Biology: Zoology: UPSC Previous Year Questions (Science and Technology)

Explanation

The mechanisms of organic evolution refer to the processes by which populations of organisms change over time, leading to the diversity of life forms seen today. These mechanisms explain how species evolve, adapt, and sometimes go extinct. The loss of limbs in snakes is explained by Lamarck’s Theory of Use and Disuse, which suggests that organs that are frequently used develop and strengthen while those that are not used weaken and eventually disappear over generations. Snakes evolved from lizard-like ancestors that originally had limbs. As they adapted to a burrowing or slithering lifestyle, they stopped using their limbs for movement. According to Lamarck’s theory, since the limbs were not used, they gradually reduced in size and eventually disappeared over many generations.

Explanation

Genetics is the study of heredity and variation in living organisms. It explores how traits are passed from parents to offspring through genes which are the units of heredity located on chromosomes.

Option (b) is correct: Pleiotropy occurs when a single gene affects multiple, seemingly unrelated phenotypic traits. Mutations in such a gene can have widespread effects due to its influence on various biological processes This occurs because the gene product (e.g., a protein) may participate in multiple biochemical or physiological pathways. For example, the gene responsible for sickle cell anemia affects multiple traits: red blood cell shape, resistance to malaria, and oxygen transport efficiency.

Explanation

Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream. They regulate various physiological processes, such as growth, metabolism, reproduction, and mood. Examples include Insulin (protein), cortisol (steroid), thyroxine, etc.

Statement 1 is correct: Somatotropin, also known as human growth hormone (HGH), is secreted by the anterior pituitary gland. Its release is stimulated by growth hormone-releasing hormone (GHRH) which is released as a result of exercise

Statement 2 is correct: In men, progesterone is synthesized not only in the Leydig cells of the testicles but also in the adrenal glands. It serves as a precursor to testosterone and plays roles in various physiological processes.

Statement 3 is correct: In females, the adrenal glands contribute to the production of androgens, including testosterone. These hormones are involved in various bodily functions, including the maintenance of muscle mass and libido.

Statement 4 is incorrect: Stress typically triggers the adrenal glands to increase the secretion of cortisol, a hormone that helps the body manage stress by regulating metabolism, inflammation, and other critical functions.

Explanation

Foot-and-mouth disease (FMD) is a highly contagious viral illness affecting cloven-hoofed animals such as cattle, sheep, goats, and pigs. The causative agent is the foot-and-mouth disease virus (FMDV), classified within the family Picornaviridae, genus Aphthovirus. FMDV is a non-enveloped, positive-sense single-stranded RNA virus. There are seven immunologically distinct serotypes of FMDV: A, O, C, SAT1, SAT2, SAT3, and Asia1, which do not confer cross-immunity. Transmission of FMDV occurs through direct contact with infected animals, exposure to contaminated feed, water, equipment, or clothing, and via aerosols over short distances. The virus is highly resilient, capable of surviving in various environmental conditions, which contributes to its rapid spread among susceptible animal populations.

Explanation

A is matched with 3: Asiatic Wild Ass (Equus hemionus khur) or Khur, is an Endangered equid found in the Little Rann of Kutch, Gujarat. It has a chestnut brown coat with a dark dorsal stripe and can run at 70 km/h. It is adapted to arid landscapes and survives on minimal water and grazes on grasses and fruits. Conservation efforts, including the Wild Ass Sanctuary, have helped stabilize its population. B is matched with 2: Barasingha (Rucervus duvaucelii) is recognized for its 12-tined antlers. It inhabits grasslands and swamps in Kanha and Dudhwa National Parks. Barasinghas are social grazers, feeding on grasses and aquatic plants. Once critically endangered due to habitat loss, their population has improved due to conservation initiatives such as habitat restoration and anti-poaching measures. C is matched with 4: Chinkara (Gazella bennettii) is a small, agile antelope found in arid and semi-arid regions like the Thar Desert. It has a reddish-buff coat, white underparts, and distinctive facial markings. Chinkaras are solitary browsers, feeding on leaves and fruits, and can survive without water for long periods. D is matched with 1: Nilgai (Boselaphus tragocamelus) is the largest Asian antelope. Males have a bluish-grey coat, while females are tawny brown. Found in grasslands, scrub forests, and agricultural areas, Nilgais are diurnal and social browsers. Their population is stable, but they are often considered agricultural pests, leading to human-wildlife conflicts in some regions.

