Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

In severe winter, a lake’s surface freezes while the bottom remains liquid due to the anomalous density behavior of water. Unlike most substances, water reaches its maximum density at 4°C, meaning that as it cools, denser water sinks while colder, lighter water (below 4°C) stays at the surface. When temperatures drop below 0°C, the surface water freezes first, forming an insulating ice layer that prevents further heat loss from the deeper water, keeping it in a liquid state. This phenomenon protects aquatic life, as it prevents the entire lake from freezing solid

Explanation

Microbial fuel cells (MFCs) are a bioelectrochemical technique, proposed to generate power using electrons from biological reactions in microorganisms.

Statement 1 is correct: These devices primarily use bacteria as catalysts to break down organic and inorganic substances, generating electrical current.

Statement 2 is incorrect: Microorganisms oxidise organic compounds, not inorganic substrates in the anode chamber, producing electrons and protons (reaction of anodes).

Statement 3 is correct: An MFC typically consists of two electrodes: the anode and the cathode. At the anode, bacteria decompose organic matter in wastewater, producing electrons and protons. The electrons travel through an external circuit to the cathode, generating electricity, while the protons move from the anode to the cathode. At the cathode, the electrons and protons combine with an electron acceptor, such as oxygen, to form water. As a result, MFCs can be implemented in wastewater treatment facilities to purify water and generate electricity.

Explanation

Moderator is used in a nuclear reactor for slowing down the neutrons produced during the fission reaction so that the chain reaction can be sustained. Due to its high moderating ratio and low neutron absorption cross section, heavy water makes a good moderator. Deuterium oxide, popularly known as heavy water (D₂O), is a hydrogen isotope with a mass double that of regular hydrogen and oxygen. However, In nuclear power reactors, heavy water can also be utilized as a coolant.

Explanation

Trans fatty acids (TFA) or trans fats are a form of unsaturated fat and come in both natural and artificial forms. Trans fats are the most harmful type of fats which can cause an adverse effect on a human body than any other dietary constituent.

Statement 1 is correct: Artificial trans fats are generated through an industrial process that adds hydrogen to liquid vegetable oils to form them more solid. That is hydrogen is made to react with the oil to produce fats that resemble pure ghee or butter. If items do not contain trans-fats, it means the food products are not made out of hydrogenated oils and animal fats/oils.

Statement 2 is incorrect: This is incorrect because not all animal fats contain trans fats. While small amounts of naturally occurring trans fats are found in some animal products, the harmful trans fats that raise cardiovascular risks are primarily from industrial hydrogenation, not from natural animal fats.

Statement 3 is correct: If items do not contain trans fats, it suggests that the oils used are less likely to harm the cardiovascular health of consumers, as oils associated with trans fats typically raise LDL (bad) cholesterol and lower HDL (good) cholesterol, contributing to plaque buildup in arteries and increasing the risk of heart attacks and strokes.

Explanation

Statement 1 is correct: An LED is a type of semiconductor light source with two leads. It is a p-n junction diode, which when turned on emits light. A fluorescent lamp is a low-pressure mercury-vapour gas-discharge light. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light.

Statement 2 is incorrect: LED bulbs are much more efficient than CFL bulbs in terms of power consumption and life years.

Statement 3 is correct: LED bulbs consume less power as compared to CFL. LED bulbs are expensive as compared to CFL bulbs. LED bulbs are much more efficient than CFL bulbs.

Explanation

Aspartame is a non-saccharide artificial sweetener approximately 200 times sweeter than sucrose, and is commonly used as a substitute of sugar in foods and beverages. The commercial names for it are NutraSweet, Equal, and Canderel. It is a methyl ester of the aspartic acid / phenylalanine dipeptide. Since Aspartame is several times sweeter than table sugar, hence food items made with small quantities of aspartame yield fewer calories on oxidation.

Explanation

Oilzapper is an eco-friendly technology for oil sludges and oil spills remediation. Oilzapping is the new technique using bacteria to get rid of oil spills. It is a bioremediation technique that involves the use of oil zapping bacteria. In essence, Oilzapper is a concoction of five distinct bacterial strains that have been immobilised and combined with a carrier substance (powdered corn cob). The Oilzapper consumes the hydrocarbon molecules found in crude oil and oily sludge, a dangerous hydrocarbon waste product produced by oil refineries, and transforms them into harmless CO₂ and water. This is exactly what its witty name implies.

Explanation

The blood group of the couple is AB Positive and O Negative. So their biological sons will have either blood group A or B. Thus we can infer that the blood group of the adopted son will be O.

Explanation

Statement 1 is correct: DVD stands for "Digital Versatile Disk" or "Digital Video Disc". It is a type of digital optical disc storage that can hold any kind of digital data but is frequently used to store pictures, audio, and video in standard definition. Blu-ray Disc is a digital disc storage format similar to CD and DVD, that is designed to record and play a large amount of data with high-definition quality.

Statement 2 is correct: Blu-ray Disc media include these features: 50GB capacity - Each disc can hold more than 10 standard DVDs.

Statement 3 is incorrect: The size of the Blu-ray disc is 120 millimetres in diameter with 1.2 millimetres thickness, which is the same as the size of a CD and DVD.

Explanation

The tissue just beneath the bark called the phloem layer is in charge of moving food produced by photosynthesis from the leaves to the roots. This process is called girdling, and it is fatal to trees because it disrupts the transport of nutrients. Without this nourishment, the roots eventually perish and stop supplying the leaves with water and nutrients. Later, the leaves wither. Because its roots are starved of vitality, a tree that has had its bark removed in a circular pattern all around near its base gradually dries up and dies.