Microbes in Human Welfare Question Answers: NCERT Class 12 Biology

The large holes in the ‘Swiss Cheese’ are due to production of a large amount of CO₂ by a bacterium named Propionibacterium sharmanii.  

Two microbes that are Useful in biotechnology are as follows:

1. 1. Bacillus thuringiensis is a gene isolated from this bacterium is introduced in cotton plants to make them able to kill butterfly caterpillars.
2. E. coli is a bacterium that is used in many biotechnology producers. Their plasmid is used as vector to introduce foreign DNA segment in desired organisms.

Escherichia coli strain RY 13 is the source or main organism for Eco RI.

Bt cotton is a genetically modified plant that has been modified to resist attack by insect pests. E.g. cotton ball worm. These are developed by introducing a gene from Bacillus thuringiensis which produces toxin in plants which is lethal to insects.  

Blue- green algae add organic matter to the soil that increase the fertility but still these are not popular as much as bio-fertilisers. This is due to several constraints which limit the application or implementation of the bio-fertilisers technology. The constraints can be environmental, technological, infrastructural, financial, unawareness, quality, marketing etc.  

Roquefort cheese is formed by ripening of cheese with the fungi Penicillium roqueforti for a particular flavor.  

Ganga runs from Gangotri in the Himalayas to Ganga Sagar in the Bay of Bengal. The Ganga Action Plant was a program launched in 1986, in April, in order for the reduction of pollution load in the River Ganga. The states involved in the Ganga Action Plan are – Uttaranchal, UP, Bihar, West Bengal and Jharkhand.

1. Lipases are used in formula of detergent and are helpful in removing oily stains from the clothes.
2. Pectinases and proteases that are used as clarifying agents in making commercial fruit and vegetable juices.

Cyclosporin- A, produced by the fungus Trichoderma polysporum is used as an immunosuppressive agent in organ transplant patients.   

Tobacco mosaic virus is a rod- shaped virus. This is the first plant virus to be discovered.  

Methanogens, anaerobically breaks down cellulosic material to produce CO₂ and H₂, and are found in

1. Anaerobic sludge in sewage treatment plants
2. Rumen of cattles, thus providing nutrition to cattles.  

For large scale production of biotechnological products, e.g. antibiotics, beverages in industries, microbes are grown in very large vessels called fermenters or bioreactors.

Cheese is formed by partial degradation of milk by different microorganisms. Swiss cheese is formed by the bacterium Propionibacterium sharmanii. Its characteristics feature is formation of large holes due to production of large holes due to production of large amount of CO₂.  

Stains are bioactive molecules, produced by the yeast Monascus purpureus. These bioactive molecules have been commercialized as the blood- cholesterol lowering agents. It acts through the competitively inhabiting enzyme which is responsible for the synthesis of cholesterol.    

Secondary waste water treatment is also known as biological treatment because in the breakdown of organic matter microorganisms are involved in this phase of waste water treatment.

The primary effluent is passed into the large aeration tanks where the organic matter in it is consumed by aerobic microbes which are later themselves digested by anaerobic bacteria and fungi in anaerobic sludge digesters.  

Several methods of biological control are being used in the pest management to keep the pollution free environment and yield clean, non- toxic and good quality products for human consumption.

Baculoviruses are a group of viruses which is used as biological control agents that occur naturally and are specific to some insects. Most of the baculoviruses belongs to the genus Nucleopolyhedro virus. These viruses are excellent candidates for species specific, narrow spectrum insecticidal application. They have been shown to have no negative impacts on plants, mammals, bird fish or even on non- target insects.

This is specially desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) Programme or when an ecologically sensitive area is being treated.  

Antibiotics are produced by the microbes are regarded as one of the most significant discoveries of the 20^th century and have greatly contributed towards the welfare of the human society.

