Excretory Products & Their Elimination

Topic: Excretory System of Amphibians; Subtopic: Renal Portal System in Frog

Keyword Definitions:

• Renal portal system: A venous network carrying blood from posterior parts of the body to kidneys before entering the heart.

• Venous connection: Link between two organs through veins allowing filtration or transport of deoxygenated blood.

• Kidney: Organ responsible for excretion and osmoregulation.

• Liver: Largest gland of the body involved in detoxification and metabolism.

Lead Question – 2025

In frog, the renal portal system is a special venous connection that acts to link:

(1) Liver and intestine

(2) Liver and kidney

(3) Kidney and intestine

(4) Kidney and lower part of body

Explanation: The renal portal system of frog collects blood from the hind limbs and posterior parts of the body and delivers it to the kidneys before entering the heart. This aids in removal of nitrogenous waste from venous blood. Therefore, it connects the kidney and lower part of the body. This arrangement helps maintain efficient filtration and circulation in amphibians.

1. The excretory organs in frogs open into which chamber?

(1) Cloaca

(2) Rectum

(3) Urinary bladder

(4) Ureter

Explanation: In frogs, urine formed by the kidneys passes through ureters and is stored temporarily in the urinary bladder before being released through the cloaca. The cloaca serves as a common chamber for digestive, urinary, and reproductive tracts. Hence, the excretory organs open into the cloaca, enabling coordinated elimination of waste and gametes through one opening.

2. Which type of excretion occurs in frogs?

(1) Uricotelic

(2) Ureotelic

(3) Ammonotelic

(4) Mixed type

Explanation: Frogs are ureotelic animals as they excrete their nitrogenous waste primarily as urea. This adaptation minimizes water loss compared to ammonotelic organisms. In aquatic environments, frogs may also release some ammonia directly through the skin, but major excretion remains ureotelic, helping them balance osmotic conditions effectively in both land and water.

3. The urinary bladder of frog opens into:

(1) Cloaca

(2) Urethra

(3) Kidney

(4) Urinogenital duct

Explanation: In frogs, the urinary bladder opens into the cloaca through a small aperture, allowing the stored urine to be expelled along with fecal matter. This common passageway simplifies the elimination process in amphibians, ensuring efficient removal of waste products while conserving body water during terrestrial life phases.

4. Which one of the following carries blood from the kidney to the heart in frog?

(1) Renal artery

(2) Renal portal vein

(3) Posterior vena cava

(4) Pulmonary vein

Explanation: The posterior vena cava carries purified blood from kidneys and other posterior organs to the heart’s right atrium. In contrast, the renal portal vein brings deoxygenated blood to kidneys for filtration. This separation ensures efficient circulation and excretion simultaneously, maintaining amphibian metabolic balance effectively.

5. The main nitrogenous waste in frogs is:

(1) Urea

(2) Ammonia

(3) Uric acid

(4) Creatinine

Explanation: Frogs excrete mainly urea as their nitrogenous waste. This compound is less toxic than ammonia and requires moderate water for excretion, suiting both aquatic and terrestrial conditions. It reflects their dual life adaptation strategy, enabling survival in diverse habitats without excessive water loss or toxicity accumulation.

6. In frogs, the renal portal vein collects blood from:

(1) Hind limbs

(2) Forelimbs

(3) Brain

(4) Heart

Explanation: The renal portal vein gathers blood from the hind limbs and posterior parts of the frog’s body and channels it into the kidneys. This enables partial filtration before reaching the heart, a unique amphibian feature enhancing waste removal efficiency during systemic venous return.

Assertion–Reason Type Question

7. Assertion (A): The renal portal system in frog aids in excretion.

Reason (R): It carries blood from posterior regions to kidneys for filtration.

(1) Both A and R are true, and R is the correct explanation of A.

(2) Both A and R are true, but R is not the correct explanation of A.

(3) A is true, R is false.

(4) A is false, R is true.

Explanation: Both assertion and reason are true, and the reason correctly explains the assertion. The renal portal system indeed assists excretion by transporting blood from hind limbs and posterior regions to kidneys for filtration. Therefore, option (1) is correct, showing integrated venous circulation in amphibians.

Matching Type Question

8. Match the following structures with their functions:

A. Kidneys  1. Reabsorption of water

B. Urinary bladder 2. Storage of urine

C. Cloaca  3. Common passage for waste

D. Skin  4. Cutaneous respiration

(1) A-1, B-2, C-3, D-4 (2) A-2, B-3, C-4, D-1 (3) A-4, B-1, C-2, D-3 (4) A-3, B-4, C-1, D-2

Explanation: Correct match: A-1, B-2, C-3, D-4. Kidneys filter and reabsorb water; the urinary bladder stores urine; the cloaca acts as a common passage; and the skin performs cutaneous respiration in amphibians. This functional coordination ensures efficient excretion and respiration under aquatic and terrestrial conditions.

Fill in the Blanks / Completion Type Question

9. In frog, urine formed in the kidneys passes through _______ to reach the urinary bladder.

(1) Ureters (2) Urethra (3) Cloaca (4) Nephridia

Explanation: In frogs, urine formed in kidneys passes through ureters to reach the urinary bladder, where it is stored temporarily before excretion through the cloaca. The ureters are paired ducts functioning as a conduit between kidneys and bladder, vital for maintaining excretory flow and osmotic balance.

Choose the Correct Statements Type Question

10. Statement I: In frog, kidneys are mesonephric type.

Statement II: Mesonephric kidneys function both as excretory and reproductive organs in males.

(1) Both statements are correct.

(2) Both statements are incorrect.

(3) Only Statement I is correct.

(4) Only Statement II is correct.

Explanation: Both statements are correct. Frogs possess mesonephric kidneys, characteristic of adult amphibians. In males, the kidneys also serve a reproductive role by transporting sperm via ureters, termed urinogenital ducts. This dual function demonstrates evolutionary adaptation linking excretion and reproduction efficiently in amphibians.

Topic: Structure of Nephron; Subtopic: Functions of Proximal and Distal Convoluted Tubules

Keyword Definitions:

• Nephron: Functional unit of kidney responsible for filtration, reabsorption, and secretion during urine formation.

• Proximal convoluted tubule (PCT): Part of nephron that reabsorbs essential ions, glucose, amino acids, and water from filtrate.

• Distal convoluted tubule (DCT): Part of nephron that regulates pH and electrolyte balance through selective reabsorption and secretion.

• Reabsorption: Process by which useful substances in filtrate return to the blood.

• Secretion: Active transfer of substances like H⁺, K⁺, and NH₃ into the tubular lumen for excretion.

Lead Question – 2025

Which of the following diagrams is correct with regard to the proximal (P) and distal (D) tubule of the Nephron?

(1) P reabsorbs HCO₃⁻, NaCl, H₂O and secretes H⁺. D reabsorbs NaCl, H₂O, HCO₃⁻ and secretes K⁺, H⁺.
(2) P reabsorbs HCO₃⁻, NaCl, H₂O and secretes H⁺, NH₃. D reabsorbs NaCl, H₂O, HCO₃⁻ and secretes K⁺, H⁺.
(3) P reabsorbs HCO₃⁻, NaCl, H₂O and secretes H⁺, NH₃. D reabsorbs H₂O, HCO₃⁻ and secretes NaCl, H⁺.
(4) P reabsorbs NaCl, HCO₃⁻ and secretes H⁺, H₂O. D reabsorbs NaCl and secretes H₂O, NH₃, K⁺.

Explanation: The correct answer is option (2). In the nephron, the proximal convoluted tubule (PCT) actively reabsorbs Na⁺, Cl⁻, HCO₃⁻, and water, while secreting H⁺ and NH₃. The distal convoluted tubule (DCT) reabsorbs Na⁺, Cl⁻, H₂O, and HCO₃⁻ under hormonal control, and secretes K⁺ and H⁺ for acid-base balance. Together, these processes maintain osmotic and ionic equilibrium in the body efficiently during urine formation.

Guessed Questions:

1. Which part of nephron is responsible for maximum water reabsorption?
(1) Distal convoluted tubule
(2) Proximal convoluted tubule
(3) Loop of Henle
(4) Collecting duct
Explanation: The proximal convoluted tubule reabsorbs around 65–70% of filtered water along with ions and nutrients, making it the major site of water reabsorption. It also reabsorbs glucose, amino acids, and bicarbonate efficiently through active transport mechanisms, contributing to the maintenance of plasma osmolarity and body fluid volume.

2. Which hormone increases reabsorption of Na⁺ in the distal convoluted tubule?
(1) Vasopressin
(2) Aldosterone
(3) Oxytocin
(4) Parathormone
Explanation: Aldosterone enhances sodium reabsorption in the distal convoluted tubule and collecting ducts, leading to increased water retention and blood volume. This process helps regulate blood pressure and electrolyte balance, maintaining homeostasis in the body. It also promotes potassium excretion through tubular secretion mechanisms.

3. Which part of nephron is impermeable to water?
(1) Descending limb of loop of Henle
(2) Ascending limb of loop of Henle
(3) Collecting duct
(4) Proximal convoluted tubule
Explanation: The ascending limb of the loop of Henle is impermeable to water but actively reabsorbs ions such as Na⁺, Cl⁻, and K⁺. This selective permeability helps establish the osmotic gradient necessary for concentrating urine in the collecting ducts under hormonal control of ADH.

4. Which segment of nephron helps in maintaining acid-base balance?
(1) Distal convoluted tubule
(2) Loop of Henle
(3) Bowman's capsule
(4) Glomerulus
Explanation: The distal convoluted tubule maintains acid-base balance by reabsorbing bicarbonate ions and secreting hydrogen and potassium ions into the lumen. This function helps regulate blood pH and prevent acidosis or alkalosis, ensuring homeostasis of the body fluids.

5. Which of the following substances is secreted in both PCT and DCT?
(1) K⁺
(2) H⁺
(3) Na⁺
(4) Cl⁻
Explanation: Hydrogen ions (H⁺) are secreted into the tubular lumen in both the proximal and distal convoluted tubules. This secretion is crucial for maintaining blood pH and excreting excess acid. Tubular cells use carbonic anhydrase to regulate hydrogen ion concentration during secretion.

6. The counter-current mechanism operates between:
(1) Loop of Henle and collecting duct
(2) Bowman’s capsule and glomerulus
(3) PCT and DCT
(4) Afferent and efferent arteriole
Explanation: The counter-current mechanism between the loop of Henle and vasa recta maintains the osmotic gradient in the medulla. This gradient facilitates water reabsorption from the collecting duct, allowing urine to become concentrated, which is essential for conserving body water.

7. (Assertion-Reason)
Assertion (A): Distal convoluted tubule is the site of selective secretion of ions.
Reason (R): DCT plays a role in maintaining electrolyte balance and blood pH.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, R is false.
(4) A is false, R is true.
Explanation: Both assertion and reason are true, and R correctly explains A. The distal convoluted tubule selectively secretes ions like H⁺ and K⁺ while reabsorbing Na⁺ and Cl⁻. This maintains ionic and pH balance, contributing to fine-tuning of urine composition.

