Q.Big holes in Swiss cheese are made by a:
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🔒 Start your 14-day free trial to unlock the full solution →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 large, distinctive holes in Swiss cheese are a fascinating example of microbial activity in food production. These holes are not mechanically created but are a natural outcome of the fermentation process.
During the ripening of Swiss cheese, a specific type of bacterium is active. This bacterium metabolizes certain compounds within the cheese and, as a byproduct of its metabolic activities, produces a significant quantity of carbon dioxide gas. As this gas accumulates and becomes trapped within the so …
The characteristic large holes in Swiss cheese are formed by a specific bacterium that produces a significant amount of carbon dioxide gas during its metabolic activity.
Cheese making is a fascinating example of how microbes are harnessed for human welfare, transforming milk into a diverse range of products. The fundamental process involves the coagulation of milk casein by microbial action, followed by ripening. Different types of microbes, and the specific conditions under which they are allowed to grow, result in the unique textures, flavours, and appearances of various cheeses.
For instance, the distinct flavour of Roquefort cheese comes from the growth of a specific fungus on it. Similarly, the iconic "Swiss cheese" with its large, distinctive holes, known as "eyes," owes its appearance to a particular bacterium.
The presence and size of holes in Swiss cheese are not accidental; they are a direct result of the metabolic activity of a specific microorganism. …
A different angle: eliminate by checking each option against what "natural fermentation" can and cannot do.
- (a) a machine — rules itself out immediately: the question already frames this as a microbial phenomenon ("made by a"), and holes that form during ripening are never mechanically punched.
- (b) a methane-producing bacterium — methane doesn't form visible trapped bubbles the way CO2 does in a semi-solid curd, and no methanogen is part of standard Swiss-cheese starter cultures. …
- KCET 2026Set UNKNOWN1 markMCQQ.The conversion of milk into curd by LAB increases the nutritional value by producing ________. (A) Vitamin A (B) Vitamin B12 (C) Vitamin C (D) Vitamin D
›Reveal solutionSolution
LAB (Lactic Acid Bacteria) convert milk to curd and, in the process, enhance its nutritional quality by producing Vitamin B12.
Step 1 — Fermentation of milk by LAB
Lactic acid bacteria (LAB), e.g. Lactobacillus, grow in milk and convert it to curd/yoghurt. They multiply in milk and produce lactic acid that coagulates and partially digests the milk proteins.
Step 2 — Nutritional enhancement
During this process, LAB also increase the content of Vitamin B12 in the curd, which improves its nutritional value in comparison to plain milk. …
- KCET 2025Set C-41 markMCQQ.Match the contents of List-I with List-II List-I(a) Bioreactors(b) Downstream processing(c) Recombinant protein(d) PCR List-II i. Insulin produced by rDNA technology ii. Vessels which convert raw material into specific Product iii. Detect mutated genes in suspected cancer potien iv. Involves separation and purification. (A) 1a – iv, b – ii, c – iii, d – i (B) 2a – i, b – ii, c – iv, d – iii (C) 3a – ii, b – i, c – iii, d – iv (D) 4a – ii, b – iv, c – i, d – iii
›Reveal solutionSolution
Match each biotechnology term to its definition; two of the four pairs (a–ii and b–iv) are enough to eliminate every wrong option.
Step 1 — Match each item on its own.
- (a) Bioreactors → (ii) Vessels which convert raw material into a specific product. A bioreactor is a vessel in which raw materials are biologically converted into specific products using microbial/plant/animal/human cells; it provides the optimal temperature, pH, substrate, salts, vitamins and oxygen. The commonly used type is the stirred-tank bioreactor. ✓
- (b) Downstream processing → (iv) Involves separation and purification. After the biosynthetic stage inside the bioreactor, the product must be separated and purified; these steps, collectively with formulation, quality control and clinical trials, are called downstream processing. ✓
- (c) Recombinant protein → (i) Insulin produced by rDNA technology. Any protein encoded by a gene expressed in a heterologous host is a recombinant protein; human insulin produced in E. coli is the standard example. ✓ …
- KCET 2025Set C-41 markMCQQ.The reserve material in prokaryotic cells are stored in the cytoplasm in the form of ….. (A) Inclusion bodies (B) Exclusion and inclusion bodies (C) Fat bodies (D) Exclusion bodies
›Reveal solutionSolution
Reserve/storage material in a prokaryote is held in non-membrane-bound cytoplasmic granules called inclusion bodies; the other three options are either wrong or invented terms.
