Day-750 | Daily MCQs | UPSC Prelims | SCIENCE AND TECHNOLOGY

Answer: A
Explanation:

Answer: D
Explanation:
Diffraction
The phenomenon in which light bends around the corner of the particles spreading into different regions of the geometrical shadow of the aperture is called Diffraction.
Interference
The phenomenon in which two waves travelling in the same direction in the same medium superpose on each other, resulting in different wave fronts is called Interference.
• Statement 1 is INCORRECT: Interference may be defined as waves emerging from two different sources, producing different wave fronts.
• Statement 2 is INCORRECT: Diffraction occurs as secondary waves that emerge from the different parts of the same wave.

Answer: B
Explanation:
Infrasound: Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.
Ultrasound: Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.
• Case 1 is CORRECT: Ultrasonic waves are passed through the metal block and detectors are used to detect the transmitted waves. If there is even a small crack, the ultrasound gets reflected back indicating the presence of flaw or defect.
• Case 2 is INCORRECT: Infrasonic waves are for monitoring earthquakes and volcanoes, charting rock and petroleum formations below the earth and other applications to study the mechanics of the earth.
• Case 3 is CORRECT: Ultrasonic waves are used to clean dirt and grease. The high frequency wave causes the particle to get detached from the surface of the object and thus, the object gets thoroughly cleaned.

Answer: A
Explanation:

Answer: B
Explanation:
• 1st device is CORRECT: A mobile phone works on a Lithium Ion battery. Rectifier is an electrical device which is embedded in a mobile charger which converts DC to AC. Thus, mobile charger as a whole converts AC to DC.
• 2nd device is INCORRECT: Inverter at home basically converts DC into AC. It converts direct current, which is produced by a battery, into alternating current. This is needed because household electrical appliances and devices work on alternating current.
• 3rd device is CORRECT: Laptop adapter works on the same principle as mobile charger. Only difference is the voltage in operation. A mobile charger reduces voltage from 220 volts to 5 volts whereas; laptop adapter generally reduces the voltage to 12 volts.

Answer: A
Explanation:
Hydrogenation is a process that reduces unsaturated fatty acid content of triglycerides by attaching hydrogen atoms at the point of unsaturation.
CH2=CH2 + H2 → CH3-CH3
(Ethene) (Hydrogen) (Ethane)

• Statement 1 is INCORRECT: By process of hydrogenation, unsaturated bonds (double or triple bonds) of the carbon atom are converted into their saturated form (single bond) by passing hydrogen gas through the oil in the presence of nickel as a catalyst.
• Statement 2 is INCORRECT: The chemical process of hydrogenation transforms liquid vegetable oil into solid fat. Groundnut oil, cotton oil, and mustard oil are examples of unsaturated molecules with double bonds. At room temperature, they are in a liquid condition. Vegetable oils, undergo hydrogen addition to generate a saturated product called vegetable ghee or vanaspati ghee, which is solid or semi-solid at room temperature due to the presence of single bonds.
• Statement 3 is CORRECT: Hydrogenation process increases the shelf life of the oil as it resists the oxidation of oil which prevents rancidity and bad smell.

Answer: C
Explanation:
Movement of water across a selectively permeable membrane is known as osmosis. This movement of water across the plasma membrane is also affected by the amount of substance dissolved in water or concentration of the solution.
Based on this, there are 3 types of solution.
1. Hypotonic solution
2. Isotonic solution
3. Hypertonic solution

Answer: A
Explanation:
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection.
• Statement 1 is INCORRECT: The cell wall is freely permeable as it allows water and nutrients freely exchanged between the cells and outer environment. It has a mesh like structure.
• Statement 2 is CORRECT: Cell wall of a plant cell is composed of cellulose, a glucose-based polysaccharide macromolecule.
• Statement 3 is INCORRECT: Cell wall is not only present in plants but also in fungi. The cell wall of fungi is composed mainly of glycoproteins. As the components of the fungal cell wall are not present in humans, this structure is an excellent target for antifungal therapy.

Answer: C
Explanation:
Cell Organelles
The cell contains different functional structures which are collectively called organelles, and they are involved in various cellular functions. Some of the Large and complex cells, including cells from multicellular organisms, need a lot of chemical activities to support their complicated structure and function. To keep these activities of different kinds, separate from each other, these cells use membrane-bound little structures within themselves.
• Pair 1 is CORRECT: Ribosomes are non-membrane bound and important cytoplasmic organelles found in close association with the endoplasmic reticulum. The primary function of the ribosomes includes protein synthesis in all living cells that ensure the survival of the cell.
• Pair 2 is CORRECT: Lysosomes are membranous organelles whose specific function is to breakdown cellular wastes and debris by engulfing it.
• Pair 3 is CORRECT: A vacuole stores salts, minerals, pigments and proteins within the cell. However, in some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.

Answer: A
Explanation:
Cell division happens when a parent cell divides into two or more cells called daughter cells. Cell division usually occurs as part of a larger cell cycle. All cells reproduce by splitting into two, where each parental cell gives rise to two daughter cells.
There are two main types of cell division in an organism – Mitosis and Meiosis

Answer: C
Explanation:
Alternating current is used to transmit electricity over a very long distance. For this transformer is used to increase or decrease the voltage of transmission.
• Statement 1 is CORRECT: Step up transformer increase the voltage to very high value like 33 kilovolts (KVs) and this way current is reduced to minimise losses.
• Statement 2 is INCORRECT: Step up transformers increase the voltage and decrease the current to minimise transmission loss.

