Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Insect-resistant cotton, commonly known as Bt cotton, has been genetically engineered by inserting a gene from the bacterium Bacillus thuringiensis (Bt). This bacterium naturally produces a protein toxic to specific insect pests, such as bollworms, but is safe for humans and non-target organisms. The Bt gene produces a protein that disrupts the digestive system of the pests upon ingestion, ultimately killing them. Bt cotton has significantly reduced the dependence on chemical insecticides and has become a widely adopted technology for pest management in cotton farming.

Explanation

Option (a) is correct: Hybridoma technology is a groundbreaking biotechnological method developed for the large-scale production of monoclonal antibodies. This technique involves the fusion of an antibody-producing B lymphocyte with a myeloma (cancer) cell, creating a hybrid cell line called a hybridoma. These hybridomas are capable of producing a single type of antibody (monoclonal) indefinitely. Monoclonal antibodies are widely used in medical diagnostics, treatment of diseases such as cancer and autoimmune disorders, and in research applications. Options (b), (c) and (d) are incorrect:

Interferons, are proteins used in antiviral therapies. They are not produced using hybridoma technology. They are typically synthesized using recombinant DNA technology. Antibiotics are derived from microorganisms like fungi and bacteria, not via hybridoma technology. Alcohol production relies on fermentation processes, not hybridoma technology.

Explanation

In computing, memory is typically measured in units such as 1 byte = 8 bit (short for binary digit) or megabytes (MB). A byte is the basic unit of digital information storage and consists of eight binary digits, commonly referred to as bits. Each bit represents a binary value of either 0 or 1, enabling a byte to store 2^8 (256) possible values, ranging from 0 to 255 in decimal notation. This structure forms the foundation of data representation in computers.

Explanation

Option 1 is incorrect: While radial tyres improve handling and durability, they primarily reduce rolling resistance, which can have a minor impact on fuel efficiency. However, their primary benefit is not directly linked to significant fuel savings.

Option 2 is correct: A streamlined body reduces aerodynamic drag, allowing the car to move more efficiently through the air. This directly improves fuel efficiency, especially at higher speeds. An example of a car with a streamlined body is the Tesla Model S. Its sleek, aerodynamic design minimizes air resistance, improving both fuel efficiency (or energy efficiency in the case of electric cars) and performance.

Option 3 is correct: Multipoint Fuel Injection ensures that the right amount of fuel is injected into each cylinder, improving combustion efficiency and reducing fuel consumption.

Option 4 is incorrect: While a catalytic converter reduces harmful emissions, it does not directly affect fuel efficiency. Its primary function is to convert toxic gases like carbon monoxide into less harmful substances. Direction: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer these items using the code given below.

Explanation

According to Newton’s first law of motion, " A body at rest will remain at rest, and a body in motion will continue in uniform motion in a straight line unless acted upon by an external force". According to Newton’s second law of motion, "The rate of change of momentum of a body is directly proportional to the applied force and occurs in the direction of the force". Assertion (A) is true: When the man whistles, he expels air from his lungs. This expelled air has mass and velocity, creating momentum in the forward direction and thus creating reaction force which pushes the man backward on the frictionless surface. This is based on Newton’s second law of motion. Reason (R) is true: The statement that ‘ if no external force acts on a system, its momentum cannot change’ is clearly stating Newton>s first law of motion which is clearly not explaining the Assertion (A). Thus, Reason (R) merely states Newton’s First Law of Motion and doen’s explain the Assertion (A) which is based on Newton’s Second Law of Motion.

Explanation

Decibels (dB) are units used to measure the intensity of sound. The decibel scale is logarithmic, meaning each 10 dB increase represents a tenfold increase in sound intensity.

Option (d) is correct: A noise level of 100 decibels corresponds to Noise from a machine shop. A sound at 100 decibels is quite loud. It is typical of sounds like those found in a machine shop or at a loud concert. For reference: 0 decibels is the threshold of hearing (just audible sound). 30-40 decibels corresponds to a quiet room. 60-70 decibels corresponds to ordinary conversation. 100 decibels is in the range of very loud noise, such as machinery or a chainsaw. Directions: The following items consist of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer these items using the code given below. (2000)

Explanation

In the case of a compact disc (CD), when sunlight or any other light source hits its surface, the following optical phenomena occur. Diffraction: The CD’s surface contains tiny, closely spaced grooves that act like a diffraction grating. This causes the light to spread out into different colors, creating the rainbow effect that is visible. Refraction: Light also passes through the transparent plastic layer of the CD, and as it enters and exits this layer, it bends due to the change in the refractive index between the plastic and air. Transmission: Some light also passes through the CD material, further contributing to the observed effects. Together, these phenomena--refraction, diffraction, and transmission--combine to produce the beautiful rainbow-like colors seen when a CD is viewed in sunlight.

Explanation

A fluorescent lamp or fluorescent tube is a gas discharge lamp that uses electricity to excite mercury vapour. The excited mercury atoms produce shortwave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. The choke coil reduces current in the circuit. A choke coil, also known as an inductor, is used in fluorescent tubes to limit the current flowing through the circuit. It provides impedance to the alternating current (AC) which helps in stabilizing the current and preventing it from reaching excessively high levels. The choke coil does not step up or step down the voltage (these functions are typically performed by a transformer).

Explanation

Option (c) is correct: A CD (Compact Disc) audio player uses a laser beam to read the digital information encoded on the surface of the disc. The laser scans the tiny pits and lands that represent the audio data, and the player converts this data into an audio signal. Options (a), (b) and (d) are incorrect:

Quartz crystal: Used in electronic devices like oscillators and watches, but not for sound reproduction in a CD player. Titanium needle: Historically used in turntables or record players (vinyl), not in CD players. Barium titanate ceramic: Used in piezoelectric devices like speakers, but not in reading CDs.

Explanation

A TV remote control typically uses radio waves to communicate with the TV set. Radio waves are a form of electromagnetic radiation that enables the remote to send signals over short distances to control the television. Radio waves are widely used in radio and television broadcasting, enabling the transmission of audio and video signals over long distances. They are also essential in wireless communication systems, including mobile phones, Wi-Fi, and satellite communication. Note: In many sources, infrared waves are identified as the mechanism behind the functioning of TV remote controls, but this option is not provided in the given choices.