Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Mycorrhizae is a symbiotic association between a fungus and a plant. The term ‘mycorrhiza’ refers to the role of the fungus in the plant’s rhizosphere, its root system. Mycorrhiza plays important roles in plant nutrition, soil biology and soil chemistry.

Statement 1 is correct: Trees host mycorrhizal fungus in their roots so they can absorb nutrients from the ground and resist the drought condition. These fungi exchange the carbon from the tree for vital nutrients including nitrogen, phosphate, and potassium from the soil.

Statement 2 is correct: Mycorrhizal plants can withstand unfavourable soil conditions, high pH levels, droughts, and poisonous heavy metals.

Statement 3 is correct: Mycorrhizae are symbiotic relationships between plant roots and specific soil fungi that are important for the ecosystem’s nutrient cycling and that help shield plants from environmental and cultural stress. Additionally, mycorrhizal fungi’s synthesis of oxalic acid contributes to disease suppression.

Explanation

Recombinant DNA technology entails changing genetic material outside of an organism to produce living organisms or their products with improved and desired traits. Using the appropriate vectors, this approach entails inserting DNA fragments from a number of sources that have the desired gene sequence. Manipulation in an organism’s genome is carried out either through the introduction of one or several new genes and regulatory elements or by decreasing or blocking the expression of endogenous genes through recombining genes and elements. Recombinant DNA technology, also known as genetic engineering, enables the transfer of genes across different species, including:

Across different species of plants: Genes can be transferred between various plant species to introduce desirable traits. From animals to plants: Animal genes can be introduced into plants to confer new characteristics. From microorganisms to higher organisms: Microbial genes can be inserted into higher organisms, such as plants or animals, to impart beneficial properties.

Explanation

Muscle contraction is a complex physiological process regulated by nerve impulses and the interaction of muscle proteins actin and myosin. Key minerals involved in muscle contraction include: Calcium (Ca), Sodium (Na), Potassium (K), Magnesium (Mg).

Option 1 is correct: Calcium ions are essential for muscle contraction. They bind to regulatory proteins within muscle fibers, facilitating the interaction between actin and myosin, the proteins responsible for muscle contraction. Without adequate calcium, muscles cannot contract properly.

Option 2 is correct: Iron helps to support continued functioning of the muscle by supporting energy production in your muscle cells, so that muscle fibres always have the energy they need to contract properly. Also supports healthy circulation so that muscles can receive additional oxygen from the bloodstream and helps muscles store oxygen to power muscle contractions.

Option 3 is correct: Sodium is crucial for initiating and transmitting nerve impulses that lead to muscle contraction. It helps generate action potentials in nerve cells, which then stimulate muscle fibers to contract. Proper sodium levels are necessary for effective communication between the nervous system and muscles.

Explanation

Viruses are microscopic infectious agents that require a host cell to reproduce. They consist of genetic material (DNA or RNA) surrounded by a protein coat (capsid). They can cause a wide range of diseases in humans, animals, and plants.

Statement 1 is correct: Viruses are obligate intracellular parasites and lack the metabolic machinery, including enzymes, to generate energy. They depend entirely on their host cells for energy and replication.

Statement 2 is incorrect: Viruses cannot replicate or survive in synthetic media alone. They require living host cells for replication. Common methods of culturing viruses include using cell cultures, embryonated eggs, or live animals.

Statement 3 is incorrect:

While some viruses are transmitted through biological vectors (e.g., mosquitoes for dengue), many are transmitted by other means such as: Respiratory droplets (e.g., influenza virus), Direct contact (e.g., herpes simplex virus), Fomites (e.g., contaminated surfaces).

Explanation

Tattoos may cause diseases because tattoo instruments come in contact with blood and bodily fluids if the instruments are used on more than one person without being sterilised. However, tattoo-related infections are uncommon in sterile, contemporary tattoo parlours using single-use needles. Hepatitis B is a bloodborne infection caused by the Hepatitis B virus (HBV) and is spread through contact with infected blood or bodily fluids. Unsafe tattooing practices, such as using unsterilized needles or contaminated ink, can easily transmit Hepatitis B. Studies show that Hepatitis B has a significantly high transmission risk through needlestick injuries or exposure to infected blood. HIV is transmitted through contact with infected blood, semen, vaginal fluids, or breast milk. Though the risk of HIV transmission through tattooing is lower compared to Hepatitis B, it exists if contaminated needles are used. Chikungunya is primarily transmitted through the bite of infected Aedes mosquitoes and is not spread through blood or contaminated instruments.

