Q.(a) Mention the common bacterium found in the anaerobic sludge during sewage treatment and also in the rumen of cattle. How is this bacterium commercially useful?
Concept understanding — Microbial Fermentation Foods
Let’s begin with something you already know. Think of a pot of milk left out in warm weather. After a few hours, it turns sour and thickens into curd. That change is not spoilage in the usual sense — it is a controlled transformation caused by tiny living organisms called microbes. This is the heart of microbial fermentation.
Fermentation is a process in which microorganisms — bacteria, yeast, or moulds — break down organic substances (like sugars) in the absence of oxygen, producing energy for themselves and, as a by‑product, substances that change the food. When we deliberately use this process to make food, we call the result microbial fermented foods.
You have eaten many of them without thinking twice: curd (yogurt), idli and dosa batter, bread, cheese, pickles, vinegar, and even the dark chocolate you might enjoy. Each of these relies on specific microbes doing their work.
The NCERT textbook (Class XII, Biology, Chapter 10: Microbes in Human Welfare) introduces fermented foods under the topic “Microbes in Household Products.” It lists curd, cheese, idli, dosa, and bread as common examples. The key point is that these are not modern inventions — they have been part of Indian and global diets for centuries.
Why does this matter? Because fermentation does three things that are valuable for us:
- Preserves food — The acids or alcohol produced by microbes prevent spoilage by harmful bacteria. Pickles stay edible for months because of lactic acid from fermentation.
- Improves digestibility — Microbes break down complex molecules. Lactose in milk becomes easier to digest in curd; the proteins in soy become more digestible in tempeh.
- Enhances flavour and texture — The tang of yogurt, the airy holes in bread, the umami of soy sauce — all come from fermentation.
Let’s look at a few examples from your daily life, as the NCERT would describe them:
- Curd (yogurt): Milk is boiled and cooled, then a small amount of previous curd (containing Lactobacillus bacteria) is added. The bacteria convert lactose into lactic acid, which thickens the milk and gives it a sour taste.
- Idli and dosa batter: Rice and urad dal are soaked, ground, and left to ferment overnight. Naturally occurring Leuconostoc and other bacteria produce carbon dioxide gas, which makes the batter rise and gives idlis their spongy texture.
- Bread: Baker’s yeast (Saccharomyces cerevisiae) ferments the sugars in dough, releasing carbon dioxide that makes the dough rise. The alcohol produced evaporates during baking.
- Cheese: Milk is curdled using rennet (an enzyme) or acid, then specific bacteria and moulds are added to ripen it. Different microbes give different cheeses their distinct flavours — for example, Penicillium roqueforti gives blue cheese its veins and sharp taste.
The NCERT emphasises that these processes are not random. They require specific conditions — temperature, pH, moisture, and the right starter culture. If the conditions go wrong, harmful microbes can grow instead. That is why traditional methods (like adding a spoonful of previous curd) are actually precise microbial techniques passed down through generations.
For a commerce or humanities student, the relevance goes beyond the kitchen. Fermented foods are a multi‑billion‑dollar industry. They involve supply chains (milk, grains, fruits), processing technology, quality control, and marketing. Understanding the basic science helps you see why a product like yogurt has a “use by” date, why some cheeses are expensive, and why traditional foods like kimchi or kombucha have become global trends.
In short: microbial fermentation is nature’s way of transforming food using invisible helpers. It is a bridge between biology and everyday life — and it has been feeding humanity long before anyone knew what a microbe was.
Microbial fermentation is a well-established topic in the NCERT Class 12 Biology curriculum, commonly explored through searches like "Microbial Fermentation Foods: definition, examples and applications" and "list microbes used in food production" ahead of CBSE board exams. Students preparing for NEET and other competitive exams often revise this alongside "Microbes in Human Welfare important questions," since it links directly to biotechnology and industrial microbiology.
- Methanogens (e.g., Methanobacterium) — found in anaerobic sludge and cattle rumen; used commercially to produce biogas (methane).
- Baculoviruses (Nucleopolyhedrovirus) — species-specific viral biocontrol agents that spare non-target organisms and leave no chemical residues.
In the anaerobic sludge digesters of a sewage-treatment plant, and inside the rumen of cattle, live a group of anaerobic bacteria called methanogens (a common example is Methanobacterium). In both places they break down organic matter in the absence of oxygen.
Commercial usefulness: methanogens produce biogas — a mixture rich in methane (CH4) together with CO2 and H2S. This biogas is a renewable fuel used for cooking, lighting and generating electricity; the same microbes power dung-based biogas plants in rural areas, turning waste into clean energy.
The bacterium is a methanogen (e.g., Methanobacterium); it is commercially useful because it produces biogas (methane), used as a fuel.
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)
- Azospirillum / Azotobacter (free-living, fix nitrogen)
- Mycorrhiza (fungi that help roots absorb phosphorus)
- Cyanobacteria (blue-green algae, fix nitrogen in rice fields)
-
Biopesticides:
- Bacillus thuringiensis (Bt) — kills caterpillars
- Trichoderma (a fungus) — controls soil-borne diseases
- Baculoviruses (viruses that attack specific insects)
- Neem extracts (a plant-based natural pesticide)
A common mistake is to think biofertilizers and biopesticides are "instant" or "magic." They are living things — they need proper storage, the right soil conditions, and time to work. They are not a replacement for all chemicals, but a smarter, long-term alternative.
In short: Biofertilizers feed the soil, biopesticides protect the crop — both using nature’s own tools. For your exams, remember the key examples and the core idea: they are renewable, safe, and sustainable. That’s the heart of the concept.
Learners revising this chapter commonly search for "Biofertilizers Biopesticides class 12 biology", "Biofertilizers Biopesticides notes class 12 biology", or "Biofertilizers Biopesticides diagram and explanation". This concept is part of the Microbes in Human Welfare chapter in the NCERT/CBSE Class 12 Biology syllabus, and revising it thoroughly helps with both board exams and general competitive-exam preparation.
- Methanogens (e.g., Methanobacterium) — found in anaerobic sludge and cattle rumen; used commercially to produce biogas (methane).
- Baculoviruses (Nucleopolyhedrovirus) — species-specific viral biocontrol agents that spare non-target organisms and leave no chemical residues.
The effective viral biocontrol agents of insect pests and plant pathogens are the Baculoviruses, particularly those of the genus Nucleopolyhedrovirus (NPV). These viruses attack insects and other arthropods.
How they support the environment:
- They are species-specific / narrow-spectrum — a given virus infects only the target pest, so they do not harm beneficial insects (pollinators, natural predators), plants, mammals or birds.
- They leave no toxic chemical residues in soil, water or produce.
- They are therefore ideal in integrated pest management (IPM) and where preserving natural ecological balance and non-target organisms is important, replacing broad-spectrum chemical pesticides.
The viral biocontrol agents are Baculoviruses (Nucleopolyhedrovirus); being species-specific and residue-free, they control pests without harming non-target organisms, supporting a chemical-free, balanced environment.
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