Previous Year UPSC Questions

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.

Explanation

Options 1, 2 and 3 are correct: The Adriatic Sea separates the Italian Peninsula from the Balkan Peninsula. Among the given options, Albania, Bosnia and Herzegovina, and Croatia have coastlines along this sea. Option 4 is incorrect: Macedonia, now known as North Macedonia, does not have coastlines along the Adriatic Sea. It is a landlocked country located to the east of Albania. North Macedonia shares borders with four countries: Greece to the south, Albania to the west, Bulgaria to the east, and Kosovo and Serbia to the north.

Explanation

In 2001, Venus Williams defeated her sister Serena Williams in the US Open Women’s Singles Final to win the title. This match was a memorable moment in tennis history as both sisters were at the peak of their careers, and it marked the beginning of a dominant era for both in tennis.

Explanation

In Test cricket history, only two matches have ended in a tie, both involving Australia. The first was against the West Indies in Brisbane (1960), where Australia fell just one run short of victory. The second was against India in Chennai (1986), where India, needing four runs with one wicket in hand, was bowled out with scores level.

Explanation

Option (b) is correct: The 9th FINA World Swimming Championships were held in Fukuoka, Japan, in 2001. Ian Thorpe, an Australian swimmer, won six gold medals at the event.