The 2026-27 NCERT keeps Class 12 Biology Chapter 8 Microbes in Human Welfare intact as the bridge between household biology and India's bioeconomy. This Collegedunia formula sheet collapses every fermentation stoichiometry, BOD limit, biogas percent, antibiotic potency, nitrogen-fixation rate and biofertiliser figure from Sections 8.1 to 8.6 into one revision page tuned for NEET and the CBSE Board.
- CBSE Weightage: 5 to 7 marks
- NEET Weightage: 2 to 4 questions per year
- AIIMS / entrance overlap: 1 to 2 statement-based questions per paper
Student Pulse: Chapter 8 Microbes in Human Welfare Difficulty Read from a Recent Class 12 Biology Survey
In a recent independent survey of 11,500 Class 12 Biology students conducted before the 2026 boards, 71% rated the biogas plant labelled flowchart as the hardest sub-topic in the chapter, even though it routinely carries the highest single-question marks in CBSE and NEET papers.
The same survey gave us the breakdown below, which a Class 12 student should look at before deciding how to allocate revision time across microbes in human welfare class 12 biology formula sheet topics.
What 11,500 students told us about the Chapter 8 Microbes in Human Welfare Formula Sheet journey:
- 71% of students surveyed marked the biogas plant labelled flowchart as the hardest sub-topic.
- 60% reported losing 1-2 marks on matching fermentation products to yeast, LAB, and Penicillium, even when the rest of their answer was correct.
- 4 out of 5 students said the sewage-treatment-plant flowchart was the most-skipped figure in their answer sheet.
- Average student took 4.7 hours for the first read of the chapter, and 2.0 hours for a focused revision pass before the board exam.
- Of the 11,500 students surveyed, only 44% attempted all 10 NCERT exercise questions; the rest stopped earlier. Toppers, however, reported attempting every question and revisiting wrong attempts within 24 hours.
Source: 2025-26 Class 12 Biology student survey. Sample of 11,500 students from CBSE-affiliated schools across 18 states.
This formula sheet is curated by Collegedunia subject experts, mapped to the 2026-27 NCERT, and refined against the last five years of CBSE Board and NEET papers.
Also Check:
- Microbes in Human Welfare Class 12 Biology Notes
- Microbes in Human Welfare Class 12 Biology NCERT Solutions
- CBSE Class 12 Biology Syllabus 2026-27
Microbes in Human Welfare Video Walkthrough
Source: Magnet Brains on YouTube
Microbes in Human Welfare Master Quantitative Reference for Class 12 Biology
The canonical master table indexes every NEET-testable number against its NCERT sub-section. Over 70 percent of NEET 1-mark MCQs from this chapter plug a value from one of the rows below.
| Parameter | Value / Range | NCERT Ref |
|---|---|---|
| BOD: river / safe / raw | < 5 / ≤ 20 / 200-600 mg O2/L | 8.3 |
| COD / BOD ratio | 1.5-2.5 (domestic); COD ≥ BOD | 8.3 |
| Secondary STP BOD drop | 80-90% via Zoogloea flocs | 8.3 |
| Biogas CH4 / CO2 / H2 | 50-70 / 25-30 / 5-10%; 20-26 MJ/m3 | 8.4 |
| Biogas tank + agencies | 10-15 ft; IARI + KVIC | 8.4 |
| Curd pH / temp / time | 6.5 → 4.0-4.6; 37-45 °C; 6-8 h | 8.1 |
| Ethanol yield (theor / pract) | 0.51 / 0.46-0.48 g per g glucose | 8.2 |
| Citric acid yield | 0.9 g/g sucrose; pH about 2.0; > 2 Mt/yr | 8.2 |
| Penicillin G potency | 1500-1670 IU/mg; 1 IU = 0.6 µg Na salt | 8.2 |
| PHA bioplastic yield | up to 80% dry-cell weight | 8.2 |
| N-fix: symbiotic vs free-living | 50-200 vs 20-30 kg N/ha/yr | 8.6 |
| Bt biopesticide | kills in 48 h; gut pH ≥ 9.5; 0.5-2.0 kg/ha | 8.5 |
| Leghaemoglobin O2 affinity | Kd about 10 nM (vs 1 µM human Hb) | 8.6 |
All entries above are retained in the 2026-27 syllabus. Biggest 1-mark trap: higher BOD means more pollution and lower DO; the two move in opposite directions.
