UGC NET — Environmental Sciences (subject code 89) · India · National Testing Agency for the University Grants Commission
Original practice questions written to the published syllabus · not past papersMicroorganisms as the engines of nutrient cycling, wastewater treatment, bioremediation and disease. GATE ES Section 3 examines it from cell structure to Monod kinetics and coliform counts.
In the exams: GATE ES Section 3; UGC NET Environmental Sciences Unit 3; ICAR AICE subject 71 Units 4–5 (bioremediation, composting)
UGC NET Environmental Sciences — Unit 3 (environmental biology and microbiology)
Microbial diversity, metabolism, growth, microbes in biogeochemical cycles, biofertilisers and biopesticides, bioremediation, wastewater microbiology, indicators and waterborne diseases.
How our questions for UGC NET spread across the units of Environmental Microbiology. Difficulty: 4 easy, 24 medium, 17 hard.
| Microbial metabolism: glycolysis, TCA cycle, electron transport | 6 | |
| Microorganisms in biogeochemical cycling | 6 | |
| Pathogens, transmission routes and indicator organisms | 6 | |
| Prokaryotic and eukaryotic microorganisms; classification and diversity | 5 | |
| Cell structure: membranes, walls, endospores, organelles | 4 | |
| Fermentation and anaerobic respiration | 4 | |
| Enzymes and enzyme kinetics | 4 | |
| Microorganisms in wastewater treatment and bioremediation | 4 | |
| Cell chemistry: proteins, nucleic acids, lipids, polysaccharides | 2 | |
| Bacterial growth: specific growth rate, doubling time, Monod model | 1 | |
| Batch and continuous culture | 1 | |
| Control of microorganisms: physical and chemical methods | 1 | |
| Coliform enumeration: MPN and membrane filtration | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
What is the 'great plate count anomaly'?
A. Media recover under 1 per cent of cells seen
Most environmental microbes do not grow on standard media, motivating culture-independent molecular methods.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which method reveals the functional genes, not just the identities, of an uncultured soil community?
A. Shotgun metagenomic sequencing
Metagenomics sequences all DNA, revealing genes and pathways; 16S amplicons mainly identify taxa; staining and plating miss most organisms.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Why do fast-growing bacterial cells contain more RNA than slow-growing cells?
D. They need more RNA-rich ribosomes for protein synthesis
Ribosome content scales with growth rate, and ribosomes are mostly rRNA.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which organism forms endospores and is used as an indicator of remote or intermittent faecal contamination?
C. Clostridium perfringens
Its spores survive long in water, indicating past contamination and protozoan removal efficiency.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which bacterium oxidises ferrous iron and contributes to acid mine drainage and bioleaching?
A. Acidithiobacillus ferrooxidans
A. ferrooxidans oxidises Fe²⁺ and sulphides at low pH.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
What is the correct sequence of stages in anaerobic digestion?
C. Hydrolysis, acidogenesis, acetogenesis, methanogenesis
Polymers are hydrolysed, fermented to acids, converted to acetate and H2, then to methane.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
How does a competitive inhibitor affect Km and Vmax?
D. Km rises; Vmax is unchanged
Competitive inhibitors compete for the active site and can be overcome by more substrate; non-competitive inhibitors lower Vmax.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which equation describes substrate inhibition, in which growth rate falls at high concentrations of a toxic substrate such as phenol?
C. The Haldane, or Andrews, equation
The Haldane form adds a substrate inhibition term to the Monod/Michaelis–Menten expression.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
At substrate concentrations far below Km, Michaelis–Menten kinetics approximate
A. first-order kinetics in substrate
When [S] << Km, v ≈ (Vmax/Km)[S], first order; when [S] >> Km, v ≈ Vmax, zero order.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Why is E. coli preferred over total coliforms as an indicator of faecal contamination?
C. It is faecal-specific; total coliforms include soil species
E. coli is faecal-specific; total coliforms include soil and plant bacteria and indicate treatment or distribution problems.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
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