UPSC Prelims 2021 Analysis

Explanation

Statement 1 is correct. Sodium lamps emit light in a 360-degree pattern, while LED lamps are directional.

Statement 2 is incorrect. LED lamps generally have a longer lifespan compared to sodium lamps.

Statement 3 is correct. Sodium lamps emit monochromatic light, whereas LED lamps offer a wider spectrum of visible light, providing significant colour advantages in street lighting.

Explanation

Mitochondrial replacement therapy (MRT) is a reproductive technique used to prevent the transmission of mitochondrial diseases from mother to child. It involves replacing defective mitochondria in an egg or embryo with healthy mitochondria from a donor. MRT can be performed either before or after in vitro fertilization to ensure that the resulting embryo does not inherit mitochondrial diseases.

Mitochondrial DNA (mtDNA), which is responsible for encoding genes essential for mitochondrial function, is inherited exclusively from the mother. Therefore, mitochondrial diseases caused by mutations in mtDNA are passed down maternally, and a child cannot inherit mitochondrial diseases from the father.

Therefore, both statements are correct.

Explanation

Cnidarians Many cnidarian species, such as corals, develop symbiotic relationships with single-celled algae called zooxanthellae. This symbiosis is crucial for the survival and growth of coral reefs.

Fungi are known to form various symbiotic relationships with other organisms, including Mycorrhizal associations with plant roots, where the fungus helps the plant absorb nutrients in exchange for carbohydrates. Lichens are a symbiotic relationship between a fungus and an algae or cyanobacteria.

Protozoa Some protozoa living in the digestive tracts of termites and ruminant animals, helping them break down cellulose.

Therefore, all three groups - cnidarians, fungi, and protozoa - have species that can form symbiotic relationships with other organisms.

Explanation

The term 'ACE2' is talked about in the context of the spread of viral diseases, particularly COVID-19.

ACE2 stands for Angiotensin-Converting Enzyme 2. It's a protein found on the surface of many cell types in the human body, including those in the lungs, heart, kidneys, and intestines.

Here's why ACE2 is significant

Receptor for SARS-CoV-2 The spike protein on the surface of the SARS-CoV-2 virus, the virus that causes COVID-19, binds to the ACE2 receptor in human cells. This binding is a critical step in the process of how the virus infects cells. Multiple organ infection Since ACE2 is expressed in various organs, it provides the virus with multiple potential entry points. This can contribute to the multi-organ complications sometimes associated with COVID-19. Focus of research Understanding the interaction between the virus and ACE2 is a major area of research for scientists developing vaccines and treatments for COVID-19.

Explanation

Ferns typically require soil and moisture to grow, as they rely on water-conducting tissues and need a substrate to anchor their roots. Lichens are a symbiotic association between a fungus and an algae or cyanobacteria. Lichens are well-adapted to survive on surfaces without soil, such as rocks, tree bark, and even bare ground, as they can obtain their nutrients and moisture directly from the air and precipitation. Lichens are sensitive to airborne pollutants, such as sulfur dioxide (SO2), nitrogen oxides (NOx), ozone (O3), and heavy metals (like lead and mercury). Sulfur dioxide, for instance, causes chlorosis (yellowing) and necrosis (cell death) in lichen thalli. This sensitivity makes lichens an effective indicator of air quality. Mosses are non-vascular plants that can grow on surfaces without soil, such as rocks, tree trunks, and even roofs. Mosses have specialised structures that allow them to absorb water and nutrients directly from the environment. Mushrooms are the reproductive structures of fungi, and they typically require a substrate, such as decaying organic matter, to grow. Mushrooms are not able to directly survive on a surface without soil or a nutrient-rich medium. Therefore, among the given options, lichens and mosses are the most likely to be found surviving on a surface without soil in the natural environment.

Explanation

Statement 1 is correct. Genetic engineering in vaccine development works by modifying the genetic material of viruses, bacteria, or lab-grown cells to produce specific proteins that trigger an immune response. Scientists first identify a target protein from a pathogen that can help the immune system recognize and fight it. They then insert the gene coding for this protein into a harmless virus, bacterial cell, or a lab-grown system, which acts as a factory to produce large amounts of the antigen. The antigen is then purified and combined with other ingredients to create the final vaccine. When injected, the vaccine stimulates the immune system to recognize and attack the actual pathogen if encountered in the future. This approach is used in various vaccines, including mRNA vaccines like those for COVID-19 and recombinant protein vaccines like the Hepatitis B vaccine.

