Excretory Products and their Elimination: NEET PYQ, 2018–2026

Answer: (B)

Glomerular filtration rate is the volume of filtrate formed per unit time by both kidneys together. In a healthy adult it is about 125 mL/min, which amounts to roughly 180 L per day. Units matter here: 125 mL/min equals 1.25 L/min only if the conversion is done carefully. Memorising the 180 L/day figure and dividing by 1440 minutes gives about 125 mL/min.

Answer: (A)

The PCT reabsorbs about two-thirds of the filtrate. Its cuboidal cells have a brush border of microvilli, and these enlarge the apical surface area for active and passive transport. This maximises reabsorption of glucose, amino acids, sodium, and water. Answers that assign secretion, mechanical strength, or gas exchange to the microvilli confuse the brush border with other cell features.

Answer: (B)

The renal corpuscle consists of the glomerulus and Bowman's capsule. The parietal layer of the capsule is simple squamous epithelium. At the urinary pole it is continuous with the proximal convoluted tubule, which is lined by cuboidal cells with a brush border. The change from flat to cuboidal cells marks the point where the filtrate enters the tubule, where most of the reabsorption then takes place. To answer, a student should fix the order of the nephron: capsule, PCT, descending limb, ascending limb, DCT, and then the collecting duct. The distractors each move one of these segments to the wrong place or use a shared feature, such as squamous lining, to link two unrelated parts.

Answer: (A)

Principle: nitrogenous wastes differ across animals. Humans convert toxic ammonia into less toxic urea in the liver, and urea is the main nitrogenous waste in urine. Ammonia is for aquatic animals, and uric acid is for birds, reptiles and insects.

Answer: (A)

Bowman's capsule has two layers: an inner visceral layer of podocytes that wraps the glomerular capillaries, and an outer parietal layer of simple squamous epithelium. The thin squamous lining forms the outer wall of the capsular space, where filtrate collects before passing into the PCT.

Answer: (A)

Principle: the ascending limb of the loop of Henle is impermeable to water, while the descending limb is permeable to water. Active salt transport happens only in the thick ascending limb, which has cuboidal cells with many mitochondria. Filtrate becomes dilute as it climbs this limb, and the pumped salt builds the medullary osmotic gradient. Therefore the answer is the thick ascending limb. The distractors fail because the descending limb is water-permeable, the thick descending limb has no salt pump, and the thin ascending limb transports salts passively.

Answer: (B)

Protonephridia (flame cells) are found in flatworms such as Planaria, in rotifers, some annelids and the cephalochordate Amphioxus. They are mainly concerned with osmoregulation.

Answer: (B)

The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule, called the peritubular capillaries. A minute vessel of this network runs parallel to Henle's loop as the U-shaped vasa recta, which is absent or highly reduced in cortical nephrons.

Answer: (A)

Principle: ultrafiltration occurs because the glomerular capillary hydrostatic pressure pushes fluid out, while the hydrostatic pressure in Bowman's capsule and the colloid osmotic pressure of plasma proteins oppose it. Net filtration pressure = P(glomerular) - [P(capsule) + π(plasma)]. Application: 60 - (18 + 32) = 10 mm Hg. Only the glomerulus drives filtration; the other two forces resist it.

Answer: (D)

Towards the centre of the inner concave surface of the kidney is a notch called the hilum, through which the ureter, blood vessels and nerves enter. Inner to the hilum is a broad funnel-shaped space, the renal pelvis, with projections called calyces.