Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

The silkworm yields the fiber of commerce during its larval stage, specifically when it starts to spin its silk cocoon. The silkworm (the larval stage of the silk moth Bombyx mori) produces the fiber of commerce during its larval stage. This stage is when the silkworm starts spinning its silk to form a protective cocoon around itself. The silk produced by the larva is collected and used commercially to make silk fabric. Therefore, the correct stage when the silkworm yields the fibre of commerce is the larva. The imago is the adult moth stage in the silkworm’s life cycle. After metamorphosis, the adult moth does not produce silk. Its role is to mate and lay eggs, continuing the life cycle. Therefore, the silkworm does not yield silk during the imago stage.

Explanation

A is matched with 2: Haemophilia is a genetic disease caused by mutations in clotting genes. It is inherited via X chromosome. Under this, blood does not clot properly due to a deficiency of clotting factors (such as Factor VIII in Haemophilia A or Factor IX in Haemophilia B). This leads to excessive bleeding even from minor injuries. B is matched with 3: Diabetes is primarily a hormonal disorder related to insulin production or the body’s inability to use insulin effectively. Type 1 diabetes is due to insufficient insulin production (autoimmune) while Type 2 is due to insulin resistance. C is matched with 1: Rickets is caused by a deficiency of vitamin D, calcium, or phosphate, leading to weakened bones. It is not genetic or hormonal but results from nutritional deficiencies. D is matched with 4: Ringworm is a fungal infection caused by dermatophytes, affecting skin, hair, nails resulting in ring-shaped patches.

Explanation

Blood glucose levels are commonly measured in milligrams per decilitre (mg/dL). This unit expresses the amount of glucose (in milligrams) present in a decilitre (0.1 liters) of blood. It is the standard measurement used in most clinical settings to monitor and diagnose conditions like diabetes. Other units include millimoles per liter (mmol/L), used in countries like the UK, where 1 mg/dL equals 0.0555 mmol/L.

Explanation

Endocrine glands secrete hormones that regulate various bodily functions, from growth and metabolism to stress responses. A is matched with 2: The gonads (ovaries in females and testes in males) are responsible for producing sex hormones. In females the ovaries secrete progesterone which plays a key role in regulating the menstrual cycle and maintaining pregnancy. In males the testes primarily produce testosterone but it also produces progesterone in smaller amounts. B is matched with 3: Known as the master gland, pituitary gland secretes growth hormone (GH) (stimulates growth, cell reproduction, and regeneration), thyroid-stimulating hormone (TSH) (regulates metabolism), prolactin (stimulates milk production), and antidiuretic hormone (ADH) (maintains water balance). C is matched with 1: Pancreas regulates blood sugar levels through insulin (lowers blood glucose) and glucagon (raises blood glucose) and plays a major role in carbohydrate, fat, and protein metabolism. D is matched with 4: The adrenal glands located on top of the kidneys produce cortisone, a glucocorticoid hormone involved in stress response, metabolism, and immune regulation. Cortisone is part of the body’s natural response to stress and inflammation.

Explanation

Option (d) is correct: During intense exercise muscles rely on anaerobic respiration (without oxygen) to produce energy quickly. This process breaks down glucose into pyruvate, which is then converted into lactic acid (or lactate) in the absence of sufficient oxygen. The buildup of lactic acid in muscle tissues lowers the pH which causes a burning sensation and muscle fatigue.

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

While a decrease in oxygen supply can contribute to fatigue but it is not the primary cause of the immediate sensation of muscle fatigue. Prolonged or intense exercise can cause microscopic damage to muscle fibers which causes delayed-onset muscle soreness (DOMS). However, this damage does not cause the immediate sensation of fatigue during exercise. Glucose is a primary energy source for muscles during exercise. While glycogen (stored glucose) depletion can contribute to fatigue during prolonged endurance activities (e.g., marathons) but it is not the primary cause of the acute fatigue and burning sensation

Explanation

The small pouch containing silica gel found in bottles of medicine (tablets or powder) is primarily used to absorb moisture. Silica gel is a desiccant, meaning it has a high affinity for water molecules. It absorbs moisture from the surrounding environment, preventing the tablets or powder from degrading due to humidity. This helps maintain the stability and efficacy of the medicine. Silica gel has a porous structure that traps water molecules through adsorption. Moisture can cause tablets to crumble or powders to clump, reducing their effectiveness and shelf life.

Explanation

The introduction of the Bt gene into the cotton genome provides effective protection against damage caused by insects, significantly reducing the need for chemical pesticides. Assertion (A) is true: Insect-resistant transgenic cotton, known as Bt cotton, has been developed by inserting the Bt gene into cotton plants. Reason (R) is true: This gene, derived from the bacterium Bacillus thuringiensis, enables the plant to produce a protein toxic to specific insect pests, such as bollworms, while being harmless to humans and non-target organisms. Since the Bt gene’s origin from Bacillus thuringiensis directly explains its role in imparting insect resistance. Hence, both the assertion and the reason are true, and the reason correctly explains the assertion.

Explanation

Cloning is the process of creating genetically identical copies of an organism, cell, or DNA sequence. It can be natural (as in identical twins) or artificial (like somatic cell nuclear transfer, used in Dolly the sheep). Assertion (A) is true: Dolly the sheep, born in 1996, was the first mammal successfully cloned from an adult somatic cell, making her a landmark achievement in biotechnology. Reason (R) is false: Dolly was not produced through in vitro fertilization (IVF), which involves the fusion of sperm and egg outside the body. She was created using somatic cell nuclear transfer (SCNT), a process in which the nucleus of a somatic cell (in Dolly’s case, a mammary gland cell) was transferred into an enucleated egg cell (an egg cell with its nucleus removed). The resulting cell was stimulated to divide and develop into an embryo, which was then implanted into a surrogate sheep for gestation.

Explanation

Assertion A is true: By the late 1990s, India’s information technology (IT) sector had experienced significant growth, establishing the country as a key player in the global IT industry. The rapid expansion of software services and exports contributed to the increasing importance of IT in India’s economic landscape. Reason R is false: While software is indeed a major export for India, the country has traditionally been stronger in software services rather than hardware manufacturing. The hardware sector in India has not been as prominent or well-developed compared to the software industry.

Explanation

Both the bullet and the monkey experience the same downward acceleration due to gravity provided the air resistance is negligible. When the hunter fires the bullet, the bullet starts moving along a curved trajectory due to the combined effects of its horizontal velocity and the vertical acceleration caused by gravity. When the monkey jumps, it also begins to fall freely under gravity with an initial vertical velocity of zero. Since the hunter aims directly at the monkey at the moment of firing, the bullet and the monkey will both fall the same vertical distance due to gravity at the same time. Therefore, the bullet will hit the monkey at the point aimed.