COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for UGC-CSIR NET/JRF, SLET, GATE, and other entrance tests – CELLULAR ORGANIZATION – Microbial Physiology and Metabolisms.
Syllabus Outline
- Microbial Growth and Physiology – Growth yield and characteristics, strategies of cell division and stress response
- Microbial Metabolism (e.g., Anabolism and Catabolism)
- Biosynthesis and Metabolic Regulation
- Photosynthesis in Microorganisms and oxygenic vs. anoxygenic photosynthesis
- Microbial Bioenergetics.
This quiz contains concept-based, most frequently asked 25 MCQs of “CELLULAR ORGANIZATION – Microbial Physiology and Metabolisms”. Each question has a single correct/most appropriate answer.
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1. E. coli is grown in a defined medium with equal glucose and lactose. The growth curve shows two exponential phases separated by a short lag. Which molecular event primarily characterises that lag?
A) Rapid hydrolysis of guanosine tetraphosphate to resume translation elongation.
B) Synthesis of β-galactosidase and lactose permease after relief of catabolite repression.
C) Allosteric inhibition of hexokinase by glucose-6-phosphate.
D) Transition from aerobic respiration to anaerobic fermentation due to oxygen depletion.
2. A Lineweaver–Burk plot (1/μ vs 1/S) has a y-intercept = 2.0 h and an x-intercept = −4.0 L·g⁻¹. What are μmax and Ks?
A) μmax = 0.5 h⁻¹, Ks = 0.25 g·L⁻¹
B) μmax = 2.0 h⁻¹, Ks = 4.0 g·L⁻¹
C) μmax = 0.5 h⁻¹, Ks = 4.0 g·L⁻¹
D) μmax = 2.0 h⁻¹, Ks = 0.25 g·L⁻¹
3. If μ = 0.0346 min⁻¹, what is the doubling time?
A) 10 minutes
B) 20 minutes
C) 30 minutes
D) 60 minutes
4. How do Nitrobacter generate NADH for the Calvin cycle, given NO₂⁻/NO₃⁻ redox potential is +0.43 V and NAD⁺/NADH is −0.32 V?
A) Use a light-driven photosystem.
B) Reverse electron transport driven by the proton motive force.
C) Ferment organics to produce NADH.
D) Direct coupling of nitrite oxidation to ferredoxin via electron bifurcation.
5. Bacteriorhodopsin in Halobacterium functions as:
A) A light-harvesting antenna transferring energy to a reaction centre.
B) A light-driven proton pump that generates proton motive force.
C) A light-driven chloride pump for osmotic balance.
D) An enzyme that oxidises water to produce oxygen.
6. The low standard redox potential of ferredoxin is critical for:
A) Reducing oxygen to water.
B) Reducing nitrogenase for N₂ fixation.
C) Oxidising NADH to NAD⁺.
D) Reducing quinones in the Q-cycle.
7. In β-oxidation, two-carbon units are released as:
A) Acetyl-CoA
B) Malonyl-CoA
C) Free acetate
D) Pyruvate
8. During the measurement of bacterial growth via optical density, deviations from Beer-Lambert’s law occur at high cell densities. This phenomenon is primarily due to:
A) The metabolic production of fluorescent pigments that interfere with absorbance.
B) Secondary scattering of light.
C) The lysis of cells in the stationary phase reduces the effective optical path length.
D) The saturation of the spectrophotometer’s photodetector.
9. Which phototrophic group uses chlorosomes with bacteriochlorophyll c/d/e for efficient low-light harvesting?
A) Cyanobacteria
B) Purple non-sulfur bacteria
C) Green sulfur bacteria
D) Heliobacteria
10. The “Red Drop” and “Emerson Enhancement” experiments provided evidence for:
A) Two distinct photosystems operating in series.
B) Cyclic electron flow in bacteria.
C) The role of ATP synthase in photophosphorylation.
D) Water splitting by the manganese cluster.
11. In cyanobacteria, phycobilisomes transfer excitation energy primarily to:
A) Photosystem I
B) Photosystem II
C) ATP synthase
D) Cytochrome b₆f
12. In Anabaena, the typical electron source for nitrogenase is:
A) Reduced ferredoxin from Photosystem I
B) NADH from the TCA cycle
C) Reduced plastoquinone from PSII
D) Hydrogen gas oxidised by hydrogenase
13. Expression of nif genes in Klebsiella pneumoniae requires:
A) High ammonium and anaerobic conditions.
B) Low ammonium and aerobic conditions.
C) Low ammonium and anaerobic conditions.
D) Constitutive expression regardless of environment.
14. Quorum sensing for bioluminescence in Vibrio fischeri is mediated by:
A) Acyl-homoserine lactone
B) Autoinducer-2
C) Oligopeptide CSP
D) Diffusible signal factor
15. A chemostat operating at steady state with a working volume of 5.0 L has a continuous inlet feed flow rate of 2.5 L/h. The microorganism being cultured has a mathematically determined maximum specific growth rate of 0.5 h−1and a half-saturation constant for the limiting substrate of 0.25 g/L. If the dilution rate is instantaneously increased to 0.6 h−1, which of the following outcomes is theoretically predicted based on Monod kinetics?
