NCERT Questions for Class 12 Biology Chapter 8 – Microbes in Human Welfare

Important Questions with Solutions of Class 12 Biology Chapter 8 – Microbes in Human Welfare

1) Define the BOD (Biochemical Oxygen Demand) test. Explain at which stage the test will be held for sewage treatment. Out of these three samples of water labeled as A (30mg/L), B (10mg/L), and C (500mg/L) which is most polluted?

Ans –

• BOD is responsible for confirming the oxygen absorption in water by microorganisms.
• Either secondary treatment or biological treatment.
• BOD is maximized in sample C & is the most polluted.

2) Define biofertilizers. Mention the bacterium added by the farmer before sowing the crop and state its uses.

Ans – Talking about biofertilizers:

• They are organisms enhancing the nutrients portion of the soil thus adding to the quality.
• In bacterium there is the presence of Azotobacter/Azospirillum.
• Used as fertilizer for plants, atmospheric nitrogen is turned into organic molecules.

3) Define stains & name the microorganisms causing them. State their medical importance.

Ans – Cholesterol-lowering drugs (Yeast), produce stains by the action of Monascuspurpureus. It stops the enzymes from cholesterol creation and can lower the blood cholesterol.

4) Define Biogas. Explain its production and the names of microbes used in this process.

Ans – Anaerobic fermentation of waste biomass produces biogas. It has methane, CO2, hydrogen, nitrogen, oxygen, and hydrogen sulfide.

Microbes often involved in this process are:

1. Hydrolytic bacteria like cellulomonas, clostridium, etc.
2. Bacteria producing hydrogen sulfide like syntrophomonas wolfei.
3. Methanogenic bacteria like methanobacterium omelianskii.

A concrete tank feeds the biogas plant. When gas is produced in the tank, as a microbial activity there is a rise in the slurry covered with a floating cover. The biogas spreads to the surroundings as an output to the biogas plant when connected to a pipe. The organic biodegradable solid waste is changed by the microbes when the humus is generated with the energy deriving as the biogas during the biogas production.

CO + H₂0 ➡ CO₂ + H₂

CO₂ + 4H₂ ➡CH₄ + 2H₂O

CH₃OH ➡ CH₄ + O₂

5) How are microbes used to decrease the use of chemical fertilizers and pesticides?

Ans – Poisonous chemicals harmful to humans and the environment are used to fight plant diseases and pests in modern society. In agriculture also pesticides are removed using natural predation i.e. pest control which includes managing butterflies, caterpillars, and other insects.

Bacillus thuringiensis (Bt.) is available as dried bacteria spores in sachets diluted in water and sprinkled in sensitive parts like the brassicas, the location of the consumption of the larvae, in which intestines toxins are then released to kill them. As a result of the bacterial sickness, the caterpillar dies but other insects survive.

6) Explain:

1. Biofertilizers enrich the fertility of soil.
2. Cyanobacteria act as biofertilizers.

Ans – a) “biofertilizers” are microorganisms acting on biological channels to enhance soil fertility for optimal crop development. These biofertilizers can add to crop output by:

1. Omission of nitrogen from the atmosphere.
2. Solubilization of insoluble fertilizer.
3. Promotion of the development of plants.
4. Absorbing of phosphorus.
5. Decomposition of plant remnants.

b) Cyanobacterium found in the leaf cavity of the water fern, Anabaena manages nitrogen content in the air and expels nitrogenous compounds in the leaf cavity.

7) Elaborate:

1. Primary sludge differs from activated sludge.
2. Changes in the sludge by anaerobic sludge digester.

State the content of biogas manufactured in the sewage treatment plant.

Ans – As sewage treatment, the primary sludge with solids like soil and small stones accumulates in the tank. This sediment of bacterial flocs accumulated in the tank undertakes biological treatment known as activated sludge.

Flocs are a combination of slime and fungal filaments, binding bacteria. This is further divided into two portions. First, the activated sludge is used as inoculum in the aeration tank. The second portion is sent back to the big tank i.e. the anaerobic sludge digester.

The consumption of the bacteria, fungus, and cellulose in the sludge is done by other bacteria. The quantity of biogas is methane, hydrogen, and carbon dioxide merged in sewage treatment plants.

Key points in Class 12 Biology Chapter 8 – Microbes in Human Welfare

What are Microbes?

Diversity in microbes includes bacteria, fungi, viruses, and protozoa. While many microbes have the potential to cause disease, there are others that are beneficial for human beings, contributing to several important processes. These range from the use of bacteria in the production of foods and cleaning up the environment to producing antibiotics.

Applications of Microbes in Human Welfare

Food Production: Microbes in the production of food items such as yogurt, cheese, bread, etc. They use fermentation processes to convert raw material into nutritional and savory products.

Waste Management: Some microbes can decompose organic matter and thus help in waste decomposition and recycling.

Biotechnology: Microbes have large applications in biotechnological works, particularly in the production of enzymes, vaccines, and genetically modified organisms. They are also used in genetic engineering and in research.

Importance of this Chapter

Knowing the microbes is very important to understand their interrelation with human welfare and the environment. Students get an overview of class 12 biology Chapter 8, where uses of microbes in industries and other vital processes have been shown. It’s a very significant fact to know while making decisions and further improvements in fields like biotechnology or healthcare. The chapter of NCERT Chapter 8 is available in PDF format.