Question and Answer:

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 with the help of a microscope, which sample would you carry and why?

Answer:
Microbes or microorganisms such as bacteria, fungi, and protozoa are omnipresent (found everywhere) but are not visible to the naked eye because they are extremely small in size (0.1 mm or less).
A common household product that shows the presence of bacteria is curd. Milk is converted into curd by the action of Lactobacillus bulgaricus and Streptococcus thermophilus.
Therefore, a small sample of curd can be carried to the biology laboratory to demonstrate the presence of bacteria under a microscope.

Question 2.
Give examples to prove that microbes release gases during metabolism.

Answer:
Microbes release gases during their metabolic activities such as fermentation.
For example, during the fermentation of dough used for making idli and dosa, bacteria produce carbon dioxide (CO₂) gas which gets trapped in the dough and makes it puff up.
Similarly, in the production of Swiss cheese, large holes are formed due to the production of a large amount of CO₂ by the bacterium Propionibacterium sharmanii.

Question 3.
In which food would you find lactic acid bacteria? Mention some of their useful applications.

Answer:
Microorganisms such as Lactobacillus and others, commonly called Lactic Acid Bacteria (LAB), grow in milk. They convert the lactose sugar of milk into lactic acid, which causes coagulation of the milk protein casein, changing milk into curd, yogurt, or cheese.

• Curd: Prepared by inoculating milk with Lactobacillus acidophilus at about 40°C or less.
• Yogurt: Produced by curdling milk with Streptococcus thermophilus and Lactobacillus bulgaricus; it has the flavor of lactic acid and acetaldehyde and is often sweetened or flavored.
• Cheese: Formed by curdling milk with lactic acid bacteria to separate the solid curd from the liquid part.

In our stomach, lactic acid bacteria also play a beneficial role by inhibiting the growth of disease-causing microbes and improving gut health.

Question 4.
Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.

Answer:

• Wheat products: Bread, Cake
• Rice products: Idli, Dosa
• Bengal gram products: Dhokla, Khandvi

All these foods are prepared by fermentation using microbes such as bacteria and yeast, which help in improving the texture, taste, and nutritional quality of the food.

Question 5.
In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

Answer:
Microbes are very useful in combating disease-causing harmful bacteria. A number of antibiotics have been isolated from microorganisms. An antibiotic is a substance which, in low concentration, inhibits the growth and metabolic activity of pathogenic organisms without harming the host.

Penicillin was the first antibiotic to be discovered by Alexander Fleming from the fungus Penicillium notatum. Antibiotics are obtained from lichens, fungi, eubacteria, and actinomycetes.

Some common antibiotics and their sources are:

• Polymyxin – Bacillus polymyxa
• Chloramphenicol – Streptomyces venezuelae
• Neomycin – Streptomyces fradiae
• Tetracycline (Terramycin) – Streptomyces rimosus
• Cephalosporin – Cephalosporium acremonium

Question 6.
Name any two species of fungus, which are used in the production of the antibiotics.

Answer:
Two species of fungus used in the production of antibiotics are:

1. Penicillium notatum – used in the production of Penicillin.
2. Cephalosporium acremonium – used in the production of Cephalosporin.

Question 7.
What is sewage? In which way can sewage be harmful to us?
Answer:
Sewage is the wastewater released from homes, industries, hospitals, offices, and other sources that contains human excreta, organic waste, and harmful microorganisms.

Harmful effects of sewage:

• It contaminates drinking water sources, spreading water-borne diseases like cholera, typhoid, and dysentery.
• It depletes oxygen in water bodies, causing the death of aquatic organisms.
• It releases foul odour and makes the environment unhygienic.
• It promotes the growth of harmful bacteria and pathogens.

Question 8.
What is the key difference between primary and secondary sewage treatment?

Answer:
The key difference between primary and secondary sewage treatment is:

• Primary treatment is a physical process that removes large particles and suspended solids from sewage through filtration and sedimentation.
• Secondary treatment is a biological process in which microorganisms decompose the organic matter present in the sewage.

In short,
👉 Primary treatment = Physical removal of solids
👉 Secondary treatment = Biological degradation of organic matter by microbes

Question 9.
Do you think microbes can also be used as source of energy? If yes, how?

Answer:
Primary treatment is a physical process that removes grit and large pieces of organic matter from sewage, while secondary treatment is a biological process in which microbes digest the organic matter present in the sewage.

Question 10.
Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

Answer:
Microbes play an important role in organic farming, which is practiced without the use of chemical fertilisers and pesticides.

1. Biofertilisers:
   Biofertilisers are living organisms that help increase soil fertility. They improve plant growth by supplying essential nutrients and are introduced into seeds, roots, or soil to mobilize nutrient availability.

