GATE — Life Sciences (XL) with Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersMicrobial cells, growth, metabolism, genetics and laboratory technique: the base for every dairy microbiology subject.
In the exams: ICAR AICE subject 36 Units 1–2; GATE XL-U Section 2 and XL-S; ICAR AIEEA-PG group 16
How our questions for GATE spread across the units of General Microbiology. Difficulty: 11 easy, 63 medium, 0 hard.
| Microbial metabolism: respiration and fermentation | 8 | |
| Classification of bacteria, yeasts, moulds and viruses | 7 | |
| Effect of temperature, pH, water activity and oxygen on growth | 7 | |
| Microbial genetics: mutation, plasmids, transformation, conjugation, transduction | 7 | |
| Microscopy: light, phase, fluorescence and electron | 6 | |
| Bacterial cell structure: wall, membrane, capsule, flagella, spores | 6 | |
| Bacteriophages | 6 | |
| Microbial nutrition and culture media | 6 | |
| Growth curve, generation time and growth measurement | 6 | |
| Sterilisation and disinfection | 6 | |
| Aseptic technique and pure-culture methods | 6 | |
| History and scope of microbiology | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which type of microscopy lets living, unstained bacteria and refractile endospores be seen clearly?
D. Phase-contrast
Phase contrast converts refractive-index differences into brightness differences. Electron microscopy needs fixed, dried specimens in a vacuum.
Further reading: Madigan et al., Brock Biology of Microorganisms
The endotoxin activity of Gram-negative bacteria resides in the:
B. Lipid A part of lipopolysaccharide
Lipid A, the membrane anchor of LPS, triggers fever and inflammation when released from lysed cells.
Further reading: Madigan et al., Brock Biology of Microorganisms
Ropy milk caused by contaminating bacteria results from:
D. Extracellular polysaccharide
Exopolysaccharides (capsule or slime material) make milk viscous and stringy. Selected EPS-producing strains give desirable texture in yoghurt.
Further reading: Robinson, Dairy Microbiology Handbook
Which mould is responsible for the blue veins of blue-veined cheeses?
B. Penicillium roqueforti
P. roqueforti grows in the fissures of pierced cheese. P. camemberti forms white rinds; A. flavus produces aflatoxins.
Further reading: Robinson, Dairy Microbiology Handbook
A virus differs from a bacterium in that a virus:
C. Contains one kind of nucleic acid and multiplies only in host cells
Virions carry one type of nucleic acid in a capsid, lack metabolism and ribosomes, and replicate only in living cells.
Further reading: Madigan et al., Brock Biology of Microorganisms
A direct microscopic count of a raw milk sample is much higher than its plate count. A likely explanation is that:
A. Microscopy also counts dead cells and resolves cells within clumps
Microscopy counts all stained cells, living or dead, and resolves cells in clumps; plates count only units able to grow.
Further reading: Robinson, Dairy Microbiology Handbook
Transfer of DNA between bacteria through direct cell-to-cell contact is called:
C. Conjugation
Conjugation needs contact (via a pilus in Gram-negatives). Transformation is uptake of free DNA; transduction is phage-mediated.
Further reading: Madigan et al., Brock Biology of Microorganisms
Which term describes reducing microbial numbers on food-contact surfaces to safe levels?
C. Sanitisation
Sanitisers are often required to give about a 5-log reduction of test organisms in a set time. Antisepsis applies to living tissue.
Further reading: Codex CXC 57 Code of Hygienic Practice for Milk and Milk Products
Rank by usual resistance to chemical disinfectants, highest first:
D. Bacterial spores, mycobacteria, vegetative bacteria
Spores are most resistant, then mycobacteria with waxy walls, then ordinary vegetative bacteria.
Further reading: Madigan et al., Brock Biology of Microorganisms
Aseptic filling machines commonly sterilise packaging material with:
B. Hot hydrogen peroxide at 30–35%
Hot concentrated H₂O₂, followed by hot air to remove residues, is standard. Ethanol and QACs are not sporicidal.
Further reading: Tetra Pak Dairy Processing Handbook
Ten here, 74 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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