Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Statement 1 is correct: Molasses is a thick, dark syrup that remains after the extraction of sugar from sugarcane or sugar beets. It is a common by-product in the sugar industry. It serves as a feedstock for producing synthetic chemical fertilizers and ethanol.

Statement 2 is correct: Bagasse, the fibrous residue left after extracting juice from sugarcane, is commonly used as a biofuel in the sugar industry to generate steam and electricity, making the process more energy-efficient.

Statement 3 is incorrect: Sugar is produced from various raw materials including sugarcane and sugar beets. Other sources for sugar production include sorghum and palm sap.

Explanation

The octopus is a mollusc in the class Cephalopoda (including squids and cuttlefish), part of the phylum Mollusca. Cephalopods are soft-bodied, bilaterally symmetrical, lack external skeletons, and have prominent heads with arms or tentacles. Octopuses lack an external shell, allowing for flexibility and the ability to squeeze through tight spaces. Their eight arms, equipped with suction cups, help with locomotion, prey capture, and interaction. Octopuses are highly intelligent, demonstrating problem-solving and tool use. Mollusca is a phylum of invertebrates, including snails, clams, and cephalopods.

Explanation

The word AIDS stands for Acquired Immuno Deficiency Syndrome. This means deficiency of the immune system, acquired during the lifetime of an individual. ‘Syndrome’ means a group of symptoms. AIDS is caused by the Human Immunodeficiency Virus (HIV), a member of a group of viruses called retrovirus. It leads to various symptoms such as Swollen lymph nodes occur due to immune system deterioration, commonly affecting the neck, armpits, and groin. Night sweats and recurring fevers are signs of opportunistic infections as the body struggles to regulate temperature. Memory loss and cognitive impairment arise when the virus affects the nervous system, leading to neurological complications. Significant weight loss results from chronic infections, metabolic changes, and increased energy demands.

Explanation

Statement 1 is incorrect: The renal artery is responsible for delivering oxygenated blood from the heart to the kidneys for filtration. After the kidneys filter the blood by removing waste products and excess substances, the cleansed blood is returned to the systemic circulation via the renal vein, not the renal artery.

Statement 2 is correct: From Bowman’s capsule, the glomerular filtrate(filtered liquid) passes into the proximal convoluted tubule (PCT), where essential substances, including glucose, are actively reabsorbed. This reabsorbed glucose along with other nutrients is then transported into the peritubular capillaries and eventually returned to the bloodstream via the renal vein. This ensures that the body retains necessary nutrients while excreting waste.

Explanation

Milk does contain several B-vitamins such as Vitamin B2 (riboflavin) and Vitamin B12 (cobalamin) along with Vitamin D, calcium, and proteins. For instance, a 200ml glass of semi-skimmed milk provides approximately 0.47 mg of riboflavin, which is about 33% of the recommended daily intake. Options (b), (c) and (d) are correct:

Vitamin A is found in foods like carrots, liver, and dairy products and is crucial for maintaining healthy skin. A deficiency in vitamin A can cause xerosis (dry, scaly skin) due to its role in maintaining healthy skin and mucous membranes. Scurvy is caused by a deficiency in vitamin C. One of its symptoms is joint pain, along with others like fatigue, swollen gums, and bruising. Vitamin C is found in citrus fruits, amla, and guava. A severe deficiency in Vitamin B1(thiamine) can result in beriberi, which affects the cardiovascular system, potentially leading to heart failure. Symptoms include shortness of breath, swelling of the lower legs, and increased heart rate. It is present in whole grains, nuts, and legumes.

Explanation

Statement 1 is correct: When hydrochloric acid (HCl) from the stomach enters the duodenum, it lowers the pH of intestinal contents. This triggers S-cells in the duodenal lining to release secretin. Secretin signals the pancreas to release bicarbonate-rich fluid. This fluid neutralizes the acid, creating an optimal environment for digestive enzymes to function.

Statement 2 is correct: Enterogastrone refers to a group of hormones secreted by the duodenal mucosa when dietary fats are present. These hormones, including secretin and cholecystokinin (CCK) slows down gastric motility and inhibit stomach secretions. This regulation ensures that chyme moves gradually from the stomach to the small intestine, promoting better fat digestion and absorption.

Explanation

Stem cells are undifferentiated cells with the potential to develop into various specialized cell types, offering promise for regenerative medicine and disease treatment

Statement 1 and 2 are incorrect: The blastocyst stage of embryos is a common source of embryonic stem cells, but it is not the only source. Stem cells can also be derived from adult tissues (adult stem cells) and umbilical cord blood. As of current techniques, obtaining embryonic stem cells typically requires the destruction of the blastocyst. Alternative methods are being actively researched to derive stem cells without causing harm to the blastocyst.

Statement 3 is correct: Stem cells, such as embryonic stem cells have the ability to self-renew and regenerate themselves in vitro indefinitely under appropriate conditions. This property makes them valuable for research and therapeutic applications.

Statement 4 is correct: Indian research centers, such as the National Centre for Biological Sciences (NCBS) and the Indian Council of Medical Research (ICMR), have successfully created a few stem cell lines capable of differentiating into multiple tissue types.

Explanation

INSAT or the Indian National Satellite System is a series of multipurpose Geostationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue needs of India.

Statement 1 is correct: The INSAT-series of satellites were launched from foreign stations like Kourou in French Guiana or Kennedy Space Center in the USA.

Statement 2 is correct: The PSLV (Polar Satellite Launch Vehicle) was used to launch many of the IRS (Indian Remote Sensing) satellites, which are used for Earth observation.

Statement 3 is correct: India’s first cryogenic engine was used for the third stage of the GSLV (Geosynchronous Satellite Launch Vehicle) for the first time in the launch of GSLV-D3 in 2010.

Statement 4 is correct: GSAT-1, India’s first geostationary communication satellite, was launched in 2001, and its payloads were designed to provide digital broadcast and communication services, including internet services.

Explanation

A satellite is an object in space that orbits or circles around a bigger object. There are two kinds of satellites: natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth). Almost every planet having at least one moon. Assertion (A) is true: Satellites are launched in the eastward direction to take advantage of the Earth’s rotational velocity, which gives the rocket an initial boost in speed. This helps the rocket reach the required escape velocity more efficiently. Reason (R) is false: While the Earth’s rotation does provide a velocity boost but it does not directly help the satellite attain escape velocity (the speed needed to break free from Earth’s gravity, approximately 11.2 km/s). Instead, the Earth’s rotation helps the satellite achieve orbital velocity (the speed needed to stay in orbit, approximately 7.8 km/s for low Earth orbit).

Explanation

Density is a measure of how much mass is packed into a given volume. Buoyancy is the tendency of an object to float in a fluid. An object floats if its density is less than the fluid’s density and sinks if its density is greater. If the densities are equal, the object remains neutrally buoyant, neither sinking nor floating. Assertion (A) is true: Iron is denser than water, so it sinks in water. However, mercury is denser than iron, so an iron ball will float on mercury. Reason (R) is false: Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water). Mercury is denser than iron, so its specific gravity is higher.