Statement 2 is correct. Bacteria and viruses are commonly used as vectors in recombinant vector vaccines. These vectors serve as delivery vehicles to transport genetic material from the target pathogen into host cells, where the antigens are produced. The host immune system then recognizes these antigens and mounts an immune response.

Explanation

Water molecules are polar, meaning they have a positive charge on one end (the hydrogen atoms) and a negative charge on the other end (the oxygen atom). This polarity allows water molecules to attract and interact with other polar or charged molecules, facilitating the dissolution of a wide range of substances in water.

Therefore, option (a) is correct.

Explanation

Statement 1 is incorrect as we know the universe is ever expanding so the distance between two stellar bodies does not change.

Statement 2 is incorrect as the Gravitational power is dependent on the mass of the object, it changes with a change in mass.

Statement 3 is incorrect Though mostly light travels in a straight line, it can be bent by Gravity.

Statement 4 is correct the speed of light does not change in a vacuum. So, it is a constant that can be used for measurement.

Explanation

Adenoviruses have double-stranded DNA genomes. Retroviruses have single-stranded RNA genomes. **Thus, statement 1 is incorrect. **

Adenoviruses are one of the many viruses that can cause the common cold. AIDS (Acquired Immunodeficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV), which is a type of retrovirus. **Thus, statement 2 is correct. **

Explanation

Bollgard I and Bollgard II technologies are mentioned in the context of developing genetically modified (GM) cotton plants resistant to insect pests.

Bollgard I This was India's first commercially approved GM crop technology introduced in 2002. It incorporates a single gene (Cry1Ac) from the bacterium Bacillus thuringiensis (Bt) into cotton plants. This Bt gene produces an insecticidal protein that targets and kills certain insect pests, particularly the American Bollworm (Helicoverpa armigera).

Bollgard II This is a more advanced technology introduced in mid-2006. It incorporates two genes (Cry1Ac and Cry2Ab) from Bt into cotton. This provides broader resistance against a wider spectrum of insect pests, including lepidopteran caterpillars like the Spodoptera species, in addition to the American Bollworm.

Explanation

The Lemongrass plant is known to be an excellent mosquito repellant.

According to a study conducted in 2011, around 95% of mosquitos from a specific range of species were either killed or completely repelled due to the intense odour of lemongrass oil.

Commonly known as Citronella oil, the impact of the essential oil from Lemongrass is known to last for around two and a half hours. For some species of mosquitos, it is even more.

Explanation

Statement 1 is correct The size of the hole in the lid regulates the amount of steam released. A larger hole permits more steam to escape, leading to reduced pressure and subsequently affecting the temperature.

Statement 2 is incorrect Boiling water can never exceed 100 degrees Celsius, regardless of the intensity of the flame beneath the pot. However, within a pressure cooker, the temperature can elevate to as high as 121 degrees Celsius. The heightened cooking temperature serves to decrease the cooking duration rather than the temperature itself. Thus, statement 2 is inaccurate.

Statement 3 is correct If the weight is heavier, it will require higher pressure to lift it, resulting in higher pressure inside the cooker before excess steam can escape. Higher pressure leads to a higher boiling point for the water inside the cooker, which in turn increases the cooking temperature. Conversely, if the weight is lighter, it results in a lower pressure inside the cooker and a lower boiling point for the water, leading to a lower cooking temperature.

Explanation

Bacteria can be cultured and grown in various artificial culture media, such as nutrient broth, agar plates, or other specific media formulations. Bacteria can metabolize and utilize the nutrients provided in these synthetic culture media to grow and reproduce.

Fungi can also be cultured in artificial media, such as potato dextrose agar, Sabouraud dextrose agar, or other specialized fungal growth media. Fungi can utilize the organic compounds and nutrients present in these synthetic media to support their growth and development.

Viruses, on the other hand, are obligate intracellular parasites and cannot be directly cultured in artificial or synthetic media. Viruses require living host cells to replicate and propagate, as they lack the necessary machinery for autonomous growth and reproduction.