Step 1 — The concept: storage without organelles
A prokaryotic cell has no membrane-bound organelles. It therefore cannot store reserve material inside a vacuole or plastid the way a eukaryote does. Instead, storage material is deposited as discrete granules lying free in the cytoplasm, not enclosed by any membrane. These granules are collectively called inclusion bodies.
Step 2 — What the inclusion bodies contain
Standard examples:
- Phosphate granules (volutin / metachromatic granules)
- Cyanophycean granules (nitrogen reserve in cyanobacteria)
- Glycogen granules (carbohydrate reserve)
- Gas vacuoles — in blue-green, purple and green photosynthetic bacteria
- Sulphur granules, poly-β-hydroxybutyrate granules
All are reserve/storage material, all sit loose in the cytoplasm.
Step 3 — Eliminate the distractors …
- KCET 2021Set C-31 markMCQQ.Identify the odd one out. (A) Ustilago (B) Alternaria (C) Colletotrichum (D) Trichoderma
›Reveal solutionSolution
Group the four fungi by class: three are Deuteromycetes and one (Ustilago) is a Basidiomycete — that is the odd one out.
Step 1 — The concept: classification of fungi
Fungi are classified largely on the basis of their sexual (perfect) stage and the morphology of the sex-spore-bearing structure:
- Phycomycetes — aseptate coenocytic mycelium (Mucor, Rhizopus, Albugo).
- Ascomycetes — sexual spores (ascospores) in a sac-like ascus (Aspergillus, Penicillium, Neurospora, Claviceps).
- Basidiomycetes — sexual spores (basidiospores) on a club-shaped basidium; includes rusts, smuts, mushrooms and bracket fungi (Ustilago, Puccinia, Agaricus).
- Deuteromycetes — the "Fungi Imperfecti": only the asexual or vegetative phase is known, so they cannot be placed by their sexual stage. NCERT's stated examples are Alternaria, Colletotrichum and Trichoderma.
Step 2 — Place each option
Fungus Class (A) Ustilago Basidiomycetes (smut of wheat/maize) (B) Alternaria Deuteromycetes (C) Colletotrichum Deuteromycetes (D) Trichoderma Deuteromycetes Step 3 — Find the misfit …
- KCET 2018Set A-11 markMCQQ.The codon on mRNA are CAU – CCU – AAA – CUG. Identify the correct sequence of amino acids. (A) His – Pro – Lys – Leu (B) Pro – His – Lys – Leu (C) His – Pro – Leu – Lys (D) Pro – Leu – Lys – His
›Reveal solutionSolution
Translate each codon with the standard genetic code, keeping the codons in the order printed.
Step 1 — The principle.
The genetic code is read as non-overlapping triplets in the 5′→3′ direction on the mRNA, and each triplet specifies one amino acid. The order of codons therefore fixes the order of amino acids exactly.
Step 2 — Decode each codon.
Codon Amino acid CAU Histidine (His) — CAU/CAC code His CCU Proline (Pro) — CCN (CCU/CCC/CCA/CCG) all code Pro AAA Lysine (Lys) — AAA/AAG code Lys CUG Leucine (Leu) — CUN all code Leu A useful check on the degeneracy: CCN is a four-fold degenerate family box (Pro), as is CUN (Leu) — the third base does not matter for either, which is why CCU is Pro and CUG is Leu.
Step 3 — Assemble the peptide. …
- KCET 2018Set A-11 markMCQQ.Identify the odd one from the following: (A) α-Interferon (B) Oncogenic virus (C) Proto-oncogenes (D) UV rays
›Reveal solutionSolution
Three of the four are causes of cancer; α-interferon is a treatment, so it is the odd one.
Step 1 — Find the common thread among three of them.
- (B) Oncogenic virus — viruses carrying viral oncogenes (v-onc) that transform normal cells into cancerous ones. A cause.
- (C) Proto-oncogenes — normal cellular genes that regulate cell growth and division; when activated by mutation they become cellular oncogenes (c-onc) and lead to oncogenic transformation. A cause.
- (D) UV rays — a physical carcinogen; UV radiation damages DNA and induces cancer (e.g. skin cancer). A cause.
So the theme is: agents/factors that cause cancer.
Step 2 — Test the remaining option against that theme. …
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