Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Photosynthesis is the process by which green plants, algae, and certain bacteria convert light energy into chemical energy, producing glucose and releasing oxygen. The functions of the chlorophyll, a green pigment, are related to the transformation of inefficient solar energy into useful chemical energy. During photosynthesis, plants capture light energy (free energy) and convert it into chemical energy, storing it as potential energy in the bonds of glucose molecules. This stored energy can later be used by the plant for various metabolic processes. 6H₂O + 6CO₂C₆H₁₂O₆ + 6O₂

Explanation

Vegetative propagation is a fascinating form of asexual reproduction where new plants grow from specialized vegetative parts like stems, roots, or leaves rather than seeds.

Statement 1 is correct: Vegetative propagation is a process in which new plants are grown from the vegetative parts of the parent plant. As this method does not involve sexual reproduction, the offspring are genetically identical to the parent, creating a clonal population. This technique ensures uniformity among the progeny, making it particularly useful for preserving desirable traits in cultivated plants.

Statement 2 is incorrect: Standard methods of vegetative propagation generally do not eliminate viruses rather they often perpetuate viral infections because the new plants are exact genetic clones of the infected parent plant.

Statement 3 is correct: Unlike seed-based propagation, which is often dependent on specific seasons, methods like cuttings, layering, or tissue culture can be carried out continuously as long as the required conditions and resources are provided. Vegetative propagation can typically be practiced year-round, particularly in controlled environmental settings. This adaptability enables the consistent production of new plants.

Explanation

Transgenic crops are developed by introducing foreign genes into a plant’s genome to confer new traits, such as pest resistance or improved nutritional content.

Statement 1 is incorrect: Budding and grafting are traditional horticultural techniques used to propagate plants. In grafting, tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. These methods do not alter the genetic makeup of the plants.

Statement 2 is correct: Cytoplasmic male sterility (CMS) refers to the complete or partial inability of plants to produce functional male gametes. Male Sterility prevents the plant from producing viable pollen, thereby rendering it incapable of self-fertilization. CMS systems are extensively used in hybrid crop production because they simplify the process of controlling male sterility, eliminating the need for manual emasculation during cross-breeding. This enhances efficiency and consistency in hybrid seed production.

Statement 3 is correct: Gene silencing refers to techniques used to suppress the expression of specific genes within an organism. In the context of transgenic crops, methods such as RNA interference (RNAi) are employed to downregulate or silence target genes, thereby conferring desired traits like pest resistance or delayed fruit ripening. One notable example of gene silencing in India is the development of Bt Cotton using RNA interference (RNAi). In Bt cotton, a gene from the soil bacterium Bacillus thuringiensis (Bt) is introduced to produce proteins that are toxic to cotton bollworm pest.

Explanation

Statement 1 is correct: Maize is a primary source for commercial starch production. Through a wet milling process, maize kernels are separated into components such as starch, oil, protein, and fiber. The extracted starch is utilized in multiple industries, including food, paper, and textiles.

Statement 2 is correct: Maize oil, also known as corn oil, can be used as a raw material for biodiesel production. Through a chemical process called transesterification, the oil reacts with short-chain alcohols such as methanol or ethanol, using a catalyst to produce biodiesel efficiently.

Statement 3 is correct: Maize plays a significant role in the production of various alcoholic beverages. Its starch is broken down into sugars, which are subsequently fermented to produce alcohol. This process is crucial in crafting drinks like bourbon whiskey, which traditionally uses a mash containing at least 51% maize.

Explanation

The animal kingdom is broadly classified into different phyla based on structural and functional characteristics.

Option (a) is correct: Arthropoda is the largest phylum in the animal kingdom, including organisms with jointed appendages, segmented bodies, and exoskeletons made of chitin. The phylum is further divided into several subphyla, two of which are:

Chelicerata (includes arachnids like mites, spiders, and scorpions) and Crustacea (includes crabs and other aquatic arthropods). The subphylum Chelicerata (e.g., spiders, scorpions) has two body regions, no antennae, four pairs of legs, and uses chelicerae for feeding, adapted to terrestrial life with book lungs. Crustacea (e.g., crabs, lobsters) has three body regions, two pairs of antennae, gills for respiration, and compound eyes, primarily adapted to aquatic habitats with specialized mandibles. Hence, the crab does not belong to the same class as the mite, spider, and scorpion.

