Q.(a)
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Biofertilizers Biopesticides
Imagine you have a garden. You want your plants to grow strong and healthy, and you also want to keep pests away. There are two main ways to do this: one is with harsh chemicals (chemical fertilizers and pesticides), and the other is with living things or natural substances. Biofertilizers and biopesticides are the second way — they are nature’s own tools for farming.
Let’s start with biofertilizers. Think of them as "living manure." A chemical fertilizer is like giving a plant a direct shot of nutrients — it works fast but can burn the soil over time. A biofertilizer, on the other hand, is a preparation containing live microorganisms (like bacteria, fungi, or algae) that help the plant get nutrients from the soil or air. For example, certain bacteria can take nitrogen from the air and convert it into a form the plant can use. The plant doesn’t get fed directly; instead, the biofertilizer helps the soil become richer and more fertile naturally.
The NCERT textbook (Class 12 Biology, Chapter 10) defines biofertilizers as organisms that enrich the nutrient quality of the soil. The main examples are Rhizobium (a bacterium that lives in root nodules of legumes and fixes nitrogen), Azospirillum and Azotobacter (free-living nitrogen-fixing bacteria), and blue-green algae (like Anabaena) which also fix nitrogen.
Now, biopesticides. These are living organisms or natural substances that control pests — insects, fungi, weeds, etc. — without using synthetic chemicals. Instead of spraying a poison that kills everything (good and bad bugs alike), a biopesticide might use a specific bacterium that only harms a particular caterpillar, or a fungus that attacks a weed. The most famous example is Bacillus thuringiensis (often called Bt), a bacterium that produces a protein toxic to certain insect larvae but harmless to humans, animals, and most other insects.
The key difference between chemical and biological agents: Biofertilizers and biopesticides are renewable, eco-friendly, and do not leave toxic residues in the soil or water. They are a cornerstone of sustainable agriculture — farming that can continue for generations without destroying the land.
Why does this matter for a commerce or humanities student? Because agriculture is not just about biology — it’s about economics, policy, and human health. Chemical fertilizers and pesticides are expensive to produce, can pollute groundwater, and their overuse leads to "superpests" that become resistant. Biofertilizers and biopesticides are often cheaper in the long run, safer for farm workers, and help maintain soil health. Governments around the world (including India) promote them through subsidies and organic farming schemes. Understanding them helps you see why "organic" food costs more, why some farmers switch to natural methods, and how environmental regulations work.
Here’s a quick summary of the main types you should know (from NCERT):
- Biofertilizers:
- Rhizobium (symbiotic with legumes) …
Part (b)Concept understanding — Antibiotic Producing Fungi
Imagine you have a wound that gets infected. Before the 20th century, that infection could easily kill you. Today, we have a weapon against such bacterial infections: antibiotics. The most famous antibiotic, penicillin, comes from a humble source — a fungus.
The intuition is simple: in nature, fungi and bacteria are rivals. They compete for the same food and space. To win this battle, some fungi have evolved a chemical weapon. They produce a substance that kills bacteria or stops them from growing. That substance is an antibiotic. So, an antibiotic-producing fungus is simply a fungus that manufactures a natural chemical to destroy or weaken bacteria.
The precise meaning is this: certain species of fungi (like Penicillium notatum or Cephalosporium acremonium) secrete secondary metabolites — chemicals not essential for their own growth — that are toxic to bacteria. These chemicals interfere with a bacterium's cell wall, its protein-making machinery, or its DNA replication. Because bacterial cells are structurally different from human cells, the antibiotic can often kill the invader without harming us.
Why does this matter? It is the foundation of modern medicine. The discovery of penicillin by Alexander Fleming in 1928 was a turning point. Before antibiotics, a simple scratch could lead to sepsis. Today, antibiotics from fungi save millions of lives every year. They are used to treat pneumonia, tuberculosis, wound infections, and many other bacterial diseases.
Antibiotics are effective only against bacteria, not against viruses (like the common cold or flu). Taking an antibiotic for a viral infection is useless and contributes to a serious problem called antibiotic resistance — where bacteria evolve to become immune to the drug.
