Question

If bacteria do not have chloroplasts, then how do they perform photosynthesis?

Answer 1

Hint: Photosynthesis is a chemical process used by green plants and few other organisms to convert light energy into chemical energy. The sugar produced by this process is converted into ATP.

Complete answer:
Photosynthesis is the phenomenon of conversion of light energy to chemical energy. The chemical energy is stored in the form of sugars in the organisms. Sunlight functions as the main source of light energy, while carbon dioxide and water are the main reactants. In the presence of sunlight, carbon dioxide and water react to form sugar molecules. The water molecules are split into hydrogen and oxygen molecules. The hydrogen molecules react with carbon dioxide and reduce them to form sugar molecules. Photosynthesis is a redox mechanism where carbon dioxide is reduced to form sugar molecules, and water molecules are oxidized to form oxygen molecules. The molecular oxygen is released as a byproduct.
In eukaryotic organisms, this occurs in the chloroplasts present in the mesophyll cells of the green leaves. Prokaryotic organisms lack double membranous structures but, still, few prokaryotic organisms like bacteria perform photosynthesis.

Photosynthesis in bacteria occurs in their photosynthetic plasma membranes. The plasma membranes of these bacteria are infolded to form a thylakoid-like structure where the chloroplasts can attach themselves. These infoldings of the plasma membrane have all of the necessary components required for photosynthesis. These structures are not enclosed in any membrane-bound organelle but have photosynthetic pigments that are organized to form photosystems. These photosystems have reaction centers and a light-harvesting complex within them, and the conversion of chemical energy from light energy occurs there. The reaction centers are arranged in sacs, or tubes, or sheets. These bacteria reduce carbon dioxide to form sugar molecules through the Calvin cycle. They can also use hydrogen sulfide as an electron donor.

The most common example of photosynthetic bacteria is Cyanobacteria or Blue-green algae. They are the most diverse group of bacteria and live in all forms of water. They use sunlight to prepare their food through the process of photosynthesis. The chlorophyll is stored in the infoldings of the plasma membrane, also called the thylakoid membrane.
Other examples of photosynthetic bacteria are- purple sulfur bacteria and green sulfur bacteria.

Note: The evolutionary studies show that the origin of photosynthesis in the eukaryotic organisms occurred from the photosynthetic prokaryotic bacteria. Stromatolites- the first organisms to perform photosynthesis, closely resemble the structure of cyanobacteria. Cyanobacteria are considered the first living photosynthetic organisms on the earth.