Chapter 3 — Immunity and Applied Microbiology
Key Concepts Quick Recap
| Term | Definition |
|---|
| Antigen | Substance that triggers immune response (foreign protein, polysaccharide) |
| Antibody (Immunoglobulin) | Protein produced by B cells; binds to antigen specifically |
| B cells | Produce antibodies (humoral immunity) |
| T cells | Cell-mediated immunity; cytotoxic T cells kill infected cells |
| Vaccination | Introducing weakened/killed pathogen or its antigen to stimulate immunity |
| Antibiotic | Substance that kills or inhibits bacterial growth |
| Fermentation | Microbial conversion of sugars to useful products (alcohol, acids) |
I. Choose the Best Answer (MCQs)
1. The first line of defence in innate immunity is: (a) T lymphocytes (b) Skin and mucous membranes (c) Antibodies (d) Memory cells
Answer(b) Skin and mucous membranes Physical barriers prevent pathogen entry: intact skin, mucous membranes lining respiratory/GI/GU tracts, cilia (sweep particles out), tears/saliva (lysozyme).
2. BCG vaccine protects against: (a) Cholera (b) Tuberculosis (c) Smallpox (d) Hepatitis B
Answer(b) Tuberculosis BCG (Bacillus Calmette-Guérin): live attenuated Mycobacterium bovis. Given at birth to protect against TB (especially tuberculous meningitis in children).
3. Penicillin kills bacteria by: (a) Disrupting cell membrane (b) Inhibiting protein synthesis (c) Inhibiting cell wall synthesis (d) Inhibiting DNA replication
Answer(c) Inhibiting cell wall synthesis Penicillin: beta-lactam antibiotic; inhibits transpeptidase (PBP = penicillin-binding protein) → prevents cross-linking of peptidoglycan → bacterial cell wall weakens → osmotic lysis. Effective only against actively growing bacteria.
4. Which microorganism is used in the production of beer? (a) Lactobacillus (b) Saccharomyces cerevisiae (c) Aspergillus niger (d) Rhizobium
Answer(b) Saccharomyces cerevisiae Baker's/Brewer's yeast: ferments glucose → ethanol + CO₂ (anaerobic). Used in: beer, wine, bread, biofuel.
5. An IgG antibody is: (a) The largest immunoglobulin (b) The first antibody produced in immune response (c) The most abundant antibody in serum (d) Found mainly in saliva
Answer(c) The most abundant antibody in serum IgG: 75-80% of serum immunoglobulins; crosses placenta (maternal immunity to newborn); long-lasting. IgM: pentamer; first antibody produced in primary response; best at complement activation. IgA: in secretions (saliva, breast milk, tears).
6. The citric acid used in food industry is produced by: (a) Saccharomyces (b) Aspergillus niger (c) Lactobacillus (d) Clostridium
Answer(b) Aspergillus niger Aspergillus niger: produces citric acid (90% of world's citric acid production) by fermentation of sucrose. Used in food and beverages as preservative/acidulant.
7. Which of the following is a probiotic organism? (a) Staphylococcus aureus (b) Lactobacillus acidophilus (c) Clostridium botulinum (d) E. coli (pathogenic)
Answer(b) Lactobacillus acidophilus Probiotics: live microorganisms that confer health benefits. Lactobacillus and Bifidobacterium species: found in yogurt, fermented foods; maintain gut microbiome, improve digestion, prevent diarrhoea.
II. Short Answer Questions
Q1. Explain the industrial applications of microorganisms.
Answer
| Product | Microorganism | Process |
|---|
| Penicillin | Penicillium chrysogenum | Submerged aerobic fermentation |
| Citric acid | Aspergillus niger | Fermentation of molasses |
| Lactic acid | Lactobacillus | Anaerobic fermentation of glucose |
| Alcohol (beer, wine) | Saccharomyces cerevisiae | Anaerobic fermentation |
| Vinegar (acetic acid) | Acetobacter aceti | Oxidation of ethanol |
| Vitamin B₁₂ | Pseudomonas, Propionibacterium | Fermentation |
| Insulin (recombinant) | E. coli (genetically engineered) | Recombinant DNA technology |
| Biogas (methane) | Methanobacterium (archaea) | Anaerobic digestion |
Q2. What are antibiotics and how are they classified?
Answer
Antibiotics: substances produced by microorganisms that kill or inhibit growth of other microorganisms.
Classification by spectrum:
- Narrow-spectrum: effective against specific group (penicillin G → Gram+; polymyxin → Gram–).
- Broad-spectrum: effective against wide range (tetracycline, chloramphenicol, ciprofloxacin).
Classification by mechanism:
- Cell wall inhibitors: penicillin, cephalosporin, vancomycin.
- Protein synthesis inhibitors: tetracycline (30S), erythromycin (50S), chloramphenicol (50S).
- DNA/RNA inhibitors: ciprofloxacin (DNA gyrase), rifampicin (RNA polymerase).
- Cell membrane disruptors: polymyxin.
Exam Checklist
- Innate: non-specific, immediate (skin, macrophages, NK cells, complement).
- Adaptive: specific, memory (B cells → antibodies; T cells → cell-mediated).
- IgG: most abundant; crosses placenta. IgM: first in infection. IgA: secretions.
- BCG: live attenuated; TB; given at birth.
- Penicillin: inhibits cell wall synthesis (peptidoglycan cross-linking).
- S. cerevisiae: alcohol/beer; A. niger: citric acid; Lactobacillus: lactic acid/yogurt.
- Antibiotic resistance: overuse → selection pressure → resistant strains.
