NCERT Solutions

I would carry a sample of Curd.

• Curd contains numerous Lactic Acid Bacteria (LAB) like Lactobacillus.
• These bacteria are easily visible under a microscope after simple staining (e.g., Crystal Violet or Methylene Blue).
• It is readily available at home and safe to handle.

• Dough rising (Idli/Dosa): The puffing up of dough is due to the production of \(CO_2\) gas by bacteria (Leuconostoc, Streptococcus).
• Bread making: Baker’s yeast (Saccharomyces cerevisiae) ferments glucose to produce ethanol and \(CO_2\). The \(CO_2\) bubbles make the bread porous and soft.
• Swiss Cheese: The large holes are due to production of a large amount of \(CO_2\) by the bacterium Propionibacterium sharmanii.
• Biogas Production: Methanogens produce Methane (\(CH_4\)), \(CO_2\), and \(H_2\) during anaerobic digestion of organic waste.

Source: Curd, Yoghurt, Cheese, Pickles.

1. Curdling of Milk: LAB convert lactose sugar of milk into lactic acid, which coagulates milk proteins (casein) to form curd.
2. Nutritional Quality: Increases Vitamin B12 content in curd.
3. Disease Prevention: In the human stomach, LAB play a beneficial role in checking the growth of disease-causing microbes (probiotic effect).

• Idli & Dosa: Made from rice and black gram (dal). Fermented by bacteria.
• Dhokla: Made from Bengal gram and rice. Fermented by bacteria.
• Bhatura: Made from wheat flour (maida). Fermented by yeast or bacteria.
• Nan: Made from wheat flour. Fermented by yeast/bacteria.

Microbes have played a major role through the production of Antibiotics.

• Antibiotics are chemical substances produced by some microbes that kill or retard the growth of other (disease-causing) microbes.
• Example: Penicillin (from fungus Penicillium notatum) kills bacteria like Staphylococcus.
• Antibiotics have greatly reduced mortality from deadly diseases like Plague, Whooping cough (Kali khasi), Diphtheria (Gal ghotu), and Leprosy (Kusht rog).

1. Penicillium notatum (Source of Penicillin).
2. Cephalosporium acremonium (Source of Cephalosporins).

Sewage: It is the municipal waste-water containing large amounts of human excreta, organic matter, and microbes.

• Pathogens: It contains disease-causing microbes (bacteria, viruses) that can cause water-borne diseases like Typhoid, Cholera, Dysentery.
• Oxygen Depletion: High organic load increases Biological Oxygen Demand (BOD), depleting dissolved oxygen in water bodies and killing aquatic life.

Yes, microbes can be used to produce energy.

• Certain bacteria called Methanogens (e.g., Methanobacterium) grow anaerobically on cellulosic material.
• They produce a large amount of Biogas (mixture of Methane, \(CO_2\), \(H_2\)).
• This process occurs in a biogas plant (gobar gas plant) using cattle dung, which is rich in these bacteria and cellulose.
• Biogas is inflammable and used as fuel for cooking and lighting.

This is accomplished through Biofertilizers and Biocontrol Agents.

• Nitrogen Fixation: Bacteria like Rhizobium (symbiotic) and Azospirillum, Azotobacter (free-living) fix atmospheric nitrogen into the soil.
• Mycorrhiza: Fungi (Glomus) form symbiotic association with plants, absorbing Phosphorus from soil.
• Cyanobacteria: Anabaena, Nostoc fix nitrogen in paddy fields.

• Bacillus thuringiensis (Bt): Produces a toxin that kills butterfly caterpillars (insect larvae).
• Trichoderma: Free-living fungi that control root pathogens.
• Baculoviruses (Nucleopolyhedrovirus): Attack insects and other arthropods.

BOD (Biochemical Oxygen Demand) is directly proportional to the amount of organic matter (polluting potential). High BOD means high pollution.

• Sample C (400 mg/L): Highest BOD. Most Polluted. Represents Untreated Sewage Water.
• Sample A (20 mg/L): Moderate BOD. Represents Secondary Effluent (after biological treatment, BOD is reduced).
• Sample B (8 mg/L): Lowest BOD. Cleanest. Represents River Water.

• (a) Single Cell Protein (SCP): Microbes like Spirulina (Blue-green algae) and Methylophilus methylotrophus (Bacteria) are grown on industrial scale. They are rich in protein and serve as an alternative protein source for humans and animals, reducing pressure on agriculture.
• (b) Soil: Microbes play a vital role in soil fertility.
  • Decomposition: Bacteria and fungi decompose organic waste (humification) releasing nutrients back into soil.
  • Nitrogen Fixation: Rhizobium and Cyanobacteria fix atmospheric nitrogen, enriching soil nitrogen content.

Order: Penicillin > Biogas > Curd > Citric acid

1. Penicillin: It is an antibiotic that saves lives by treating deadly infectious diseases. Health/Life is the highest priority.
2. Biogas: Provides a renewable, clean energy source for rural areas and helps in waste management. Energy and sanitation are critical.
3. Curd: Provides nutritional value (Vitamin B12) and gut health (probiotic). Important for health but less critical than antibiotics or energy.
4. Citric acid: Used mainly as a food preservative and flavoring agent. Industrial importance, but lower priority for general welfare compared to others.

Biofertilizers enrich soil fertility through:

1. Nitrogen Fixation: Bacteria like Rhizobium (symbiotic) and Azotobacter (free-living) convert atmospheric nitrogen into ammonia/nitrates, which are usable by plants.
2. Phosphorus Solubilization: Fungi in Mycorrhiza absorb phosphorus from the soil and pass it to the plant.
3. Organic Matter: Cyanobacteria add organic matter to the soil, improving its texture and water-holding capacity.