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

Explanation

Human bones are rigid organs that form the skeleton. They provide structure, support, protection for internal organs, and enable movement. Bones are also classified based on their development and function as either axial (skull, spine, ribs, and sternum) or appendicular (limbs and girdles).The human skeleton consists of approximately 206 bones. A is matched with 4: The sternum, commonly known as the breastbone is a flat bone situated at the center of the thoracic cage, connects to the ribs via costal cartilage. It plays a vital role in protecting the heart and lungs while serving as a structural anchor for the ribcage. B is matched with 1: The clavicle, or collarbone is an S-shaped bone which stabilizes the shoulder girdle and assists in transmitting mechanical forces from the upper limb to the axial skeleton. C is matched with 2: The patella, known as the kneecap is a sesamoid bone embedded within the tendon of the quadriceps muscle, protecting the knee joint. D is matched with 3: The scapula, or shoulder blade is a flat, triangular bone located on the posterior aspect of the ribcage, playing a key role in shoulder movement and provides attachment sites for numerous muscles involved in upper limb motion.

Explanation

Statement 1 is correct: Tapeworms, belonging to the class Cestoda are fascinating parasites with a unique reproductive strategy. Each segment of their body, called a proglottid, contains both male and female reproductive organs, making them hermaphroditic. This adaptation allows tapeworms to self-fertilize or cross-fertilize, ensuring reproductive success even in limited host environments. Their reproductive efficiency is one reason they thrive as internal parasites.

Statement 2 is correct: Roundworms, or nematodes (phylum Nematoda), exhibit sexual dimorphism, meaning individuals are either male or female. Males are typically smaller and possess specialized structures like spicules for mating. This separation of sexes enhances genetic diversity, a critical factor for survival in diverse environments. Nematodes are one of the most abundant and diverse groups of animals on Earth, found in almost every ecosystem.

Statement 3 is correct: Filariasis is caused by parasitic nematodes like Wuchereria bancrofti and Brugia malayi, which are transmitted to humans via mosquito vectors. These tiny worms reside in the lymphatic system, causing lymphatic filariasis (commonly called elephantiasis). This disease exemplifies the intricate relationship between hosts, parasites, and vectors. Nematodes like these highlight the importance of vector control in managing parasitic diseases.

Statement 4 is incorrect: The Guinea worm (Dracunculus medinensis) is not an annelid (segmented worm) but a nematode. This parasitic roundworm causes dracunculiasis, a disease associated with painful blister formation as the adult worm emerges from the skin. Nematodes are unsegmented and possess a simple body structure adapted for parasitism. This parasite’s lifecycle is intricately linked to water sources, making safe drinking water a key preventive measure.