GATE 2021 Question Paper XL S Life Sciences - Microbiology

Q.1 – Q.5 Multiple Choice Question (MCQ), carry ONE mark each (for each wrong
answer: – 1/3).

Q.1 Antonie van Leeuwenhoek observed several microscopic organisms under
his hand-made microscope. He described them as

(A) Bacteria.

(B) Fungi.

(C) Animalcules.

(D) Bacteriophages.

Q.2 Which ONE of the following pathways oxidizes 1 mole of glucose to 2 moles
of pyruvic acid along with one mole each of ATP, NADH and NADPH, in
Pseudomonas spp., but not in Bacillus spp.?

(A) Gluconeogenesis

(B) Embden-Meyerhoff Pathway (EMP)

(C) Entner-Doudoroff (ED) Pathway

(D) Pentose Phosphate Pathway (PPP)

Q.3 Water balance in extreme halophiles such as Halobacterium is maintained
by cell surface glycoproteins consisting of

(A) glycine and lysine.

(B) lysine and histidine.

(C) glycine.

(D) aspartate and glutamate.

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Q.4 Nocardia spp. are not amenable to the classical method of Gram staining
due to the presence of

(A) N-acetyltalosaminuronic acid in the cell wall.

(B) thick peptidoglycan.

(C) mycolic acid.

(D) keto-deoxy-octulosonic acid.

Q.5 Protists belonging to the genus Trichonympha thrive in the gut of termites.
They help the termites use wood as a food source. This relationship is an
example of

(A) parasitism.

(B) competition.

(C) commensalism.

(D) mutualism.

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Q.6 – Q.9 Multiple Select Question (MSQ), carry ONE mark each (no negative marks).

Q.6 Which of the following is/are used as electron donor/s for CO2 reduction
during photosynthesis in purple sulfur bacteria?

(A) Hydrogen sulfide

(B) Thiosulfates

(C) Methane

(D) Sulfates

Q.7 Which of the following catalyze(s) substrate-level phosphorylation?

(A) ATP synthase

(B) Succinate thiokinase

(C) Phosphofructokinase

(D) Pyruvate kinase

Q.8 Which of the following method(s) can be applied to identify a bacterial
species?

(A) Fluorescent in situ hybridization (FISH)

(B) Polymerase chain reaction (PCR) followed by sequencing of the amplicon

(C) Gram staining

(D) Acid-fast staining

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Q.9 Which of the following event(s) would contribute to the induction of lac
operon in a wild-type strain of E. coli?

(A) Accumulation of allolactose in the cell

(B) Direct binding of cAMP to the promoter DNA

(C) Binding of cAMP to a specific protein leading to its interaction with the
promoter

(D) Elimination of cAMP from the cell

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Q.10 Numerical Answer Type (NAT), carry ONE mark each (no negative marks).

Q.10 One mole of a circular bacterial plasmid was digested with a high-fidelity
restriction enzyme. The plasmid has five restriction sites for the enzyme
used. The number of moles of fragments released upon cleavage at all sites
is________.

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Q.11 – Q.16 Multiple Choice Question (MCQ), carry TWO mark each (for each wrong
answer: – 2/3).

Q. 11 Under anaerobic fermentative growth conditions, one mole of glucose yields
22 grams of Streptococcus faecalis or 8.6 grams of Zymomonas mobilis. The
molar growth yield (YATP) for (i) S. faecalis and (ii) Z. mobilis will be

(A) (i) 11 and (ii) 4.3

(B) (i) 22 and (ii) 4.3

(C) (i) 22 and (ii) 8.6

(D) (i) 11 and (ii) 8.6

Q. 12 The order of abundance of quinones (ubiquinone [UQ], menaquinone [MQ]
and demethylmenaquinone [DMQ]) in E. coli growing anaerobically on
fumarate is

(A) UQ > DMQ > MQ

(B) MQ > DMQ >UQ

(C) MQ = DMQ > UQ

(D) MQ > UQ > DMQ

Q. 13 What is the number of ATPs generated per molecule of NADH during
oxidative phosphorylation in E. coli via (i) NDH-1 and cytochrome bo
complex or (ii) the NDH-2 and cytochrome bd complex? (Assume H+/ATP =
3)

(A) (i) 2.00 and (ii) 3.67

(B) (i) 3.00 and (ii) 2.67

(C) (i) 2.70 and (ii) 0.67

(D) (i) 2.50 and (ii) 0.50

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Q. 14 Match the Immunoglobulin classes with their function

Immunoglobulin Function

(i) IgE (p) protects the fetus

(ii) IgG (q) first antibody to be produced in response to infection

(iii) IgM (r) provides localized protection of mucosal surfaces

(iv) IgA (s) mediates allergic reaction

(t) directly lyses the target cells

(A) (i)- (s), (ii)-(p), (iii)-(q), (iv)-(r)
(B) (i)- (p), (ii)-(t), (iii)-(q), (iv)-(r)
(C) (i)- (q), (ii)-(p), (iii)-(t), (iv)-(r)
(D) (i)- (r), (ii)-(p), (iii)-(t), (iv)-(s)

Q. 15 The figure shows the profiles of quantitative real-time PCR (qRT-PCR) tests
for SARS-CoV-2 conducted on the throat swab samples of three individuals
(X, Y and Z). Tests were carried out under identical conditions. Dotted line
represents the threshold fluorescent value. Identify the correct statement on
the status of the COVID-19 tests of the individuals based on their qRT-PCR
profiles.

(A) X and Y are negative; Z is positive
(B) X and Y are positive; There is no apparent difference in their viral load
(C) X and Y are positive; X has the highest viral load
(D) X and Y are positive; Y has the highest viral load

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Q.16 The rate of appearance of recombinant E. coli strains containing different
genes after a mating between Hfr and F⁻ strains is shown in the graph (left).
The approximate location of different genes (p, q, r, s, t, x, and y) along the
Hfr chromosome is also shown (right). Based on this information, identify
the recombinants X, Y and Z.

(A) X is x+, Y is r+ and Z is p+

(B) X is p+, Y is r+ and Z is x+

(C) X is x+, Y is p+ and Z is r+

(D) X is p+, Y is x+ and Z is r+

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Q.17 – Q.20 Numerical Answer Type (NAT), carry TWO mark each (no negative marks).

Q.17 The genome of a bacterium encodes for 10 different surface antigens, whose
expression can be turned ‘ON’ or ‘OFF’ randomly and independently. The
number of possible antigenic combinations is__________.

Q.18 Suppose the mRNAs in a newly discovered bacteria are composed of only
two distinct nucleotides (as opposed to four found in all known organisms).
Considering that the organism has no nucleotide modification systems, the
number of nucleotides required per codon to encode at least 20 distinct
amino acids will be________.

Q. 19 The decimal reduction time (D) for reducing 1012 spores of Clostridium
botulinum to 1 spore at 111°C will be_______ min (in integer). The D value
is 0.2 min at 121°C. The increase in temperature required to change D to
1/10th of its initial value (Z value) is 10°C.

Q. 20 The generation time of E. coli is 30 minutes. For an exponentially growing
culture, the initial number of bacteria required to reach a number of 109 in
2 hours is_________×107 (round off to two decimal places).

END OF THE QUESTION PAPER

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