Here are the key points to remember:
- Source: The most famous antibiotic-producing fungus is Penicillium, which gives us penicillin. Another is Cephalosporium, which produces cephalosporins. …
Part (a)
(i) Two reasons for using cow-dung rather than domestic sewage in a biogas plant:
- Cow-dung is rich in methanogenic bacteria (e.g. Methanobacterium) already present in the rumen/dung, giving faster, more reliable biogas production.
- Cattle dung is available in large, steady amounts on farms and is a thick slurry ideal for anaerobic digestion, whereas sewage is dilute and variable. …
Part (a): Cow-dung is used in a biogas plant because it is rich in methanogenic bacteria and available in bulk as a workable slurry; the spent slurry is used as nutrient-rich manure.
Part (b): Streptokinase (from Streptococcus) treats myocardial infarction, statin (from Monascus purpureus) lowers blood cholesterol, and cyclosporin A (from Trichoderma polysporum) prevents organ-transplant rejection.
Part (a)
(i) Why cow-dung, not domestic sewage?
- Cattle dung is naturally rich in methanogenic bacteria (such as Methanobacterium) carried over from the cattle rumen, so anaerobic digestion and methane (biogas) production begin readily and efficiently.
- Cow-dung is produced in large, dependable quantities on farms and forms a thick slurry well suited to the biogas digester, whereas sewage is dilute, variable and less predictable as a feedstock.
(ii) Use of the spent (unspent) slurry
After the biogas has been drawn off, the residual slurry is a rich manure (biofertiliser) and is returned to the fields to improve soil fertility. …
Showing the 12 most recent of 56 on this concept.
- CBSE 2026Set A1 markMCQQ.Which of the following cyanobacteria fixes atmospheric nitrogen?(a) Nostoc(b) Anabaena(c) Oscillatoria(d) All of these
›Reveal solutionSolution
All the listed cyanobacteria are nitrogen fixers; the correct option is (d).
Cyanobacteria (blue-green algae) are autotrophic aquatic and terrestrial microbes that can fix atmospheric nitrogen and are used as biofertilizers, especially in paddy fields. Nostoc, Anabaena and Oscillatoria are all exa …
- CBSE 2026Set A1 markMCQQ.With the help of what are butterfly caterpillars controlled?(a) Pseudomonas(b) Trichoderma(c) Bacillus thuringiensis(d) Baculovirus
›Reveal solutionSolution
Bacillus thuringiensis is used to control butterfly caterpillars; the correct option is (c).
Bacillus thuringiensis (Bt) is a bacterium used as a biocontrol agent against insect pests. Dried Bt spores are mixed with water and sprayed onto crops. When eaten by the larvae (caterpillars) of butterflies and moths, the toxin (crystal protein) is released in their gut and kills them, while being harmless to other …
- CBSE 2026Set ANNUAL1 markMCQQ.Microbes (micro-organism) found in the form of biofertilizer is(a) Agrobacterium(b) Bacillus thuringiensis(c) Baculoviruses(d) Rhizobium
›Reveal solutionSolution
Biofertilisers are living organisms that enrich soil nutrient quality; Rhizobium (a symbiotic N2-fixer in legume root nodules) is a classic bacterial biofertiliser.
Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into a usable form, enriching soil fertility - hence it is used as a biofertiliser. Agrobacterium is used as …
- CBSE 2026Set ANNUAL1 markQ.Which fungus is used as biological control in the treatment of plant diseases?
›Reveal solutionSolution
Trichoderma species are free-living fungi widely used as biological control agents to protect plant roots from fungal pathogens.
Trichoderma is a genus of free-living fungi commonly found in root ecosystems, and several species act as effective biocontrol agents against a number of plant pathogens, reducing the need for chemical fungicides. This is one of th …
- CBSE 2026Set ANNUAL1 markMCQQ.Cyanobacteria are useful biofertilizers in the field of(a) Wheat(b) Paddy(c) Maize(d) Sugarcane
›Reveal solutionSolution
Cyanobacteria (blue-green algae) are nitrogen-fixing biofertilizers especially valuable in flooded paddy fields.
Cyanobacteria such as Nostoc, Anabaena, and Oscillatoria are photosynthetic, nitrogen-fixing prokaryotes that enrich soil with organic matter and fix atmospheric nitrogen into forms plants can use, increasing soil fertility.
