Microbes in Human Welfare Question Answers: NCERT Class 12 Biology

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.

Aerobic degradation is more important as naturally occurring aerobic and facultative microbes (bacteria, fungi, Protozoa and others) in the waste water can rapidly oxidize soluble organic and nitrogenous compounds. Mechanical addition of oxygen helps in making the process faster and most of the pathogenic content of the effluent is then removed.  

Chemicals from fertilisers and pesticides are highly toxic to human beings and animals alike and have been polluting our environment. For the reduction of environmental degradation which is caused by chemical, microbes, can be used both as fertilisers and pesticides and can be known as bio-fertilisers and bio-pesticides, simultaneously.

Microbes are used as bio-fertilisers to enrich the soil nutrients example: Rhizobium, Azotobacter, Azospirillum etc. which can fix atmospheric nitrogen in the soil. Bacillus thuringiensis bacteria acts as bio-pesticides to control the growth of the insect pests.

Trichoderma, fungal species, is effective biocontrol agents of several plant pathogens. Baculovirus used as biological control agents in genus Nucleopolyhedrovirus are excellent for species specific, narrow spectrum insecticidal applications.   

A broad spectrum antibiotic that can inhibits the growth of both Gram positive and Gram negative bacteria. Examples: Tetracyclins, phenicols, fluoroquinolones, third generation and fourth generation antibiotics is cephalosporins which is commonly known.  

Viruses parasitizing bacteria are called bacteriophages. These viruses do not actually eat bacteria, they directly infect and replicates within the bacteria.  

The Streptococcus bacterium which produces Streptokinase is used as an ‘Clot buster’. This enzyme has a fibrinolytic activity that breaks down the clots which formed in the blood vessels of patients who have undergone myocardial infraction. This helps in the prevention of heart attacks in these patients that can otherwise occur because of occlusion by the clots.  

Bio-fertilisers are the organisms that enrich the nutrient quality of the soil. The main source of bio- fertilizers are bacteria, fungi and cyanobacteria.

Examples:

1. Azospirillum, Rhizobium and Azotobacter can fix atmospheric nitrogen in the soil.
2. Blue green algae like Anabaena, Nostoc, Occilatoria add organic matter to the soil and responsible for increase its fertility.    

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.  

a. Prior to year1985, only few cities and towns had sewage treatment plants. Most of the sewage water of urban as well as rural areas was discharged directly into rivers resulting in their pollution. Importance of microbial treatment of sewage was then released and more sewage treatment plants were established.

Still, they are not sufficient due to increasing urbanization and production of much larger quantities of sewage as when compared to the earlier days. By realizing the importance of microbes in the control of pollution, the Ministry of Environment and Forests has initiated development of sewage treatment plants under the National River Conservation Authority.

b. The Ganga Action Plan (GAP) was a program launched in 1986, in April, in order for the reduction of pollution load on the river. A steering committee of the National River Conservation Authority reviewed the progress of the GAP and necessary correction.

Scientists and religious leaders formed a theory on the causes of the river’s apparent self -purification effect, in which diseases that was water borne such as dysentery and cholera are eliminated by killing thin caused organisms. Thus, by this prevention occurs from large scale epidemics.

Some studies have reported that the river retains more oxygen than is typical for comparable rivers; this could be important factor that leads to fewer disease agents which are being present in the water. National River Ganga Basin Authority (NRGBA) was established by the Central Government of India, on 20^th February 2009 under section 33 of the Environment Protection Act, 1986. It is also declared as the National river of India.

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.  

The raw material for biogas production is excreta, i.e. dung of cattle. The biogas plant has a concrete tank (10- 15 feet deep) in which bio- wastes and slurry of dung is collected.

The tank has a floating cover which rises on production of gas in the tank Methano- bacterium in the dung act on the bio- wastes to produce biogas. The gas produces is supplied to nearby houses by an outlet. Through another outlet, they spent slurry is removed to be used as fertilizer. Biogas is used for cooking and lightening.   

It’s a natural and eco- friendly concept. It employs the use of organisms for the population control of pathogens and pests in an ecosystem. Classical examples are Trichoderma which is antagonist, i.e. against many soil borne plant pathogens.

Similarly, Penicillium inhabits the growth of Staphylococcus and therefore has been successfully used in the production of penicillin antibiotic to control human bacterial pathogens. Bacillus thuringiensis acts as bio-pesticide to control insect.

Baculovirus is used as an biological control agents for the genus Nucleo- polyhedovirus which are excellent for species- specific- narrow spectrum insecticidal application. The overall biological control of pests is considered much more beneficial in an ecological sensitive area.    

1. If untreated sewage is discharged directly into rivers, it will lead to serious water pollution with the organic matter and pathogenic bacteria, Protozoa and many other diseases. The water, is used, will cause outbreaks of water borne diseases.
2. In anaerobic sludge digestion, anaerobic bacteria, digest the aerobic bacteria and the fungi in the sludge and the remaining organic matter.

During this digestion, bacteria produce a mixture of gases like methane, hydrogen sulphide and carbon dioxide. These gases, biogas can be used as source of energy.  

The most common food item that are curd, yoghurt contains Lactic Acid Bacteria (LAB) of Lactobacillus species. Curd is formed by adding a small amount of curd to milk, which acts as a starter. Microbes present in starter multiply at suitable temperature and convert milk into the curd.

Acids releases by LAB during the growth coagulation and partially digest milk protein, casein thus increased the digestibility of milk protein.

Application of LAB:

1. Improves nutritional quality of milk by increasing Vitamin B₁₂.
2. Checks disease- causing microbes in stomach.

Some bioactive molecules of fungal origin have been reported for their role in restoring good health of humans.

Fungus Trichoderma polysporum produces Cyclosporin- A which is used as an immunosuppressive agent in organ transplant patients. Yeast Monococcus purpureus produces Statins that have been commercialized as blood cholesterol lowering agents.   

Lipases enzyme were used in the formulation of detergent that cause breakdown of oils and thus help in removing oily and greasy stains from the clothes. These are obtained from Candia lipolytica and Geotrichum candidum.  

The chemical nature of biogas is CH₄, CO₂, H₂ and a trace amount of H₂S Methanobacteria, a type of methanogen is employed for biogas production.