A) The specific growth rate will spontaneously increase to 0.6 h−1to match the new dilution rate, maintaining steady state.
B) The substrate concentration in the reactor will decrease due to increased mixing efficiency.
C) The culture will undergo washout because the dilution rate exceeds the critical growth limit.
D) The organism will enter a stationary phase due to nutrient toxicity at high flow rates.
16. At very high substrate concentration (S → ∞), the specific growth rate μ in the Haldane model tends toward:
A) ∞
B) Zero
C) Ks/Ki
D) μmax/2
17. In the context of the bacterial cell cycle, the “C period” refers to:
A) The time interval between cell division and the initiation of DNA replication.
B) The time required to replicate the entire chromosome.
C) The time interval between the termination of replication and cell division.
D) The duration of the cytokinesis process.
18. Mutant strains of Escherichia coli lacking specific TCA cycle enzymes exhibit distinct phenotypes under anaerobic conditions. Which of the following phenotypes is observed in a mutant lacking α-ketoglutarate dehydrogenase during anaerobic fermentation?
A) Inability to grow on glucose.
B) Overproduction of succinate due to upregulation of the glyoxylate bypass.
C) Auxotrophy for succinyl-CoA-derived amino acids.
D) Enhanced resistance to oxidative stress due to heme accumulation.
19. In the Stickland reaction utilised by Clostridium species for amino acid fermentation:
A) One amino acid acts as an electron donor, and another acts as an electron acceptor.
B) Amino acids are polymerised into peptides for energy storage.
C) Amino acids are converted directly to glucose via gluconeogenesis.
D) Urea is the primary byproduct.
20. Which intermediate of the TCA cycle accumulates in E.coli mutants lacking Isocitrate Dehydrogenase and forces the cell to utilise the Glyoxylate Bypass for growth on acetate?
A) Citrate
B) Isocitrate
C) Succinate
D) Malate
21. The thermodynamic distinction between purple sulfur bacteria and green sulfur bacteria regarding NAD(P)⁺ reduction is:
A) Green sulfur bacteria use reverse electron transport; purple bacteria reduce NAD(P)⁺ directly via ferredoxin.
B) Purple bacteria require reverse electron transport; green bacteria reduce NAD(P)⁺ directly via ferredoxin.
C) Both require reverse electron transport because bacterial reaction centres cannot reduce pyridine nucleotides.
D) Purple bacteria use water as a donor, removing the need for NAD(P)⁺ reduction.
22. In Cyanobacteria, the Phycobilisomes are attached to the cytosolic face of the thylakoid membrane and transfer energy primarily to:
A) Photosystem I
B) Photosystem II
C) ATP Synthase
D) Cytochrome b6f
23. In the bacterial Phosphotransferase System, which of the following events does not occur during the transport of Glucose?
I – PEP acts as the initial phosphoryl donor.
II – EIIA-Glc becomes predominantly unphosphorylated.
III – Unphosphorylated EIIA-Glc binds to LacY and inhibits lactose uptake.
IV – Adenylate Cyclase is activated by phosphorylated EIIA-Glc.
A) I and II only
B) I, II, and III only
C) I, II, III, and IV
D) IV only
24. Which statements about Ks are correct?
I – Ks is the substrate concentration at which μ = ½ μmax.
II – High Ks indicates high substrate affinity.
III – Ks is inversely proportional to uptake affinity.
IV – Low Ks gives an advantage in oligotrophic environments.
A) I, II and IV
B) I, II and III
C) II and III
D) I, III and IV
25. Assertion (A): The stationary phase of bacterial growth is characterised by a cryptic growth phenomenon where the net growth rate is zero.
Reason (R): In the stationary phase, the rate of cell division is exactly balanced by the rate of cell death, fueled by the lysis products of dead cells.
A) Both A and R are true, and R is the correct explanation of A.
B) Both A and R are true, but R is not the correct explanation of A.
C) A is true, but R is false.
D) A is false, but R is true.
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References
- Cooper, G. M. (2022). The Cell: A Molecular Approach, Sinauer Associates, 9th Edition
- Willey, J. M., Sandman, K. M., & Wood, D. H. (2022). Prescott’s Microbiology, McGraw-Hill, 12th Edition
- Kumar, P., & Mina, U. (2025). Life Sciences: Fundamentals and Practice – Part I & II, Pathfinder Academy, 9th Edition
- Verma, P. S., & Agarwal, V. K. (2022). Cell Biology, Genetics, Molecular Biology, Evolution and Ecology, S. Chand Publishing, 1st Edition
- Singh, B. D. (2020). Genetics, Kalyani Publishers
- Nelson, David L. & Cox, Michael M. (2021). Lehninger Principles of Biochemistry, W. H. Freeman, 8th Edition
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