Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

The rate at which an object cools depends on its surface area-to-volume ratio and temperature difference with the surroundings. A higher surface area-to-volume ratio allows more heat to be dissipated into the surroundings, leading to faster cooling. The sphere has the largest surface area compared to the cube and circular plate. The larger the surface area, the more heat can be radiated or transferred to the surroundings, which leads to a faster cooling rate. The sphere cools faster than the circular plate and cube for the same radius. The more heat the sphere can radiate, the quicker it will reach room temperature compared to objects with smaller surface areas. Note: Here, we can ignore the impact of volume as the sphere, disc or cube all are hollow with negligible thickness.

Explanation

Statement 1 is incorrect: According to Rayleigh scattering, light with shorter wavelengths (e.g., blue light) is scattered more than light with longer wavelengths (e.g., red light).

Statement 2 is incorrect: The refractive index of water is approximately 1.33, so the speed of light in water is about 1/1.33 0.75° the speed in a vacuum.

Statement 3 is correct: Radio waves are a type of electromagnetic radiation generated when electrical charges oscillate in an antenna. These oscillations create alternating electric and magnetic fields that propagate as waves. This principle is the basis of wireless communication technologies like radio, TV, and mobile networks.

Statement 4 is correct: The Doppler effect is used in radar guns to measure the speed of moving vehicles by analyzing the frequency shift of reflected radio waves.

Explanation

A mirage is primarily caused by terrestrial heating and the refraction of light. Mirage causes deceptive appearance of a distant object or objects caused by light ray bending (refraction) in different density layers of air. Terrestrial Heating: The ground is intensely heated by the sun (such as a hot road or desert). This heats the air near the surface, making it less dense than the cooler air above. The temperature gradient creates a gradient in the refractive index of the air. Refraction of Light: Light from the sky or distant objects passes through the layers of air with varying temperatures and densities. The light bends (refracts) as it moves from cooler, denser air to hotter, less dense air. This bending creates the illusion of water or a mirrored surface on the ground.

Explanation

Assertion (A) is true: Synthetic detergents, unlike soap, work efficiently in hard water because they do not form insoluble scum with calcium and magnesium ions, which are present in hard water. This enables better lathering. Reason (R) is true: Synthetic detergents are mainly non-ionic or anionic, allowing them to form soluble complexes with calcium and magnesium ions, preventing scum formation. Unlike soap, which forms insoluble salts, these detergents continue to lather in hard water. Reason (R) correctly explains Assertion (A) because synthetic detergents form soluble complexes with calcium and magnesium, preventing scum and aiding lathering in hard water. Direction: The following item consists of two statements. One labeled as the ‘Assertion (A)’ and the other as "Reason (R)". You have to answer this item using the code given below:

Explanation

Dichogamy refers to the condition in a bisexual flower where the male (androecium) and female (gynoecium) reproductive organs mature at different times to prevent self-pollination. This ensures cross-pollination between different plants or flowers which increases genetic diversity.

Explanation

Stem cutting is a common asexual propagation method where a section of the stem, with at least one node and some leaves is cut from a parent plant and rooted to grow a new, genetically identical plant. This method helps maintain desirable plant traits. Bougainvillea, carnations, grapes, and cocoa can all be propagated by stem cuttings. Bougainvillea is propagated using hardwood(during the dormant season) or softwood (during spring/summer from young growth) cuttings depending on the season. Carnations: Stem cuttings taken from side shoots in spring/ summer. Must have two nodes and leaves for successful propagation. Grapes: Dormant hardwood cuttings taken during winter with 3 nodes. Ideal for maintaining grapevine traits. Cocoa: Propagated using young, tender stem cuttings during the rainy season. Cuttings should have at least two nodes and leaves.

Explanation

The mechanisms of organic evolution refer to the processes by which populations of organisms change over time, leading to the diversity of life forms seen today. These mechanisms explain how species evolve, adapt, and sometimes go extinct. The loss of limbs in snakes is explained by Lamarck’s Theory of Use and Disuse, which suggests that organs that are frequently used develop and strengthen while those that are not used weaken and eventually disappear over generations. Snakes evolved from lizard-like ancestors that originally had limbs. As they adapted to a burrowing or slithering lifestyle, they stopped using their limbs for movement. According to Lamarck’s theory, since the limbs were not used, they gradually reduced in size and eventually disappeared over many generations.

Explanation

Genetics is the study of heredity and variation in living organisms. It explores how traits are passed from parents to offspring through genes which are the units of heredity located on chromosomes.

Option (b) is correct: Pleiotropy occurs when a single gene affects multiple, seemingly unrelated phenotypic traits. Mutations in such a gene can have widespread effects due to its influence on various biological processes This occurs because the gene product (e.g., a protein) may participate in multiple biochemical or physiological pathways. For example, the gene responsible for sickle cell anemia affects multiple traits: red blood cell shape, resistance to malaria, and oxygen transport efficiency.

Explanation

Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream. They regulate various physiological processes, such as growth, metabolism, reproduction, and mood. Examples include Insulin (protein), cortisol (steroid), thyroxine, etc.

Statement 1 is correct: Somatotropin, also known as human growth hormone (HGH), is secreted by the anterior pituitary gland. Its release is stimulated by growth hormone-releasing hormone (GHRH) which is released as a result of exercise

Statement 2 is correct: In men, progesterone is synthesized not only in the Leydig cells of the testicles but also in the adrenal glands. It serves as a precursor to testosterone and plays roles in various physiological processes.

Statement 3 is correct: In females, the adrenal glands contribute to the production of androgens, including testosterone. These hormones are involved in various bodily functions, including the maintenance of muscle mass and libido.

Statement 4 is incorrect: Stress typically triggers the adrenal glands to increase the secretion of cortisol, a hormone that helps the body manage stress by regulating metabolism, inflammation, and other critical functions.

Explanation

Foot-and-mouth disease (FMD) is a highly contagious viral illness affecting cloven-hoofed animals such as cattle, sheep, goats, and pigs. The causative agent is the foot-and-mouth disease virus (FMDV), classified within the family Picornaviridae, genus Aphthovirus. FMDV is a non-enveloped, positive-sense single-stranded RNA virus. There are seven immunologically distinct serotypes of FMDV: A, O, C, SAT1, SAT2, SAT3, and Asia1, which do not confer cross-immunity. Transmission of FMDV occurs through direct contact with infected animals, exposure to contaminated feed, water, equipment, or clothing, and via aerosols over short distances. The virus is highly resilient, capable of surviving in various environmental conditions, which contributes to its rapid spread among susceptible animal populations.