Q.Citric acid is produced by which of the following microorganism.

Showing the 12 most recent of 23 on this concept.

1. CBSE 2026Set V11 markMCQ
   Q.Match the List-I with List-II List-I A. Rhizobium B. Clostridium C. Aspergillus D. Methanogens List-II

   1. Citric acid
   2. Gobar gas
   3. N2 fixation symbiotically
   4. Butyric acid

   (a) A-1, B-2, C-3, D-4

   (b) A-2, B-1, C-3, D-4

   (c) A-3, B-4, C-1, D-2

   (d) A-4, B-2, C-1, D-3

   ›Reveal solutionSolution

   Rhizobium–symbiotic N2 fixation, Clostridium–butyric acid, Aspergillus–citric acid, Methanogens–gobar gas.

   • A. Rhizobium → symbiotic nitrogen fixation in legume root nodules (3)
   • B. Clostridium (C. butyricum) → butyric acid (4)
   • C. Aspergillus (A. niger) → citric acid (1) …

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2. CBSE 2026Set ANNUAL1 markMCQ
   Q.Yeast is used in the production of :

   (a) ethyl alcohol

   (b) paneer

   (c) acetic acid

   (d) curd

   ›Reveal solutionSolution

   Yeast (Saccharomyces cerevisiae) ferments sugars to produce ethyl alcohol — used in brewing and baking.

   Yeast, particularly Saccharomyces cerevisiae (baker's/brewer's yeast), carries out anaerobic fermentation of sugars, converting glucose into ethyl alcohol (ethanol) and CO₂. This fermentation is the basis of the beverage/brewing industry (wine, beer, whisky). Pan …

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3. CBSE 2026Set ANNUAL1 markMCQ
   Q.The most common substrate used in distilleries for the production of ethanol is _________.

   (a) Molasses

   (b) Soya meal

   (c) Corn meal

   (d) Groundgram

   ›Reveal solutionSolution

   Molasses, the sugar-rich waste by-product of sugar manufacture, is the cheap and widely-available substrate that Indian distilleries ferment (using yeast) to produce industrial and beverage ethanol.

   Industrial production of ethanol relies on microbial fermentation, in which yeasts, chiefly Saccharomyces cerevisiae, convert fermentable sugars anaerobically into ethanol and carbon dioxide. The choice of substrate is largely an economic one, and in India (and many sugarcane-growing countries), the substrate of choice is molasses -- the thick, dark syrup that remains after sucrose crystals have been extracted from sugarcane juice during sugar manufacture. Molasses still contains a substantial amount of residual sugar, making it an inexpensive, abundant raw material that would otherwise be a low-value by-product; it is diluted, inoculated with yeast, and allowed to ferment in large vats, after which the resulting 'wash' is distilled to concentrate th …

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4. CBSE 2025Set 57/4/11 markMCQ
   Q.Bioactive molecule Cyclosporin A used for human welfare is derived from : (A) Propionibacterium sharmanii (B) Monascus purpureus (C) Trichoderma polysporum (D) Aspergillus niger

   ›Reveal solutionSolution

   Cyclosporin A, a crucial immunosuppressive agent used in organ transplant patients, is derived from the fungus Trichoderma polysporum.

   Microbes, often associated with disease, play an incredibly diverse and beneficial role in human welfare, extending far beyond our initial perceptions. Among their many contributions is the production of a wide array of bioactive molecules, which are substances that have a specific effect on living organisms. These molecules have revolutionized medicine and various industries, offering solutions to complex health challenges.

   One such vital bioactive molecule is Cyclosporin A. Its discovery marked a significant breakthrough in medical science, particularly in the field of organ transplantation. When a patient receives an organ from a donor, their immune system naturally recognizes the new organ as "foreign" and mounts an attack to reject it. This immune response, while essential for fighting infections, becomes a major hurdle in successful transplantation.

   Important

   Cyclosporin A functions as an immunosuppressive agent, meaning it dampens or suppresses the body's immune response. This action is critical for preventing the rejection of transplanted organs, allowing the patient's body to accept the new organ and significantly improving the success rate and long-term prognosis for transplant recipients.

   The remarkable ability to produce Cyclosporin A is found in a specific microorganism. This molecule is derived from the fungus Trichoderma polysporum. This particular fungus synthesizes Cyclosporin A as part of its natural metabolic processes, and scientists have harnessed this capability for therapeutic use.

   Let's briefly consider the other options provided, as they also represent microbes known for producing other important substances, as per NCERT: …

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5. CBSE 2025Set 57/5/11 markMCQ
   Q.Large scale industrial production of Butyric acid for human welfare is done using the microbe : (A) Aspergillus sp. (B) Streptococcus sp. (C) Clostridium sp. (D) Trichoderma sp.

   ›Reveal solutionSolution

   Butyric acid is industrially produced by anaerobic fermentation using Clostridium species, which naturally yield high concentrations of this short-chain fatty acid. The correct option is (C).

