Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

Statement 1 is correct: PV technology directly converts sunlight into electricity using semiconductor materials like silicon. When sunlight hits the PV cells, it excites electrons, generating Direct Current (DC) electricity. This is a clean and efficient method of harnessing solar energy for electricity. Solar thermal systems use solar collectors to capture the Sun’s heat. This heat is typically used to produce steam, which drives turbines connected to generators, producing electricity. Solar thermal is often used in large-scale power plants and heating systems.

Statement 2 is incorrect: PV systems initially produce Direct Current (DC), which is then converted to Alternating Current (AC) using inverters for compatibility with the electrical grid and household appliances. Solar Thermal systems generate heat, which is used to produce AC electricity through conventional turbines and generators.

Statement 3 is incorrect: India has established manufacturing capabilities for both Solar Thermal and Photovoltaic technologies. The country is expanding its PV manufacturing capacity, aiming to become self-sufficient and reduce reliance on imports.

Explanation

Hibernation is a survival strategy employed by various animals to endure periods of reduced food availability and harsh environmental conditions, typically during winter. This state is characterized by significantly lowered metabolic rates, decreased body temperatures, and reduced physiological activities. Many bat species enter hibernation during colder months when their insect prey becomes scarce. During hibernation, bats can experience a substantial drop in body temperature and significant reduction in metabolic rate. They often hibernate communally in caves, mines, or other sheltered locations that provide stable, cold environments. Bears undergo a form of hibernation known as torpor, which is less extreme than the hibernation observed in smaller mammals. During torpor, bears experience a moderate decrease in body temperature and metabolic rate. They remain in dens throughout the winter months, surviving on stored body fat. Notably, female bears give birth during this period and are capable of nursing their cubs without leaving the den. Species such as ground squirrels and certain mice enter deep hibernation during which they significantly lower their body temperatures and metabolic rates. This state allows them to conserve energy and survive extended periods without food. Rodents often prepare for hibernation by accumulating fat reserves and creating insulated nests or burrows to protect against the cold.

Explanation

The carbon cycle is a biogeochemical process where carbon atoms continuously move between the atmosphere, oceans, soil, and living organisms through processes like photosynthesis, respiration, decomposition, and combustion. Through photosynthesis, plants absorb atmospheric CO₂ to produce glucose, while animals release CO₂ through respiration, and when organisms die, decomposition returns their carbon to the soil and atmosphere, completing this vital planetary cycle.

Statement 1 is correct: Volcanic eruptions release CO₂ stored in Earth’s mantle into the atmosphere, contributing to the carbon cycle.

Statement 2 is correct: Respiration is the process by which organisms, including plants and animals, convert organic compounds into energy, producing CO₂ as a byproduct. This CO₂ is then released into the atmosphere.

Statement 3 is incorrect: Photosynthesis is the process by which green plants, algae, and some bacteria absorb CO₂ from the atmosphere and, using sunlight, convert it into glucose and oxygen. This process removes CO₂ from the atmosphere.

Statement 4 is correct: When organisms die, decomposers like bacteria and fungi break down their organic matter, resulting in the release of CO₂ back into the atmosphere through the process of decomposition.

Explanation

Ecological succession is the process of change in the species structure of an ecological community over time. Types of Succession:

Primary Succession occurs on newly formed or exposed land where no previous life existed (e.g., bare rock, lava flows). Pioneer species like lichens and mosses initiate the process, gradually leading to the development of soil and a stable ecosystem. Secondary Succession happens in areas where an ecosystem previously existed but was disturbed (e.g., after a forest fire or flood). Soil is already present, and recovery occurs more quickly than in primary succession.

Option (b) is correct: Lichens are among the first organisms to colonize bare rock or barren environments, breaking down minerals to create soil and paving the way for other plants and organisms. They are unique composite organisms resulting from a symbiotic association between a fungus and a photosynthetic partner, which can be either green algae or cyanobacteria. In this partnership, the fungal component, known as the mycobiont, provides structure and protection, while the photosynthetic partner, referred to as the photobiont, contributes nutrients through photosynthesis.

Explanation

After harvest, fruits and vegetables remain metabolically active, with respiration being a key manifestation of this activity. Respiration involves the breakdown of stored nutrients to release energy for cellular processes. This process can be effectively slowed by lowering the temperature, which decreases the metabolic rate. Since harvested fruits and vegetables are no longer connected to the plant’s roots, they cannot acquire additional nutrients. As a result, they rely entirely on their stored nutrients for energy. Once these reserves are depleted, the produce begins to degrade. Therefore, controlling the rate of respiration through proper storage conditions, such as refrigeration, is crucial to preserving fruits and vegetables for longer periods and maintaining their quality.

Explanation

Ball bearings are used to reduce friction between the surfaces. A ball bearing is a specific kind of rolling-element bearing that uses balls to keep the bearing races apart. A ball bearing’s main functions are to support radial and axial loads and lessen rotational friction. In order to reduce friction between surfaces and also because the effective area of contact between the wheel and axle is reduced, ball bearings are used in bicycles, vehicle axles, etc.

Explanation

A rainbow is formed when sunlight interacts with raindrops in the atmosphere, and this process involves three key physical phenomena: dispersion, refraction, and internal reflection. Dispersion occurs as sunlight, which consists of multiple colors, is separated into its constituent wavelengths when it passes through a raindrop, with each color bending by a different angle. Refraction takes place at the interface of air and water when sunlight enters the raindrop, causing the light to bend due to a change in its speed. This bending happens twice--first as the light enters the drop and again as it exits. Internal reflection occurs when the light, after being refracted, reflects off the inner surface of the raindrop. The combined effect of these phenomena results in the formation of a colorful arc in the sky, known as a rainbow.

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

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.