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Q2:
Give examples to prove that microbes release gases during metabolism.
Solution :
1. Physiological Mechanism of Microbial Respiration
Microbes, specifically yeast and various bacteria, utilize metabolic pathways such as fermentation and anaerobic respiration to generate ATP. During these processes, intracellular enzymatic reactions lead to the production of volatile gaseous byproducts, most notably carbon dioxide ($CO_2$). These gases are released into the surrounding medium or substrate, providing the chemical foundation for industrial applications in food science and bioenergy.
2. Empirical Examples of Gas-Producing Microbes
| Process/Product | Microbial Agent | Gas Released | Mechanism |
|---|---|---|---|
| Dough Fermentation (Bread) | Saccharomyces cerevisiae | $CO_2$ | Ethanolic fermentation |
| Swiss Cheese Production | Propionibacterium sharmanii | $CO_2$ | Propionic acid fermentation |
| Biogas Production | Methanogens (e.g., Methanobacterium) | $CH_4, CO_2, H_2$ | Anaerobic methanogenesis |
3. Detailed Analysis of Specific Metabolic Reactions
Step 1: Alcoholic Fermentation in Dough
Baker’s yeast, Saccharomyces cerevisiae, performs anaerobic respiration on the sugars present in flour. The metabolic equation is defined as:
$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + 2ATP$ [Per Glycolysis and Fermentation pathways]
The accumulation of $CO_2$ gas within the dough matrix leads to the formation of air pockets, causing the dough to "rise" or become aerated.
Step 2: Large Hole Formation in Swiss Cheese
The characteristic large holes in Swiss cheese are created by the rapid release of $CO_2$ gas by the bacterium Propionibacterium sharmanii during the maturation process. As the gas is trapped within the protein curd, it creates distinct gas pockets [Visual representation of gas entrapment below].
Step 3: Methanogenesis in Biogas Plants
In the anaerobic digestion of organic waste (sewage or animal dung), methanogens act upon cellulose and other organic materials. These bacteria produce biogas, a mixture composed primarily of methane ($CH_4$) and carbon dioxide ($CO_2$).
Reaction: $CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$ [Per anaerobic metabolic breakdown of organic acids]
4. Summary of Observations
The metabolic activities of these microorganisms result in distinct physical changes in their substrates: bread becomes porous, cheese develops voids, and anaerobic digesters generate flammable gases. These observations provide irrefutable evidence that gaseous molecules are essential metabolic end-products of microbial activity.
Final Solution: The production of gases ($CO_2$, $CH_4$) by microbes such as Saccharomyces cerevisiae in bread dough, Propionibacterium sharmanii in Swiss cheese, and methanogens in biogas plants proves that microbes release gases as metabolic byproducts.
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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