are capable of doing photosynthesis. The difference is that they use different methods for the photosynthetic process. Algae and Cyanobacteria use water for photosynthesis releasing oxygen while green sulphur bacteria and purple sulphur bacteria use sulphide and hydrogen sulphide for photosynthesis and are incapable of releasing oxygen. Hence algae and cyanobacteria comes under oxygenic photrophs and green sulphur and purple sulphur bacteria comes under anoxygenic phototrophs.

Another similarity among these microorganisms is that they are all unicellular.

Part - B

Compare and contrast Oxygenic phototrophs and Anoxygenic phototrophs

	Cyanobacteria	Purple sulphur bacteria
Phylogenetic affliation	Cyanobacteria	Proteobacteria
Photosystem	Both photosystem 1 and photosystem 2 are used	Only photosystem 1 is used
Electron donor	Water (H2O)	Hydrogen sulphide (H2S) or Hydrogen(H2)
Electron acceptor	Oxygen (O2)	Sulphur oxidised to give Sulphuric acid
Carbon source	CO2	CO2/CH4(methane)
Metabolism	Capable of photosynthesis using water as an electron donor and produces oxygen as a byproduct	Capable of photosynthesis using hydrogen sulphide as electron donor and produces sulphur which is oxidised to give sulphuric acid
Relationship to oxygen	Oxygen is produced during light reaction	Oxygen is not produced during light reaction
Preferred Habitats	oceans, fresh water, damp soil	sulfur springs and illuminated anoxic zones of lakes
Other characteristics	ATP is produced by non-cyclic photophosphorylation Photosynthetic pigment is Chlorophyll	ATP is produced by cyclic photophosphorylation Photosynthetic pigment is Bacteriochlorophyll