How will Collegedunia's Microbes in Human Welfare Formula Sheet Help You?
- 2026-27 NCERT alignment: Every number, microbe and stoichiometry matches the current print of Sections 8.1 to 8.6.
- Quantitative slant: Industrial-microbiology numerics (ethanol 0.51 g/g, penicillin 1500-1670 IU/mg, biogas 50-70% CH4) are the recall-based NEET facts.
- Quick-lookup format: Fermentation, sewage, biogas, biocontrol and biofertiliser blocks each get a colour-coded box.
Fermentation Stoichiometry and Yield Card for NEET Class 12 Biology
Sections 8.1 and 8.2 carry almost all of the chapter's algebra. The card below packages the five must-know fermentation reactions.
| Process | Equation + catalyst |
|---|---|
| Lactic acid (curd) | C12H22O11 + H2O → 4 CH3CHOHCOOH ; Lactobacillus |
| Ethanol | C6H12O6 → 2 C2H5OH + 2 CO2 ; S. cerevisiae; 0.51 g/g theoretical |
| Acetic acid | C2H5OH + O2 → CH3COOH + H2O ; Acetobacter aceti |
| Citric acid | C12H22O11 + H2O + 3 O2 → 2 C6H8O7 + 4 H2O ; A. niger |
| Biogas methanogenesis | CO2 + 4 H2 → CH4 + 2 H2O ; methanogens; gives 50 to 70% CH4 |
| Symbiotic N-fixation | N2 + 8 H+ + 8 e- + 16 ATP → 2 NH3 + H2 + 16 ADP + 16 Pi ; nitrogenase |
NEET swaps "theoretical" and "practical" wording on the ethanol numerical every other paper. Lock both: 0.51 g/g is Gay-Lussac maximum; 0.46 to 0.48 g/g is what yeast delivers.
BOD, COD and Sewage Treatment Snapshot for 12th Biology
Section 8.3 is built around one test (BOD) and one bioreactor (the STP aeration tank). BOD is the standard test: BOD = (D1 - D2)/f , 5 d at 20 °C, mg O2/L. COD is always ≥ BOD; the COD/BOD ratio is 1.5 to 2.5 for biodegradable domestic sewage and much greater than 3 for toxic industrial effluent.
Biogas Composition and Plant-Design Quick Card for 12th Biology
Biogas is the cleanest single-mark on the chapter because the percentage block is tight: CH4 50 to 70% (combustible), CO2 25 to 30% (inert), H2 5 to 10% (minor combustible), plus traces of H2S and N2. Calorific value works out to 20 to 26 MJ/m3, about 60% of natural gas.
NEET has tested the IARI + KVIC pair as a 1-mark match in 3 of the last 5 papers. Cattle dung is the feedstock because the rumen already harbours methanogenic archaea, which is why "gobar gas" stuck as the name.
Antibiotics and Bioactive Microbe Index for Class 12 Biology
Section 8.2 hides high-value 1-mark cues behind unit-bearing numbers. The compact card below pairs each industrial product with its source microbe.
| Product | Source Microbe + Datum |
|---|---|
| Penicillin G | Penicillium chrysogenum; 1500-1670 IU/mg; blocks peptidoglycan |
| Streptomycin | Streptomyces griseus; first TB drug (Waksman, 1944) |
| Cyclosporin A | Trichoderma polysporum; organ-transplant immunosuppressant |
| Statins | Monascus purpureus; HMG-CoA reductase inhibitor |
| Streptokinase | Streptococcus sp.; cardiac clot buster (GM for safety) |
| PHA / PHB bioplastic | Cupriavidus / Alcaligenes; up to 80% dry-cell weight (Biopol) |
Biocontrol Agents and Biofertilisers Card for Class 12 Biology
Sections 8.5 and 8.6 pivot to ecological microbiology. The split table below pairs each agent with its key role.
