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

Explanation

The combination of ribosomes and the endoplasmic reticulum plays a pivotal role in protein synthesis. Ribosomes are the molecular machines responsible for translating messenger RNA (mRNA) into polypeptide chains, which then fold into functional proteins. They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum. The ER is a network of membranous tubules within the cell. The rough ER (RER) is studded with ribosomes on its cytoplasmic surface, making it the site of protein synthesis for proteins destined for secretion or for use in the cell membrane. After synthesis, these proteins are folded and undergo post-translational modifications within the RER.

Explanation

Cell death is a fundamental biological process crucial for maintaining cellular homeostasis, development, and defense mechanisms in multicellular organisms. There are two primary types of cell death: papoptosis and necrosis.

Option (a) is correct: The cellular and molecular control of programmed cell death is called apoptosis, a regulated process triggered by physiological or pathological signals. It ensures the removal of damaged or harmful cells without harming the organism. Key processes include cell shrinkage, DNA fragmentation, and the formation of apoptotic bodies, which are engulfed by nearby cells or macrophages.

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.

Explanation

Assertion (A) is false: Humans have 46 chromosomes (23 pairs), one of which determines sex. This pair consists of XX in females and XY in males. During reproduction, the mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome. If a sperm carrying an X chromosome fertilizes the egg, the offspring will be female (XX), whereas if a sperm carrying a Y chromosome fertilizes the egg, the offspring will be male (XY). Since the sperm determines the final chromosomal combination, the father plays the major role in sex determination. Reason (R) is true: Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

Explanation

The silkworm yields the fiber of commerce during its larval stage, specifically when it starts to spin its silk cocoon. The silkworm (the larval stage of the silk moth Bombyx mori) produces the fiber of commerce during its larval stage. This stage is when the silkworm starts spinning its silk to form a protective cocoon around itself. The silk produced by the larva is collected and used commercially to make silk fabric. Therefore, the correct stage when the silkworm yields the fibre of commerce is the larva. The imago is the adult moth stage in the silkworm’s life cycle. After metamorphosis, the adult moth does not produce silk. Its role is to mate and lay eggs, continuing the life cycle. Therefore, the silkworm does not yield silk during the imago stage.

Explanation

A is matched with 2: Haemophilia is a genetic disease caused by mutations in clotting genes. It is inherited via X chromosome. Under this, blood does not clot properly due to a deficiency of clotting factors (such as Factor VIII in Haemophilia A or Factor IX in Haemophilia B). This leads to excessive bleeding even from minor injuries. B is matched with 3: Diabetes is primarily a hormonal disorder related to insulin production or the body’s inability to use insulin effectively. Type 1 diabetes is due to insufficient insulin production (autoimmune) while Type 2 is due to insulin resistance. C is matched with 1: Rickets is caused by a deficiency of vitamin D, calcium, or phosphate, leading to weakened bones. It is not genetic or hormonal but results from nutritional deficiencies. D is matched with 4: Ringworm is a fungal infection caused by dermatophytes, affecting skin, hair, nails resulting in ring-shaped patches.

Explanation

Blood glucose levels are commonly measured in milligrams per decilitre (mg/dL). This unit expresses the amount of glucose (in milligrams) present in a decilitre (0.1 liters) of blood. It is the standard measurement used in most clinical settings to monitor and diagnose conditions like diabetes. Other units include millimoles per liter (mmol/L), used in countries like the UK, where 1 mg/dL equals 0.0555 mmol/L.

Explanation

Endocrine glands secrete hormones that regulate various bodily functions, from growth and metabolism to stress responses. A is matched with 2: The gonads (ovaries in females and testes in males) are responsible for producing sex hormones. In females the ovaries secrete progesterone which plays a key role in regulating the menstrual cycle and maintaining pregnancy. In males the testes primarily produce testosterone but it also produces progesterone in smaller amounts. B is matched with 3: Known as the master gland, pituitary gland secretes growth hormone (GH) (stimulates growth, cell reproduction, and regeneration), thyroid-stimulating hormone (TSH) (regulates metabolism), prolactin (stimulates milk production), and antidiuretic hormone (ADH) (maintains water balance). C is matched with 1: Pancreas regulates blood sugar levels through insulin (lowers blood glucose) and glucagon (raises blood glucose) and plays a major role in carbohydrate, fat, and protein metabolism. D is matched with 4: The adrenal glands located on top of the kidneys produce cortisone, a glucocorticoid hormone involved in stress response, metabolism, and immune regulation. Cortisone is part of the body’s natural response to stress and inflammation.

Explanation

Option (d) is correct: During intense exercise muscles rely on anaerobic respiration (without oxygen) to produce energy quickly. This process breaks down glucose into pyruvate, which is then converted into lactic acid (or lactate) in the absence of sufficient oxygen. The buildup of lactic acid in muscle tissues lowers the pH which causes a burning sensation and muscle fatigue.

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

While a decrease in oxygen supply can contribute to fatigue but it is not the primary cause of the immediate sensation of muscle fatigue. Prolonged or intense exercise can cause microscopic damage to muscle fibers which causes delayed-onset muscle soreness (DOMS). However, this damage does not cause the immediate sensation of fatigue during exercise. Glucose is a primary energy source for muscles during exercise. While glycogen (stored glucose) depletion can contribute to fatigue during prolonged endurance activities (e.g., marathons) but it is not the primary cause of the acute fatigue and burning sensation