UPSC 1999 Science and Technology Questions with Answers

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.

Explanation

Capillarity, also known as capillary action, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. Capillarity is crucial in various natural and artificial processes, where the balance of forces drives the liquid into confined spaces.

Option (a) is correct: The tiny pores in the blotting paper act as capillaries and draw the ink through them.

Option (b) is incorrect: This is primarily due to hydrostatic pressure and not capillary action. Water moves through soil and rock layers due to pressure gradients rather than the effects of surface tension.

Option (c) is correct: This is due to capillarity. The fine fibers in the cloth act as capillaries, drawing water into them.

Option (d) is correct: Capillary action, along with transpiration pull and root pressure, helps move water through the tiny xylem vessels in plants.

Explanation

Cryogenics is a branch of physics that focuses on the production and study of materials and phenomena at extremely low temperatures, typically below -150 degree celsius. At these temperatures, materials exhibit unique physical properties that are not observed under normal conditions.

Option (a) is correct: Cryogenics has three major applications:

Space Travel: Used in rocket propulsion with cryogenic fuels like liquid hydrogen (LH2) and liquid oxygen (LOX) for efficient and high-energy space missions. Surgery: Applied in cryosurgery to destroy diseased tissue using extremely low temperatures, benefiting fields like dermatology and oncology. Magnetic Levitation: Enables superconducting magnets in Maglev trains and devices by cooling materials to achieve zero electrical resistance, allowing frictionless transportation.

Explanation

When light passes from one medium to another, its speed and direction change due to differences in the refractive indices of the two media. This phenomenon is known as refraction.

Statement 1 is correct: In a denser medium (with a higher refractive index), light travels slower. When light moves into a less dense medium (with a lower refractive index), it speeds up. As a result, the light bends away from the normal (the imaginary line perpendicular to the surface at the point of incidence). The object appears to be closer from the surface than it actually is, as seen in the case of a coin in water when viewed from above.

Statement 2 is correct: If a person is underwater looking at a coin above the surface, the coin appears higher than its actual position, not lower. This is because light bends away from the normal when moving from water (denser) to air (rarer).

Explanation

Statement 1 is correct: The filament in a light bulb is typically made of tungsten. When the filament is not uniform, the thinner sections tend to heat up more, leading to higher temperatures and stress, which can cause premature failure.

Statement 2 is correct: Light bulbs typically contain an inert gas, like argon, to prevent oxidation of the filament and improve lifespan. Complete evacuation of the bulb is not possible. A small quantity of gases left behind which expands on heating by heat through filament. If the bulb is not evacuated properly, the filament would burn out quickly causing the bulb to have a short life.

Statement 3 is correct: The wires supporting the filament are designed to withstand high temperatures. However if they are not robust enough or if the filament heats up too much, and they can melt, causing the bulb to fail.

Explanation

Statement 1 is correct: Most car batteries are 12-volt lead-acid batteries. This is the standard voltage for automotive applications as it provides sufficient power for starting the engine and running electrical systems in vehicles.

Statement 2 is incorrect: The electrolyte used in a car battery is sulfuric acid (H₂SO₄), not hydrochloric acid. Sulfuric acid is mixed with distilled water to create the electrolyte solution, which facilitates the electrochemical reactions in the battery.

Statement 3 is incorrect: The electrodes in a car battery are made of lead (Pb) and lead dioxide (PbO), not copper. The negative electrode (anode) is made of pure lead, and the positive electrode (cathode) is made of lead dioxide.

Statement 4 is correct: The capacity of a car battery is expressed in ampere-hours (Ah). This unit measures the amount of charge a battery can deliver over time. For example, a 50 Ah battery can theoretically deliver 1 ampere of current for 50 hours or 5 amperes for 10 hours.

Explanation

Barium is used in X-ray imaging because it effectively absorbs X-rays, which makes it show up clearly on X-ray images. This property helps in creating a clear contrast between the stomach and surrounding tissues, allowing doctors to examine the stomach’s structure more easily.