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

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.

Explanation

The king cobra (Ophiophagus hannah) is a snake whose diet primarily consists of other snakes, including venomous species such as kraits, pythons, and even other cobras. The name "Ophiophagus" literally means "snake-eater." King Cobras are solitary creatures and are primarily active during the day (diurnal). King Cobras are found in forests, grasslands, and hilly terrains across South and Southeast Asia. The King Cobra is the longest venomous snake in the world, growing up to 5.6 meters (18.5 feet).

Explanation

The pH level of blood in a normal person typically ranges from 7.35 to 7.45. This is considered slightly alkaline and is crucial for maintaining the proper function of enzymes and other biochemical processes in the body. The normal pH range of blood is tightly regulated by the body through mechanisms like buffer systems (such as the bicarbonate buffer system) to prevent drastic shifts in pH that could be harmful. A pH below 7.35 is considered acidosis, while a pH above 7.45 is considered alkalosis. Both conditions can disrupt normal physiological processes. The body maintains this narrow pH range to ensure optimal conditions for enzyme activity, oxygen transport, and metabolic reactions.

Explanation

Assertion (A) is true: The liver plays a crucial role in the digestion of fats. The liver’s primary role is to produce bile, which is essential for the digestion and absorption of fats. Bile is stored in the gallbladder and released into the small intestine when fat is detected in the stomach. Bile emulsifies fats by breaking them down into smaller droplets. This makes it easier for digestive enzymes, primarily lipase from the pancreas, to act on the fats and break them down further. Reason (R) is false: The liver does not produce fat-digesting enzymes. The production of fat-digesting enzymes occurs in the pancreas, not the liver. Lipase enzyme is secreted by the pancreas and is responsible for breaking down triglycerides (fats) into glycerol and fatty acids. Lipase works on the small fat droplets that have been emulsified by bile.

Explanation

Option (a) is correct:

The echidna is a monotreme, a group of egg-laying mammals that includes the platypus and echidna. Unlike most mammals, monotremes do not give birth to live young. They lay eggs and after laying eggs, the female echidna incubates them in a special pouch-like structure on her abdomen. Once the eggs hatch, the mother nurses her young by secreting milk from mammary glands, though monotremes do not have nipples. The milk oozes through the skin and the young lap it up.They are found in Australia and New Guinea and are adapted to a variety of environments, including forests and deserts. Options (b), (c) and (d) are incorrect:

Kangaroos are marsupials, meaning they give birth to live young that are underdeveloped at birth. The baby, called a joey, continues to develop in the mother’s pouch. Porcupines are placental mammals and they give birth to live young. These mammals develop their young inside the mother’s body before birth. Whales are placental mammals and give birth to live young after a long gestation period.

Explanation

The Gambusia fish (Gambusia affinis) or mosquito fish is highly effective in controlling mosquito populations in stagnant water such as ponds and wells. These fish feed on mosquito larvae, reducing the number of adult mosquitoes. As biological control agents, Gambusia fish offer a natural and chemical-free method for controlling mosquitoes. They are particularly useful in limiting the spread of diseases like malaria, dengue, and Zika. By consuming mosquito larvae in standing water, they help decrease the overall mosquito population, supporting public health efforts.

Explanation

Primates are a diverse group of mammals divided into two major categories: monkeys and apes. While monkeys and apes share common ancestors, they differ significantly in their characteristics, behavior, and evolutionary history.

Option (c) is correct: Langurs are Old World monkeys(and not ape) and belong to the family Cercopithecidae. Unlike apes, langurs have tails, a key feature that distinguishes them from apes. They are primarily found in South and Southeast Asia. These monkeys are known for their long limbs and often live in large social groups. Langurs feed on leaves, fruits, and seeds, and are often seen foraging in groups. Their tails help them maintain balance while moving through the trees. They are also much smaller in size than the great apes like gorillas. Options (a), (b) and (d) are incorrect:

Gibbons are lesser apes, belonging to the family Hylobatidae. They are known for their remarkable brachiation (swinging from tree to tree using their long arms), making them one of the most agile primates. Gibbons are found in Southeast Asia and are relatively small compared to other apes. Gorillas are great apes, the largest of all living primates belonging to the family Hominidae. Gorillas are native to Central Africa and live in groups led by a dominant male known as a silverback. Gorillas are primarily terrestrial, spending most of their time on the ground, unlike the gibbon, which is arboreal. Gorillas, like all apes, do not have tails, and they share a close genetic relationship with humans. Orangutans are great apes of the genus Pongo. They are highly intelligent and spend most of their time in trees, primarily in the rainforests of Borneo and Sumatra. Orangutans have remarkable cognitive abilities, using tools and even creating nests to sleep in.