Chapter Overview & Weightage
This chapter is a guaranteed scorer — it’s mostly application-based factual recall about how microbes are used in food, sewage treatment, biogas production, and as biocontrol agents. NEET and CBSE both pull questions on specific microbe-product matches.
Typical CBSE weightage: marks per year. NEET pulls MCQs.
| Year | Marks | Question type |
|---|---|---|
| 2019 | 5 | Sewage treatment process |
| 2020 | 3 | Microbe-product matching |
| 2021 | 5 | Biogas production explanation |
| 2022 | 3 | Antibiotics and their producers |
| 2023 | 5 | Activated sludge process diagram |
| 2024 | 5 | Biocontrol agents in agriculture |
Key Concepts You Must Know
- Household microbes: Lactobacillus (curd), Saccharomyces (bread, beer), Aspergillus niger (citric acid)
- Industrial products: ethanol (yeast), antibiotics (penicillin from Penicillium notatum)
- Sewage treatment: primary (physical) and secondary (biological) treatment
- Activated sludge process and floc formation
- Biogas production: methanogens like Methanobacterium in anaerobic digesters
- Biocontrol: Bacillus thuringiensis (Bt) for pest control
- Biofertilisers: Rhizobium (legumes), Azospirillum, mycorrhiza
- Statins from Monascus purpureus (cholesterol-lowering)
- Streptokinase from Streptococcus (clot-buster)
- Cyclosporin A from Trichoderma polysporum (immunosuppressant)
Important Formulas
No formulas — instead, key matching tables for revision.
| Product | Microbe |
|---|---|
| Curd | Lactobacillus |
| Bread | Saccharomyces cerevisiae |
| Citric acid | Aspergillus niger |
| Penicillin | Penicillium notatum |
| Streptomycin | Streptomyces griseus |
| Statins | Monascus purpureus |
| Cyclosporin A | Trichoderma polysporum |
Primary: physical removal (sedimentation) → Secondary: aerobic digestion in tanks (BOD reduction) → Anaerobic sludge digesters → Effluent release
Solved Previous Year Questions
PYQ 1 (CBSE 2021, 5 marks)
Explain the process of biogas production. Name the major component and the microbes responsible.
Biogas is produced in anaerobic digesters by methanogenic bacteria such as Methanobacterium. Cattle dung is mixed with water and fed into the digester. Bacteria first break down complex organics into fatty acids, then methanogens convert these to methane () and . Methane is the major component (50-70%). The slurry residue is used as biofertiliser.
PYQ 2 (CBSE 2023, 5 marks)
Describe the activated sludge process in sewage treatment with the help of a diagram.
After primary treatment, sewage flows into aeration tanks. Air is pumped vigorously, allowing aerobic microbes to multiply rapidly, forming masses called flocs (mesh of bacteria + fungal filaments). These consume organic matter, drastically reducing BOD. The sewage is then sent to settling tanks where flocs sediment as activated sludge. A part is recycled as inoculum; the rest goes to anaerobic digesters where methanogens produce biogas. Treated effluent is released after BOD reduction.
PYQ 3 (CBSE 2024, 5 marks)
What are biocontrol agents? Give two examples and explain their mechanism.
Biocontrol agents are organisms used to control pests without chemical pesticides. (1) Bacillus thuringiensis (Bt): produces a toxin that crystallises in the gut of insect larvae, rupturing it and killing the pest. Used as Bt-cotton, Bt-brinjal. (2) Trichoderma: a free-living fungus that fights plant pathogens in roots. Used as a biocontrol fungus for soil-borne plant diseases.
Difficulty Distribution
| Difficulty | % of CBSE Qs | Typical type |
|---|---|---|
| Easy | Direct microbe-product matching | |
| Medium | Sewage/biogas process explanations | |
| Hard | Comparison or experimental design questions |
Expert Strategy
Make flashcards for every microbe-product pair in NCERT. The chapter has roughly 20 such pairs, and questions ask 1-2 every year.
Draw the activated sludge flowchart from memory: Sewage → Primary → Aeration → Settling → (recycle/digester) → Effluent. This labelled diagram is worth 3 marks of the 5-mark question.
For NEET, watch for “which microbe produces X?” — the most-tested ones are penicillin, statins (Monascus), cyclosporin A, and streptokinase. Memorise these four cold.
Common Traps
Confusing Penicillium (the fungus, antibiotic producer) with Penicillin (the drug). One is the source, the other is the product. Same with Streptomyces vs Streptomycin.
Saying biogas is “pure methane”. Biogas is roughly 50-70% methane, with and traces of .
Mixing up biofertiliser with biocontrol. Biofertilisers add nutrients (Rhizobium fixes N). Biocontrol kills pests (Bt). Both are biological but with different roles.