Uses of microorganisms - class-XI

Antibiotics are chemical substances, which are produced by some microbes and kill or retard the growth of other ( disease-causing ) microbes. Penicillin was the first antibiotic discovered. Penicillin inhibits bacterial growth by inhibiting cell wall formation, hence, killing the bacteria.

Nostoc is a cyanobacterium. Along with bacteria, Nostoc belongs to the prokaryotic organisms as they do not possess the well-defined nucleus and double membrane-bound organelles. In statement 2, Penicillium is a fungus but Spirogyra is an alga. Thus, the correct option is A.

An antibiotic is a type of antimicrobial substance active against bacteria and is the most important type of antibacterial agent for fighting bacterial infections. Antibiotic medications are widely used in treatment and prevention. They have an important role in dental antibiotic prophylaxis where their use may prevent. So, the correct option is "A" (Prevention of the growth of bacteria).

In 1857, Pasteur showed that lactic acid fermentation is caused by living organisms, In 1877, working to improve the French brewing industry, Pasteur published his famous paper on fermentation,"Studies on fermentation". He defined fermentation (incorrectly) as "Life without air",but correctly showed that specific types of microorganisms cause specific types of fermentations and specific end-products.

The sugarcane is a plant which belongs to the group of monocots. The plant contains a high amount of sugar. The juice from this plant or the molasses can be used for the process of alcohol formation. The sucrose which is present in the plant is fermented to produce ethanol by the process of anaerobic fermentation. 

Alcohol is commercially produced using a process called as fermentation. In alcoholic fermentation, pyruvate from glycolysis is converted to acetaldehyde and then to ethanol and carbon dioxide. So, the correct answer is option C.

Fermentation is accompanied by the liberation of carbon dioxide gas. The process is used in baking breads because the liberated carbon dioxide helps the dough to rise. 

In a strenuous workout, the oxygen supply to the body tissues is not received completely. To produce the necessary energy in the absence of oxygen, the pyruvate molecule at the end of glycolysis is utilised in fermentation to produce lactic acid.

• Rhizobium is a nitrogen fixation bacteria found in soil.
• Penicillium is an antibiotic used for making medicines and antibiotics.

Pyruvate is the output of glycolysis where one molecule of glucose breaks down into two molecules of pyruvate. Anaerobically, pyruvic acid is broken down to form lactate in animals and ethanol  in plants and microorganisms. In alcoholic fermentation, pyruvate from glycolysis is converted to acetaldehyde and then ethanol and carbon dioxide. Ethanol fermentation which is a biological process of converting sugars to cellular energy is performed by yeasts in the absence of oxygen. hence this is considered as a anaerobic process. 

In non biological fixation of nitrogen when the plant dies the fixed nitrogen is released making it available to other plants and this helps to fertilize the soil. The great majority of legumes have this association but a few genera do not. In farming practices fields are rotated through various crops like clover and buckwheat which are known as green manure.

By the use of Haber process, fixation of nitrogen can be done artifically.

Phosphate rock is too insoluble for direct use, and is commonly treated with sulfuric acid to make a mixture of calcium sulfate and the more soluble calcium hydrogen phosphate, called superphosphate.The use of superphosphate usually supplies adequate calcium. 

Nitrogen fixation is a process in which nitrogen(N₂) in the atmosphere is converted into ammonia (NH₃) and useful compounds. Atmospheric nitrogen or molecular dinitrogen (N₂) is relatively inert: it does not easily react with other chemicals to form new compounds.