UPSC 2021: Nexus 61—70

Savannah Controls, Hydrosphere Depths, Volcanic Soils & Molecular Vectors. [Set A]

Question 61

Ecosystem Controls

The vegetation of savannah consists of grassland with scattered small trees, but extensive areas have no trees. The forest development in such areas is generally kept in check by one or more or a combination of some conditions. Which of the following are such conditions?

Burrowing animals and termites
Fire
Grazing herbivores
Seasonal rainfall
Soil properties

Select the correct answer using the code given below.

Official Verdict: (c) 2, 3 and 4

The Core Concept: Savannahs represent a dynamic ecological equilibrium between grasses and woody trees governed by three environmental keystones: periodic fires (2) which scorch young tree saplings while grasses survive via deep subterranean rootstocks; heavy grazing herbivores (3) like zebras and elephants which trample seedlings and browse foliage; and harsh seasonal rainfall (4) with prolonged multi-month droughts that prevent a closed forest canopy from forming. Burrowing animals/termites and local soil variations are localized ecological features, not regional macro-controls that check tree dominance across whole biomes.

Tethered to: REALM 38: Grassland Biomes

Question 62

Global Hydrology

With reference to the water on the planet Earth, consider the following statements:

The amount of water in the rivers and lakes is more than the amount of groundwater.
The amount of water in polar ice caps and glaciers is more than the amount of groundwater.

Which of the statements given above is/are correct?

Official Verdict: (b) 2 only

The Core Concept: Fresh water represents approximately 2.5% of all water on Earth. Of this tiny freshwater slice: Glaciers and polar ice caps lock away the lion's share at roughly 68.7%; Groundwater makes up approximately 30.1%; while all surface freshwater in lakes, rivers, and swamps combined constitutes less than 1.2% (with lakes holding ~0.26% and rivers only ~0.006%). Thus, Glaciers > Groundwater > Surface Waters, proving Statement 1 false and Statement 2 true.

Tethered to: REALM 85: Hydrological Cycle

Question 63

Economic Plant Ecology

Consider the following statements:

Moringa (drumstick tree) is a leguminous evergreen tree.
Tamarind tree is endemic to South Asia.
In India, most of the tamarind is collected as minor forest produce.
India exports tamarind and seeds of moringa.
Seeds of moringa and tamarind can be used in the production of biofuels.

Which of the statements given above are correct?

Official Verdict: (b) 3, 4 and 5

The Core Concept: Botanical checks: Moringa (Moringa oleifera) belongs to family Moringaceae (not Fabaceae/legumes) and is deciduous in dry conditions (Statement 1 is false). Tamarind (Tamarindus indica) is native and indigenous to tropical Africa, not endemic to South Asia (2 is false). In India, tribal communities collect vast quantities of wild tamarind as Minor Forest Produce (MFP) through TRIFED channels (3 is true). India is the world's leading exporter of tamarind pulp and moringa seed oil (4 is true), and both oils have high lipid content suitable for transesterification into biodiesel (5 is true).

Tethered to: REALM 59: Medicinal & Aromatic Crops

Question 64

Pedology & Petrology

The black cotton soil of India has been formed due to the weathering of

(a) brown forest soil
(b) fissure volcanic rock
(c) granite and schist
(d) shale and limestone

Official Verdict: (b) fissure volcanic rock

The Core Concept: The black cotton soil (Regur) across the Deccan plateau is an in-situ residual soil formed by the subaerial denudation and chemical weathering of Cretaceous fissure volcanic basaltic lava flows (the Deccan Traps). Rich in montmorillonite clay minerals, iron, lime, and magnesium, it exhibits intense self-ploughing characteristics (swelling when wet, developing deep cracks when dry), making it ideal for rainfed cotton cultivation.

Tethered to: REALM 37: Major Soil Types

Question 65

Vaccine Biotechnology

With reference to recent developments regarding 'Recombinant Vector Vaccines', consider the following statements:

Genetic engineering is applied in the development of these vaccines.
Bacteria and viruses are used as vectors.

Which of the statements given above is/are correct?

Official Verdict: (c) Both 1 and 2

The Core Concept: Both statements are scientifically accurate. In recombinant vector vaccines, recombinant DNA technology and genetic engineering are employed to isolate the gene encoding a pathogen's protective antigen (like the SARS-CoV-2 spike protein) and splice it into a safe carrier chassis (1 is true). While modified, non-replicating viruses (such as Adenoviruses in Covishield, Sputnik, and J&J) are the most common vectors, attenuated bacteria (such as engineered Salmonella or Listeria) are also actively developed and utilized as delivery vectors in modern clinical vaccinology (2 is true).