8. (Matching Type)
Match the following parts of nephron with their respective functions:
List I – Part of Nephron
A. PCT
B. Loop of Henle
C. DCT
D. Collecting duct

List II – Function
(i) Water conservation under ADH
(ii) Maximum reabsorption of solutes
(iii) Osmotic gradient maintenance
(iv) Acid-base regulation

(1) A-(ii), B-(iii), C-(iv), D-(i)
(2) A-(iii), B-(iv), C-(ii), D-(i)
(3) A-(iv), B-(i), C-(ii), D-(iii)
(4) A-(ii), B-(i), C-(iii), D-(iv)
Explanation: The correct match is A-(ii), B-(iii), C-(iv), D-(i). The PCT performs maximum reabsorption, the loop of Henle maintains osmotic gradient, DCT regulates acid-base balance, and the collecting duct conserves water under the action of ADH, ensuring proper urine concentration.

9. (Fill in the Blanks)
The hormone _______ acts on the collecting duct to increase water reabsorption.
(1) Aldosterone
(2) ADH
(3) Calcitonin
(4) Oxytocin
Explanation: ADH (antidiuretic hormone) acts on the collecting ducts, making them more permeable to water. This enhances water reabsorption into the bloodstream, reducing urine volume and conserving body fluids during dehydration, thereby maintaining osmotic balance and hydration.

10. (Choose the Correct Statements)
Statement I: Loop of Henle helps in urine concentration.
Statement II: PCT performs selective reabsorption of glucose and amino acids.
(1) Both statements are correct.
(2) Both statements are wrong.
(3) Only Statement I is correct.
(4) Only Statement II is correct.
Explanation: Both statements are correct. The loop of Henle establishes a hyperosmotic medullary gradient essential for urine concentration, while the proximal convoluted tubule reabsorbs glucose and amino acids actively, maintaining blood composition and nutrient balance.

Topic: Human Excretory System; Subtopic: Regulation of Kidney Function

Keyword Definitions:
• Juxta Glomerular Apparatus (JGA): A specialized region of the nephron that regulates glomerular filtration rate (GFR) through renin secretion.
• Renin: An enzyme secreted by juxtaglomerular cells that initiates the renin–angiotensin–aldosterone mechanism to control blood pressure and GFR.
• Glomerular Filtration Rate (GFR): The rate at which plasma is filtered through glomeruli into the renal tubules.
• Macula Densa: Specialized cells in the distal tubule that detect Na⁺ concentration and regulate renin release.
• Angiotensin II: A hormone that causes vasoconstriction and stimulates aldosterone secretion to increase GFR.

Lead Question - 2024 (Jhajjhar)

Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Juxta Glomerular Apparatus (JGA) plays an important role in regulation of glomerular filtration rate (GFR).

Reason (R): A fall in GFR can activate the J.G. cells to release renin which can stimulate the glomerular blood flow and thereby bring the GFR to normal level.

In the light of the above statements, choose the correct answer from the options given below:
1. Both (A) and (R) are True and (R) is the correct explanation of (A).
2. Both (A) and (R) are True but (R) is not the correct explanation of (A).
3. (A) is True but (R) is False.
4. (A) is False but (R) is True.

Explanation (Answer: 1. Both (A) and (R) are True and (R) is the correct explanation of (A)):
JGA regulates GFR through the renin–angiotensin–aldosterone system. When GFR decreases, macula densa cells sense low Na⁺ and trigger juxtaglomerular cells to release renin. Renin forms angiotensin II, causing vasoconstriction of efferent arterioles and enhancing glomerular pressure, thus restoring normal GFR and maintaining renal homeostasis effectively.

1. The main function of proximal convoluted tubule (PCT) is:
1. Filtration of blood
2. Reabsorption of useful substances
3. Secretion of ammonia
4. Formation of urea

Explanation (Answer: 2. Reabsorption of useful substances):
The PCT is lined by microvilli-bearing cuboidal cells that reabsorb about 65% of filtrate, including glucose, amino acids, Na⁺, Cl⁻, and water, through active and passive transport. This helps conserve essential nutrients and maintain ionic balance in the body while ensuring that waste substances remain in the filtrate for excretion.

2. Which hormone increases water reabsorption from distal tubules and collecting ducts?
1. Aldosterone
2. Renin
3. Vasopressin (ADH)
4. Angiotensin II

Explanation (Answer: 3. Vasopressin (ADH)):
Antidiuretic hormone (ADH), secreted by the posterior pituitary, increases the permeability of distal tubules and collecting ducts to water. This enhances water reabsorption, producing concentrated urine and maintaining osmotic balance. Deficiency of ADH causes diabetes insipidus, characterized by excessive water loss and dilute urine formation.

3. Which part of nephron helps to maintain hyperosmolarity of medulla?
1. Bowman's capsule
2. Loop of Henle
3. Proximal convoluted tubule
4. Collecting duct

Explanation (Answer: 2. Loop of Henle):
The Loop of Henle, particularly its descending and ascending limbs, creates a counter-current multiplier system. The descending limb allows water reabsorption, while the ascending limb actively transports Na⁺ and Cl⁻ into the medulla. This establishes a concentration gradient essential for producing concentrated urine and conserving water in the body.

4. Urea is synthesized in:
1. Kidney
2. Liver
3. Lungs
4. Intestine

Explanation (Answer: 2. Liver):
Urea is produced in the liver through the ornithine cycle (urea cycle) as the major nitrogenous waste product of amino acid metabolism. It is transported via blood to the kidneys, where it is excreted in urine. The process detoxifies ammonia, maintaining nitrogen balance and preventing neurotoxic effects in the body.

5. Bowman’s capsule surrounds:
1. Collecting duct
2. Glomerulus
3. Loop of Henle
4. Distal tubule

Explanation (Answer: 2. Glomerulus):
Bowman’s capsule, a double-walled cup-like structure, encloses the glomerulus—a tuft of capillaries. Together they form the renal corpuscle, the site of blood filtration. The hydrostatic pressure in glomerular capillaries forces plasma components into Bowman’s space, initiating urine formation while retaining blood cells and larger proteins.

6. The counter-current mechanism in the kidney operates between:
1. Bowman’s capsule and collecting duct
2. PCT and DCT
3. Loop of Henle and vasa recta
4. Glomerulus and PCT

Explanation (Answer: 3. Loop of Henle and vasa recta):
The Loop of Henle and vasa recta together maintain osmotic gradient in renal medulla. The descending limb of the loop and ascending limb of vasa recta facilitate counter-current exchange, ensuring efficient water and solute reabsorption. This gradient helps concentrate urine and conserve water, vital in mammals living in dry environments.

7. (Assertion–Reason Type)
Assertion (A): Aldosterone increases sodium reabsorption in the nephron.
Reason (R): It enhances permeability of collecting ducts to water.
1. Both (A) and (R) are true, and (R) explains (A).
2. Both (A) and (R) are true, but (R) does not explain (A).
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.

Explanation (Answer: 3. (A) is true but (R) is false):
Aldosterone promotes reabsorption of Na⁺ and excretion of K⁺ in distal tubule and collecting ducts, leading to water retention indirectly. However, water permeability is mainly controlled by ADH, not aldosterone. Hence, the reason is false though the assertion correctly describes aldosterone’s sodium-conserving function in maintaining electrolyte balance.

8. (Matching Type)
Match the parts of nephron with their functions:
A. Bowman’s capsule – (i) Filtration
B. PCT – (ii) Reabsorption
C. Loop of Henle – (iii) Concentration gradient
D. DCT – (iv) Secretion

1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–i, D–ii
4. A–iv, B–iii, C–ii, D–i

Explanation (Answer: 1. A–i, B–ii, C–iii, D–iv):
Each nephron segment performs distinct roles: Bowman’s capsule filters plasma, PCT reabsorbs nutrients, Loop of Henle establishes medullary gradient, and DCT secretes ions to maintain acid–base balance. Together, they ensure efficient filtration, reabsorption, secretion, and excretion to maintain homeostasis in the renal system.

9. (Fill in the Blanks)
The hormone ______ increases permeability of the collecting duct to water.
1. Aldosterone
2. Vasopressin
3. Angiotensin II
4. Renin

Explanation (Answer: 2. Vasopressin):
Vasopressin or antidiuretic hormone (ADH) increases water permeability in collecting ducts by stimulating aquaporin channel insertion. This promotes water reabsorption, reducing urine volume. When body water decreases, ADH secretion rises to maintain osmotic balance. Its deficiency leads to excretion of large volumes of dilute urine in diabetes insipidus.

10. (Choose the Correct Statements)
Statement I: The Loop of Henle maintains medullary osmotic gradient.
Statement II: Vasa recta maintains counter-current exchange with the Loop of Henle.
1. Both statements are true.
2. Both statements are false.
3. Statement I is true but Statement II is false.
4. Statement I is false but Statement II is true.

Explanation (Answer: 1. Both statements are true):
The Loop of Henle functions as a counter-current multiplier, concentrating solutes in the medulla, while the vasa recta acts as a counter-current exchanger preserving this gradient. Together, they enable kidneys to produce hypertonic urine, conserve water, and maintain osmotic equilibrium in body fluids efficiently under varying hydration conditions.

Topic: Human Excretory System; Subtopic: Structure and Function of Nephron

Keyword Definitions:

• Nephron: The structural and functional unit of the kidney responsible for urine formation.

• Loop of Henle: U-shaped structure in nephron involved in concentration of urine.

• Proximal Convoluted Tubule (PCT): Tubular part that reabsorbs water, ions, and nutrients from filtrate.

• Distal Convoluted Tubule (DCT): Tubular segment involved in selective secretion and reabsorption of ions.

• Ascending Limb: Part of loop of Henle impermeable to water but allows ion transport.

• Descending Limb: Permeable to water but not to solutes.

Lead Question – 2024 (Jhajjar)
Which part of human nephron is impermeable to water?
1. Proximal convoluted tubule
2. Distal convoluted tubule
3. Ascending limb of loop of Henle
4. Descending limb of loop of Henle

Explanation: The correct answer is Ascending limb of loop of Henle. This segment of nephron is impermeable to water but allows active transport of Na+, K+, and Cl− ions into the medullary interstitium. This process helps create a concentration gradient essential for urine concentration. The descending limb, conversely, is highly permeable to water and not to solutes.

1. Which part of nephron is mainly responsible for reabsorption of glucose and amino acids?
1. Loop of Henle
2. Proximal convoluted tubule
3. Distal convoluted tubule
4. Collecting duct
Explanation: The correct answer is proximal convoluted tubule. About 65% of the filtrate, including glucose, amino acids, and electrolytes, is reabsorbed here through active transport. The PCT also reabsorbs water via osmosis, maintaining osmolarity of body fluids and contributing significantly to the formation of concentrated urine.

2. Which of the following parts of nephron helps in counter-current mechanism?
1. PCT and DCT
2. Loop of Henle and vasa recta
3. Bowman’s capsule and collecting duct
4. Loop of Henle and glomerulus
Explanation: The correct answer is loop of Henle and vasa recta. These two structures create and maintain the osmotic gradient in the renal medulla. The descending limb allows water reabsorption, while the ascending limb pumps ions out, establishing counter-current multiplication essential for concentrated urine formation.

