Microbes In Human Welfare Class 12th Biology CBSE Solution

Class 12th Biology CBSE Solution

Exercises
Question 1.

Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes under a microscope, which sample would you carry and why?


Answer:

Curd can be preferred as sample from home to observe bactaria in laboratory. A small amount of curd contains large amount of lactobacillus which could be observed under light microscope using normal staining methods. Lactobacillus also known as lactic acid bactaria. They convert milk into curd by producing lactic acid.



Question 2.

Give examples to prove that microbes release gases during metabolism.


Answer:

Fungi and bactaria can breakdown organic compounds using fermentation. They release CO2 during this process. Common examples which show microbes release gases are:


• Dough of idli and dosa gives puffed up appearance because of release of CO2 during the process of fermentation by bactaria.


• Dough of bread is puffed up because of fermatation by Saccharomyces cerevisiae.


• The large holes in Swiss cheese are caused due to production of a large amount of CO2 during fermentation by a bacterium named Propionibacterium sharmanii.



Question 3.

In which food would you find lactic acid bacteria? Mention some of their useful applications.


Answer:

Lactic acid bactaria produce lactic acid by fermentation.


• They are found in curd, they are responsibe for formation of curd from milk by producing lactic acid.


• In humans, they have flora in oral cavity. intestinal tract and vagina where they play a benificial role.


• They are also present in decaying plants


• They have several applications especially in fermentation industry. LAB are involved in making yogurt, cheese, cultured butter, sour cream, sausage, cucumber pickles, olives and sauerkraut.



Question 4.

Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.


Answer:

Some of the traditional Indian fermented foods are:


• Made from wheat: Filebi, Seera, Bhaturu, Kulcha, gulgule


• Made from rice: Idli, dosa, chitou, torani, aska, selroti


• Made from bengal gram: dhokla, khaman



Question 5.

In which way have microbes played a major role in controlling diseases caused by harmful bacteria?


Answer:

Microbes help in various ways in controlling and fighting diseases


• Many microbes are involved in production of antibiotics. Antibiotics are chemicals that are produce by some microbes ( most commonly bactaria and fungi) that kill other microbes.


• Microbiome in our body protect us from pathogens just by taking space.


• Microbes have shown to protect us from auto-immune diseases.



Question 6.

Name any two species of fungus, which are used in the production of the antibiotics.


Answer:

Many microbes are involved in production of antibiotics. Antibiotics are chemicals that are produce by some microbes ( most commonly bactaria and fungi) that kill other microbes.


• Penicillium chrysogenum- produces antibiotic penicillin which is effective against several bactarial infections by staphylococci and streptococci


• Cephalosporium- produces cephalosporins hamper the formation of peptidoglycan layer in bactaria and hence, act as a antibiotic against them.



Question 7.

What is sewage? In which way can sewage be harmful to us?


Answer:

Sewage is municipal waste water which contains large amount of organic matter and microbes. Many of this microbes are pathogenic and hence, sewage cannot be directly poured into water bodies from where the water is used for daily purposes. It should be treated properly in sewage treatment plants and then used.



Question 8.

What is the key difference between primary and secondary sewage treatment?


Answer:

Primary sewage treatment is to remove large and small solids through filtration and sedimentation while secondary treatment also known as biological treatment used microbes to consume organic matter. Primary treatment reduces BOD upto 20 to 30 percent. Secondary treatment reduces BOD upto 80 percent.



Question 9.

Do you think microbes can also be used as source of energy? If yes, how?


Answer:

Definitely, microbes can be used in production of energy. Methanogens are bactarium that are involved in production of biogas which is commonly known as gobar gas.


A typical biogas plant is made up of a concrete tank which is 10-15 feet deep in which


bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet that is connected through a pipe to supply biogas to nearby houses.


• Also certain microbes such as Saccharomyces cerevisiae are involved in prodution of bioethanol that helps in reduction of CO2 emission.



Question 10.

Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.


Answer:

Various bactaria, fungi and cyanobactaria are used in organic farming instead of chemical fertilizers and pesticides. Biofertilizers are organisms that help in enriching the soil with nutrients.


• Rhizobium, Azospirillum and Azotobacter help in nitrogen fixation and hence, enrich the soil with nitrogen.


• Fungi such as mycorrhiza form symbiont relationship with plants and absorbs phosphorus from soil and passes it to the plant.


• Cyanobactaria help in nitrogen fixation and is an important biofertilizer.


• Blue green algae adds organic matter to the soil.


• Bio-pesticides such as Bacillus thuringiensis produces a toxin that kills the insect pests


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



Question 11.

Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?


Answer:

BOD (Biochemical Oxygen Demand) is the determination the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.The higher the BOD, higher is the pollution potential of water.


The highest BOD is of sample C and hence, it will be untreated sewage water which is the most polluted . The river water should have least BOD hence, it will be the sample B. The seconday effluent would have higher BOD than river water by less than that of untreated sewage and hence, it is the sample A.


• Sample A- secondary effluent


• Sample B- river water


• Sample C- untreated sewage



Question 12.

Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.


Answer:

• Cyclosporin A is produced by Trichoderma polysporum and Cylindrocarpon lucidum which lowers the activity of T-cells of immune system.


• Statins are obtained from Aspergillus terreus and Phoma sp. which reduce production of Low Density Cholesterol in liver.



Question 13.

Find out the role of microbes in the following and discuss it with your teacher.

(a) Single cell protein (SCP)

(b) Soil


Answer:

a) Single cell protein (SCP): They are the dried cells of micro organisms that are used as animal feed and dietary protein supplement. The micro-organisms used belong to bactaria, fungi and algae. Aspergillus nigerSaccharomyces cerevisiae and others are used in its production.


b) Soil: Microbes play an important role in maintaining the fertility of soil. Bactaria, fungi and cyanobactaria are mainly involved in it. Certain microbes such as Rhizopus help in nitrogen fixation.



Question 14.

Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.

Biogas, Citric acid, Penicillin and Curd


Answer:

The importance of substances in decreasing order is


Pencillin, Biogas, Curd and Citric acid


Pencillin is an important antibiotic which helps in fighting against various bactaria; infections , hence , it is important for human welfare. Biogas is an eco friendly source of energy and helps in curbing pollution. Curd is a souce of Vitamin B12 and it has several benefits as food. Citric acid is used as a preservative in food industry.



Question 15.

How do biofertilisers enrich the fertility of the soil?


Answer:

Biofertilizers are organisms that help in enriching the soil with nutrients. Example of few microbes that are common biofertilizers are as below:


• Rhizobium, Azospirillum and Azotobacter help in nitrogen fixation and hence, enrich the soil with nitrogen.


• Fungi such as mycorrhiza form symbiont relationship with plants and absorbs phosphorus from soil and passes it to the plant.


• Cyanobactaria help in nitrogen fixation and is an important biofertilizer.