Explanation

Animal mating behavior is incredibly diverse and fascinating, encompassing a wide range of strategies for finding a mate and ensuring reproductive success. From the elaborate courtship rituals of birds-of-paradise to the fierce competition of stags locking antlers, the animal kingdom showcases a variety of tactics. Some animals form monogamous pair bonds that can last a lifetime, demonstrating a different approach to mating and raising offspring. The variety of mating behaviors reflects the diverse evolutionary pressures shaping each species’ reproductive success.

Option (a) is correct: The wolf (Canis lupus) is monogamous animal. They typically form lifelong pair bonds, with mated pairs remaining together until one partner dies, after which the surviving wolf may find a new mate. This monogamous behavior is integral to the social structure of wolf packs, which are often composed of the breeding pair and their offspring.

Explanation

Viviparous animals give birth to live young, rather than laying eggs. However most echinoderms reproduce through external fertilization, releasing eggs and sperm into the water column. Viviparity is relatively rare among echinoderms. Notable exceptions include certain species of brittle stars and sea stars, such as Cryptasterina hystera, which exhibit viviparous reproduction.

Explanation

A is matched with 2: Arber and Smith discovered endonucleases (restriction enzymes). They are enzymes that cut DNA at specific sequences, essential for genetic engineering and molecular biology. These restriction enzymes, such as EcoRI, allow precise DNA modifications, facilitating cloning, genome mapping, and recombinant DNA technology, forming the foundation of modern genetic research and biotechnology applications. B is matched with 1: Feldman developed transgenic plants using Agrobacterium T-DNA. It is a method for introducing foreign genes into plant genomes. This technique revolutionized agriculture by creating genetically modified crops like Bt cotton with enhanced traits like pest resistance and drought tolerance. C is matched with 4: Polymerase Chain Reaction (PCR) was discovered by Kary Mullis. It enables rapid DNA amplification, crucial in forensic science, disease diagnosis, and genetic research. Using DNA polymerase and temperature cycling, PCR exponentially multiplies DNA sequences, allowing precise genetic analysis. It plays a pivotal role in applications like DNA fingerprinting and infectious disease testing. D is matched with 3: Reverse Transcriptase was discovered by Temin and Baltimore. It is an enzyme that synthesizes DNA from RNA which is crucial in retrovirus replication like HIV. This discovery advanced virology and led to antiretroviral therapies. It is also widely used in complementary DNA (cDNA) synthesis, enabling gene expression studies and recombinant DNA technology advancements.

Explanation

Viroids are small, circular, single-stranded RNA molecules that infect plants. They do not encode proteins and rely entirely on the host’s cellular machinery for replication. Viroids are among the smallest known infectious agents.

Explanation

Assertion (A) is true: Alcohol, including whisky is a diuretic. It inhibits the production of vasopressin (also known as antidiuretic hormone or ADH), which is responsible for regulating water retention in the body. When vasopressin levels drop, the kidneys produce more urine, leading to increased urination. This effect explains why alcohol consumption causes increased thirst and dehydration-related symptoms after drinking. Reason (R) is false: Alcohol actually inhibits the secretion of vasopressin, rather than speeding it up. Vasopressin helps the kidneys reabsorb water, and when its secretion is reduced, the body loses more water through urine, causing dehydration and increased urination. Alcohol interferes with the brain’s communication pathways, affecting areas controlling balance, memory, speech, and judgment. Alcohol slows down the central nervous system, impairing coordination and judgment. Alcohol can cause intellectual impairment, headaches, memory loss, and slowed thinking.