3. The main function of loop of Henle is to:
1. Filter blood
2. Maintain salt gradient
3. Secrete urea
4. Reabsorb glucose
Explanation: The correct answer is maintain salt gradient. The loop of Henle concentrates urine by establishing a hyperosmotic gradient in the medulla through differential permeability to water and solutes. This gradient enables water reabsorption in the collecting duct under the influence of antidiuretic hormone (ADH).

4. Which of the following segments reabsorbs maximum water in nephron?
1. Distal convoluted tubule
2. Collecting duct
3. Proximal convoluted tubule
4. Ascending limb of loop of Henle
Explanation: The correct answer is proximal convoluted tubule. About 70% of the filtered water is reabsorbed here by osmosis due to the reabsorption of solutes. The process is independent of hormonal control and plays a major role in maintaining body fluid balance and osmolarity.

5. Which hormone increases water permeability of the collecting duct?
1. Aldosterone
2. Antidiuretic hormone (ADH)
3. Parathyroid hormone
4. Cortisol
Explanation: The correct answer is antidiuretic hormone (ADH). ADH increases the permeability of the distal tubule and collecting duct to water by inserting aquaporin channels, leading to increased reabsorption of water. It helps maintain water balance and plasma osmolarity, preventing dehydration under conditions of water shortage.

6. The main site of selective secretion of ions like K+ and H+ in nephron is:
1. Loop of Henle
2. Proximal convoluted tubule
3. Distal convoluted tubule
4. Bowman’s capsule
Explanation: The correct answer is distal convoluted tubule. The DCT plays a key role in selective secretion and reabsorption, particularly of ions such as potassium and hydrogen. It helps maintain acid-base balance and ionic equilibrium in the body under hormonal regulation, mainly aldosterone.

Assertion-Reason Question
7. Assertion (A): Ascending limb of loop of Henle is impermeable to water.
Reason (R): This helps create osmotic gradient in the medulla essential for water reabsorption.
1. Both A and R are true, and R explains A
2. Both A and R are true, but R does not explain A
3. A is true but R is false
4. A is false but R is true
Explanation: The correct answer is both A and R are true, and R explains A. The impermeability of ascending limb prevents water exit while solutes are actively transported out, generating a hyperosmotic interstitial gradient. This gradient drives water reabsorption from the descending limb and collecting ducts, concentrating urine.

Matching Type Question
8. Match the following parts of nephron with their functions:
A. PCT        I. Reabsorption of glucose and water
B. Loop of Henle      II. Concentration of urine
C. DCT          III. Selective secretion of ions
D. Collecting duct   IV. Final concentration of urine
1. A-I, B-II, C-III, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-II, C-I, D-IV
4. A-I, B-III, C-II, D-IV
Explanation: The correct answer is A-I, B-II, C-III, D-IV. The PCT reabsorbs glucose, ions, and water, loop of Henle creates concentration gradient, DCT regulates ion secretion, and the collecting duct performs final urine concentration under ADH influence, maintaining osmotic homeostasis efficiently.

Fill in the Blanks Question
9. The hormone _______ regulates water reabsorption in distal convoluted tubule and collecting duct.
1. Aldosterone
2. ADH
3. Insulin
4. Cortisol
Explanation: The correct answer is ADH (Antidiuretic Hormone). Secreted by the posterior pituitary, ADH increases water permeability of nephron tubules, conserving water during dehydration. It controls urine concentration and helps maintain osmolarity, demonstrating the role of hormonal control in renal physiology.

Choose the Correct Statements Question
10. Statement I: The ascending limb of loop of Henle is impermeable to water.
Statement II: It allows active reabsorption of Na+ and Cl− ions.
1. Both statements are correct
2. Both statements are incorrect
3. Statement I is correct, II is incorrect
4. Statement I is incorrect, II is correct
Explanation: Both statements are correct. The ascending limb of loop of Henle actively transports Na+ and Cl− ions into medullary interstitium but remains impermeable to water, facilitating the counter-current mechanism that concentrates urine and regulates water balance in the body.

Topic: Structure and Function of Nephron; Subtopic: Juxta-medullary Nephron and Urine Concentration Mechanism

Keyword Definitions:
• Nephron: Functional unit of kidney responsible for filtration, reabsorption, and secretion.
• Juxta-medullary nephron: Type of nephron with long Loop of Henle extending deep into the medulla.
• Loop of Henle: U-shaped tubular part that concentrates urine by counter-current mechanism.
• Medulla: Inner region of kidney containing pyramids and collecting ducts.
• Counter-current mechanism: Process that maintains osmotic gradient in the kidney medulla.

Lead Question - 2024
Choose the correct statement given below regarding juxta-medullary nephron:
(1) Renal corpuscle of juxta-medullary nephron lies in the outer portion of the medulla.
(2) Loop of Henle of juxta-medullary nephron runs deep into medulla.
(3) Juxta-medullary nephrons outnumber the cortical nephrons.
(4) Juxta-medullary nephrons are located in the columns of Bertini.

Explanation:
The Loop of Henle of juxta-medullary nephron runs deep into the medulla, enabling urine concentration. These nephrons constitute about 15% of total nephrons and play a vital role in water conservation through the counter-current mechanism. Their renal corpuscles are near the corticomedullary junction. Hence, option (2) is correct.

1. Which structure in juxta-medullary nephron helps in maintaining osmotic gradient?
(1) Bowman’s capsule
(2) Collecting duct
(3) Loop of Henle
(4) Distal convoluted tubule

Explanation:
The Loop of Henle of juxta-medullary nephron plays a critical role in maintaining osmotic gradient through counter-current multiplication. Its long descending and ascending limbs allow differential permeability to water and ions, ensuring hyperosmotic urine formation. This mechanism is vital for water balance and kidney efficiency. Hence, option (3) is correct.

2. Which of the following statements correctly differentiates cortical and juxta-medullary nephrons?
(1) Cortical nephrons have longer loops of Henle.
(2) Juxta-medullary nephrons have shorter loops of Henle.
(3) Cortical nephrons have shorter loops, while juxta-medullary nephrons have longer loops.
(4) Both have equal length loops.

Explanation:
Cortical nephrons have short loops of Henle extending slightly into the medulla, while juxta-medullary nephrons have long loops extending deep into the medulla. This structural difference allows juxta-medullary nephrons to concentrate urine efficiently. Therefore, option (3) is correct.

3. The counter-current mechanism in the kidney operates between:
(1) Afferent arteriole and glomerulus
(2) Descending limb and ascending limb of Loop of Henle
(3) Bowman’s capsule and collecting duct
(4) Distal and proximal convoluted tubules

Explanation:
The counter-current mechanism functions between the descending and ascending limbs of the Loop of Henle and between vasa recta and Loop of Henle. This mechanism maintains a concentration gradient for reabsorption of water, aiding urine concentration. Hence, option (2) is correct.

4. The vasa recta in juxta-medullary nephrons:
(1) Absorbs glucose
(2) Participates in counter-current exchange
(3) Filters blood plasma
(4) Secretes ADH

Explanation:
The vasa recta, a capillary network around the Loop of Henle in juxta-medullary nephrons, plays a major role in the counter-current exchange mechanism. It helps maintain medullary osmotic gradient by exchanging water and solutes, ensuring concentrated urine formation. Hence, option (2) is correct.

5. Which of the following parts of the nephron is impermeable to water?
(1) Descending limb of Henle’s loop
(2) Ascending limb of Henle’s loop
(3) Collecting duct
(4) Proximal convoluted tubule

Explanation:
The ascending limb of Henle’s loop is impermeable to water but allows sodium and chloride ions to diffuse, contributing to the medullary osmotic gradient. This feature aids in water reabsorption from descending limb and collecting duct. Thus, option (2) is correct.

6. ADH acts on which part of the nephron to increase water reabsorption?
(1) Proximal tubule
(2) Loop of Henle
(3) Distal convoluted tubule and collecting duct
(4) Bowman’s capsule

Explanation:
Antidiuretic hormone (ADH) acts mainly on the distal convoluted tubule and collecting duct, increasing their permeability to water. This leads to more water reabsorption, concentrating urine during dehydration. Therefore, option (3) is correct.

Assertion-Reason Question
7. Assertion (A): Juxta-medullary nephrons help in producing concentrated urine.
Reason (R): Their long loops of Henle extend deep into the renal medulla.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.

Explanation:
Both the assertion and reason are true. The juxta-medullary nephrons have long loops of Henle extending deep into the medulla, creating a high osmotic gradient. This enables the kidney to produce concentrated urine through counter-current mechanisms. Hence, option (1) is correct.

Matching Type Question
8. Match the following:
A. Loop of Henle – (i) Reabsorption of NaCl
B. Collecting duct – (ii) Action of ADH
C. Vasa recta – (iii) Counter-current exchange
D. Bowman’s capsule – (iv) Filtration of blood

(1) A-i, B-ii, C-iii, D-iv
(2) A-iii, B-i, C-ii, D-iv
(3) A-i, B-iii, C-ii, D-iv
(4) A-ii, B-iv, C-i, D-iii

Explanation:
Loop of Henle reabsorbs NaCl; collecting duct responds to ADH; vasa recta facilitates counter-current exchange; and Bowman’s capsule performs filtration. These sequentially maintain fluid balance and urine concentration. Therefore, option (1) is correct.

Fill in the Blanks Question
9. The descending limb of Henle’s loop is permeable to ______ but impermeable to ______.
(1) Na⁺, Cl⁻
(2) Water, NaCl
(3) Glucose, Water
(4) Urea, Na⁺

Explanation:
The descending limb of Henle’s loop is permeable to water but impermeable to NaCl. This allows water reabsorption into the medullary interstitium, aiding urine concentration. Hence, option (2) is correct.

Choose the Correct Statements Question
10. Statement I: Cortical nephrons have a short Loop of Henle.
Statement II: Juxta-medullary nephrons have a long Loop of Henle that helps in concentration of urine.
(1) Both statements I and II are true.
(2) Both statements I and II are false.
(3) Statement I is true, Statement II is false.
(4) Statement I is false, Statement II is true.

Explanation:
Both statements are true. Cortical nephrons have shorter loops aiding limited concentration, whereas juxta-medullary nephrons have long loops of Henle extending deep into the medulla, enabling the kidney to conserve water and concentrate urine effectively. Hence, option (1) is correct.

Topic: Structure and Function of Nephron; Subtopic: Counter Current Mechanism and Tubular Reabsorption

Keyword Definitions:
• Nephron: Functional unit of the kidney responsible for urine formation through filtration, reabsorption, and secretion.
• Loop of Henle: U-shaped part of nephron important in concentrating urine through counter current mechanism.
• Descending Limb: Permeable to water but impermeable to electrolytes, allowing water reabsorption.
• Proximal Convoluted Tubule (PCT): First tubular part of nephron lined by brush border cells aiding reabsorption.
• Counter Current Mechanism: System that maintains osmotic gradient in the renal medulla aiding water reabsorption.

