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

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

Explanation

The small pouch containing silica gel found in bottles of medicine (tablets or powder) is primarily used to absorb moisture. Silica gel is a desiccant, meaning it has a high affinity for water molecules. It absorbs moisture from the surrounding environment, preventing the tablets or powder from degrading due to humidity. This helps maintain the stability and efficacy of the medicine. Silica gel has a porous structure that traps water molecules through adsorption. Moisture can cause tablets to crumble or powders to clump, reducing their effectiveness and shelf life.