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Q2:
Give examples to prove that microbes release gases during metabolism.
Solution :
Theoretical Foundation: Microbial Metabolic Pathways
Microbes, such as bacteria and fungi (yeasts), generate gases as metabolic byproducts during the process of anaerobic respiration or fermentation. These gases are released when microorganisms catabolize organic substrates (like sugars) in the absence of oxygen, utilizing metabolic pathways such as the Embden-Meyerhof-Parnas (EMP) pathway followed by specialized fermentation. [Per the principles of Cellular Respiration and Biochemistry].
Step 1: Analysis of Carbon Dioxide ($CO_2$) in Fermentation
In the process of baking, the yeast Saccharomyces cerevisiae (Baker’s yeast) is added to dough containing carbohydrates. The yeast undergoes fermentation, resulting in the production of ethanol and carbon dioxide gas:
$C_6H_{12}O_6 \xrightarrow{Zymase} 2C_2H_5OH + 2CO_2 \uparrow$
The released $CO_2$ gas gets trapped in the gluten-rich dough, causing it to rise (leaven), which provides visual evidence of microbial gas release. [By the Principle of Alcoholic Fermentation].
Step 2: Analysis of Carbon Dioxide ($CO_2$) in Dairy Processing
In the production of "Swiss cheese," the bacterium Propionibacterium sharmanii is utilized. This bacterium ferments lactate into propionic acid, acetic acid, and large quantities of carbon dioxide gas:
$CH_3CHOHCOOH \rightarrow CH_3CH_2COOH + CH_3COOH + CO_2 \uparrow$
The accumulation of this $CO_2$ gas within the cheese matrix creates the characteristic "large holes" observed in Swiss cheese. [Per Microbiology of Food Science].
Step 3: Analysis of Methane ($CH_4$) in Methanogenesis
Methanogens, such as Methanobacterium, are anaerobic archaea found in the rumen of cattle and in sewage treatment plants. They reduce $CO_2$ using hydrogen to produce methane gas ($CH_4$):
$CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$
This gas, commonly known as biogas or swamp gas, is highly combustible and provides definitive experimental proof of metabolic gas production. [Per the Law of Conservation of Mass in Biochemical Reactions].
Visual Representation of Microbial Gas Accumulation
Comparative Summary Table
| Microorganism | Process | Gas Released | Observable Effect |
|---|---|---|---|
| S. cerevisiae | Fermentation | $CO_2$ | Leavening of dough |
| P. sharmanii | Propionic fermentation | $CO_2$ | Large holes in Swiss cheese |
| Methanobacterium | Methanogenesis | $CH_4$ | Biogas production |
Final Solution: Microbes release gases as metabolic byproducts; specific examples include the release of $CO_2$ by Saccharomyces cerevisiae in bread making, the release of $CO_2$ by Propionibacterium sharmanii in Swiss cheese production, and the release of $CH_4$ by methanogenic bacteria during anaerobic digestion.
More Questions from Class 12 Biology Microbes in Human Welfare EXERCISES
- Q1: 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 with the help of a microscope, which sample would you carry and why?
- Q1: 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 with the help of a microscope, which sample would you carry and why?
- Q2: Give examples to prove that microbes release gases during metabolism.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q8: What is the key difference between primary and secondary sewage treatment?
- Q8: What is the key difference between primary and secondary sewage treatment?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q11: 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?
- Q11: 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?
- Q12: Find out the name of the microbes from which Cyclosporin \(A\) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q12: Find out the name of the microbes from which Cyclosporin (A) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(b): Find out the role of microbes in the following and discuss it with your teacher. (b) Soil
- Q13(b): Find out the role of microbes in the following and discuss it with your teacher. (b) Soil
- Q14: 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
- Q14: 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
- Q15: How do biofertilisers enrich the fertility of the soil?
- Q15: How do biofertilisers enrich the fertility of the soil?
CBSE Solutions for Class 12 Biology Microbes in Human Welfare
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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