Lead Question – 2024
Given below are two statements:

Statement I: In the nephron, the descending limb of loop of Henle is impermeable to water and permeable to electrolytes.
Statement II: The proximal convoluted tubule is lined by simple columnar brush border epithelium and increases the surface area for reabsorption.

Choose the correct answer from the options given below:
(1) Both Statement I and Statement II are false
(2) Statement I is true but Statement II is false
(3) Statement I is false but Statement II is true
(4) Both Statement I and Statement II are true

Explanation: The correct answer is (3) Statement I is false but Statement II is true. The descending limb of loop of Henle is permeable to water but impermeable to electrolytes, allowing water to move out into the hyperosmotic medulla. The PCT is lined by brush border cuboidal epithelium, which increases the surface area for efficient reabsorption of nutrients and ions.

1. Which part of the nephron is primarily responsible for reabsorption of glucose and amino acids?
(1) Distal convoluted tubule
(2) Proximal convoluted tubule
(3) Loop of Henle
(4) Collecting duct

Explanation: The correct answer is (2) Proximal convoluted tubule. The PCT reabsorbs almost all glucose, amino acids, vitamins, and ions through active and passive transport. Its brush border epithelium provides a large surface area, ensuring about 65% of filtrate is reabsorbed back into the bloodstream effectively.

2. The loop of Henle maintains osmotic gradient in the medulla mainly by:
(1) Active transport of water
(2) Counter current mechanism
(3) Filtration pressure
(4) Osmotic balance of Bowman's capsule

Explanation: The correct answer is (2) Counter current mechanism. The loop of Henle’s descending and ascending limbs run in opposite directions. The descending limb allows water exit while the ascending limb pumps out Na+ and Cl− ions, creating a medullary osmotic gradient essential for concentrating urine.

3. Which of the following is impermeable to water?
(1) Descending limb of loop of Henle
(2) Ascending limb of loop of Henle
(3) Proximal convoluted tubule
(4) Collecting duct

Explanation: The correct answer is (2) Ascending limb of loop of Henle. This segment is impermeable to water but actively transports sodium and chloride ions into the medullary interstitium, increasing osmolarity, while water remains in the lumen, helping to concentrate urine downstream.

4. Which epithelium lines the proximal convoluted tubule?
(1) Simple squamous epithelium
(2) Simple columnar brush border epithelium
(3) Ciliated columnar epithelium
(4) Transitional epithelium

Explanation: The correct answer is (2) Simple columnar brush border epithelium. The microvilli increase surface area for selective reabsorption of solutes and water. Mitochondria-rich cells in PCT provide energy for active transport processes like sodium-potassium exchange and glucose reabsorption.

5. The main function of the loop of Henle is:
(1) Filtration of blood
(2) Active secretion of hydrogen ions
(3) Maintenance of osmotic gradient in medulla
(4) Absorption of glucose

Explanation: The correct answer is (3). The loop of Henle plays a vital role in urine concentration by establishing an osmotic gradient via the counter current mechanism, where descending and ascending limbs exchange solutes and water to facilitate water conservation and concentrated urine formation.

6. Which part of nephron secretes potassium and hydrogen ions into filtrate?
(1) PCT
(2) Loop of Henle
(3) DCT
(4) Bowman's capsule

Explanation: The correct answer is (3) DCT. The distal convoluted tubule actively secretes K+ and H+ ions to maintain ionic and acid-base balance. It also reabsorbs Na+ and water under aldosterone control, fine-tuning the final composition of urine.

7. Assertion–Reason Type:
Assertion (A): Ascending limb of loop of Henle is impermeable to water.
Reason (R): It actively transports NaCl into the medullary interstitium.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true

Explanation: The correct answer is (1). Both statements are true, and R correctly explains A. Active NaCl transport in ascending limb increases medullary osmolarity, helping in water reabsorption from descending limb and collecting duct to produce concentrated urine.

8. Matching Type:
Match the following parts of nephron with their main function:

A. Bowman's capsule — I. Filtration
B. PCT — II. Reabsorption of glucose
C. Loop of Henle — III. Osmotic gradient
D. DCT — IV. Secretion of K+ and H+

(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-IV, D-III
(3) A-IV, B-I, C-II, D-III
(4) A-III, B-IV, C-I, D-II

Explanation: The correct answer is (1). Bowman's capsule filters plasma, PCT reabsorbs glucose and amino acids, Loop of Henle maintains osmotic gradient, and DCT secretes ions for acid-base regulation, collectively ensuring urine formation and homeostasis.

9. Fill in the Blanks:
The counter current system operates between the __________ and the vasa recta to maintain osmotic balance.
(1) PCT
(2) Loop of Henle
(3) DCT
(4) Collecting duct

Explanation: The correct answer is (2) Loop of Henle. Counter current interaction between the loop of Henle and vasa recta maintains medullary osmotic gradient. This mechanism ensures water reabsorption and helps in producing concentrated urine during water conservation.

10. Choose the Correct Statements:
Statement I: The descending limb of loop of Henle allows water reabsorption.
Statement II: The ascending limb is permeable to Na+ and Cl− but not water.
(1) Both I and II are true
(2) Both I and II are false
(3) I is true but II is false
(4) I is false but II is true

Explanation: The correct answer is (1). In nephron physiology, the descending limb allows water to move out passively into medulla, while the ascending limb transports Na+ and Cl− ions but restricts water movement, together aiding urine concentration.

Topic: Excretory System; Subtopic: Renin-Angiotensin Mechanism

Keyword Definitions:

• Renin: An enzyme secreted by juxtaglomerular cells of kidney in response to low blood pressure or sympathetic stimulation.

• Angiotensinogen: A plasma protein produced by liver, converted to Angiotensin I by renin.

• Angiotensin I: An inactive precursor formed from angiotensinogen by renin action.

• Angiotensin II: Active peptide causing vasoconstriction and aldosterone release, increasing blood pressure.

• Aldosterone: Hormone from adrenal cortex that promotes Na+ and water reabsorption in distal tubules.

• Juxtaglomerular Cells (JG Cells): Specialized kidney cells that detect blood pressure and secrete renin.

• Distal Convoluted Tubule: Part of nephron where fine regulation of electrolyte and water reabsorption occurs.

• Glomerular Blood Pressure: Pressure in glomerular capillaries that drives filtration of blood.

• Na+ Reabsorption: Process of sodium ions being absorbed back into blood from filtrate, important for water balance.

• Renin-Angiotensin Mechanism: Hormonal system regulating blood pressure and fluid balance through sequential activation of renin, angiotensin, and aldosterone.

• Sequence: The correct order of physiological events in a process.

Lead Question - 2023 (Manipur):

Arrange the events of Renin-Angiotensin mechanism in correct sequence:

(A) Activation of JG cells and release of renin
(B) Angiotensin II activated release of aldosterone
(C) Fall in glomerular blood pressure
(D) Reabsorption of Na+ and water from distal convoluted tubule
(E) Angiotensinogen is converted to Angiotensin I and then to Angiotensin II

Choose the correct answer from the options given below:

1. (C), (A), (E), (B), (D)
2. (A), (D), (E), (C), (B)
3. (A), (D), (C), (B), (E)
4. (B), (A), (E), (D), (C)

Explanation: The correct sequence is (C), (A), (E), (B), (D). A fall in glomerular blood pressure (C) triggers juxtaglomerular cells to release renin (A). Renin converts angiotensinogen to angiotensin I, then to angiotensin II (E). Angiotensin II stimulates aldosterone release (B), which promotes Na+ and water reabsorption in the distal tubule (D). This sequence restores blood pressure. Each step is interconnected, ensuring fluid-electrolyte balance and maintaining systemic blood pressure, crucial for renal and cardiovascular homeostasis. This mechanism exemplifies a tightly regulated hormonal feedback system in humans.

Guessed NEET UG MCQs:

1. Single Correct Answer MCQ: Which enzyme converts angiotensinogen to angiotensin I?
(A) Renin
(B) Aldosterone
(C) Angiotensinase
(D) ACE
Explanation: The correct answer is Renin. Renin is secreted by juxtaglomerular cells in response to low blood pressure. It catalyzes the conversion of angiotensinogen, produced in the liver, into angiotensin I, which is subsequently converted into active angiotensin II by ACE in lungs. This initiates the hormonal cascade regulating blood pressure and electrolyte balance in humans. The process ensures systemic circulation is maintained.

2. Single Correct Answer MCQ: Which hormone increases Na+ and water reabsorption in distal tubules?
(A) Angiotensin II
(B) Aldosterone
(C) Renin
(D) ADH
Explanation: Aldosterone is the correct answer. Secreted by adrenal cortex under angiotensin II stimulation, it acts on distal convoluted tubules and collecting ducts, enhancing sodium and water reabsorption, increasing blood volume and pressure. This is a critical component of the renin-angiotensin-aldosterone system. It maintains electrolyte homeostasis and prevents hypotension, ensuring proper kidney function and systemic fluid balance in the human body.

3. Single Correct Answer MCQ: Which peptide causes vasoconstriction and stimulates aldosterone release?
(A) Angiotensin I
(B) Angiotensin II
(C) Renin
(D) Natriuretic peptide
Explanation: Angiotensin II is correct. It is generated from angiotensin I by ACE. Angiotensin II constricts blood vessels, increasing systemic vascular resistance, and stimulates aldosterone secretion from adrenal cortex. This dual effect elevates blood pressure and promotes Na+ and water retention. It is central to the renin-angiotensin system, critical for maintaining homeostasis during hypotension or dehydration, ensuring effective circulatory perfusion.

4. Single Correct Answer MCQ: What triggers renin release from JG cells?
(A) High blood pressure
(B) Fall in glomerular blood pressure
(C) Increased Na+ intake
(D) Angiotensin II levels
Explanation: Fall in glomerular blood pressure is correct. Juxtaglomerular cells sense reduced perfusion and respond by releasing renin. This enzyme converts angiotensinogen to angiotensin I, continuing the renin-angiotensin cascade. This feedback mechanism corrects hypotension, restores blood volume and pressure, and ensures kidney filtration function remains optimal. The system exemplifies the body's precise regulation of circulatory homeostasis and electrolyte balance.

5. Single Correct Answer MCQ: Which organ produces angiotensinogen?
(A) Kidney
(B) Liver
(C) Adrenal gland
(D) Lungs
Explanation: The liver is correct. Angiotensinogen is synthesized by hepatocytes and released into circulation. It serves as the substrate for renin, which converts it to angiotensin I, later forming angiotensin II. This precursor is vital for the renin-angiotensin system, regulating blood pressure and sodium-water balance. Without angiotensinogen, renin’s effect on systemic circulation and renal perfusion would be impaired, disrupting homeostasis.

6. Single Correct Answer MCQ: Which enzyme converts angiotensin I to angiotensin II?
(A) Renin
(B) ACE
(C) Aldosterone
(D) Reninase
Explanation: ACE (Angiotensin-Converting Enzyme) is correct. Present in lung endothelium, ACE cleaves angiotensin I to angiotensin II, a potent vasoconstrictor and aldosterone stimulator. This step is essential for elevating blood pressure and enhancing Na+ and water reabsorption. ACE inhibitors block this, reducing hypertension. The enzyme’s activity ensures effective renal and cardiovascular homeostasis in humans.