Tethered to: REALM 317: Vaccination Technologies

Question 66

Assisted Reproductive Genetics

In the context of hereditary diseases, consider the following statements:

Passing on mitochondrial diseases from parent to child can be prevented by mitochondrial replacement therapy either before or after in vitro fertilization of egg.
A child inherits mitochondrial diseases entirely from mother and not from father.

Which of the statements given above is/are correct?

Official Verdict: (c) Both 1 and 2

The Core Concept: Both statements are genetically immutable. Mitochondria possess their own distinct circular genome (mtDNA) and are passed down exclusively via maternal inheritance; sperm contribute only nuclear DNA during fertilization because paternal mitochondria in the sperm tail disintegrate upon entry (Statement 2 is true). Mitochondrial Replacement Therapy (MRT / three-parent baby technique) prevents mutant mtDNA transmission by transplanting the mother's healthy nuclear material into a donor egg with healthy mitochondria; this can be done before fertilization (Maternal Spindle Transfer) or after fertilization (Pronuclear Transfer) (Statement 1 is true).

Tethered to: REALM 307: Chromosomal & Genetic Diseases

Question 67

Agricultural Biotechnology

Bollgard I and Bollgard II technologies are mentioned in the context of

(a) clonal propagation of crop plants
(b) developing genetically modified crop plants
(c) production of plant growth substances
(d) production of biofertilizers

Official Verdict: (b) developing genetically modified crop plants

The Core Concept: Bollgard I and Bollgard II are proprietary genetically modified pest-resistant cotton varieties (Bt cotton) engineered by inserting insecticidal crystal protein genes from the soil bacterium Bacillus thuringiensis. Bollgard I incorporated a single gene (Cry1Ac) to protect against the American bollworm. Bollgard II expresses two distinct toxin proteins (Cry1Ac and Cry2Ab) to prevent target bollworms from developing resistance.

Tethered to: REALM 259: Transgenic Plants & GM Crops

Question 68

Applied Thermodynamics

In a pressure cooker, the temperature at which the food is cooked depends mainly upon which of the following?

Area of the hole in the lid
Temperature of the flame
Weight of the lid

Select the correct answer using the code given below.

Official Verdict: (c) 1 and 3 only

The Core Concept: Water boils when its vapor pressure equals the surrounding chamber pressure. Inside a sealed cooker, the maximum equilibrium pressure is mechanically fixed by physics: $P_{total} = P_{atm} + (Weight\ of\ the\ vent\ whistle / Area\ of\ the\ vent\ hole)$. Because the boiling point of water rises with higher pressure, the cooking temperature is dictated entirely by the weight of the lid/vent regulator (3) and the area of the vent hole (1). The flame temperature (2) merely alters the speed of steam generation and cooking rate, not the equilibrium boiling temperature once the weight starts venting.

Tethered to: REALM 74: Heat, Temp & Thermodynamics

Question 69

Microbiological Culture

Consider the following:

Bacteria
Fungi
Virus

Which of the above can be cultured in artificial/synthetic medium?

Official Verdict: (a) 1 and 2 only

The Core Concept: Bacteria and Fungi are complete cellular organisms possessing their own metabolic and reproductive machinery; they grow and multiply readily on cell-free synthetic/artificial agar plates containing simple nutrients, salts, and carbon sources (1 and 2 are true). Viruses, on the other hand, are non-cellular obligate intracellular parasites completely devoid of ribosomes and metabolic enzymes. They are metabolically inert outside a host and cannot be cultured in an artificial synthetic medium; they require living cells (tissue culture, embryonated eggs, or whole organisms) to replicate.

Tethered to: REALM 128: Viruses, Prokaryotes, Eukaryotes

Question 70

Virology & Pathology

Consider the following statements:

Adenoviruses have single-stranded DNA genomes whereas retroviruses have double-stranded DNA genomes.
Common cold is sometime caused by an adenovirus whereas AIDS is caused by a retrovirus.

Which of the statements given above is/are correct?

Official Verdict: (b) 2 only

The Core Concept: Statement 1 scrambles basic virology: Adenoviruses are non-enveloped viruses with double-stranded DNA (dsDNA) genomes. Retroviruses (such as HIV) possess single-stranded RNA (ssRNA) genomes; they use reverse transcriptase to transcribe their RNA into DNA inside host cells. Statement 2 is entirely correct: while rhinoviruses cause most colds, adenoviruses frequently trigger common colds, bronchitis, and sore throats, while AIDS is caused by the Human Immunodeficiency Virus (HIV), a retrovirus.

Tethered to: REALM 128: Viruses, Prokaryotes, Eukaryotes