Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Aerobic respiration is the process by which glucose is completely oxidized in the presence of oxygen to produce carbon dioxide, water, and energy (in the form of ATP). The overall reaction is:

C₆H₁₂O₆ + 6O₂ 6CO₂ + 6H₂O+ Energy (ATP)

Explanation

Fish, especially oily fish like salmon, mackerel, and sardines are rich in polyunsaturated fatty acids (PUFAs) such as omega-3 fatty acids (e.g., EPA and DHA). These fatty acids are essential for various health benefits such as:

Reducing the risk of cardiovascular diseases.

Improving brain function and development.

Reducing inflammation.

Explanation

A is matched with 4: Malaria is Caused by protozoan parasites of the genus Plasmodium (e.g., Plasmodium falciparum, Plasmodium vivax), transmitted through the bite of infected female Anopheles mosquitoes. India’s National Malaria Elimination Programme (NMEP) aims to eliminate malaria by 2030 under the National Center for Vector Borne Diseases Control (NCVBDC). WHO has approved RTS, S/AS01 (Mosquirix) vaccine for children. B is matched with 3: Polio is caused by the poliovirus (genus Enterovirus) which spreads via contaminated food, water, or contact. Widely available vaccines (OPV and IPV) prevent polio. India’s Pulse Polio Programme launched in 1995 achieved polio-free certification in 2014. C is matched with 2: Tuberculosis is caused by Mycobacterium tuberculosis. It primarily affects the lungs and spreads through the air. The BCG vaccine provides TB prevention in children. India’s National Tuberculosis Elimination Programme (NTEP) offers free treatment and nutrition support under Nikshay Poshan Yojana, aiming for elimination by 2025. D is matched with 1: Ringworm is a fungal infection caused by dermatophytes such as Trichophyton, Microsporum, or Epidermophyton. It affects the skin, hair, or nails, spreading through direct skin contact or contaminated surfaces.

Explanation

Haemophilia is a genetic disorder where the 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.

Explanation

Options (a), (b) and (c) are incorrect: Protein analysis lacks the precision needed for identifying individual genetic relationships, as protein expression can be influenced by multiple factors. Chromosome counting determines the number of chromosomes but cannot identify specific genetic relationships. Quantitative analysis of DNA measures the quantity of DNA but does not provide the unique genetic markers necessary for establishing paternity.

Option (d) is correct: DNA fingerprinting is the most accurate and reliable technique to establish paternity. This method analyzes specific regions of the DNA that are highly variable among individuals, called short tandem repeats (STRs). A child inherits half of their DNA from the mother and the other half from the father, making DNA fingerprinting a powerful tool to match the genetic profiles of the child and the alleged parent.

Explanation

Surface tension is the force that acts on the surface of a liquid, causing it to contract and minimize its surface area. This effect occurs because molecules at the surface of the liquid experience a net inward force due to the attractive forces between the molecules. As a result, the liquid tends to form shapes that have the least surface area, such as spherical droplets. This tendency to minimize surface area is why liquid droplets form spherical shapes in free space, as a sphere has the smallest surface area for a given volume.

Explanation

A vector quantity is a physical quantity that has both magnitude and direction. In addition to how much of a quantity there is, you also need to know the direction in which it acts. Some examples of vector quantities include force, velocity, acceleration and displacement. Momentum is a vector quantity because it has both magnitude and direction (it depends on the direction of motion and the velocity of the object).

Explanation

Option (a) is correct: The working principle of a washing machine is Centrifugation. It is a process used to separate substances of different densities by spinning them at high speed. In a washing machine, the centrifugal force generated during the spin cycle helps remove water from the clothes along with dirt and stain.

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

Dialysis is a process used to remove waste products and excess fluids from the blood in patients with kidney failure. It involves the diffusion of solutes across a semipermeable membrane. Reverse osmosis is a water purification process that uses a semipermeable membrane to remove ions, molecules and larger particles from water. It is commonly used in desalination and water filtration systems. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. While diffusion plays a role in processes like the mixing of detergents in water but it is not the main working principle of a washing machine.

Explanation

Paramagnetism refers to the property of a material that is weakly attracted to an external magnetic field due to the presence of unpaired electrons in its atomic or molecular structure. When placed in a magnetic field, these unpaired electrons align their magnetic moments in the direction of the field, causing a weak but positive magnetization. However, this effect disappears once the external field is removed.

Option (c) is correct: Oxygen (O₂) is paramagnetic because it has two unpaired electrons in its molecular orbital configuration, making it weakly attracted to a magnetic field. Options (a), (b) and (d) are incorrect:

Iron is ferromagnetic (not always paramagnetic), meaning it is strongly attracted to magnetic fields. Hydrogen and Nitrogen are diamagnetic, meaning they are weakly repelled by magnetic fields due to their paired electrons. Directions: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer this item using the code given below.

Explanation

A comet is a small celestial body composed of ice, dust, and rocky material that orbits the Sun in an elliptical path. When it gets close to the Sun, the heat causes its icy nucleus to vaporize, forming a glowing coma.

Option (c) is correct: The tail of a comet is directed away from the Sun due to the solar wind and radiation pressure exerted by the Sun. The Sun emits charged particles (mainly electrons and protons) that interact with the comet’s nucleus and coma, pushing gas and dust away. This creates a glowing tail that always points opposite the Sun, regardless of the comet’s orientation. The tail’s direction can change as the comet moves, influenced by factors like solar wind intensity, the coma’s shape, and the Sun’s magnetic field.