Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

A is matched with 2: Potassium bromide is widely used in the photographic industry. It acts as a restrainer in photographic developers and is used in the preparation of photographic emulsions. B is matched with 4: Potassium nitrate, also known as saltpeter, is a key ingredient in gunpowder due to its oxidizing properties. It releases oxygen during combustion, aiding in the rapid burning of other materials. C is matched with 1: Potassium sulphate is an important fertilizer that supplies potassium, a vital nutrient for plant growth. It is especially used in chloride-sensitive crops like potatoes, tobacco, and citrus fruits because it contains no chloride ions. D is matched with 3: Monopotassium tartrate is extensively used in baking. It helps stabilize egg whites, prevents sugar crystallization, and is a component of baking powder, contributing to the leavening process in cakes and bread.

Explanation

An amalgam is an alloy of mercury with another metal. While many metals can form amalgams, iron does not readily form one because it has a very low affinity for mercury under normal. On the other hand, metals like zinc, copper, and magnesium can form amalgams.

Explanation

Assertion A is true: Phenyl, a common household germicide, contains phenol derivatives that disrupt bacterial cell membranes and denature proteins, making it effective against germs. Reason R is true: Phenol, also called carbolic acid, is a well-known antiseptic and disinfectant due to its ability to kill bacteria, fungi, and viruses. This explains the germicidal property of phenyl. Thus, both Assertion (A) and Reason (R) are true, and R correctly explains A.

Explanation

Water pollution in rivers is primarily measured by the Dissolved Oxygen (DO) level, which indicates the amount of oxygen available for aquatic organisms. A low DO level signifies high pollution, as pollutants like organic waste decompose and consume oxygen, making the water uninhabitable for aquatic life. BOD (Biochemical Oxygen Demand) is the amount of oxygen required by microorganisms to decompose organic matter in water over a specific period (usually 5 days at 20°C). High BOD indicates organic pollution, such as from sewage or agricultural runoff, while low BOD signifies cleaner water. COD (Chemical Oxygen Demand) is the total amount of oxygen required to chemically oxidize both organic and inorganic matter in water. COD provides a broader measure of pollution than BOD, including oxygen demand from inorganic substances.

Explanation

Ergotism is historically known as "St. Anthony’s Fire" is directly linked to the consumption of grains (such as rye, barley, wheat, and oats) contaminated with the ergot fungus (Claviceps purpurea). The fungus infects the grains, producing sclerotia (ergot bodies) that contain toxic alkaloids. These alkaloids can cause two forms of ergotism:

Convulsive ergotism which is cracterized by seizures, hallucinations, and muscle spasms. Gangrenous ergotism which leads to restricted blood flow, causing tissue death and gangrene in extremities.

Explanation

In industrial applications, a wide range of microorganisms are used due to their ability to carry out various biochemical processes that are beneficial for different industries. The following microorganisms are widely used:

Bacteria is used in industries such as fermentation, bioremediation, and food production (e.g., yogurt, cheese, and antibiotics). Microalgae is used in the production of biofuels, aquaculture feed, and nutraceuticals. They are also involved in carbon sequestration. Fungi is widely used in the pharmaceutical industry for the production of antibiotics (such as penicillin) and enzymes. They are also used in fermentation and the production of organic acids.

Explanation

A is matched with 4: Fruit develops from the ovary of the flower after fertilization. The ovary, which contains the ovules, transforms into the fruit as the seeds inside mature. This process is an essential part of the plant’s reproductive cycle. B is matched with 1: Seed originates from the ovule after fertilization. The ovule, located inside the ovary, contains the female gamete (egg cell). Once fertilized by the male gamete (pollen), the ovule develops into a seed, which contains the embryo and stored food for the new plant. C is matched with 3: Wood is produced from the stem of the plant. The stem, with its vascular tissues (xylem and phloem), supports the plant and transports nutrients. The xylem, which is a type of vascular tissue, forms the wood, providing structural support and helping in water transport. D is matched with 2: Starch is primarily produced in the leaf. During photosynthesis leaves use sunlight, water, and carbon dioxide to produce glucose. Some of this glucose is converted into starch, a storage form of sugar, and is stored in the chloroplasts of the leaf.

Explanation

Statement (a) is correct: Starch and cellulose are both found in plants. Starch serves as an energy reserve and cellulose is a structural component of plant cell walls. Statement (b) is correct: Both starch and cellulose are polymers made up of repeating units (monomers) of glucose. Starch and cellulose are polysaccharides Statement (c) is incorrect: While starch gives a blue-black color with iodine, cellulose does not give any significant color reaction with iodine under normal conditions. Starch is a polysaccharide composed of glucose units and gives a blue-black color when iodine is added, which is a characteristic test for starch. Starch occurs in plants in the form of granules, and these are particularly abundant in seeds (especially the cereal grains) and tubers, where they serve as a storage form of carbohydrates. The Cellulose, a fibrous carbohydrate found in all plants, is the structural component of plant cell walls. Cellulose is also a polymer of glucose but its structure differs from starch. Cellulose does not form the characteristic blue-black color with iodine due to the difference in the way glucose molecules are linked in cellulose. Statement (d) is correct: Both starch and cellulose are made up of glucose molecules, but in different forms. Starch consists of alpha-glucose while cellulose consists of beta-glucose.

Explanation

A is matched with 4: Hugo de Vries proposed the Mutation Theory in the early 20th century which suggested that new species arise through sudden, discontinuous changes (mutations) in genetic material. B is matched with 3: Darwin>s Theory of Evolution was published in 1859 (On the Origin of Species). It explains evolution through natural selection and gave key concepts include adaptive radiation, survival of the fittest, and descent with modification. C is matched with 1: George Beadle and Edward Tatum proposed the One Gene One Enzyme Hypothesis, which states that each gene is responsible for producing a single enzyme that controls a specific biochemical reaction. D is matched with 2: Jacob and Monod>s Operon Concept was introduced in 1961 which explains how gene regulation in prokaryotes (e.g., lac operon in E. coli). It is key for understanding antibiotic resistance and gene expression.

Explanation

The Tambalacoque tree (Sideroxylon grandiflorum), also known as the Dodo tree, usually relied on the Dodo bird for seed germination. The seeds of this tree required scarification (softening of the seed coat) through the Dodo>s digestive system. The Dodo (Raphus cucullatus), a flightless bird endemic to Mauritius, became extinct in the late 1600s due to over-hunting by humans and the introduction of non-native animals like rats and pigs. After the extinction of the Dodo, natural reproduction of the Tambalacoque tree declined significantly.