Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Transplanted seedlings often experience root injury during transplantation, which can lead to difficulties in establishment and growth. The majority of the water that is finally delivered to the plant’s top growth is absorbed by tiny roots that are farther from the plant and are covered by even smaller hairs. These delicate roots are typically killed after a transplant either by being chopped to reduce the size of the root ball or by drying out. It’s referred to as transplant shock. Transplant shock refers to a number of stresses that occur in recently transplanted trees and shrubs. It involves failure of the plant to root well, consequently the plant establishes poorly in the landscape. New transplants frequently experience stress due to a shortage of water because their root systems are not yet well established. Water stressed plants may be more vulnerable to harm from other factors, such as the environment, insects, or disease.

Explanation

Fundamental forces of nature can be categorised in four categories like Gravitational force, Weak Nuclear force, Electromagnetic force and Strong Nuclear force. Notably, latter three forces are all part of the Standard Model of physics Gravity and the electromagnetic force both have an unlimited range. However, despite its infinite reach, gravity is the weakest of the four fundamental forces. In contrast, the strong nuclear force is the strongest but operates only over a very short range. Strong Nuclear Force > Electromagnetic Force > Weak Nuclear Force > Gravitational Force. Options (b), (c) and (d) are correct:

Electromagnetic Force is weaker than the strong nuclear force. It acts between electrically charged particles. It also has infinite range and is attractive or repulsive. The Weak Nuclear Force is very weak and causes radioactive decay. It governs particle decay. It has a short-range. Strong Nuclear Force as the name suggests is very strong but has a short-range. It holds protons and neutrons inside the nucleus of the atom.

Explanation

Brinjal is a resilient crop that thrives even in drought-prone areas and is cultivated throughout most of the country. In India, Bt brinjal was the first food crop to undergo evaluation for potential commercial release.

Statement 1 is incorrect: A gene called cry1Ac from the soil bacterium Bacillus thuringiensis(and not fungus) was inserted into the brinjal to develop Bt Brinjal. This brinjal has been genetically modified to withstand insects like the Brinjal Fruit and Shoot Borer (Leucinodes orbonalis).

Statement 2 is incorrect: Farmers will be free to save and sow as many seeds from Bt Brinjal open-pollinated cultivars as they like. They are not terminator seeds.

Statement 3 is correct: Public resistance to Bt brinjal in India was driven by fears of allergic reactions, toxicity and long-term health effects.

Statement 4 is correct: Environmentalists feared that introducing Bt brinjal could negatively impact biodiversity. The primary concern was the potential for cross-pollination with native brinjal varieties, which could lead to genetic contamination and loss of indigenous strains.

Explanation

Genetic engineering is the direct manipulation of an organism’s genes using biotechnology techniques, allowing for the alteration of its DNA.

Statement 1 is correct: GE crops have been engineered to withstand drought conditions which allows them to maintain productivity under water scarcity. For instance, genetically modified wheat with enhanced drought tolerance has been developed.

Statement 2 is correct: Biofortification through genetic engineering has led to crops with enhanced nutritional profiles. Example: Golden Rice has been engineered to produce beta-carotene, a precursor of vitamin A.

Statement 3 is incorrect: Genetic engineering for space-specific traits (like enhanced photosynthesis in low light or microgravity) is not a major application of genetically engineered plants presently. Research is ongoing into growing plants in space (Ex-NASA’s experiments with growing lettuce on the International Space Station) but these efforts primarily focus on optimizing growth conditions rather than genetically engineering plants.

Statement 4 is correct: Genetic engineering has been used to delay ripening and spoilage in fruits and vegetables. For example: Flavr Savr Tomato is the first commercially available genetically engineered crops, designed to ripen more slowly and extend shelf life.

Explanation

Biopesticides are various biologically active natural substances that exist in nature and have inhibitory effects on crop diseases and insect pests. In general, the creation of biopesticide depends to a large extent on biological resources.

Option (d) is correct:

Three major classes of biopesticides are:

Class of Biopesticides Description Examples Microbial Pesticides Consist of microorganisms (bacteria, fungi, viruses, or protozoa) as active ingredients for pest control. These may be naturally occurring, dead or alive, or genetically engineered. Bacillus thuringiensis (Bt) - produces toxins harmful to specific insects. Fungal Biopesticides Some fungi act as biopesticides by infecting and killing pests. Entomopathogenic fungi target insects, while others combat plant pathogens. Entomopathogenic fungi - infect and kill insects. Plant-Incorporated-Protectants (PIPs) Pesticidal substances that plants produce from inserted genetic material. Genetically modified corn and cotton, Neem oil (Azadirachta indica) - possesses insecticidal properties.

Explanation

Statement 1 is correct: Ultraviolet (UV) radiation effectively neutralizes harmful microorganisms like bacteria, viruses, and protozoa. It damages their DNA by disrupting the thymine bases, preventing reproduction and rendering them harmless.

