Excretory System – NDA Biology PYQs

NDA 2024-II

Q. 1. Which part of nephron of the human kidney is responsible for filtration of blood for excretion?

(a) Collecting duct

(b) Renal vein

(c) Ureter

(d) Bowman’s capsule

Answer: (d) Bowman’s capsule

Explanation: Bowman’s capsule is a cup-shaped structure at the start of each nephron. It encloses the glomerulus: a knot of capillaries. Blood is filtered under pressure from the glomerular capillaries into Bowman’s capsule. This filtrate contains water, urea, glucose, salts, and amino acids. The filtered fluid then passes into the renal tubule for further processing. The collecting duct reabsorbs water; the ureter carries urine to the bladder; the renal vein returns cleaned blood to circulation. Concept Tested: Bowman’s capsule: site of blood filtration in the nephron (glomerular filtration)

★ JOVIK Exam Insight NDA frequently tests the structure of the nephron. Bowman’s capsule:  filtration. Proximal convoluted tubule (PCT):  reabsorption of glucose, amino acids, water. Loop of Henle:  concentration of urine. Collecting duct:  final water reabsorption.

 NDA 2017-I

Q. 2. Kidney secretes an enzyme, which changes plasma protein angiotensinogen into angiotensin. The enzyme is

(a) Renin

(b) Nitrogenase

(c) Hydrolase

(d) Mono-oxygenase

Answer: (a) Renin

Explanation: Renin is an enzyme secreted by specialised cells (juxtaglomerular cells) of the kidney when blood pressure falls. It acts on angiotensinogen (a plasma protein made in the liver) to produce angiotensin I, which is then converted to angiotensin II. Angiotensin II raises blood pressure by causing vasoconstriction and stimulating aldosterone secretion. This pathway is called the Renin–Angiotensin–Aldosterone System (RAAS). Concept Tested: Renin: kidney enzyme that converts angiotensinogen to angiotensin; part of the RAAS blood pressure regulation pathway

 NDA 2016-II

Q. 3. Statement I: Too much salt content in diet could be one of the reasons for kidney failure.

Statement II: High salt may cause high blood pressure.

(a) Both the statements are individually true and Statement II is the correct explanation of Statement I

(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I

(c) Statement I is true but Statement II is false

(d) Statement I is false but Statement II is true

Answer: (a) Both the statements are individually true and Statement II is the correct explanation of Statement I

Explanation: Statement I is correct: a high-salt diet can contribute to kidney failure over time. Statement II is also correct: excess dietary salt raises blood pressure (hypertension) by increasing blood volume. Statement II explains Statement I because chronic high blood pressure damages the delicate blood vessels of the kidney (glomeruli), progressively impairing kidney function and eventually leading to chronic kidney disease or kidney failure. Concept Tested: High dietary salt → hypertension → kidney damage → kidney failure; Statement II correctly explains Statement I

 NDA 2013-II

Q. 4. Which one among the following substances is never excreted out through urine under normal circumstances in any healthy individual?

(a) Urea

(b) Sodium

(c) Amino acid

(d) Potassium

Answer: (c) Amino acid

Explanation: In a healthy kidney, amino acids are completely reabsorbed in the proximal convoluted tubule (PCT) by active transport. Under normal circumstances, no amino acids appear in the urine. Urea is the primary nitrogenous waste and is always excreted in urine. Sodium and potassium are regulated: both are partially excreted depending on the body’s needs, but amino acids are never normally excreted. Their presence in urine (aminoaciduria) indicates kidney disease or a metabolic disorder. Concept Tested: Amino acids are completely reabsorbed in the PCT and are not excreted in normal urine

★ JOVIK Exam Insight The rule for filtration and reabsorption in the nephron: glucose and amino acids are FULLY reabsorbed in the PCT under normal conditions: they should never appear in urine. If glucose appears (glucosuria), it indicates diabetes mellitus. If amino acids appear (aminoaciduria), it indicates kidney or metabolic disease.

---