   Concept & Intuition

   Butyric acid (butanoic acid) is a four-carbon carboxylic acid with a pungent smell, used in food flavouring, perfume esters, and as a precursor for cellulose acetate butyrate plastics. Large-scale production relies on microbial fermentation because chemical synthesis is less economical and yields unwanted by-products.

   The key is choosing a microbe that naturally produces butyric acid as its main fermentation end-product. Not all bacteria or fungi do this. For instance, Aspergillus and Trichoderma are fungi used for citric acid and cellulase production, respectively — they don’t make butyric acid. Streptococcus species produce lactic acid (homofermentative) or a mix of acids, but not butyric acid in significant amounts.

   Clostridium species, especially Clostridium butyricum and Clostridium tyrobutyricum, are obligate anaerobes that carry out butyric acid fermentation. They convert sugars (like glucose) into butyric acid, along with hydrogen gas and carbon dioxide, via the butyrate pathway. This is the classic “butyric fermentation” used in industry.

   Watch out

   A common mistake is to confuse butyric acid with lactic acid or citric acid. Remember: Clostridium → butyric acid; Lactobacillus/Streptococcus → lactic acid; Aspergillus niger → citric acid.

   Step-by-step reasoning

   1. Identify the product

      Butyric acid is a volatile fatty acid (C₄H₈O₂). Its industrial production requires a microbe that can channel carbon flux toward butyrate, not ethanol, lactate, or other acids.

   2. Eliminate non-butyric producers

      • Aspergillus sp. (fungus): Used for citric acid, gluconic acid, and enzymes. Does not produce butyric acid.
      • Streptococcus sp. (bacterium): Lactic acid bacteria; homofermentative strains produce only lactic acid. …

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6. CBSE 2025Set 57/6/11 markMCQ
   Q.Bottled fruit juices are clearer as compared to those made at home, as they are clarified by the use of : (A) Lipases and pectinases (B) Pectinases and proteases (C) Proteases and cellulases (D) Nucleases and lipases

   ›Reveal solutionSolution

   Bottled fruit juices are clearer than homemade ones because industrial processes use enzymes, primarily pectinases and proteases, to break down the suspended particles that cause cloudiness.

   When you make fruit juice at home, you often notice it's quite pulpy and cloudy. This is because the process of crushing or blending fruit releases not just the liquid, but also tiny fragments of fruit pulp, cell wall material, and other suspended particles. These particles, though small, are numerous enough to scatter light, giving the juice its characteristic opaque or cloudy appearance.

   Commercial fruit juice manufacturers, however, aim for a clear, appealing product. To achieve this, they employ specific enzymes that act on the components causing the cloudiness. The two primary enzymes used for this clarification process are pectinases and proteases.

   Let's understand their roles:

   • Pectinases: Fruits contain a complex polysaccharide called pectin, which is a major component of plant cell walls and the middle lamella that glues plant cells together. When fruit is processed, pectin can be released into the juice, forming a colloidal suspension that makes the juice thick, viscous, and cloudy. Pectinases are enzymes that specifically break down pectin into smaller, soluble molecules. By doing so, they reduce the viscosity of the juice, release more liquid from the pulp, and most importantly, eliminate the suspended pectin particles that contribute significantly to the cloudiness.

   • Proteases: While pectin is a major culprit, proteins present in the fruit can also contribute to the turbidity and haze in juice. These proteins can aggregate or denature, forming fine suspended particles that make the juice cloudy, especially over time. Proteases are enzymes that break down proteins into smaller peptides and amino acids, which are much more soluble and do not cause cloudiness.

   Note

   The use of these enzymes not only clarifies the juice but can also increase the yield of juice extracted from the fruit, as breaking down cell wall components like pectin allows more liquid to be released. …

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7. CBSE 2025Set ANNUAL1 markMCQ
   Q.An Enzyme that is used for bottled fruit juice to make more clean and clear.

   (a) Lipase, Amylase

   (b) Pectinase, Protease

   (c) Lactase, Sucrase

   (d) Nuclease, Ptyalin

   ›Reveal solutionSolution

   Pectinases break down pectin and proteases break down proteins that otherwise make fruit juice cloudy, giving a clear product.

   Freshly extracted fruit juice contains suspended pectin and protein particles that make it cloudy. Adding pectinase (which hydrolyses pectin) and protease (which hydrolyses proteins) breaks these particles down, allowing them to be removed and yielding a clear, more attractive juice — this is a well-known industrial application of enzymes mentioned in the NCERT text on microbes in …

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8. CBSE 2025Set ANNUAL1 markMCQ
   Q.Citric acid is produced by:

   (a) Lactobacillus

   (b) Acetobacter aceti

   (c) Clostridium butylicum

   (d) Aspergillus niger

   ›Reveal solutionSolution

   Citric acid, an important industrial organic acid, is commercially produced by fermentation using the fungus Aspergillus niger.