Statement 2 is incorrect: UV radiation does not remove chemical compounds or gases that cause undesirable odors in water. These require additional processes like activated carbon filtration or oxidation techniques.

Statement 3 is incorrect: UV radiation does not affect solid particles, turbidity, or water clarity. These issues require mechanical filtration or sedimentation processes, such as sand filters or coagulation methods.

Explanation

A stem cell is a special type of cell that can develop into different cell types and has the ability to self-renew, helping in growth, repair, and regeneration of tissues in the body.

Statement 1 is incorrect: Stem cells are not exclusive to mammals. They can be derived from a variety of organisms, including plants, non-mammalian animals, and other sources. For instance, plants have meristematic cells (responsible for the root and shoot growth of plants), which function similarly to stem cells in animals.

Statement 2 is correct: Stem cells, especially induced pluripotent stem cells (iPSCs) and embryonic stem cells, are used in drug screening and toxicity testing. They help in assessing drug responses in a controlled laboratory setting.

Statement 3 is correct: Stem cells have significant applications in regenerative medicine, including treatments for blood disorders (like leukemia), neurodegenerative diseases, and tissue repair. Bone marrow transplants, for example, rely on hematopoietic stem cells.

Explanation

The Big Bang theory states that at some point of time the entire space was contained in a single point of very high density and temperature, from where the Universe has been witnessing expansion in all directions ever since. According to Hubble’s law, the expansion of the universe is such that the velocity at which the galaxy is moving away from the observer is increasing with time.

Statement 1 is correct: Cosmic Microwave Background (CMB) is thought to be leftover radiation from the Big Bang, i.e., the time when the universe began. According to the theory, when the universe was born it underwent rapid inflation and expansion. (The universe is still expanding today, and the expansion rate appears different depending on observation). The CMB represents the heat left over from the Big Bang.

Statement 2 is correct: American astronomer Edwin Hubble was the first to describe the redshift phenomenon (galactic redshift) and tie it to an expanding universe (galaxies are drifting apart). Redshift and Blueshift describe how light changes with movement of objects in space closer or farther from us. While moving away, the light is shifted to the red end of the spectrum, as its wavelength gets longer. While moving closer, the light moves to the blue end of the spectrum, as its wavelength gets shorter. Galactic Redshift is related to the expanding Universe concept.

Statement 3 is incorrect: Movement of asteroids in space is due to gravity and it is not linked with the concept of expansion of the universe.

Statement 4 is incorrect: The occurrence of supernova explosions (powerful stellar explosions in which a single star becomes as bright as 109 stars like the sun) helps in studying the distribution of elements throughout the universe. These elements travel on to form new stars, planets and everything else in the universe. But this is not considered as evidence for the continued expansion of the universe.

Explanation

Biomass gasification is a process that converts biomass (organic materials like wood, crop residues, and animal waste) into syngas (synthetic gas) by heating it in a controlled environment with limited oxygen or steam.

Statement 1 is correct: Rice husk, groundnut shells, and coconut shells can all be utilised in the biomass gasification process.

Statement 2 is incorrect: Biomass gasification involves burning of biomass in a limited supply of air to provide a combustible gas consisting of carbon monoxide, carbon dioxide, hydrogen, methane, water, nitrogen, along with contaminants like small char particles, ash and tars.

Statement 3 is incorrect: Combustible syngas is frequently used as a fuel for internal combustion engines or as a step in the synthesis of other compounds. Consequently, the flammable gases produced by biomass gasification can be used for direct heat generation as well as in internal combustion engines.

Explanation

Graphene is a single layer of carbon atoms arranged in a hexagonal honeycomb lattice, making it the thinnest, strongest, and most conductive material known. It has remarkable applications in electronics, energy storage, and nanotechnology due to its high strength, flexibility, and conductivity.

Statement 1 is correct: Graphene, a two-dimensional, atomic-scale, honeycomb lattice is an allotrope of carbon in which one atom forms each vertex. It is the basic structural unit of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Graphene has remarkably good electrical conductivity.

Statement 2 is correct: It is often cited as about 100 times stronger than the strongest steel with a hypothetical thickness of 3.35°(approx.) which is equal to the thickness of a graphene sheet. Carbon atoms are linked together in a single layer to form the hexagonal structure that makes up graphene. Graphene is so much thinner than paper (a million times thinner), that it is actually regarded as two dimensional.

Statement 3 is incorrect: Graphene is a single layer (monolayer) of carbon atoms, not silicon, tightly bound in a hexagonal honeycomb lattice. It is an allotrope of carbon in the form of a plane of sp2-bonded atoms with a molecular bond length of 0.142 nanometres.

Statement 4 is correct: Graphene is often produced as a powder and as a dispersion in a polymer matrix. This dispersion is supposedly suitable for advanced composites, paints and coatings, lubricants, oils and functional fluids, capacitors and batteries, thermal management applications, display materials, etc. Graphene is often cited as a promising material for use as conducting electrodes in devices like touch screens, LCDs, and organic LEDs due to its excellent electrical conductivity and high transparency