Anti is a Gk. word that means ‘against’ and bio means ‘life’, together they mean ‘against life’, whereas with the reference to human beings, they are ‘pro life’ and not against. Antibiotics are the chemical substances that are produced by some microbes and which can kill or retard the growth of other microbes. Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu), and leprosy, which had killed millions all over the globe. Today, we cannot imagine a world without antibiotics because there are various vaccines which is used to bacteria by developing the immunity through these antibiotics.   

Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer both are produced without the distillation whereas whiskey, brandy and rum are produced by distillation of the fermented broth.

Distillation increases the alcohol content in alcoholic drinks. That is why for producing certain alcoholic drinks, distillation is required.

Their common characteristics is that they produce organic acids as part of their metabolism and are therefore, used for commercial and industrial production of the same.

1. Aspergillus niger for citric acid.
2. Clostridium butylicum for butyric acid.
3. Lactobacillus for lactic acid.   

If our intestine harbors microbial flora exactly similar to that found in the rumen of cattle, we woeuld be able to digest the cellulose present in our foods because the microbes present in the rumen of cattle, collectively called methanogens, are capable of digesting cellulose as they have Cellulase enzyme.  

Curd can be used as a sample for the study of microbes. Curd contains numerous lactic acid bacteria (LAB) or Lactobacillus. These bacteria produce acids that coagulate and digest milk proteins. A small drop of curd contains millions of bacteria, which can be easily observed under a microscope.

Microbes play an important role in organic farming, which is done without the use of chemical fertilizers and pesticides. Bio-fertilizers are living organisms which help increase the fertility of soil. It involves the selection of beneficial micro-organisms that help in improving plant growth through the supply of plant nutrients. Bio-fertilizers are introduced in seeds, roots, or soil to mobilize the availability of nutrients. Thus, they are extremely beneficial in enriching the soil with organic nutrients. Many species of bacteria and cyanobacteria have the ability to fix free atmospheric nitrogen. Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc andOscillitoria are examples of nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effective and eco-friendly.

Microbes can also act as bio-pesticides to control insect pests in plants. An example of bio-pesticides is Bacillus thuringiensis, which produces a toxin that kills the insect pests. Dried bacterial spores are mixed in water and sprayed in agricultural fields. When larvae of insects feed on crops, these bacterial spores enter the gut of the larvae and release toxins, thereby it. Similarly,Trichoderma are free living fungi. They live in the roots of higher plants and protect them from various pathogens.

Baculoviruses is another bio-pesticide that is used as a biological control agent against insects and other arthropods.

Biological oxygen demand (BOD) is the method of determining the amount of oxygen required by micro-organisms to decompose the waste present in the water supply. If the quantity of organic wastes in the water supply is high, then the number of decomposing bacteria present in the water will also be high. As a result, the BOD value will increase.

Therefore, it can be concluded that if the water supply is more polluted, then it will have a higher BOD value. Out of the above three samples, sample C is the most polluted since it has the maximum BOD value of 400 mg/L. After untreated sewage water, secondary effluent discharge from a sewage treatment plant is most polluted. Thus, sample A is secondary effluent discharge from a sewage treatment plant and has the BOD value of 20 mg/L, while sample B is river water and has the BOD value of 8 mg/L.

Hence, the correct label for each sample is:

(a) Single cell protein (SCP)

A single cell protein is a protein obtained from certain microbes, which forms an alternate source of proteins in animal feeds. The microbes involved in the preparation of single cell proteins are algae, yeast, or bacteria. These microbes are grown on an industrial scale to obtain the desired protein. For example, Spirulina can be grown on waste materials obtained from molasses, sewage, and animal manures. It serves as a rich supplement of dietary nutrients such as proteins, carbohydrate, fats, minerals, and vitamins. Similarly, micro-organisms such as Methylophilus and methylotrophus have a large rate of biomass production. Their growth can produce a large amount of proteins.

