[Answers with Explanation] UPSC prelims GS1 paper 2021

Q61. 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?

1. Burrowing animals and termites
2. Fire
3. Grazing herbivores
4. Seasonal rainfall
5. Soil properties

Select the correct answer using the code given below.

(a) 1 and 2
(b) 4 and 5
(c) 2, 3 and 4
(d) 1, 3 and 5

Solution C

Burrowing animals and termites: Can influence soil properties and vegetation structure but are not primary factors in limiting forest development in savannahs.

Grazing herbivores: Grazing by large herbivores like zebras, wildebeests, and gazelles is a significant factor in shaping savannah ecosystems.

Fire: Fire is a key factor in maintaining savannah ecosystems. It prevents the establishment of tree cover, allowing grasses to dominate. Regular fires prevent trees from becoming established and maintain the balance of grassland to woodland.

Seasonal rainfall: Savannahs are characterized by seasonal rainfall, often with long dry periods that can limit tree growth. The rainfall pattern creates conditions that favor grasses over trees, contributing to the characteristic appearance of savannahs.

Soil properties: The soil in savannahs might be nutrient-poor or not conducive for tree growth, but it is not the primary factor that defines the biome.

Q62. With reference to the water on the planet Earth, consider the following statements:

1. The amount of water in the rivers and lakes is more than the amount of groundwater.
2. 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?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Solution B

Bar chart showing the distribution of water on, in, and above the Earth.

Statement 1 is incorrect: Groundwater represents a much larger portion of Earth’s fresh water than rivers and lakes. Groundwater accounts for roughly 30.1% of the Earth’s fresh water, while rivers and lakes combined contain only about 0.3%.

Statement 2 is correct. Ice caps and glaciers store most of the Earth’s fresh water. Around 68.7% of the world’s fresh water is trapped in ice caps, glaciers, and permanent snow.

Q63. Consider the following statements:

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

Which of the statements given above are correct?

(a) 1, 2, 4 and 5
(b) 3, 4 and 5
(c) 1, 3 and 4
(d) 1, 2, 3 and 5

Solution B

Moringa, commonly known as the drumstick tree, is indeed an evergreen tree but it is not leguminous. So, statement 1 is incorrect.

The tamarind tree is native to tropical Africa and not endemic to South Asia. It has been widely cultivated in South Asia but originated in Africa. Therefore, statement 2 is incorrect.

Statement 3 is correct. In India, tamarind is often collected as a minor forest produce, especially in various tribal areas.

Statement 4 is correct. India is one of the major producers of tamarind and moringa seeds, and it does export them to various countries.

Statement 5 is correct. Moringa seeds have been studied for their potential use in biofuel production. Tamarind seeds also contain oil that has been explored for biofuel production.

Q64. 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

Solution B

The black cotton soil of India, also known as Regur soil, is primarily formed due to the weathering of volcanic rocks, particularly basalt. These soils are rich in minerals and are known for their moisture-retention capacity, making them suitable for cotton cultivation.

The black soil in India is found in the states like Maharashtra, Gujarat, Madhya Pradesh, Telangana and Karnataka which is called Deccan Trap region of India.

Q65. With reference to recent developments regarding ‘Recombinant Vector Vaccine’, consider the following statements:

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

Which of the statements given above is/are correct?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Solution C

Recombinant Vector Vaccines are a type of vaccine that is made using genetic engineering techniques. These vaccines use a virus, or sometimes a bacterium, as a vector to carry a piece of DNA that codes for a part of a pathogen (such as a protein from a virus or bacterium). This genetic material is inserted into a harmless vector, which then delivers it into host cells. This stimulates an immune response against the pathogen without causing disease.

Statement 1 is correct: Genetic engineering is the manipulation of DNA, and it is used to create recombinant vector vaccines.

Statement 2 is also correct: Bacteria (e.g., Salmonella) and viruses (e.g., adenoviruses) are used as vectors to deliver the desired DNA into the host cells.

Q66. In the context of hereditary diseases, consider the following statements:

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

Which of the statements given above is/are correct?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Solution C

Statement 1 is correct: Mitochondrial replacement therapy (MRT) is a form of in vitro fertilization that involves replacing defective mitochondria with healthy mitochondria from a donor. This process can help prevent the transmission of mitochondrial diseases from mother to child. It is typically done before fertilization, during the process of creating embryos in the laboratory.

Statement 2 is correct: Mitochondria are cellular organelles responsible for producing energy, and they contain their own DNA, separate from the nuclear DNA found in chromosomes. A child inherits mitochondrial DNA (mtDNA) exclusively from the mother, as the mitochondria in sperm are usually lost during fertilization. Therefore, mitochondrial diseases, which are caused by mutations in mtDNA, are passed down only through the maternal line.

Q67. 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

Solution B

Bollgard I and Bollgard II refer to specific genetically modified (GM) technologies used in cotton plants. These technologies involve the insertion of genes from the bacterium Bacillus thuringiensis (Bt) into the cotton plant’s genome.

Bollgard I: This was the first generation of Bt cotton, which contained one Bt gene. This gene enabled the plant to produce a protein that is toxic to specific insect pests, particularly the bollworm, a major pest in cotton farming. By producing this toxin, the GM cotton plants became resistant to the bollworm.

Bollgard II: This is the second generation of Bt cotton and an advancement over Bollgard I. Bollgard II contains two different Bt genes, which allow the plant to produce two different proteins, both of which target the bollworm. This dual-toxin approach was developed to delay the potential development of resistance in the target insects.

Q68. In a pressure cooker, the temperature at which the food is cooked depends mainly upon which of the following?

1. Area of the hole in the lid
2. Temperature of the flame
3. Weight of the lid

Select the correct answer using the code given below.

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Solution C

Inside a pressure cooker, the boiling point is increased by increasing the pressure. Hence, cooking is faster. Therefore, the temperature at which food is cooked is affected by the pressure and not the temperature of the flame. This can also be understood by understanding why cooking is difficult on hills. At high altitudes, atmospheric pressure is lower, reducing the boiling point of water as compared to that at sea level.

Q69. Consider the following:

1. Bacteria
2. Fungi
3. Virus

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

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Solution A

Bacteria: They can be grown in artificial or synthetic media. Various nutrient media are used to grow bacteria in the laboratory, and the composition can be tailored to the nutritional needs of the specific bacterium.

Fungi: Like bacteria, fungi can also be cultured in artificial media. Various types of media are used for the cultivation of fungi, depending on the species and growth requirements.

Viruses: Unlike bacteria, many of which can be grown on an artificial nutrient medium, viruses require a living host cell for replication. . Infected host cells (eukaryotic or prokaryotic) can be cultured and grown, and then the growth medium can be harvested as a source of virus.

Q70. Consider the following statements:

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

Which of the statements given above is/are correct?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Solution B

Statement 1 is incorrect: Adenoviruses have double-stranded DNA genomes, not single-stranded. Retroviruses, on the other hand, have single-stranded RNA genomes, not double-stranded DNA genomes.

Statement 2 is correct: The common cold can be caused by different viruses, including adenoviruses. AIDS is caused by the Human Immunodeficiency Virus (HIV), which is a retrovirus.

Adenoviruses are common viruses that cause a range of illness. They can cause cold-like symptoms, fever, sore throat, bronchitis, pneumonia, diarrhea, and pink eye (conjunctivitis).
HIV is called a retrovirus because it works in a back-to-front way. Unlike other viruses, retroviruses store their genetic information using RNA instead of DNA, meaning they need to ‘make’ DNA when they enter a human cell in order to make new copies of themselves.

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