1. Many species of bacteria and cyanobacteria can fix free atmospheric nitrogen.

• Rhizobium – Symbiotic bacterium found in the root nodules of leguminous plants.
• Azospirillum and Azotobacter – Free-living nitrogen-fixing bacteria.
• Anabaena, Nostoc, and Oscillatoria – Nitrogen-fixing cyanobacteria.

Biofertilisers are eco-friendly and cost-effective, enriching the soil with organic nutrients.

2. Biopesticides:
   Microbes can also act as biopesticides to control insect pests in plants.

• Bacillus thuringiensis (Bt) – Produces a toxin that kills insect larvae when sprayed on crops.
• Trichoderma – A free-living fungus found in root ecosystems that protects plants from pathogens.
• Baculoviruses – Used as biological control agents against insects and other arthropods.

Thus, the use of microbes as biofertilisers and biopesticides reduces the dependence on chemical fertilisers and pesticides, maintaining soil health and environmental balance.

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 (Biological Oxygen Demand) refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. It is a measure of the organic matter present in the water. The greater the BOD, the higher the level of pollution.

The BOD value of clean water is generally between 1 and 2 mg/L. As the amount of organic pollution increases, BOD also increases. Grossly polluted water may have a BOD around 20 mg/L or more.

In the given problem, the BOD values of the three samples are:

• Sample A – 20 mg/L
• Sample B – 8 mg/L
• Sample C – 400 mg/L

Among these, Sample C has the highest BOD value, hence it is the most polluted.

Correct labelling:

• Sample A (20 mg/L) – Secondary effluent discharged from a sewage treatment plant
• Sample B (8 mg/L) – Relatively clean river water
• Sample C (400 mg/L) – Untreated sewage water

Most polluted sample: Sample C (BOD = 400 mg/L)

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:

1. Cyclosporin A – obtained from the fungus Trichoderma polysporum.

• It is used as an immunosuppressive drug, mainly during organ transplantation to prevent rejection.

1. Statins – obtained from the fungus Monascus purpureus.

• Statins act as blood cholesterol-lowering agents by competitively inhibiting the enzyme responsible for cholesterol synthesis.

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):

• Single Cell Protein refers to protein-rich microbial biomass used as food or feed.
• Microorganisms such as Spirulina, Methylophilus methylotrophus, Chlorella, and Yeast are used for producing SCP.
• SCP is a good source of proteins, vitamins, fats, carbohydrates, and minerals.
• Example: Spirulina is a rich source of protein and can be grown easily on materials like waste water, molasses, or even agricultural wastes.
• It helps in solving the problem of protein deficiency and is used as a supplementary food for humans and animals.

(b) Soil:

• Microbes play an important role in maintaining soil fertility and structure.
• Bacteria, fungi, and cyanobacteria help in the decomposition of organic matter and the recycling of nutrients like nitrogen, phosphorus, and carbon.
• Nitrogen-fixing bacteria such as Rhizobium, Azospirillum, and Azotobacter convert atmospheric nitrogen into forms usable by plants.
• Actinomycetes help in humus formation and give the soil its characteristic earthy smell.

Thus, microbes in SCP provide food and nutrition, while in soil, they help maintain fertility and nutrient balance.

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 order of arrangement of products according to their decreasing importance is:
Penicillin → Biogas → Citric acid → Curd

Reasons:

• Penicillin is the most important product for the welfare of human society. It is an antibiotic used to control various bacterial diseases, saving millions of lives.
• Biogas is the second most important product. It is an eco-friendly and renewable source of energy, used for cooking, lighting, and generating power.
• Citric acid is the next important product. It is widely used as a food preservative and in the food and beverage industry.
• Curd is the least important among these, though beneficial as a nutritious food product obtained by the action of Lactobacillus bacteria on milk.

Hence, the products in decreasing order of their importance are:
👉 Penicillin → Biogas → Citric acid → Curd

Question 15.
How do biofertilisers enrich the fertility of the soil?

Answer:
Biofertilisers are living microorganisms that enrich the nutrient quality of the soil. They increase soil fertility by making nutrients available to plants through natural processes such as nitrogen fixation, phosphate solubilisation, and decomposition of organic matter.

Ways in which biofertilisers enrich soil fertility:

1. Nitrogen fixation:

• Certain bacteria and cyanobacteria fix atmospheric nitrogen into forms usable by plants.
• Examples: Rhizobium (symbiotic), Azospirillum, Azotobacter (free-living), and Anabaena, Nostoc (cyanobacteria).

2. Phosphate solubilisation:

• Some bacteria and fungi convert insoluble phosphates into soluble forms that plants can absorb.

3. Decomposition of organic matter:

• Microorganisms decompose plant and animal residues, releasing essential nutrients back into the soil.

4. Mycorrhizal association:

• Fungi like Glomus form symbiotic associations with plant roots, increasing the uptake of phosphorus and water.

Thus, biofertilisers help maintain soil fertility, reduce the dependence on chemical fertilisers, and promote eco-friendly sustainable agriculture.