   Microorganisms are widely used to produce organic acids at an industrial scale because microbial fermentation is cheaper and more scalable than chemical synthesis. Each acid is associated with a specific, well-known microbe in the NCERT syllabus:

   • Citric acid — Aspergillus niger (a fungus/mould)
   • Acetic acid (vinegar) — Acetobacter aceti (a bacterium)
   • Butyric acid — Clostridium butylicum
   • Lactic acid — Lactobacillus …

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9. CBSE 2025Set ANNUAL1 markMCQ
   Q.Which of the following micro-organisms is used for production of citric acid in Industries ?

   (a) Aspergillus niger

   (b) Lactobacillus bulgaris

   (c) Rhizopus nigricans

   (d) Penicillium citrinum

   ›Reveal solutionSolution

   The mould Aspergillus niger is the standard industrial micro-organism used to ferment sugars into citric acid.

   Citric acid, widely used as a food preservative/flavouring agent and in various industries, is produced industrially through fermentation using the fungus Aspergillus niger, which is cultured on a sugar-rich substrate (such as molasses) under controlled aerobic conditions; the fungus's metabolism, under specific conditions (e.g. limited manganese), diverts a large fraction of the sugar into citric acid, which is then extracted and purified. Lactobacillus bulgaris (used in yogurt fermentation) and Rhizopus nigricans and Penicillium citrinum are other micro-organisms used industrially, but the …

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10. CBSE 2025Set ANNUAL1 markMCQ
    Q.Which of the following is wrongly matched ?

    (i) Butyric acid - rincidity of butter

    (ii) Lipases - fat digesting enzyme

    (iii) Cyclosporin A - immunosuppressive agent

    (iv) Streptokinase - blood cholesterol lowering agent

    ›Reveal solutionSolution

    Streptokinase is a clot-dissolving (thrombolytic) agent used to clear blood clots in heart-attack patients, NOT a cholesterol-lowering agent — so pairing (iv) is wrong.

    Check each pair:

    • (i) Butyric acid – rancidity of butter: correct. Butyric acid, produced by bacterial (e.g. Clostridium butyricum) fermentation of butter fat, is responsible for the characteristic smell/taste of rancid butter.
    • (ii) Lipases – fat digesting enzyme: correct. Microbial lipases (e.g. from fungi) break down fats and are used in detergents and food/dairy processing to hydrolyse triglycerides.
    • (iii) Cyclosporin A – immunosuppressive agent: correct. Cyclosporin A, produced by the fungus Trichoderma polysporum, is widely used in organ-transplant patients to suppress the immune response and prevent organ rejection. …

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11. CBSE 2024Set 57/2/11 markMCQ
    Q.Which one of the following pairs is not correctly matched ? (A) Clostridium butylicum – Butyric acid (B) Trichoderma polysporum – Cyclosporin A (C) Monascus purpureus – Citric Acid (D) Streptococcus – Streptokinase

    ›Reveal solutionSolution

    The pair that is not correctly matched is (C) Monascus purpureus – Citric Acid, because Monascus purpureus produces a cholesterol-lowering agent (statins), not citric acid.

    Let’s walk through each option carefully, because this question tests your grasp of which microbe is famous for which industrial product — a classic NCERT-based topic from the chapter on Microbes in Human Welfare.

    Option (A): Clostridium butylicum – Butyric acid. This is correct. Clostridium butylicum is a bacterium used in the industrial production of butyric acid. Butyric acid is a short-chain fatty acid with applications in food flavouring, perfumes, and as a chemical intermediate. NCERT explicitly mentions this pairing.

    Option (B): Trichoderma polysporum – Cyclosporin A. This is also correct. Trichoderma polysporum is a fungus that produces Cyclosporin A, a powerful immunosuppressant drug used in organ transplant patients to prevent rejection. This is a well-known example from the NCERT section on biological control and pharmaceutical products.

    Option (C): Monascus purpureus – Citric Acid. This is the incorrect match. Monascus purpureus is a fungus (a type of red yeast) that produces statins — specifically, a compound called monacolin K, which lowers blood cholesterol. Citric acid, on the other hand, is produced by Aspergillus niger (a different fungus). NCERT clearly states that Monascus purpureus is used for producing blood-cholesterol-lowering agents, not citric acid.

    Note

    A common confusion arises because Monascus is indeed used in food fermentation (like red yeast rice), but its famous pharmaceutical product is a statin, not citric acid. Citric acid’s microbial source is Aspergillus niger. …

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12. CBSE 2024Set A11 markMCQ
    Q.Which micro-organism is useful in production of citric acid?

    (a) Acetobacter aceti

    (b) Penicillium notatum

    (c) Aspergilus niger

    (d) Clostridium butylicum

    ›Reveal solutionSolution

    Citric acid is produced industrially by the fungus Aspergillus niger.

    Microbes are used for producing many organic acids. Aspergillus niger (a fungus) is used for the commercial production of citric acid. (Acetobacter aceti produces acetic acid, Clostridium butylicum …

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