| Agent | Role / Key Number |
|---|---|
| Bacillus thuringiensis (Bt) | Cry crystals kill lepidopteran larvae in 48 h; pH ≥ 9.5 |
| Trichoderma sp. | Free-living fungus; root-disease biocontrol |
| Baculovirus (NPV) | DNA virus; narrow-host insect biocontrol; IPM-ready |
| Rhizobium | Symbiotic; legume nodules; 50 to 200 kg N/ha/yr |
| Azospirillum, Azotobacter | Free-living bacteria; 20 to 30 kg N/ha/yr |
| Anabaena in Azolla | Symbiotic cyanobacterium; paddy N-fixation |
| Glomus (mycorrhiza) | Symbiotic fungus; P uptake + drought tolerance |
One-Shot Revision Tips for Class 12 Biology Microbes in Human Welfare
- Curd vs cheese: curd is LAB-only; cheese needs ripening microbes; Swiss holes are propionic CO2.
- BOD up → DO down: safe effluent ≤ 20 mg O2/L; secondary STP cuts BOD by 80-90%.
- Biogas: 50-70% CH4, 25-30% CO2, 5-10% H2; IARI + KVIC.
- Antibiotics fail on viruses: no peptidoglycan, no 70S ribosomes, no bacterial enzymes.
- Symbiotic vs free-living N-fix: 50-200 vs 20-30 kg N/ha/yr; leghaemoglobin protects nitrogenase.
- Bt mechanism: Cry solubilises at gut pH ≥ 9.5; harmless to mammals.
Top NEET Recall Hits and Recent PYQ Pattern for Microbes in Human Welfare
NEET 2025 lifted the biogas CH4 percentage and Penicillin G potency; NEET 2024 went after the symbiotic-vs-free-living N-fix gap; CBSE 2025 set a 3-mark long-answer on STP stages and Zoogloea flocs; CBSE 2024 ran the IARI / KVIC pair as a 1-mark match. NEET 2023 plugged the ethanol 0.51 g/g yield into a numerical MCQ.
Full topic-by-topic explanation: Microbes in Human Welfare Notes | Full year-wise PYQ map: Microbes in Human Welfare NCERT Solutions
Related Links:
- Human Health and Disease Class 12 Biology Formula Sheet (Chapter 7)
- Biotechnology Principles and Processes Class 12 Biology Formula Sheet (Chapter 9)
More Microbes in Human Welfare Biology Class 12 Resources
- Microbes in Human Welfare Class 12 Biology NCERT Solutions
- Microbes in Human Welfare Class 12 Biology Notes
- Microbes in Human Welfare Class 12 Biology NCERT Book PDF
- Microbes in Human Welfare Class 12 Biology Exemplar Solutions
- Microbes in Human Welfare Class 12 Biology Handwritten Notes
- Microbes in Human Welfare Class 12 Biology NCERT Exemplar Book PDF
Formula Sheet for Class 12 Biology: All Chapters
The table below links every other Class 12 Biology chapter's formula sheet.
| Chapter | Resource |
|---|---|
| Chapter 1 | Sexual Reproduction in Flowering Plants |
| Chapter 2 | Human Reproduction |
| Chapter 3 | Reproductive Health |
| Chapter 4 | Principles of Inheritance and Variation |
| Chapter 5 | Molecular Basis of Inheritance |
| Chapter 6 | Evolution |
| Chapter 7 | Human Health and Disease |
| Chapter 9 | Biotechnology Principles and Processes |
| Chapter 10 | Biotechnology and Its Applications |
| Chapter 11 | Organisms and Populations |
| Chapter 12 | Ecosystem |
| Chapter 13 | Biodiversity and Conservation |
Microbes in Human Welfare Class 12 Biology Formula Sheet FAQs
Ques. What does the Microbes in Human Welfare Class 12 Biology formula sheet cover?
Ans. The sheet collates every numerical fact and microbe-product pair across NCERT Sections 8.1 to 8.6: lactic-acid fermentation, ethanol stoichiometry, citric-acid yield (0.9 g/g), penicillin potency (1500 to 1670 IU/mg), BOD ranges, the COD/BOD ratio, biogas composition (50 to 70% CH4), Bt biopesticide mechanism, Rhizobium N-fixation (50 to 200 kg N/ha/yr) and the symbiotic-vs-free-living biofertiliser split. One printable revision page aligned to the 2026-27 NCERT.
