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

Explanation

Statement I is incorrect:

Viruses are the most abundant biological entities in marine ecosystems, with 10 million viruses per milliliter of seawater. Marine viruses, such as cyanophages and bacteriophages, infect phytoplankton, bacteria, and archaea, driving biogeochemical cycles.

Statement II is incorrect:

Bacteriophages (phages) infect only bacteria, not all microbes. Lytic phages (e.g., T4) destroy bacteria like E. coli within 20-30 minutes, while lysogenic phages (e.g., lambda) integrate into host genomes.

Statement III is incorrect:

Viruses manipulate host transcription, e.g., adenoviruses (Ad5) use E1A/E1B proteins to hijack RNA polymerase II, enhancing cyclin E and viral gene expression by 10-100 fold and suppressing IFN-. HIV uses Tat protein to boost transcription by 1000-fold; SARS-CoV-2 suppresses interferon pathways by 80%.

Explanation

Some species of ants such as leafcutter ants (of genus Atta and Acromyrmex) are well-known for cultivating fungi. These ants cut leaves and use them to grow fungi in specialized underground gardens. The fungi serve as the primary food source for the ant colony. This relationship between ants and fungi is a classic example of mutualism where both species benefit. The ants provide the fungi with a controlled environment and a constant supply of plant material while the fungi provide the ants with a nutritious food source. Leafcutter ants are primarily found in Central and South America,

Explanation

Option (b) is correct: The major challenge in developing a malaria vaccine is that humans do not achieve complete immunity through natural infection. Partial immunity can develop after repeated exposure but it is not sufficient to prevent reinfection as the immune system fails to completely clear the parasite. The malaria parasite’s high mutation rate enables it to evade the immune system, further complicating efforts to develop an effective vaccine.

Option (a) is incorrect: Although malaria is caused by various Plasmodium species (e.g., P. falciparum, P. vivax) but this diversity is not the primary obstacle to vaccine development. Vaccines can target shared stages of the parasite’s lifecycle, allowing scientists to address multiple species. While species variation presents a challenge, it is not the main barrier in creating an effective vaccine against malaria.

Option (c) is incorrect: Vaccines have been successfully developed for a wide range of pathogens, including viruses, bacteria, and parasites like malaria.

Option (d) is incorrect: Though humans are the intermediate host for the Plasmodium parasite, they are also crucial in the parasite’s lifecycle. The mosquito is the definitive host, where the parasite undergoes sexual reproduction. In humans the parasite undergoes asexual reproduction inside the liver and red blood cells, making humans essential in the lifecycle.

Explanation

Hepatitis B is a viral infection that primarily affects the liver and can lead to chronic disease. HIV is a virus that attacks the immune system, weakening the body’s ability to fight infections.

Statement 1 is correct: Hepatitis B transmission occurs through contact with infected blood, semen, or other body fluids. It’s 50 to 100 times more contagious than HIV because it can survive longer outside the body and can be transmitted with a smaller amount of the virus. HIV (Human Immunodeficiency Virus) needs a higher viral load and specific conditions to spread.

Statement 2 is correct: The Hepatitis B virus attacks and damages the liver, causing inflammation and scarring (called cirrhosis). This chronic inflammation weakens the liver and makes it more susceptible to liver cancer. Liver cancer specifically hepatocellular carcinoma (HCC) is strongly associated with chronic HBV infection. People with chronic Hepatitis B infection have a much higher risk of developing HCC compared to those who do not have the infection.

Explanation

Genetic disorders are caused by abnormalities in an individual’s DNA, inherited from parents or arising from mutations. They can affect structure, function, or production of proteins. Types include single-gene disorders (e.g., cystic fibrosis), chromosomal disorders (e.g., Down syndrome), and multifactorial disorders (e.g., diabetes), impacting health, development, or metabolism.