7. Assertion-Reason MCQ:
Assertion (A): Angiotensin II increases systemic blood pressure.
Reason (R): It causes vasoconstriction and aldosterone release.
(A) Both A and R are true, and R is the correct explanation of A
(B) Both A and R are true, but R is not the correct explanation of A
(C) A is true, R is false
(D) A is false, R is true
Explanation: Option (A) is correct. Angiotensin II elevates systemic blood pressure by constricting arterioles and stimulating aldosterone release, which enhances Na+ and water reabsorption. This combination increases blood volume and vascular resistance. Both assertion and reason are true, and the reason correctly explains the mechanism by which blood pressure is raised. This highlights the physiological feedback in renin-angiotensin-aldosterone system.

8. Matching Type MCQ: Match the following:
1. Renin    A. Vasoconstriction
2. Angiotensin II    B. Converts angiotensinogen to angiotensin I
3. Aldosterone    C. Increases Na+ reabsorption
(A) 1-B, 2-A, 3-C
(B) 1-C, 2-B, 3-A
(C) 1-A, 2-B, 3-C
(D) 1-B, 2-C, 3-A
Explanation: Correct option is 1-B, 2-A, 3-C. Renin catalyzes angiotensinogen to angiotensin I, angiotensin II induces vasoconstriction and aldosterone release, and aldosterone promotes Na+ and water reabsorption in distal tubules. This precise matching illustrates the sequential physiological events in the renin-angiotensin-aldosterone system, maintaining blood pressure and fluid-electrolyte homeostasis.

9. Fill in the Blanks / Completion MCQ: ___________ cells detect low glomerular pressure and release renin.
(A) Podocytes
(B) Juxtaglomerular
(C) Macula densa
(D) Mesangial
Explanation: Juxtaglomerular cells is correct. These specialized cells of the kidney sense reduced glomerular perfusion or low blood pressure and respond by secreting renin. This initiates the renin-angiotensin cascade, ultimately increasing blood volume and pressure. The system provides rapid, effective feedback control of renal perfusion and electrolyte balance, critical for cardiovascular and renal stability in the body.

10. Choose the correct statements MCQ:
Statement I: Angiotensin II stimulates aldosterone secretion.
Statement II: Aldosterone promotes Na+ and water reabsorption in distal tubule.
(A) Both I and II are correct
(B) Only I is correct
(C) Only II is correct
(D) Neither I nor II is correct
Explanation: Option (A) is correct. Angiotensin II, produced from angiotensin I by ACE, stimulates aldosterone release from the adrenal cortex. Aldosterone acts on distal tubules, increasing Na+ and water reabsorption, raising blood volume and pressure. Both statements are accurate, representing essential steps of renin-angiotensin-aldosterone mechanism, demonstrating the integrated control of renal and cardiovascular homeostasis in humans.

Topic: Excretion and Osmoregulation; Subtopic: Excretory Structures in Animals

Keyword Definitions:
• Contractile vacuole: A cell organelle that expels excess water from unicellular organisms to maintain osmotic balance.
• Water vascular system: A network of fluid-filled canals in echinoderms used for locomotion and circulation.
• Canal system: System of canals in sponges facilitating water flow and nutrient distribution.
• Flame cells: Specialized excretory cells in flatworms that remove metabolic waste.
• Osmoregulation: The process by which organisms maintain water and solute balance.

Lead Question - 2023 (Manipur)
Match List - I with List - II
List-I List-II
(A) Contractile vacuole (I) Asterias
(B) Water vascular system (II) Amoeba
(C) Canal system (III) Spongilla
(D) Flame cells (IV) Taenia
Choose the correct answer from the options given below:
1. (IV) (II) (I) (III)
2. (I) (III) (II) (IV)
3. (III) (II) (I) (IV)
4. (II) (I) (III) (IV)

Explanation:
The contractile vacuole in Amoeba expels excess water to maintain osmotic balance (A-II). The water vascular system in Asterias facilitates locomotion and circulation (B-I). The canal system in Spongilla allows water flow and nutrient distribution (C-III). Flame cells in Taenia remove metabolic wastes efficiently (D-IV). This systematic correlation of excretory and locomotory structures across organisms highlights their adaptation to respective habitats. Hence, the correct answer is option 4.

1. Which structure in Paramecium helps in osmoregulation?
1. Cilia
2. Contractile vacuole
3. Nucleus
4. Pellicle

Explanation:
The contractile vacuole in Paramecium accumulates excess water and expels it out of the cell to prevent bursting due to osmotic pressure. This organelle is crucial for maintaining intracellular water balance in freshwater unicellular organisms. Hence, option 2 is correct.

2. Water vascular system is characteristic of:
1. Annelida
2. Arthropoda
3. Echinodermata
4. Mollusca

Explanation:
The water vascular system is a unique feature of echinoderms, like starfish and sea urchins. It consists of canals and tube feet that aid in locomotion, feeding, and respiration. This hydrostatic system distinguishes echinoderms from other invertebrates. Hence, option 3 is correct.

3. Flame cells are found in:
1. Annelids
2. Platyhelminthes
3. Nematodes
4. Molluscs

Explanation:
Flame cells

are specialized excretory cells found in flatworms (Platyhelminthes) such as Taenia. They function in osmoregulation and excretion by filtering metabolic wastes. The flickering cilia resemble flames, aiding water movement through tubules. Hence, option 2 is correct.

4. Canal system in sponges helps in:

1. Reproduction

2. Digestion

3. Circulation of water and nutrients

4. Locomotion

Explanation:

The canal system in sponges (Spongilla) allows continuous flow of water, bringing oxygen and nutrients while removing wastes. Choanocytes and pores in this system facilitate circulation, feeding, and respiration. Thus, it is essential for sponge survival. Hence, option 3 is correct.

5. Single Correct Answer:

The main function of contractile vacuole is:

1. Nutrition

2. Osmoregulation

3. Respiration

4. Locomotion

Explanation:

The contractile vacuole collects excess water entering by osmosis and periodically expels it from unicellular organisms, maintaining water balance. It does not participate in nutrition, respiration, or locomotion. Hence, option 2 is correct.

6. Which animal possesses both a canal system and spicules?

1. Taenia

2. Spongilla

3. Asterias

4. Amoeba

Explanation:

Spongilla, a freshwater sponge, has a canal system for water circulation and spicules that provide structural support. This combination aids in filtration, nutrient transport, and protection. Hence, option 2 is correct.

7. Assertion-Reason:

Assertion (A): Starfish moves using tube feet.

Reason (R): Tube feet are part of the water vascular system that operates via hydraulic pressure.

1. Both A and R are true and R explains A

2. Both A and R are true but R does not explain A

3. A is true but R is false

4. Both A and R are false

Explanation:

The tube feet of starfish, powered by the water vascular system, enable locomotion through hydraulic pressure. This explains the assertion perfectly. Hence, option 1 is correct.

8. Matching Type:

Match the excretory structure with its organism.

A. Malpighian tubules — (i) Cockroach

B. Nephridia — (ii) Earthworm

C. Flame cells — (iii) Taenia

D. Contractile vacuole — (iv) Amoeba

1. A-(i), B-(ii), C-(iii), D-(iv)

2. A-(ii), B-(iii), C-(iv), D-(i)

3. A-(iii), B-(iv), C-(i), D-(ii)

4. A-(iv), B-(i), C-(ii), D-(iii)

Explanation:

Malpighian tubules in cockroach (A-i), nephridia in earthworm (B-ii), flame cells in Taenia (C-iii), and contractile vacuole in Amoeba (D-iv) are their respective excretory structures. These adaptations help each organism maintain osmotic balance and remove wastes efficiently. Hence, option 1 is correct.

9. Fill in the blanks:

The __________ system of starfish helps in locomotion and food handling.

1. Excretory

2. Water vascular

3. Digestive

4. Respiratory

Explanation:

The water vascular system of starfish uses hydraulic pressure in tube feet for locomotion, attachment, and food handling. It is integral to movement and predation. Hence, option 2 is correct.

10. Choose the correct statements:

Statement I: Flame cells are specialized excretory cells in flatworms.

Statement II: Contractile vacuoles are found in multicellular animals.

1. Both statements are true

2. Statement I is true, Statement II is false

3. Statement I is false, Statement II is true

4. Both statements are false

Explanation:

Flame cells exist in flatworms to remove metabolic wastes (Statement I is true). Contractile vacuoles are found in unicellular organisms like Amoeba, not multicellular animals (Statement II is false). Hence, option 2 is correct. 

Topic: Types of Nitrogenous Wastes; Subtopic: Excretory Nature of Arthropods (Cockroach)

Keyword Definitions:

• Ammonotelic: Organisms that excrete nitrogenous waste primarily as ammonia, e.g., most aquatic animals.

• Ureotelic: Animals that excrete urea as the main nitrogenous waste, e.g., mammals, amphibians.

• Uricotelic: Organisms that excrete uric acid, conserving water efficiently, e.g., birds, reptiles, and insects like cockroaches.

• Malpighian Tubules: Excretory structures in insects that remove nitrogenous wastes as uric acid.

Lead Question – 2023 (Manipur)

The Cockroach is:
1. Ammonotelic only
2. Uricotelic only
3. Ureotelic only
4. Ureotelic and Uricotelic

Explanation:
Cockroaches are uricotelic organisms. Their excretory system, consisting of Malpighian tubules, converts nitrogenous waste into uric acid, which is insoluble and conserves water effectively. This adaptation suits terrestrial life by minimizing water loss. Uric acid is eliminated along with fecal matter, thus maintaining osmotic balance. Hence, option 2 is correct.

1. Which of the following organisms is ammonotelic?
1. Frog
2. Human
3. Fish
4. Lizard

Explanation:
Ammonotelic animals excrete nitrogen as ammonia, a highly toxic but easily diffusible compound. Aquatic animals like fish directly release ammonia into surrounding water due to its solubility. This mode of excretion is efficient in aquatic environments but unsuitable for terrestrial life. Hence, option 3 is correct.

2. Which excretory organ is present in cockroach?
1. Flame cells
2. Nephridia
3. Malpighian tubules
4. Kidneys

Explanation:
Cockroaches possess Malpighian tubules that function as excretory organs. These slender tubular structures absorb nitrogenous wastes and convert them into uric acid. The uric acid is then expelled along with feces through the hindgut. This adaptation reduces water loss. Hence, option 3 is correct.

3. Which of the following pairs is correctly matched?
1. Earthworm – Flame cells
2. Cockroach – Nephridia
3. Human – Malpighian tubules
4. Cockroach – Uricotelic

Explanation:
Cockroach is a uricotelic insect that excretes uric acid through Malpighian tubules. These tubules absorb wastes from the hemolymph and discharge them into the gut. This mechanism conserves water efficiently. Hence, option 4 is correct.