Explanation

A food chain represents the transfer of energy through a series of organisms, starting from green plants (primary producers) and progressing through successive consumers. For example: Grasses Grasshopper Frog Snake Hawk/ Eagle. Each step in the food chain is referred to as a trophic level, indicating the organism’s position in the chain. Food chains begin with producers and end with top carnivores. In marine ecosystems, phytoplankton serve as primary producers. These include:

Diatoms (unicellular algae) Coccolithophores (unicellular eukaryotic protists), Cyanobacteria (blue-green algae such as Synechococcus, Prochlorococcus, Nostoc, and Spirogyra) Dinoflagellates (flagellated protists) Crustaceans, a group of arthropods that includes crabs, lobsters, shrimp, krill, and barnacles, feed on diatoms. In turn, herrings, a type of fish, consume crustaceans, completing this segment of the marine food chain.

Explanation

Statement 1 is correct: PV technology directly converts sunlight into electricity using semiconductor materials like silicon. When sunlight hits the PV cells, it excites electrons, generating Direct Current (DC) electricity. This is a clean and efficient method of harnessing solar energy for electricity. Solar thermal systems use solar collectors to capture the Sun’s heat. This heat is typically used to produce steam, which drives turbines connected to generators, producing electricity. Solar thermal is often used in large-scale power plants and heating systems.

Statement 2 is incorrect: PV systems initially produce Direct Current (DC), which is then converted to Alternating Current (AC) using inverters for compatibility with the electrical grid and household appliances. Solar Thermal systems generate heat, which is used to produce AC electricity through conventional turbines and generators.

Statement 3 is incorrect: India has established manufacturing capabilities for both Solar Thermal and Photovoltaic technologies. The country is expanding its PV manufacturing capacity, aiming to become self-sufficient and reduce reliance on imports.

Explanation

Hibernation is a survival strategy employed by various animals to endure periods of reduced food availability and harsh environmental conditions, typically during winter. This state is characterized by significantly lowered metabolic rates, decreased body temperatures, and reduced physiological activities. Many bat species enter hibernation during colder months when their insect prey becomes scarce. During hibernation, bats can experience a substantial drop in body temperature and significant reduction in metabolic rate. They often hibernate communally in caves, mines, or other sheltered locations that provide stable, cold environments. Bears undergo a form of hibernation known as torpor, which is less extreme than the hibernation observed in smaller mammals. During torpor, bears experience a moderate decrease in body temperature and metabolic rate. They remain in dens throughout the winter months, surviving on stored body fat. Notably, female bears give birth during this period and are capable of nursing their cubs without leaving the den. Species such as ground squirrels and certain mice enter deep hibernation during which they significantly lower their body temperatures and metabolic rates. This state allows them to conserve energy and survive extended periods without food. Rodents often prepare for hibernation by accumulating fat reserves and creating insulated nests or burrows to protect against the cold.

Explanation

The carbon cycle is a biogeochemical process where carbon atoms continuously move between the atmosphere, oceans, soil, and living organisms through processes like photosynthesis, respiration, decomposition, and combustion. Through photosynthesis, plants absorb atmospheric CO₂ to produce glucose, while animals release CO₂ through respiration, and when organisms die, decomposition returns their carbon to the soil and atmosphere, completing this vital planetary cycle.

Statement 1 is correct: Volcanic eruptions release CO₂ stored in Earth’s mantle into the atmosphere, contributing to the carbon cycle.

Statement 2 is correct: Respiration is the process by which organisms, including plants and animals, convert organic compounds into energy, producing CO₂ as a byproduct. This CO₂ is then released into the atmosphere.

Statement 3 is incorrect: Photosynthesis is the process by which green plants, algae, and some bacteria absorb CO₂ from the atmosphere and, using sunlight, convert it into glucose and oxygen. This process removes CO₂ from the atmosphere.

Statement 4 is correct: When organisms die, decomposers like bacteria and fungi break down their organic matter, resulting in the release of CO₂ back into the atmosphere through the process of decomposition.

Explanation

Ecological succession is the process of change in the species structure of an ecological community over time. Types of Succession:

Primary Succession occurs on newly formed or exposed land where no previous life existed (e.g., bare rock, lava flows). Pioneer species like lichens and mosses initiate the process, gradually leading to the development of soil and a stable ecosystem. Secondary Succession happens in areas where an ecosystem previously existed but was disturbed (e.g., after a forest fire or flood). Soil is already present, and recovery occurs more quickly than in primary succession.

Option (b) is correct: Lichens are among the first organisms to colonize bare rock or barren environments, breaking down minerals to create soil and paving the way for other plants and organisms. They are unique composite organisms resulting from a symbiotic association between a fungus and a photosynthetic partner, which can be either green algae or cyanobacteria. In this partnership, the fungal component, known as the mycobiont, provides structure and protection, while the photosynthetic partner, referred to as the photobiont, contributes nutrients through photosynthesis.