Previous Year UPSC Questions

Explanation

Mycorrhiza is a symbiotic association between fungi and the roots of higher plants. In this relationship, the fungi help the plants by increasing water and nutrient absorption (especially phosphorus), while the plants provide carbohydrates (like glucose) to the fungi. This mutualistic relationship is beneficial to both organisms and plays a crucial role in plant growth and soil health.

Explanation

Indian Standard Time (IST) is calculated based on the 82.5°E longitude, which passes through Mirzapur, Uttar Pradesh. IST is 5 hours 30 minutes ahead of Greenwich Mean Time (GMT+5:30). Since the Earth rotates 360° in 24 hours, it covers 15° of longitude per hour which means that for every degree of longitude, there is a 4-minute difference in local time. Shillong is located at 92°E longitude, which is 9.5° east of the IST reference meridian. By multiplying this difference with 4 minutes per degree, we get a time difference of 9.5 × 4 = 38 minutes. Since local time increases towards the east, Shillong will be 38 minutes ahead of IST. Therefore, if it is 10:00 AM IST then the local time in Shillong will be 10:38 AM.

Explanation

The Krishna-Godavari basin is a large sedimentary basin on the east coast of India, formed by the Krishna and Godavari rivers. It extends into the Bay of Bengal and is known for its significant hydrocarbon reserves, including both oil and natural gas. The Ravva offshore block, a prolific oil and gas producing area, is located within this basin. The basin’s geological history and structure have created favorable conditions for the accumulation of hydrocarbons, making it a crucial region for India’s energy sector.

Explanation

Maracaibo is a major city in northwestern Venezuela, situated on the western side of Lake Maracaibo, connected to the Gulf of Venezuela and the Caribbean Sea. Its strategic location and the discovery of vast oil reserves in the Maracaibo Basin have led to its development as a crucial port for the petroleum industry. Maracaibo serves as a primary hub for the export of crude oil and refined petroleum products, contributing significantly to Venezuela’s economy.

Explanation

Assertion (A) is true: Chile holds a prominent position in the global copper market, consistently ranking among the top producers worldwide. Its copper mining industry is a significant contributor to the nation’s economy and plays a crucial role in supplying copper to meet global demand. This sustained high level of production underscores Chile’s importance in the international copper trade. Reason (R) is true: Chile possesses exceptionally large deposits of porphyry copper, a type of ore deposit that is a primary source of copper globally. These deposits are characterized by their large size and relatively low-grade ore, but their sheer scale makes them economically viable for large-scale mining operations. The abundance of porphyry copper deposits in Chile is the fundamental reason for its substantial copper production and its leading role in the world market. The geological endowment of this resource directly explains Chile’s capacity to produce such significant quantities of copper. Thus, both A and R are true and R is the correct explanation of A.

Explanation

Endoscopy is a medical procedure that uses a flexible tube with a light and camera (endoscope) to explore the inside of the body, such as the stomach, intestines, or other organs. The technique relies on the phenomenon of total internal reflection to transmit light through fiber-optic cables inside the endoscope. Total internal reflection occurs when light traveling through a denser medium (such as glass or optical fibers) strikes the boundary with a less dense medium (like air) at a certain angle, causing the light to reflect entirely back into the denser medium instead of refracting out.

Explanation

A is correctly matched with 4: Mount Rainier, a prominent stratovolcano in the Cascade Range, is located in the state of Washington within the United States. It is the high-est mountain in the state and a significant landmark in the Pacific Northwest. B is correctly matched with 1: Mount Etna, situated in Sicily, Italy, is one of the most active volcanoes in the world and the largest in Europe. C is correctly matched with 2: Paricutin, a cinder cone volcano located in the Mexican state of Michoacán, is notable for its relatively recent and well-documented formation. It emerged from a cornfield in 1943 and continued to erupt for nine years, eventually reaching a height of 424 meters. D is correctly matched with 3: Taal Volcano, a complex volcano located on the island of Luzon in the Philippines, is characterized by its unique setting within a lake-filled caldera. The volcano has a history of explosive eruptions, and it is considered one of the most active volcanoes in the Philippines.

Explanation

Option (c) is correct: Formic acid is the substance that many ants inject when they bite. This acid is produced in their venom glands and is responsible for the characteristic pain or burning sensation felt after an ant bite. Formic acid is also used by ants for defense, and some species, like fire ants, use it in larger quantities to cause more intense reactions in their prey or threats.

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

Acetic acid is a concentrated form of acetic acid, commonly found in vinegar, but it is not involved in the venom of ants. Methanol is a type of alcohol, not present in ant venom. Stearic acid is a fatty acid commonly found in animal fats and plant oils, but it is not the compound found in ant venom.

Explanation

Option (c) is correct: Eye donation typically involves the donation of the cornea, the transparent, dome-shaped layer at the front of the eye. The cornea is crucial for focusing light on the retina and plays a key role in vision. Corneal transplants are performed to restore vision in people suffering from corneal blindness or damage, which can result from conditions like injury, infections, or diseases.

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

The iris controls the amount of light entering the eye by adjusting the size of the pupil. While important for vision, the iris is not typically used in eye donation. The retina is the light-sensitive layer at the back of the eye responsible for sending visual information to the brain. Retinal transplants are highly complex and not commonly done in eye donation. The lens focuses light on the retina but is not commonly donated for transplant.

Explanation

A is matched with 1: Adrenaline, produced by adrenal gland is associated with the body’s response to stress, especially during situations of anger, fear, or danger. It triggers the "fight or flight" response, increasing heart rate, blood pressure, and energy supply. B is matched with 3: Estrogen is indeed the primary female sex hormone that regulates the development of female reproductive tissues and secondary sexual characteristics such as breast development and menstruation. C is matched with 4: Insulin is a hormone that regulates blood glucose levels, facilitating the uptake of glucose by cells for energy. D is matched with 2: Pheromones are chemicals released by animals or humans that influence the behavior of others, particularly related to attracting partners through the sense of smell.