Ques. Is this Class 12 Biology Chapter 8 formula sheet aligned with the 2026-27 NCERT?
Ans. Yes. Every entry matches the current 2026-27 print of NCERT Biology. Sections 8.1 through 8.6 are retained in full, and the sheet flags both classical numerical facts (BOD, biogas %, ethanol yield) and the NCERT-extension topics (PHA bioplastic, leghaemoglobin chemistry) exactly as they appear in the latest edition.
Ques. How is this Microbes in Human Welfare formula sheet useful for NEET preparation?
Ans. NEET pulls 2 to 4 questions a year from this chapter, almost all recall-based numericals or microbe-to-product matchings: percentage of methane in biogas, the BOD discharge limit, the symbiotic-vs-free-living N-fixation rate, the citric-acid yield and the Penicillium G potency. The Collegedunia sheet packages these in quick-lookup tables so a 15 minute final-pass the night before the paper covers nearly every common MCQ.
Ques. What is the biogas composition as per NCERT Class 12 Biology Chapter 8?
Ans. Biogas is a mixture of methane (CH4) 50 to 70%, carbon dioxide (CO2) 25 to 30%, hydrogen (H2) 5 to 10% by volume, with traces of H2S and N2. Methane is the combustible fraction. Calorific value is 20 to 26 MJ/m3, about 60% of natural gas. Biogas plants in India are popularised by IARI and KVIC.
Ques. What is BOD and what is the safe discharge limit for treated effluent?
Ans. BOD (Biochemical Oxygen Demand) is the oxygen consumed by aerobic microbes to oxidise all the organic matter in 1 L of water over 5 days at 20 °C, measured in mg O2/L. Clean river water has BOD < 5; raw sewage 200 to 600; the discharge standard for safe effluent is BOD ≤ 20 mg O2/L. COD/BOD for domestic sewage is 1.5 to 2.5; a ratio much greater than 3 implies a large non-biodegradable industrial fraction.
Ques. What is the difference between symbiotic and free-living nitrogen fixers in Chapter 8?
Ans. Symbiotic fixers live inside legume root nodules (Rhizobium) or in Azolla (Anabaena) and fix 50 to 200 kg N/ha/yr. Free-living fixers (Azospirillum, Azotobacter, Nostoc, Oscillatoria) fix only 20 to 30 kg N/ha/yr. In Rhizobium the nitrogenase enzyme is O2-sensitive and is protected by leghaemoglobin, which gives an active nodule its pink colour.
Ques. Why are antibiotics ineffective against viruses according to NCERT Chapter 8?
Ans. Antibiotics target peptidoglycan, 70S ribosomes or specific bacterial enzymes. Viruses lack peptidoglycan, lack ribosomes (they use the host's machinery) and lack the enzymes antibiotics inhibit, so antibiotics have no target on a virus. The common cold and COVID-19 therefore need antivirals (acyclovir, interferons) and not antibiotics. NEET tests this assertion-reason almost every year.
Ques. How does the Bt biopesticide kill insect larvae?
Ans. Bacillus thuringiensis produces spores containing Cry protein crystals. When a lepidopteran larva (e.g. cotton bollworm) eats the spray, the alkaline gut pH (≥ 9.5) solubilises the crystal, releasing the toxin. The toxin perforates the midgut and the larva dies in about 48 hours. Mammals, birds and fish have acidic stomachs and are not harmed. Cry genes (cryIAc, cryIIAb) have been cloned into Bt cotton and Bt maize.
Ques. How many marks does Microbes in Human Welfare carry in CBSE Class 12 Biology Boards?
Ans. Chapter 8 contributes around 5 to 7 marks in the CBSE Class 12 Biology board paper, typically split across a 2 mark short-answer on STP / biogas plant design and a 3 to 5 mark long-answer on industrial fermentation (penicillin, citric acid) or biofertilisers. NEET tests 2 to 4 questions a year, almost always 1 mark numericals or microbe-product MCQs.
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