Option (d) is correct:

Color blindness is a sex-linked recessive disorder carried on the X chromosome. In the above case, the woman suffers from color blindness but her husband does not. Woman’s Genotype: Since the woman has color blindness, her genotype must be X^cX^c (as both X chromosomes carry the color blindness allele). Man’s Genotype: Since the man does not have color blindness, his genotype must be XY (as the Y chromosome does not carry the color blindness gene). Children’s Genotypes:

Son: A son inherits his X chromosome from his mother and his Y chromosome from his father. Since the mother has the X^c chromosome, the son’s genotype will be X^cY, meaning the son will suffer from color blindness. Daughter: A daughter inherits one X chromosome from her mother and one X chromosome from her father. Since the father has a normal X chromosome, the daughter’s genotype will be X^cX. Since color blindness is a recessive trait, the daughter will be a carrier but won’t suffer from color blindness.

Explanation

The flying fox is a type of megabat belonging to the Pteropus genus in the Pteropodidae family. These large bats have wingspans ranging from 1.5 to 1.8 meters and are known for their fox-like faces, which is how they got their name. Flying foxes are found mostly in tropical and subtropical areas, particularly in coastal regions and tropical forests of India. As frugivores, they primarily feed on fruit and play a vital role in pollination and seed dispersal, contributing to the health of their ecosystems. Unlike smaller insect-eating bats, flying foxes do not rely on echolocation. Instead, they use their sharp vision to navigate and find food. This makes them unique compared to other bat species.

Explanation

Salamander-Python-Kangaroo sequence follows a correct evolutionary progression:

Salamanders are amphibians to the class Amphibia.

Amphibians evolved from fish and are characterized by their ability to live both in water (as larvae) and on land (as adults). Pythons are reptiles in the class Reptilia which have evolved from amphibians. Reptiles are vertebrates with dry skin, and they lay eggs on land (as opposed to amphibians, which generally need water for reproduction). Kangaroos are mammals, specifically marsupials in the class Mammalia. Mammals evolved from reptiles. Kangaroos are one of the few mammals that give birth to underdeveloped offspring, which then continue to develop in a pouch.

Explanation

The giant panda (Ailuropoda melanoleuca) belongs to the Ursidae family, which includes all modern bears such as grizzly, polar, and black bears. Though classified as carnivores, giant pandas are mainly herbivores, with bamboo making up to 99% of their diet. They have a unique "thumb" (modified wrist bone) that helps them grasp bamboo. These solitary creatures are recognized by their black and white fur and have a slow metabolism due to their low-calorie diet. Pandas are found in the mountainous regions of China and are classified as vulnerable because of habitat loss and low reproductive rates. Females are only fertile for a few days each year, making reproduction difficult. Conservation efforts have helped increase their population. The giant panda is a symbol of wildlife conservation and through panda diplomacy, it has helped strengthen diplomatic ties between China and other countries. IUCN Status: The IUCN Red List (International Union for Conservation of Nature) currently classifies the giant panda as Vulnerable.

Explanation

The Dugong (Dugong dugon) is a marine mammal found in shallow coastal waters of the Indo-Pacific. It is closely related to manatees. The dugong has a torpedo-shaped body with a fluked tail (similar to a whale’s) and two front flippers. Its skin is grayish-brown, and it has a rounded, wrinkled face that helps it forage for seagrass, its primary food source. Dugongs can grow up to 3 meters in length and weigh up to 400 kg. Dugongs are herbivores and feed mainly on seagrass, earning them the nickname "sea cows". They play a crucial role in maintaining healthy seagrass ecosystems. However, dugongs are vulnerable due to habitat loss, hunting, bycatch, and seagrass degradation. Conservation efforts focus on protecting their habitats through marine protected areas and reducing fishing gear entanglements.

Explanation

The intriguing phenomenon of sexual cannibalism, where the female kills the male after copulation, is observed in some species of spiders. In certain species like the Australian redback spider and the black widow, the female spider consumes the male after mating.

Option (a), (b) and (d) are incorrect:

Dragonflies do not exhibit sexual cannibalism in the same way spiders do. While females may sometimes be aggressive toward males, they do not typically kill them after copulation. In honeybees, the male (drone) dies after mating, but this is not due to the female killing him. After mating, the drone’s genitalia are ripped off during copulation, leading to death. Pit vipers, such as rattlesnakes, do not exhibit sexual cannibalism. After mating, the male and female go separate ways. There is no phenomenon where the female kills the male after copulation.