4. In which form do reptiles excrete nitrogenous waste?
1. Ammonia
2. Urea
3. Uric acid
4. Creatinine

Explanation:
Reptiles are uricotelic animals that excrete nitrogenous waste as uric acid. Uric acid is insoluble in water and precipitates as crystals, minimizing water loss. This adaptation allows reptiles to survive in dry terrestrial environments. Hence, option 3 is correct.

5. Which excretory substance requires the least amount of water for elimination?
1. Ammonia
2. Urea
3. Uric acid
4. Creatinine

Explanation:
Uric acid is the least soluble form of nitrogenous waste and thus requires minimal water for excretion. It is advantageous for terrestrial animals, especially insects, birds, and reptiles. Ammonia needs maximum water, while urea requires an intermediate amount. Hence, option 3 is correct.

6. Which of the following statements about Malpighian tubules is true?
1. Found in mammals
2. Help in water reabsorption
3. Found in insects for excretion
4. Secrete digestive enzymes

Explanation:
Malpighian tubules are slender excretory organs found in insects like cockroaches. They collect nitrogenous wastes from hemolymph, convert them into uric acid, and discharge them into the gut for elimination. They play a vital role in osmoregulation. Hence, option 3 is correct.

7. Assertion (A): Cockroach excretes nitrogenous waste as uric acid.
Reason (R): It helps in water conservation during excretion.
1. Both (A) and (R) are true and (R) correctly explains (A)
2. Both (A) and (R) are true but (R) is not correct explanation
3. (A) is true, (R) is false
4. (A) is false, (R) is true

Explanation:
Cockroach excretes uric acid due to its terrestrial habitat, conserving water effectively. Uric acid is insoluble and excreted as a solid paste, minimizing fluid loss. Both statements are true, and (R) correctly explains (A). Hence, option 1 is correct.

8. Match the following animals with their type of excretion:
A. Fish — 1. Uricotelic
B. Human — 2. Ammonotelic
C. Bird — 3. Ureotelic

1. A-2, B-3, C-1
2. A-3, B-1, C-2
3. A-1, B-2, C-3
4. A-2, B-1, C-3

Explanation:
Fish are ammonotelic, excreting ammonia directly. Humans are ureotelic, excreting urea via kidneys, and birds are uricotelic, conserving water by excreting uric acid. Thus, the correct matching is A-2, B-3, C-1. Hence, option 1 is correct.

9. Fill in the blank: The main excretory product of cockroach is _______.
1. Ammonia
2. Urea
3. Uric acid
4. Creatinine

Explanation:
Cockroaches excrete nitrogen mainly in the form of uric acid, making them uricotelic. Uric acid being water-insoluble prevents excessive water loss, an adaptation crucial for terrestrial insects. Hence, option 3 is correct.

10. Choose the correct statements:
Statement I: Malpighian tubules in cockroach perform both excretion and osmoregulation.
Statement II: Cockroaches excrete urea as their main waste product.
1. Both I and II are correct
2. Both I and II are incorrect
3. I is correct, II is incorrect
4. I is incorrect, II is correct

Explanation:
Malpighian tubules of cockroach perform both excretory and osmoregulatory functions by removing wastes and balancing ions. However, the main excretory product is uric acid, not urea. Thus, Statement I is correct and Statement II is incorrect. Hence, option 3 is correct.

Topic: Mechanism of Urine Formation; Subtopic: Counter-Current Mechanism in Loop of Henle

Keyword Definitions:

• Loop of Henle: U-shaped portion of the nephron responsible for concentration and dilution of urine.

• Ascending Limb: The segment impermeable to water, which actively transports Na+ and Cl− ions.

• Medullary Osmotic Gradient: The difference in solute concentration between cortex and medulla that helps concentrate urine.

• Counter-Current Mechanism: Process maintaining high osmolarity in medulla by opposite flow of filtrate and blood.

Lead Question - 2023 (Manipur)

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R)

Assertion (A): Ascending limb of the loop of Henle is impermeable to water and allows transport of electrolytes actively or passively.
Reason (R): Dilution of filtrate takes place due to efflux of electrolytes in the medullary fluid.

In light of the above statements, choose the correct answer from the options given below:
1. (A) is True, (R) is False
2. (A) is False, (R) is True
3. Both (A) and (R) are True and (R) is the correct explanation of (A)
4. Both (A) and (R) are True but (R) is not the correct explanation of (A)

Explanation:
Both statements are true, and the Reason correctly explains the Assertion. The ascending limb of the loop of Henle is impermeable to water but allows active reabsorption of Na+ and Cl−. This movement of electrolytes into the medullary fluid leads to dilution of the filtrate. Hence, option 3 is correct.

1. The descending limb of the loop of Henle is permeable to:
1. Water only
2. NaCl only
3. Both water and NaCl
4. Neither water nor NaCl

Explanation:
The descending limb of Henle’s loop allows only water to pass through due to aquaporin channels but is impermeable to solutes like NaCl. As water exits, filtrate becomes hypertonic toward the medulla. This selective permeability maintains osmotic balance essential for urine concentration. Hence, option 1 is correct.

2. The counter-current multiplier system operates between:
1. Bowman’s capsule and collecting duct
2. Descending and ascending limbs of Henle’s loop
3. Proximal and distal convoluted tubules
4. Loop of Henle and vasa recta

Explanation:
The counter-current multiplier works between the descending and ascending limbs of Henle’s loop. The descending limb loses water while the ascending limb actively transports ions, creating an osmotic gradient. This mechanism is vital for concentrating urine in the renal medulla. Hence, option 2 is correct.

3. Which hormone increases water reabsorption from the distal tubule and collecting duct?
1. Aldosterone
2. Antidiuretic hormone (ADH)
3. Renin
4. Erythropoietin

Explanation:
Antidiuretic hormone (ADH), secreted by the posterior pituitary, enhances water reabsorption in the distal tubule and collecting duct by increasing aquaporin channels. This conserves body water and concentrates urine. Its release is triggered by dehydration or increased plasma osmolarity. Hence, option 2 is correct.

4. Which part of the nephron actively transports Na+ but is impermeable to water?
1. Proximal convoluted tubule
2. Descending limb
3. Ascending limb
4. Collecting duct

Explanation:
The ascending limb of Henle’s loop actively reabsorbs Na+ and Cl− ions into the interstitial fluid but is impermeable to water. This creates a hypertonic medullary interstitium that drives water reabsorption in other nephron parts. Hence, option 3 is correct.

5. Which of the following is not a function of the kidneys?
1. Osmoregulation
2. Detoxification of blood
3. Regulation of blood pressure
4. Secretion of digestive enzymes

Explanation:
Kidneys regulate osmotic balance, remove nitrogenous wastes, control blood pressure via renin release, and secrete erythropoietin. However, secretion of digestive enzymes occurs in glands of the gastrointestinal tract, not in the kidneys. Hence, option 4 is correct.

6. Match the following parts of the nephron with their primary functions:

A. Proximal Convoluted Tubule — 1. Active ion transport
B. Loop of Henle — 2. Concentration of urine
C. Distal Convoluted Tubule — 3. Reabsorption of nutrients

1. A-3, B-2, C-1
2. A-1, B-3, C-2
3. A-2, B-1, C-3
4. A-3, B-1, C-2

Explanation:
Proximal Convoluted Tubule reabsorbs glucose, amino acids, and ions. Loop of Henle helps in urine concentration by counter-current action. Distal Convoluted Tubule fine-tunes ion reabsorption by active transport under hormonal control. Hence, the correct matching is A-3, B-2, C-1. Option 1 is correct.

7. Assertion (A): Aldosterone increases Na+ reabsorption in the distal tubule.
Reason (R): It helps increase water reabsorption indirectly by osmotic effect.
1. Both (A) and (R) are true and (R) correctly explains (A)
2. Both (A) and (R) are true but (R) is not correct explanation
3. (A) is true, (R) is false
4. (A) is false, (R) is true

Explanation:
Aldosterone acts on the distal tubule and collecting duct, enhancing Na+ reabsorption. The osmotic effect of sodium retention promotes passive water reabsorption, maintaining volume and pressure. Both statements are true and (R) correctly explains (A). Hence, option 1 is correct.

8. Fill in the blank: The functional unit of the kidney is _______.
1. Nephron
2. Glomerulus
3. Collecting duct
4. Loop of Henle

Explanation:
The nephron is the structural and functional unit of the kidney, performing filtration, reabsorption, and secretion. Each kidney contains about one million nephrons, ensuring removal of waste and maintenance of fluid balance. Hence, option 1 is correct.

9. Choose the correct statements:
Statement I: Filtration occurs in Bowman’s capsule.
Statement II: Tubular reabsorption occurs in the distal tubule only.
1. Both I and II are correct
2. Both I and II are incorrect
3. I is correct, II is incorrect
4. I is incorrect, II is correct

Explanation:
Filtration of blood occurs in Bowman’s capsule through the glomerular membrane, forming filtrate. Tubular reabsorption occurs mainly in the proximal tubule and partly in other nephron segments, not just the distal tubule. Hence, Statement I is correct and II is incorrect. Option 3 is correct.

10. Which part of nephron plays a major role in counter-current exchange?
1. Vasa recta
2. Distal convoluted tubule
3. Bowman’s capsule
4. Collecting duct

Explanation:
Vasa recta, the capillary network surrounding the loop of Henle, facilitates counter-current exchange of solutes and water, maintaining medullary osmotic gradient. It prevents washout of solutes while ensuring efficient reabsorption. This sustains concentrated urine formation. Hence, option 1 is correct.

Topic: Regulation of Kidney Function; Subtopic: Role of Hormones in Urine Formation

Keyword Definitions:

• ADH (Antidiuretic Hormone): A hormone secreted by the posterior pituitary that promotes water reabsorption in kidney tubules.

• ANF (Atrial Natriuretic Factor): A hormone from the atria of the heart causing vasodilation and promoting sodium excretion.

• Osmoreceptors: Specialized hypothalamic receptors detecting blood osmolarity changes, regulating thirst and ADH secretion.

• GFR (Glomerular Filtration Rate): The rate at which plasma is filtered by the glomeruli per minute, reflecting kidney function.

Lead Question - 2023
Which of the following statements are correct?
A. An excessive loss of body fluid from the body switches off osmoreceptors
B. ADH facilitates water reabsorption to prevent diuresis.
C. ANF causes vasodilation
D. ADH causes increase in blood pressure
E. ADH is responsible for decrease in GFR.
Choose the correct answer from the options given below:
(1) A, B and E only
(2) C, D and E only
(3) A and B only
(4) B, C and D only

Explanation: ADH (vasopressin) increases water reabsorption from distal tubules and collecting ducts, preventing diuresis and raising blood pressure. ANF, secreted by the atria, induces vasodilation and decreases renin release, counteracting ADH. Osmoreceptors activate when water loss occurs, not deactivate. GFR rises under ADH influence. Hence, correct answer is (4) B, C and D only.

1. Which hormone primarily regulates water reabsorption in kidney tubules?
(1) Aldosterone
(2) Cortisol
(3) ADH
(4) ANF
Explanation: ADH increases permeability of distal tubules and collecting ducts, enhancing water reabsorption and maintaining osmotic balance. It acts via aquaporin-2 channels, reducing urine volume and preventing dehydration. Released from the posterior pituitary when osmolarity rises, ADH helps restore fluid balance and normal blood pressure. Hence, correct answer is (3) ADH.