(b) Soil

Microbes play an important role in maintaining soil fertility. They help in the formation of nutrient-rich humus by the process of decomposition. Many species of bacteria and cyanobacteria have the ability to fix atmospheric nitrogen into usable form.Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria.

The order of arrangement of products according to their decreasing importance is:

Penicillin- Biogas − Citric acid − Curd

Penicillin is the most important product for the welfare of human society. It is an antibiotic, which is used for controlling various bacterial diseases. The second most important product is biogas. It is an eco-friendly source of energy. The next important product is citric acid, which is used as a food preservative. The least important product is curd, a food item obtained by the action oflactobacillus bacteria on milk. 

Hence, the products in the decreasing order of their importance are as follows:

Penicillin- Biogas − Citric acid − Curd

Bio-fertilizers are living organisms which help in increasing the fertility of soil. It involves the selection of beneficial micro-organisms that help in improving plant growth through the supply of plant nutrients. These are introduced to seeds, roots, or soil to mobilize the availability of nutrients by their biological activity. Thus, they are extremely beneficial in enriching the soil with organic nutrients. Many species of bacteria and cyanobacteria have the ability to fix free atmospheric nitrogen. Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants. Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria. Bio-fertilizers are cost effective and eco-friendly.

The examples of bacteria that release gases during metabolism are:

(a) Bacteria and fungi carry out the process of fermentation and during this process, they release carbon dioxide. Fermentation is the process of converting a complex organic substance into a simpler substance with the action of bacteria or yeast. Fermentation of sugar produces alcohol with the release of carbon dioxide and very little energy.

(b) The dough used for making idli and dosa gives a puffed appearance. This is because of the action of bacteria which releases carbon dioxide. This CO₂ released from the dough gets trapped in the dough, thereby giving it a puffed appearance.

Lactic acid bacteria can be found in curd. It is this bacterium that promotes the formation of milk into curd. The bacterium multiplies and increases its number, which converts the milk into curd. They also increase the content of vitamin B₁₂ in curd.

Lactic acid bacteria are also found in our stomach where it keeps a check on the disease-causing micro-organisms.

     1.  Wheat:

Product: Bread, cake, etc.

2.      Rice:

Product: Idli, dosa

3.      Bengal gram:

Product: Dhokla, Khandvi

Several micro-organisms are used for preparing medicines. Antibiotics are medicines produced by certain micro-organisms to kill other disease-causing micro-organisms. These medicines are commonly obtained from bacteria and fungi. They either kill or stop the growth of disease-causing micro-organisms. Streptomycin, tetracycline, and penicillin are common antibiotics. Penicillium notatumproduces chemical penicillin, which checks the growth of staphylococci bacteria in the body. Antibiotics are designed to destroy bacteria by weakening their cell walls. As a result of this weakening, certain immune cells such as the white blood cells enter the bacterial cell and cause cell lysis. Cell lysis is the process of destroying cells such as blood cells and bacteria.

Antibiotics are medicines that are produced by certain micro-organisms to kill other disease-causing micro-organisms. These medicines are commonly obtained from bacteria and fungi.

The species of fungus used in the production of antibiotics are:

Sewage is the municipal waste matter that is carried away in sewers and drains. It includes both liquid and solid wastes, rich in organic matter and microbes. Many of these microbes are pathogenic and can cause several water- borne diseases. Sewage water is a major cause of polluting drinking water. Hence, it is essential that sewage water is properly collected, treated, and disposed.

Yes, microbes can be used as a source of energy. Bacteria such as Methane bacterium is used for the generation of gobar gas or biogas.

The generation of biogas is an anaerobic process in a biogas plant, which consists of a concrete tank (10−15 feet deep) with sufficient outlets and inlets. The dung is mixed with water to form the slurry and thrown into the tank. The digester of the tank is filled with numerous anaerobic methane-producing bacteria, which produce biogas from the slurry. Biogas can be removed through the pipe which is then used as a source of energy, while the spent slurry is removed from the outlet and is used as a fertilizer.