Question

QUESTION 4 [10] Write briefly on the process of photosynthesis as it occurs in bacteria. QUESTION 5 [20] Discuss on the role of alcohol, lactic acid, and mixed acids during fermentation.

Answer 1

4. Photosynthesis is the physico-chemical process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds.

Photosynthetic bacterias are special types of bacteria that contain light absorbing pigments and reaction centers which make them capable of converting light energy into chemical energy.

Cyanobacteria contain chlorophyll while other forms of bacteria contain bacteriochlorophyll. Although bacteriochlorophyll resembles chlorophyll, it absorbs light of a longer wavelength than chlorophyll. Bacteriochlorophyll a is the most common form of bacteriochlorophyll but other forms include b, c, d, e, f and g.

Bacteria that contain bacteriochlorophyll do not use water as an electron donor and therefore do not produce oxygen. This is known as anoxygenic photosynthesis. Cyanobacteria perform photosynthesis using water as an electron donor in a similar manner to plants. This results in the production of oxygen and is known as oxygenic photosynthesis.

Classification of Photosynthetic Bacteria
Oxygenic photosynthetic bacteria perform photosynthesis in a similar manner to plants. They contain light-harvesting pigments, absorb carbon dioxide, and release oxygen. Cyanobacteria or Cyanophyta are the only form of oxygenic photosynthetic bacteria known to date. There are, however, several species of Cyanobacteria. They are often blue-green in color and are thought to have contributed to the biodiversity on Earth by helping to convert the Earth’s early oxygen-deficient atmosphere to an oxygen-rich environment. This transformation meant that most anaerobic organisms that thrived in the absence of oxygen eventually became extinct and new organisms that were dependent on oxygen began to emerge.

Cyanobacteria are mostly found in water but can survive on land, in rocks, and even in animal shells (or fur), and in coral. They are also known to be endosymbiont, which means they can live within the cells or body of another organism in a mutually beneficial way. Cyanobacteria also tend to live in extreme weather conditions, such as Antarctica, and are interesting to scientists because they may indicate a chance for life on other planets such as Mars.

Anoxygenic photosynthetic bacteria consume carbon dioxide but do not release oxygen. These include Green and Purple bacteria as well as Filamentous Anoxygenic Phototrophs (FAPs), Phototrophic Acidobacteria, and Phototrophic Heliobacteria.

5.Fermentation is an alternative energy yielding process for respiration, which is preferred by organisms that are facultative or obligate anaerobes.

Fermentation is mainly classified under 2 categories; alcoholic and lactic acid.

The former occurs when the byproduct pyruvate is converted to ethanol and carbon dioxide. On the other hand, in the latter type, pyruvate is converted to lactic acid

The main purpose of alcohol fermentation is production of ATP, the energy currency for cells.It takes place under anaerobic conditions.

Carbon dioxide and ethanol are waste products from the perspective of yeast.

Fermentation of lactic acid is a common cellular process, which takes place in many bacteria, yeast, and human muscle cells.Lactic acid fermentation is an alternative pathway to produce energy under low oxygen conditions, especially due to severe straining or extreme exercising. The muscles get deprived of oxygen, causing the cells to undertake the lactic acid pathway for quicker energy requirements. The result is production of lactic acid in these parts leading to stiffness or cramps.

The bacteria that make yogurt carry out lactic acid fermentation.

Mixed acid fermentation occur when bacteria utilize two or more different pathways in the terminal steps of fermentation.

Enteric Gammaproteobacteria like E. coli are facultative anaerobes and so use aerobic respiration in the presence of oxygen and anaerobic respiration if there are suitable alternative electron acceptors such as nitrate, fumarate and TMAO that they are able to utilize.

In the absence of acceptors like nitrate, fumarate and TMAO these bacteria will ferment glucose to a mixture of acetate, formate, lactate and succinate acids plus ethanol