2. Which of the following hormones causes vasodilation and reduces blood pressure?
(1) ADH
(2) Renin
(3) ANF
(4) Angiotensin II
Explanation: ANF (Atrial Natriuretic Factor) is secreted by the atria in response to high blood volume. It promotes vasodilation, increases sodium and water excretion, and decreases blood pressure. It acts antagonistically to the renin-angiotensin-aldosterone system. Thus, the correct answer is (3) ANF, as it relaxes vascular smooth muscles and reduces cardiac workload.

3. Which part of the nephron is directly affected by ADH for water reabsorption?
(1) Proximal convoluted tubule
(2) Loop of Henle
(3) Distal convoluted tubule and collecting duct
(4) Glomerulus
Explanation: ADH targets the distal convoluted tubule and collecting duct, inserting aquaporin-2 channels into their membranes to enhance water permeability. This process concentrates urine and conserves body water. Proximal reabsorption is independent of ADH, whereas ADH acts on the later nephron parts. Hence, the correct answer is (3) Distal convoluted tubule and collecting duct.

4. Which condition triggers ADH release from the posterior pituitary?
(1) Low blood osmolarity
(2) High water intake
(3) Dehydration and increased osmolarity
(4) Low sodium concentration
Explanation: ADH is released when plasma osmolarity increases, typically during dehydration. Osmoreceptors in the hypothalamus sense this rise and signal the posterior pituitary to release ADH, promoting renal water reabsorption and restoring osmotic balance. Thus, ADH secretion increases during dehydration, making the correct answer (3) Dehydration and increased osmolarity.

5. Which hormone reduces the release of renin from the juxtaglomerular apparatus?
(1) ANF
(2) ADH
(3) Aldosterone
(4) Angiotensin II
Explanation: ANF inhibits renin release from juxtaglomerular cells, thus blocking the renin-angiotensin-aldosterone pathway. This action leads to decreased sodium reabsorption and reduced blood volume and pressure. By opposing aldosterone and angiotensin II, ANF maintains cardiovascular homeostasis. Therefore, the correct answer is (1) ANF.

6. Which of the following increases GFR by causing afferent arteriole dilation?
(1) ANF
(2) ADH
(3) Aldosterone
(4) Angiotensin II
Explanation: ANF dilates afferent arterioles and constricts efferent arterioles, increasing glomerular capillary pressure and enhancing GFR. This allows more filtration of sodium and water, promoting diuresis. Angiotensin II, by contrast, reduces GFR via vasoconstriction. Hence, the correct answer is (1) ANF, which elevates GFR to excrete excess fluid.

Assertion-Reason Question
7. Assertion (A): ADH increases urine concentration.
Reason (R): ADH enhances sodium reabsorption in distal tubules.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true but R is false.
(4) A is false but R is true.
Explanation: ADH increases urine concentration by promoting water, not sodium, reabsorption in distal tubules and collecting ducts. It makes the tubular membrane permeable to water via aquaporins, thus conserving water without affecting sodium directly. Hence, A is true but R is false, so the correct answer is (3).

Matching Type Question
8. Match the following hormones with their functions:
A. ADH — (i) Water reabsorption
B. ANF — (ii) Vasodilation
C. Renin — (iii) Conversion of angiotensinogen to angiotensin I
D. Aldosterone — (iv) Sodium reabsorption
(1) A-(i), B-(ii), C-(iii), D-(iv)
(2) A-(ii), B-(i), C-(iii), D-(iv)
(3) A-(i), B-(iv), C-(ii), D-(iii)
(4) A-(iii), B-(ii), C-(iv), D-(i)
Explanation: ADH controls water reabsorption, ANF induces vasodilation, renin converts angiotensinogen to angiotensin I, and aldosterone promotes sodium reabsorption in distal nephron segments. Together, these maintain fluid balance and blood pressure. Therefore, the correct match is (1) A-(i), B-(ii), C-(iii), D-(iv).

Fill in the Blanks Question
9. __________ hormone is secreted by the heart’s atria and promotes sodium excretion, lowering blood pressure.
(1) Aldosterone
(2) ADH
(3) ANF
(4) Renin
Explanation: ANF (Atrial Natriuretic Factor) is a cardiac hormone released when atrial walls stretch due to increased blood volume. It promotes natriuresis, diuresis, and vasodilation, effectively lowering blood pressure. It antagonizes aldosterone and ADH, ensuring balance in fluid regulation. Correct answer is (3) ANF.

Choose the Correct Statements Question
10. Statement I: ADH increases permeability of collecting ducts to water.
Statement II: ANF enhances water retention and raises blood pressure.
(1) Both statements are true.
(2) Both statements are false.
(3) Statement I is true, Statement II is false.
(4) Statement I is false, Statement II is true.
Explanation: ADH indeed increases the permeability of collecting ducts to water, thereby conserving fluid and concentrating urine. ANF performs the opposite function; it decreases water reabsorption and lowers blood pressure through vasodilation and natriuresis. Thus, Statement I is true, while Statement II is false, making (3) the correct answer.

Topic: Excretory Systems; Subtopic: Types of Excretory Organs in Animals

Lead Question - 2023

Match List I with List II.
List I | List II
A. Taenia | I. Nephridia
B. Paramoecium | II. Contractile vacuole
C. Periplaneta | III. Flame cells
D. Pheretima | IV. Urecose gland
Choose the correct answer from the options given below:
(1) A-III, B-II, C-IV, D-I
(2) A-II, B-I, C-IV, D-III
(3) A-I, B-II, C-III, D-IV
(4) A-I, B-II, C-IV, D-III

Answer: (1) A-III, B-II, C-IV, D-I. In Taenia, excretion occurs through flame cells (protonephridia). Paramoecium uses contractile vacuoles to expel excess water. Periplaneta (cockroach) has urecose glands for excretion, while Pheretima (earthworm) uses nephridia to remove metabolic waste. Each excretory structure is adapted to the habitat and osmotic needs of the organism, ensuring proper removal of nitrogenous wastes and maintenance of internal homeostasis.

Keyword Definitions:

• Taenia: A parasitic flatworm which excretes nitrogenous waste via flame cells.

• Paramoecium: Unicellular ciliate protozoan, uses contractile vacuole to maintain osmotic balance.

• Periplaneta: Cockroach, insect with urecose glands for excretion.

• Pheretima: Earthworm, annelid with nephridia to remove metabolic waste.

• Flame cells: Specialized excretory cells found in flatworms for osmoregulation.

• Contractile vacuole: Organelle that pumps out excess water from protozoans.

• Nephridia: Tubular excretory organ in annelids for nitrogenous waste removal.

• Urecose gland: Excretory structure in insects to remove nitrogenous waste.

1. Single Correct Answer:

Which excretory structure is present in flatworms?
(1) Nephridia
(2) Urecose gland
(3) Flame cells
(4) Contractile vacuole

Answer: (3) Flame cells. Flatworms like Taenia use flame cells for excretion and osmoregulation, expelling nitrogenous wastes and excess water through a network of tubules.

2. Single Correct Answer:

Contractile vacuoles are found in:
(1) Earthworm
(2) Paramoecium
(3) Cockroach
(4) Taenia

Answer: (2) Paramoecium. Contractile vacuoles expel excess water to maintain osmotic balance in freshwater protozoans like Paramoecium, preventing cell lysis.

3. Single Correct Answer:

Nephridia are characteristic of:
(1) Taenia
(2) Paramoecium
(3) Pheretima
(4) Periplaneta

Answer: (3) Pheretima. Earthworms have nephridia for excreting nitrogenous waste, removing urea and other metabolic products while maintaining osmotic balance in soil environments.

4. Single Correct Answer:

Urecose glands are found in:
(1) Paramoecium
(2) Cockroach
(3) Taenia
(4) Earthworm

Answer: (2) Cockroach. Insects like Periplaneta possess urecose glands that eliminate nitrogenous wastes and regulate water balance in the hemolymph.

5. Single Correct Answer:

Flame cells primarily function in:
(1) Digestion
(2) Osmoregulation
(3) Respiration
(4) Locomotion

Answer: (2) Osmoregulation. Flame cells in flatworms regulate water content and excrete nitrogenous wastes, aiding in maintaining internal osmotic balance in freshwater environments.

6. Single Correct Answer:

Which excretory organ helps freshwater protozoans remove excess water?
(1) Nephridia
(2) Flame cells
(3) Contractile vacuole
(4) Urecose gland

Answer: (3) Contractile vacuole. In Paramoecium, contractile vacuoles pump out excess water entering by osmosis to prevent cell swelling and maintain cytoplasmic balance.

7. Assertion-Reason:

Assertion A: Earthworms possess nephridia.
Reason R: Nephridia excrete metabolic wastes in annelids.
(1) A true, R false
(2) A false, R true
(3) Both true, R explains A
(4) Both true, R does not explain A

Answer: (3) Both true, R explains A. Earthworms have nephridia that remove nitrogenous wastes and regulate internal water balance, supporting metabolic homeostasis.

8. Matching Type:

Match animals with their excretory structures:
List I | List II
A. Taenia | I. Flame cells
B. Paramoecium | II. Contractile vacuole
C. Pheretima | III. Nephridia
D. Periplaneta | IV. Urecose gland
Options:
(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-IV, D-III
(3) A-III, B-IV, C-I, D-II
(4) A-IV, B-III, C-II, D-I

Answer: (1) A-I, B-II, C-III, D-IV. Taenia uses flame cells, Paramoecium uses contractile vacuoles, Pheretima has nephridia, and Periplaneta uses urecose glands.

9. Fill in the Blanks:

The excretory organ of cockroach is ________.
Options: (1) Nephridia (2) Flame cells (3) Urecose gland (4) Contractile vacuole

Answer: (3) Urecose gland. Periplaneta utilizes urecose glands to remove nitrogenous wastes and maintain osmotic homeostasis.

Subtopic: Nephron Structure and Types

Keyword Definitions:

• Nephron: Structural and functional unit of the kidney responsible for filtration, reabsorption, and secretion of blood to form urine.

• Cortical Nephron: Nephrons with glomeruli in the outer cortex and short loops of Henle, primarily involved in excretion and reabsorption.

• Juxtamedullary Nephron: Nephrons with glomeruli near the corticomedullary junction and long loops of Henle, important in urine concentration.

• Loop of Henle: U-shaped part of nephron that establishes osmotic gradient in medulla for water reabsorption.

• Cortex: Outer region of kidney containing glomeruli and proximal/distal convoluted tubules.

• Medulla: Inner region of kidney containing loop of Henle and collecting ducts.

• Glomerulus: Capillary tuft where blood filtration occurs.

• Filtration: Process of removing water and solutes from blood into Bowman’s capsule.

• Reabsorption: Movement of essential solutes and water from tubules back into blood.

• Secretion: Active transport of substances from blood to tubular fluid for excretion.

• Osmotic Gradient: Difference in solute concentration that drives water movement in kidney.

