UPSC Prelims 2011 Analysis

Explanation

Heavy water is employed in nuclear reactors as a neutron moderator , slowing down neutron production and bringing stability to the fission reaction .

Explanation

The Bt-brinjal is a genetically modified form of the traditional brinjal.

The 'Bt' in Bt-brinjal stands for Bacillus thuringiensis, a bacterium that naturally produces a toxin that is harmful to certain pests. The gene from this bacterium is inserted into the brinjal, making it resistant to certain pests.

This modification does not aim to improve its taste, make it drought-resistant, or extend its shelf-life. Therefore, the primary objective of developing Bt-brinjal is to make it pest-resistant.

Explanation

The reason why the surface of a lake freezes in severe winter, but the water at its bottom is still liquid is due to the unique property of water. Water attains its maximum density at 4C. When a lake cools, the surface water loses heat, becomes denser and sinks. This process continues until all the water in the lake is at 4C. With further cooling, a stable, lighter layer of water forms at the surface. When this surface water freezes, it floats and stays at the surface of the lake until a solid sheet of ice is formed. The water at the bottom remains liquid because it is denser and hence, does not rise to the surface to freeze.

Explanation

Antioxidants are substances that can prevent or slow damage to cells caused by free radicals, unstable molecules that the body produces as a reaction to environmental and other pressures. They are sometimes called free-radical scavengers".

They can protect against the cell damage that free radicals cause, reducing the risk of many non-communicable diseases. Therefore, the option that best describes the role of antioxidants is that they neutralize the free radicals produced in the body during metabolism.

Explanation

It signifies to the customers that the food products are not made out of hydrogenated oils. Trans fat is an unsaturated fatty acid which is obtained by adding hydrogen to liquid vegetable oils to make them more solid. Trans fat is considered to be unhealthy as they increase the risk of heart disease .

Explanation

Aspartame is indeed several times sweeter than table sugar, meaning that a smaller amount of aspartame is required to achieve the same level of sweetness in food items compared to sugar. Since aspartame is used in smaller quantities due to its high sweetness, the overall calorie content of the food item is reduced. This is because aspartame provides fewer calories per unit weight compared to sugar. Upon ingestion, aspartame is metabolized in the body into compounds that do not yield calories. Therefore, even though it is sweet, it does not contribute significantly to the calorie intake, making it suitable for use in low-calorie food products

Explanation

The Blu-ray Disc (BD) is indeed different from the traditional DVD in several ways. Firstly, the DVD supports Standard Definition video while BD supports High Definition video. This means that the quality of video that can be stored and played back on a BD is significantly higher than that on a DVD. Secondly, the BD format has several times more storage capacity compared to a DVD. This allows for more data to be stored on a single disc. However, the third statement is incorrect. The thickness of both BD and DVD is 1.2 mm, not 2.4 mm for BD as mentioned in the statement. Therefore, only the first two statements are correct.

Explanation

When the bark of a tree is removed in a circular fashion near its base, it damages the phloem, which is responsible for transporting sugars and other nutrients produced by photosynthesis in the leaves down to the roots for energy and growth. This process is called translocation. With the phloem damaged, the roots are starved of the energy they need for essential functions such as absorption of water and minerals from the soil, leading to their gradual drying up and eventual death.

Explanation

Bluetooth and Wi-Fi are both wireless technologies but they serve different purposes and have different characteristics. Bluetooth uses a 2.4 GHz radio frequency band, whereas Wi-Fi can use 2.4 GHz or 5 GHz frequency band, so statement (a) is correct.

Statement (b) is incorrect because Bluetooth is primarily used for connecting devices and creating a personal area network (PAN), not for Wireless Local Area Networks (WLAN). Wi-Fi, on the other hand, is used for WLAN and for internet access, not for Wireless Wide Area Networks (WWAN).

Statement (c) is also incorrect. Both Bluetooth and Wi-Fi technologies do not require the devices to be in the line of sight of each other.

Explanation

Asteroids are indeed small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material, so statement 1 is correct.

However, statement 2 is incorrect. Asteroids are found mostly between the orbits of Mars and Jupiter, in the asteroid belt, while comets are found in the outer solar system, not between Venus and Mercury.

Statement 3 is correct as comets, when they approach the sun, show a perceptible glowing tail due to the vapourisation of their icy components, while asteroids do not.

Explanation

The knowledge of the arrangement or relative positions of genes or DNA sequences on a chromosome indeed has several benefits. It allows us to understand the pedigree of livestock (Statement 1) as it helps in tracing the genetic traits and lineage of animals.

It also aids in developing disease-resistant animal breeds (Statement 3) by identifying and manipulating specific genes responsible for disease resistance.

However, it is not accurate to say that it enables us to understand the causes of all human diseases (Statement 2).

Explanation

The artificial satellite orbiting around the Sun does not fall down, the reason being is that the attraction of the Earth provides the necessary acceleration for its motion. This acceleration is constant in magnitude but changes its direction. The force acting towards the centre on a particle executing uniform circular motion is called Centripetal force and to balance the Centripetal force there is a pseudo force called Centrifugal force. In case of satellite orbiting around the earth, both these forces are equal and opposite.

Explanation

A geostationary orbit is a type of geosynchronous orbit, which means it has the same orbital period as the rotation of the Earth. This is why satellites in geostationary orbits appear to be stationary in the sky from the perspective of an observer on Earth. The orbit is indeed circular and lies in the plane of the Earth's equator. This is necessary for the satellite to remain above the same location on the Earth's surface.

However, the altitude of a geostationary orbit is approximately 35,786 kilometers, or 22,236 miles, above the Earth's equator.

Explanation

Given the parents' blood groups are AB positive and O negative, their biological children can only have blood groups A, B, or O (all possibly Rh positive or negative due to the O negative parent). Since the three sons have A positive, B positive, and O positive blood groups, and only the biological children can have these blood groups derived from the parents, the adopted son must have the O positive blood group, fitting the scenario as the child not biologically linked to the parents' genotypes.

Explanation

A Virtual Private Network, or VPN, is a technology that creates a secure, encrypted connection over the internet. It allows users to access their organization's network securely, even when they are not directly connected to it. This is done by transmitting data through a server, which encrypts the information to prevent unauthorized access. The VPN essentially extends a private network across a public network, like the internet, allowing remote users to send and receive data as if they were directly connected to the private network. Therefore, it provides users access to their organizations network while maintaining the security of the information transmitted.