Explanation

An optical illusion is characterized by visually perceived images that differ from object than reality. The information that is gathered by the eye is processed in the brain that gives a perception that does not tally with a physical measurement of the stimulus source.

Statement 1 is correct: There are no known objects of a similar size as the sun (or moon) when it is high in the sky. The sun, however, appears even larger when it is low in the sky because we can see distant objects near the horizon that we know to be large. Thus, the size of the sun at dusk is a visual illusion.

Statement 2 is correct: There are many different colours in light. Red is the colour that moves the farthest out of all of those others. As the sun sets, crimson (deep, rich red colour) is the final hue to be seen. Red is the last colour to appear when the other colours begin to fade. Therefore, the colour of the sun at dawn is due to optical illusion.

Statement 3 is incorrect: Moon being visible at dawn is not an optical illusion as the moon is visible somewhere in the sky at dawn during the entire half of the cycle of phases from Full Moon to just before New Moon.

Statement 4 is correct: Light is constantly emitted by stars. Before reaching our sight, this light passes through a number of layers of the earth’s atmosphere. Because different layers of atmosphere have different refractive indices, stars appear to be blinking/twinkling.

Statement 5 is incorrect: The Polestar (Pole Star or North Star) is visible because of its alignment with Earth’s rotational axis, not due to any optical effect.

Explanation

Statement 1 is correct: The Also known as " God Particle" is associated with the Higgs field, which permeates the universe. Elementary particles acquire mass through their interaction with this field. Without the Higgs mechanism, particles would remain massless, preventing the formation of atoms and, consequently, the existence of matter as we know it. This discovery confirms the Standard Model’s explanation of mass acquisition.

Statement 2 is incorrect: The Part of Invisible energy field, if Higgs field doesn’t ok provide mass to particles then there will be no gravity and no life. is not a key item that will open the way for teleportation but it will certainly help to understand mass, time and travel in time and space.

Statement 3 is incorrect: In the near or far future, the Higgs Boson may help us to create an unbelievable energy source which can pave the way for better fuels for our Nuclear missions but at present, direct connection between detection of Higgs Bosons and creation of better fuels for nuclear missions is not established.

Explanation

After harvest, fruits and vegetables remain metabolically active, with respiration being a key manifestation of this activity. Respiration involves the breakdown of stored nutrients to release energy for cellular processes. This process can be effectively slowed by lowering the temperature, which decreases the metabolic rate. Since harvested fruits and vegetables are no longer connected to the plant’s roots, they cannot acquire additional nutrients. As a result, they rely entirely on their stored nutrients for energy. Once these reserves are depleted, the produce begins to degrade. Therefore, controlling the rate of respiration through proper storage conditions, such as refrigeration, is crucial to preserving fruits and vegetables for longer periods and maintaining their quality.

Explanation

Ball bearings are used to reduce friction between the surfaces. A ball bearing is a specific kind of rolling-element bearing that uses balls to keep the bearing races apart. A ball bearing’s main functions are to support radial and axial loads and lessen rotational friction. In order to reduce friction between surfaces and also because the effective area of contact between the wheel and axle is reduced, ball bearings are used in bicycles, vehicle axles, etc.

Explanation

A rainbow is formed when sunlight interacts with raindrops in the atmosphere, and this process involves three key physical phenomena: dispersion, refraction, and internal reflection. Dispersion occurs as sunlight, which consists of multiple colors, is separated into its constituent wavelengths when it passes through a raindrop, with each color bending by a different angle. Refraction takes place at the interface of air and water when sunlight enters the raindrop, causing the light to bend due to a change in its speed. This bending happens twice--first as the light enters the drop and again as it exits. Internal reflection occurs when the light, after being refracted, reflects off the inner surface of the raindrop. The combined effect of these phenomena results in the formation of a colorful arc in the sky, known as a rainbow.