Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

A is matched with 3: Asiatic Wild Ass (Equus hemionus khur) or Khur, is an Endangered equid found in the Little Rann of Kutch, Gujarat. It has a chestnut brown coat with a dark dorsal stripe and can run at 70 km/h. It is adapted to arid landscapes and survives on minimal water and grazes on grasses and fruits. Conservation efforts, including the Wild Ass Sanctuary, have helped stabilize its population. B is matched with 2: Barasingha (Rucervus duvaucelii) is recognized for its 12-tined antlers. It inhabits grasslands and swamps in Kanha and Dudhwa National Parks. Barasinghas are social grazers, feeding on grasses and aquatic plants. Once critically endangered due to habitat loss, their population has improved due to conservation initiatives such as habitat restoration and anti-poaching measures. C is matched with 4: Chinkara (Gazella bennettii) is a small, agile antelope found in arid and semi-arid regions like the Thar Desert. It has a reddish-buff coat, white underparts, and distinctive facial markings. Chinkaras are solitary browsers, feeding on leaves and fruits, and can survive without water for long periods. D is matched with 1: Nilgai (Boselaphus tragocamelus) is the largest Asian antelope. Males have a bluish-grey coat, while females are tawny brown. Found in grasslands, scrub forests, and agricultural areas, Nilgais are diurnal and social browsers. Their population is stable, but they are often considered agricultural pests, leading to human-wildlife conflicts in some regions.

Explanation

Animal mating behavior is incredibly diverse and fascinating, encompassing a wide range of strategies for finding a mate and ensuring reproductive success. From the elaborate courtship rituals of birds-of-paradise to the fierce competition of stags locking antlers, the animal kingdom showcases a variety of tactics. Some animals form monogamous pair bonds that can last a lifetime, demonstrating a different approach to mating and raising offspring. The variety of mating behaviors reflects the diverse evolutionary pressures shaping each species’ reproductive success.

Option (a) is correct: The wolf (Canis lupus) is monogamous animal. They typically form lifelong pair bonds, with mated pairs remaining together until one partner dies, after which the surviving wolf may find a new mate. This monogamous behavior is integral to the social structure of wolf packs, which are often composed of the breeding pair and their offspring.

Explanation

Viviparous animals give birth to live young, rather than laying eggs. However most echinoderms reproduce through external fertilization, releasing eggs and sperm into the water column. Viviparity is relatively rare among echinoderms. Notable exceptions include certain species of brittle stars and sea stars, such as Cryptasterina hystera, which exhibit viviparous reproduction.

Explanation

A is matched with 2: Arber and Smith discovered endonucleases (restriction enzymes). They are enzymes that cut DNA at specific sequences, essential for genetic engineering and molecular biology. These restriction enzymes, such as EcoRI, allow precise DNA modifications, facilitating cloning, genome mapping, and recombinant DNA technology, forming the foundation of modern genetic research and biotechnology applications. B is matched with 1: Feldman developed transgenic plants using Agrobacterium T-DNA. It is a method for introducing foreign genes into plant genomes. This technique revolutionized agriculture by creating genetically modified crops like Bt cotton with enhanced traits like pest resistance and drought tolerance. C is matched with 4: Polymerase Chain Reaction (PCR) was discovered by Kary Mullis. It enables rapid DNA amplification, crucial in forensic science, disease diagnosis, and genetic research. Using DNA polymerase and temperature cycling, PCR exponentially multiplies DNA sequences, allowing precise genetic analysis. It plays a pivotal role in applications like DNA fingerprinting and infectious disease testing. D is matched with 3: Reverse Transcriptase was discovered by Temin and Baltimore. It is an enzyme that synthesizes DNA from RNA which is crucial in retrovirus replication like HIV. This discovery advanced virology and led to antiretroviral therapies. It is also widely used in complementary DNA (cDNA) synthesis, enabling gene expression studies and recombinant DNA technology advancements.

Explanation

Viroids are small, circular, single-stranded RNA molecules that infect plants. They do not encode proteins and rely entirely on the host’s cellular machinery for replication. Viroids are among the smallest known infectious agents.

Explanation

Assertion (A) is true: Alcohol, including whisky is a diuretic. It inhibits the production of vasopressin (also known as antidiuretic hormone or ADH), which is responsible for regulating water retention in the body. When vasopressin levels drop, the kidneys produce more urine, leading to increased urination. This effect explains why alcohol consumption causes increased thirst and dehydration-related symptoms after drinking. Reason (R) is false: Alcohol actually inhibits the secretion of vasopressin, rather than speeding it up. Vasopressin helps the kidneys reabsorb water, and when its secretion is reduced, the body loses more water through urine, causing dehydration and increased urination. Alcohol interferes with the brain’s communication pathways, affecting areas controlling balance, memory, speech, and judgment. Alcohol slows down the central nervous system, impairing coordination and judgment. Alcohol can cause intellectual impairment, headaches, memory loss, and slowed thinking.

Explanation

Assertion (A) is false: Glycine, serine, and tyrosine are non-essential amino acids which means they can be synthesized by the human body and do not need to be obtained through diet. Glycine and serine are produced from intermediate metabolites such as glucose and tyrosine is derived from phenylalanine, an essential amino acid. Hence, their dietary intake is not compulsory. Reason (R) is true: Essential amino acids are those that the human body cannot synthesize on its own and must be obtained from the diet. There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are vital for protein synthesis and other metabolic functions.

Explanation

Speciation is the process by which new and distinct species evolve from a common ancestor. Hugo deVries believed that mutation caused speciation and hence called it saltation (single step large mutation). Mutations are permanent changes in the DNA sequence, which can lead to new traits in a population. Some mutations provide adaptive advantages, increasing survival and reproduction. Over time, accumulation of mutations can result in significant genetic divergence, leading to speciation.

Explanation

Ticks and mites belong to the class Arachnida making them closely related to spiders and scorpions. They possess eight legs (in their adult stage), two body segments (cephalothorax and abdomen), and lack antennae, distinguishing them from insects. Ticks are primarily ectoparasites, feeding on the blood of vertebrates, while mites can be parasitic, free-living, or plant-feeding. Examples include the Deer Tick (Ixodes scapularis), which spreads Lyme disease, and the Scabies Mite (Sarcoptes scabiei), responsible for scabies.

Explanation

Platelets are more numerous than white blood cells in the bloodstream. The concentration of platelets ranges from 150,000 to 450,000 per microliter of blood whereas white blood cells are present at concentrations of about 4,000 to 11,000 per microliter. Platelets are essential for blood clotting, while WBCs are part of the immune system and are less numerous.

Option (a), (b) and (c) are incorrect:

Veins are more numerous than arteries and hold a significantly larger portion of the body’s blood at any given time. Approximately 70% of the body’s blood volume is found in the venous system at rest, as veins act as capacitance vessels that can expand to store blood. Arteries, on the other hand, carry oxygenated blood away from the heart and are under higher pressure, but they hold a smaller volume of blood compared to veins. Blood is composed of two main components: plasma (the liquid portion) and blood cells (red blood cells, white blood cells, and platelets). Blood cells make up approximately 45% of the total blood volume, a measure known as the hematocrit. The remaining 55% is plasma, which consists of water, proteins, electrolytes, and other dissolved substances. White blood cells (WBCs) are produced primarily in the bone marrow, not exclusively in lymph nodes. Lymph nodes play a role in the maturation and activation of certain types of WBCs, such as lymphocytes, but they are not the primary site of WBC production. Other organs, such as the spleen and thymus, also contribute to the development and function of WBCs.