Answer: B
Explanation:
A spherical mirror is a mirror that has the shape of a piece cut out of a spherical surface. There are two types of spherical mirrors: concave mirror and convex mirror.
• Statement 1 is INCORRECT: Concave mirror is used in solar cookers. The reason behind using this mirror is because concave mirrors reflect light falling on it to a single focal point. This increases the heat at the focal point. This way food is cooked.
• Statement 2 is CORRECT: Concave mirror is used as shaving mirror. This is because when the face is placed close to a concave mirror, within the focus of the mirror, it produces a magnified and erect image of the face. Since an enlarged or magnified image of the face can be seen in the concave mirror, it becomes easier to make a smooth shave.
Applications of Concave Mirrors
• Shaving mirror
• Head mirrors.
• Ophthalmoscope.
• Astronomical telescopes.
• Headlights.
• Solar furnaces.
Applications of Convex Mirrors
• Rear view mirrors
• In ATMs for security purposes
• In reflector lights

Answer: C
Explanation:
Total Internal Reflection.
It is a complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium. The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle.
• Example 1 is CORRECT: A mirage is an optical phenomenon that creates the illusion of water and results from the refraction of light through a non-uniform medium. Mirages occur on sunny days. The role of the sun is to heat the roadway to high temperatures. This heated roadway in turn heats the surrounding air, keeping the air just above the roadway at higher temperatures than that day’s average air temperature. Hot air tends to be less optically dense than cooler air. This causes total internal reflection and creates an illusion of water.

Answer: B
Explanation:

Answer: A
Explanation:
• Pair 1 is CORRECT: Ferromagnetic materials exhibit a strong attraction towards magnets. They don’t necessarily produce their own magnetic field; only magnets produce a magnetic field. Ferromagnetic materials simply pull themselves towards magnets. They have a strong attraction towards magnets.
• Pair 2 is INCORRECT: Diamagnetic materials are those that repel magnets. They don’t exhibit any attraction to magnets. Rather, diamagnetic materials exhibit the opposite behaviour i.e. they repel magnets.
• Pair 3 is INCORRECT: Paramagnetic materials exhibit a weak attraction towards magnets. They still pull themselves towards magnets, but paramagnetic materials are much weaker than ferromagnetic materials.

Answer: A
Explanation:
The cells in complex multicellular organisms, like human beings, are organized into tissues, which are groups of similar cells that work together on a specific task.
• Both Statements are CORRECT and Statement 2 is the CORRECT explanation of Statement 1.
• Statement 1 is CORRECT: Tissues are only found in Multicellular organisms. Since, multicellular organisms have complex biological tasks which are performed by specialised groups of cells. In unicellular organisms, all the functions like ingestion, digestion, locomotion etc is performed by a single cell.
• Statement 2 is CORRECT and is the CORRECT explanation of statement 1: For efficient functioning of organs and organ system in a multicellular organism. Some of the common tissues are blood, muscles etc.

Answer: C
Explanation:
Simple permanent tissues in plants are broadly classified into 3 types – Parenchyma, Collenchyma and Sclerenchyma.
• Pair 1 is CORRECT: Parenchyma is involved in the storage of food. It is made up of cellulose and comprises a thin cell wall. In addition to photosynthesis and storing cooked food, they are also helpful in gas trading.
• Pair 2 is CORRECT: Collenchyma provide flexibility in plants. It allows bending of various parts of a plant like tendrils and stems of climbers without breaking.
• Pair 3 is CORRECT: It makes the plant hard and stiff. For example – husk of a coconut is made up of sclerenchyma.

Answer: C
Explanation:
Ligaments and tendons are fibrous tissues which support the skeletal system of animal body. Each muscle contains only one tendon whereas each joint contains many ligaments. A tendon injury will typically cause increased pain with contraction of the tendon’s associated muscle, while a ligament injury will not cause pain since ligaments attach bone to bone. Both types of injuries, however, can result in increased pain with joint movement.
1. Statement 1 is CORRECT: Tendons connect muscles to bones whereas ligaments connect bone to bone.
2. Statement 2 is CORRECT: Tendons are fibrous tissues with great strength but limited flexibility whereas, ligament joints are very elastic.

Answer: B
Explanation:
All living beings are broadly classified into 5 Kingdoms based on cell structure, mode and source of nutrition and body organisation. It is based on the classification of Robert Whittaker. These are:
1. Monera
2. Protista
3. Fungi
4. Plantae
5. Animalia
• Statement 1 is INCORRECT: Fungi are multicellular organisms and are not capable of photosynthesis. This difference in the mode of nutrition is the parameter of differentiation between plants and fungi. They are heterotrophic because they use complex organic compounds as sources of energy and carbon.
• Statement 2 is CORRECT: Although most of the plants are autotrophs as they photosynthesize their own food. But some plants like – Pitcher plant and Venus Fly Trap are heterotrophs. They are also known as insectivorous plants. They depend on others for food.
• Statement 3 is CORRECT: Porifera are non-motile animals attached to some solid support. They are commonly known as Sponges and are commonly found in marine habitat.

Answer: C
Explanation:
Vertebrate animals are grouped into six classes based on factors like- mode of sexual reproduction, scales on body, warm blooded or cold-blooded feature, respiration mode etc. These are:
1. Cyclostomata
2. Pisces (or fishes)
3. Amphibia
4. Reptiles
5. Aves (or birds)
6. Mammals
• 1st Feature is CORRECT: Like mammals, birds are warm blooded. This means that they can maintain a constant body temperature by generating internal heat.
• 2nd Feature is CORRECT: All birds have four chambered heart like human beings. Four chambers are – 2 Atria and 2 Ventricles.
• 3rd Feature is CORRECT: Birds are oviparous. It means that they lay eggs. Viviparous animals, like mammals, give birth to young ones.