…
- CBSE 2026Set ANNUAL1 markMCQQ.Which bacterial species acts as an bio-insecticide ?(a) LAB(b) Bacillus thuringiensis(c) Acetobacter aceti(d) Streptococcus
›Reveal solutionSolution
Bacillus thuringiensis (Bt) produces crystal (Cry) proteins toxic to insect larvae and is widely used as a biological insecticide.
Bacillus thuringiensis forms proteinaceous crystals during a particular phase of its growth that contain a toxic insecticidal protein. When ingested by an insect larva, the toxin is activated in the alkaline gut environment, damaging the gut lining and killing the insect — this is used commercially as Bt-based bio-insecticide (dried spore-crystal formulations) and is also the …
- CBSE 2026Set ANNUAL1 markMCQQ.Assertion (A): Rhizobium leguminosorum is a symbiotic bacterium found in the root nodules of leguminous plants. Reason (R): This bacterium has the ability to fix atmospheric sulphur into sulphur dioxide.(a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.(b) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.(c) Assertion is true but Reason is false.(d) Assertion is false but Reason is true.
›Reveal solutionSolution
Rhizobium leguminosorum is indeed a symbiotic bacterium in leguminous root nodules (Assertion true), but it fixes atmospheric NITROGEN into ammonia — not sulphur into sulphur dioxide (Reason false).
Assertion: Rhizobium species live symbiotically in the root nodules of leguminous plants (like pea, gram, beans) — true; this is a classic example of a biofertilizer relationship.
…
- CBSE 2026Set ANNUAL1 markMCQQ.Which one of the following is commonly found in root ecosystem and control several plant pathogens?(a) Rhizobium(b) Bacillus thuringiensis(c) Trichoderma(d) Azospirillum
›Reveal solutionSolution
Trichoderma is a soil fungus of the root ecosystem used as a biocontrol agent against many plant pathogens.
Biocontrol agents are living organisms used to control plant diseases and pests instead of chemicals. Trichoderma species are free-living fungi very common in the root ecosystems (rhizosphere) and are effective biocontrol agents against several soil-borne plant pathogens.
…
- CBSE 2026Set ANNUAL1 markQ.Alexander Fleming, Ernst Chain and Howard Florey were awarded the Nobel Prize in 1945 for the discovery of _________.
›Reveal solutionSolution
The blank is penicillin — the antibiotic from the mould Penicillium notatum whose discovery earned Fleming, Chain and Florey the 1945 Nobel Prize.
In the CBSE/NCERT Microbes in Human Welfare chapter, Alexander Fleming accidentally noticed that the mould Penicillium notatum killed Staphylococcus bacteria in a culture plate. Ernst Chain and Howard …
- CBSE 2025Set X11 markQ.Members of genus ____________ form mycorrhiza and absorb phosphorous from soil and supply it to the plant.
›Reveal solutionSolution
Members of the genus Glomus form mycorrhiza and supply phosphorus to plants.
Many members of the fungal genus Glomus form a symbiotic association (mycorrhiza) with the roots of higher plants. The fungal partner absorbs phosphorus from the soil and passes it to the plant; the association al …
- CBSE 2025Set ANNUAL1 markMCQQ.The Bacteria found in the root nodules of Leguminous plants is-(a) Rhizobium(b) Azotobacter(c) Staphylococus(d) Lactobacillus
›Reveal solutionSolution
Rhizobium is the nitrogen-fixing bacterium that lives symbiotically in the root nodules of leguminous plants.
Rhizobium is a gram-negative, symbiotic, nitrogen-fixing bacterium that infects the roots of leguminous plants (e.g. pea, gram, soybean) and induces the formation of root nodules. Inside the nodules it converts atmospheric nitrogen (N2) into ammonia using the nitrogenase enzyme, making fixed nitrogen available to the plant, while the plant in turn supplies the bacterium with carbohydrates. Azotobacter is a free …
- CBSE 2025Set F1 markMCQQ.Which of the following fixes nitrogen?(a) Anabaena(b) Ulva(c) Ulothrix(d) Spirogyra
›Reveal solutionSolution
Anabaena fixes atmospheric nitrogen.
Anabaena is a filamentous cyanobacterium (blue-green alga) that fixes atmospheric nitrogen (N2) into usable forms in specialised cells called heterocysts. It acts as a biofertiliser (e.g. Anabaena in the fern Azolla enriches rice fi …
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