GATE General Microbiology: practice questions

1 · History and scope of microbiology · easy

Preservation of food by heating it in sealed containers was first practised, without knowledge of microbes, by:

1. Louis Pasteur
2. Nicolas Appert
3. Alexander Fleming
4. John Tyndall

2 · History and scope of microbiology · medium

Viruses were first recognised when tobacco mosaic disease was shown to be caused by an agent that:

1. Was killed by boiling but not by filtering
2. Grew on agar but only in the dark
3. Passed through bacteria-proof filters
4. Was visible as rods under oil immersion

3 · Microscopy: light, phase-contrast, fluorescence and electron · medium

Using the relation d = 0.61 λ / NA, what is the resolution limit for green light of 550 nm with an objective of numerical aperture 1.25?

1. 268 nm
2. 220 nm
3. 440 nm
4. 721 nm

4 · Viruses and bacteriophages · medium

In lysogeny, a temperate phage:

1. Integrates its DNA into the host chromosome as a prophage
2. Lyses the host cell within minutes of infection every time
3. Exits the cell by budding through a lipid envelope
4. Destroys the host chromosome and replaces it with its own

5 · Microbial nutrition and culture media · medium

On MacConkey agar, a lactose-fermenting Gram-negative rod gives pink-red colonies. Which components respectively make the medium selective and differential?

1. Neutral red selects; peptone with sodium chloride differentiates
2. Lactose selects; bile salts with crystal violet differentiate by colour
3. Bile salts/crystal violet select; lactose/neutral red differentiate
4. Agar selects; bile salts with lactose differentiate by colony size

6 · Growth curve, generation time and growth kinetics · medium

A yeast culture makes 5 g/L of cells while consuming 10 g/L of glucose. The cell yield coefficient Y(X/S) is:

1. 0.05 g/g
2. 5.0 g/g
3. 0.5 g/g
4. 2.0 g/g

7 · Control of microorganisms: physical and chemical agents and death kinetics · medium

Viable counts fall from 10⁶ to 10² CFU/mL in 12 minutes at a constant temperature. The D-value is:

1. 2 min
2. 4 min
3. 12 min
4. 3 min

8 · Microbial genetics: mutation, plasmids, transformation, transduction and conjugation · medium

A mutation in which a purine is replaced by a pyrimidine is called a:

1. Deletion
2. Transition
3. Transversion
4. Frameshift

9 · Aseptic technique and laboratory biosafety · easy

Most food-borne bacterial pathogens such as Salmonella and Listeria monocytogenes are handled in the laboratory as:

1. Risk group 1 organisms
2. Risk group 4 organisms
3. Risk group 2 organisms
4. Organisms with no risk classification

10 · Aseptic technique and laboratory biosafety · medium

Cultures and contaminated plates from a food microbiology laboratory should be disposed of by:

1. Leaving open under UV light overnight
2. Pouring into the drain with tap water
3. Autoclaving them before any disposal
4. Placing in general waste in sealed bags