Lead Question - 2023:

Given below are statements: One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Nephrons are of two types: Cortical & Juxta medullary, based on their relative position in cortex and medulla.
Reason R: Juxta medullary nephrons have short loop of Henle whereas, cortical nephrons have longer loop of Henle.
In the light of the above statements, choose the correct answer from the options given below:
(1) A is true but R is false
(2) A is false but R is true
(3) Both A and R are true and R is the correct explanation of A.
(4) Both A and R are true but R is NOT the correct explanation of A.

Answer & Explanation: (1) A is true but R is false. Nephrons are correctly classified as cortical and juxtamedullary based on glomerular position in cortex and medulla. However, the loop of Henle in juxtamedullary nephrons is longer, not shorter, to establish a significant osmotic gradient for urine concentration. Cortical nephrons have short loops since their role is mainly filtration and reabsorption with minimal contribution to medullary osmotic gradient. Thus, while the assertion is correct, the reason is incorrect. Proper understanding of nephron types, loop lengths, and their physiological functions clarifies renal excretory mechanisms and adaptation for water conservation in mammals.

1. Which nephron type is primarily responsible for concentrating urine?
(1) Cortical nephron
(2) Juxtamedullary nephron
(3) Both equally
(4) Neither
Explanation: Juxtamedullary nephrons, with long loops of Henle extending deep into the medulla, create a strong osmotic gradient, allowing efficient water reabsorption and urine concentration. Correct answer is (2).

2. Where are glomeruli of cortical nephrons located?
(1) Outer cortex
(2) Medulla
(3) Corticomedullary junction
(4) Renal pelvis
Explanation: Cortical nephrons have glomeruli situated in the outer cortex, enabling short loops of Henle primarily for filtration and reabsorption. Correct answer is (1).

3. What is the main function of the loop of Henle?
(1) Filtration
(2) Secretion
(3) Osmotic gradient formation for water reabsorption
(4) Hormone secretion
Explanation: The loop of Henle establishes a medullary osmotic gradient essential for water reabsorption, facilitating urine concentration. Correct answer is (3).

4. Cortical nephrons have _______ loops of Henle.
(1) Long
(2) Short
(3) Medium
(4) Variable
Explanation: Cortical nephrons possess short loops of Henle because their primary role is filtration and reabsorption rather than establishing a medullary osmotic gradient. Correct answer is (2).

5. Juxtamedullary nephrons are located at:
(1) Outer cortex
(2) Corticomedullary junction
(3) Medulla only
(4) Renal pelvis
Explanation: Juxtamedullary nephrons have glomeruli near the corticomedullary junction, allowing loops of Henle to extend deep into medulla, crucial for water reabsorption. Correct answer is (2).

6. The functional unit of the kidney is:
(1) Bowman’s capsule
(2) Nephron
(3) Glomerulus
(4) Collecting duct
Explanation: Nephron, comprising glomerulus, tubules, and loop of Henle, is the structural and functional unit performing filtration, reabsorption, and secretion. Correct answer is (2).

Assertion-Reason Question
7. Assertion (A): Juxtamedullary nephrons enable water conservation.
Reason (R): They have long loops of Henle extending into medulla.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: Long loops of Henle in juxtamedullary nephrons generate an osmotic gradient for maximal water reabsorption, facilitating water conservation. Both statements are correct, and R explains A. Correct answer is (1).

Matching Type Question
8. Match nephron type with loop of Henle length:
A. Cortical – i. Short
B. Juxtamedullary – ii. Long
(1) A-i, B-ii
(2) A-ii, B-i
(3) Both short
(4) Both long
Explanation: Cortical nephrons have short loops, juxtamedullary nephrons have long loops for establishing medullary osmotic gradient. Correct answer is (1).

Fill in the Blanks Question
9. The nephron segment responsible for filtration of blood is the _______.
(1) Loop of Henle
(2) Bowman’s capsule
(3) Distal tubule
(4) Collecting duct
Explanation: Bowman’s capsule, containing glomerulus, filters blood plasma into nephron to initiate urine formation. Correct answer is (2).

Choose the Correct Statements Question
10. Statement I: Cortical nephrons have short loops of Henle.
Statement II: Juxtamedullary nephrons have long loops extending into medulla.
(1) Only Statement I correct
(2) Only Statement II correct
(3) Both I and II correct
(4) Both I and II incorrect
Explanation: Cortical nephrons possess short loops; juxtamedullary nephrons possess long loops extending into medulla for concentrating urine. Both statements are correct. Correct answer is (3).

Subtopic: Nitrogenous Waste and Terrestrial Adaptations

Keyword Definitions:

• Nitrogenous Wastes: Metabolic waste products formed from the breakdown of proteins and nucleic acids, primarily ammonia, urea, and uric acid.

• Ammonotelic: Animals that excrete nitrogen mainly as ammonia, highly toxic and soluble in water.

• Ureotelic: Animals that excrete nitrogen primarily as urea, less toxic and water-soluble.

• Uricotelic: Animals that excrete nitrogen as uric acid, low toxicity and conserves water.

• Terrestrial Adaptations: Physiological modifications enabling animals to survive in land environments with limited water availability.

Lead Question – 2022 (Abroad)
Terrestrial adaptations necessitated the production of:
1. Highly toxic nitrogenous wastes like urea and uric acid
2. Lesser toxic nitrogenous wastes like urea and uric acid
3. Lesser toxic nitrogenous wastes like ammonia and urea
4. Highly toxic nitrogenous wastes like ammonia and urea

Explanation:
The correct answer is Lesser toxic nitrogenous wastes like urea and uric acid. Terrestrial animals must conserve water while excreting nitrogenous wastes. Ammonia is highly toxic and requires large water volumes for excretion, unsuitable for land habitats. Urea and uric acid are less toxic and can be excreted with minimal water loss. Ureotelic and uricotelic excretion systems represent evolutionary adaptations to terrestrial life, enabling efficient nitrogen elimination without causing toxicity, dehydration, or disturbance in electrolyte balance. These adaptations are crucial for survival in arid and semi-arid environments.

1. Which of the following excretes nitrogen primarily as uric acid?
1. Frog
2. Lizard
3. Fish
4. Amphibian
Explanation: The correct answer is Lizard. Lizards are terrestrial and uricotelic, excreting nitrogen as uric acid, conserving water. Frogs and amphibians excrete mostly ammonia or urea, requiring more water. Fish are ammonotelic. Uricotelic excretion minimizes water loss and toxicity, an essential adaptation for land-dwelling species, maintaining osmotic and nitrogen balance efficiently.

2. Ammonia is highly toxic because:
1. It is insoluble in water
2. It reacts with urea
3. It disrupts acid-base balance and requires dilution
4. It is less soluble
Explanation: Ammonia is highly toxic due to its ability to disturb acid-base balance and nerve function. Ammonotelic animals require large volumes of water to dilute ammonia for excretion. Terrestrial adaptations favor urea or uric acid production, which are less toxic and water-efficient. This explains why land-dwelling animals produce urea or uric acid instead of ammonia.

3. Ureotelic animals primarily excrete nitrogen as:
1. Ammonia
2. Urea
3. Uric acid
4. Nitrate
Explanation: The correct answer is Urea. Ureotelic animals convert ammonia into urea in the liver. Urea is less toxic, water-soluble, and can be excreted with minimal water loss. This adaptation allows terrestrial animals like mammals to conserve water while efficiently eliminating nitrogen, avoiding the high toxicity associated with direct ammonia excretion.

4. Which excretory adaptation minimizes water loss in birds?
1. Ammonotelic
2. Ureotelic
3. Uricotelic
4. Nephrotoxic
Explanation: Uricotelic excretion, as in birds, produces uric acid, a white paste, conserving water. Unlike ammonia or urea, uric acid requires minimal water for excretion. This adaptation enables survival in arid habitats, allowing birds to maintain water balance while effectively eliminating nitrogenous wastes from protein metabolism.

5. Which organ primarily converts ammonia into urea in mammals?
1. Kidney
2. Liver
3. Heart
4. Spleen
Explanation: The correct answer is Liver. In mammals, the liver converts toxic ammonia into less toxic urea via the urea cycle. This process reduces toxicity, conserves water, and facilitates safe nitrogen excretion. Kidneys then excrete urea in urine. This is a key adaptation for terrestrial life.

6. Which nitrogenous waste is most soluble in water?
1. Urea
2. Uric acid
3. Ammonia
4. Creatinine
Explanation: Ammonia is highly soluble in water, facilitating rapid excretion in aquatic animals. Terrestrial animals convert ammonia to urea or uric acid, which are less toxic and can be excreted with minimal water, conserving water for survival on land. Solubility alone is insufficient; toxicity and water availability are critical.

7. Assertion-Reason Type:
Assertion (A): Terrestrial animals excrete urea or uric acid instead of ammonia.
Reason (R): Ammonia is highly toxic and requires large volumes of water for excretion.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Explanation: Correct answer is option 1. Terrestrial adaptations favor production of urea or uric acid to conserve water and reduce toxicity. Ammonia is unsuitable due to high toxicity and the large water volume required for safe excretion, making ureotelism and uricotelism critical evolutionary adaptations for land-dwelling animals.

8. Matching Type:
Match the animal with its excretory product:
A. Frog – (i) Uric acid
B. Lizard – (ii) Urea
C. Fish – (iii) Ammonia
D. Mammal – (iv) Urea
1. A–ii, B–i, C–iii, D–iv
2. A–iii, B–i, C–iii, D–iv
3. A–iv, B–ii, C–iii, D–i
4. A–iii, B–ii, C–i, D–iv
Explanation: Correct answer is option 2. Frogs (amphibians) excrete ammonia in water, lizards produce uric acid, fish excrete ammonia, and mammals excrete urea. These adaptations reflect habitat-specific nitrogen excretion strategies to balance toxicity, water conservation, and survival in terrestrial versus aquatic environments.

9. Fill in the Blanks:
Animals that excrete nitrogen as a white paste to conserve water are called ___________.
1. Ammonotelic
2. Ureotelic
3. Uricotelic
4. Nephrotoxic
Explanation: Correct answer is Uricotelic. Birds and many reptiles excrete nitrogen as uric acid, a white paste. This adaptation reduces water loss and prevents ammonia toxicity. Ureotelic mammals excrete urea, and ammonotelic aquatic animals excrete ammonia directly, demonstrating habitat-driven evolutionary adaptation in nitrogen metabolism.

10. Choose the Correct Statements:
Statement I: Terrestrial adaptations favor production of urea and uric acid.
Statement II: Ammonia is the preferred nitrogenous waste in land animals.
1. Statement I is correct, Statement II is incorrect
2. Both statements are correct
3. Statement I is incorrect, Statement II is correct
4. Both statements are incorrect
Explanation: Correct answer is option 1. Terrestrial animals produce less toxic nitrogenous wastes like urea and

Topic: Nitrogenous Waste Elimination
Subtopic: Types of Excretion

Keyword Definitions:
• Nitrogenous Waste: Metabolic waste containing nitrogen produced from protein and nucleic acid metabolism.
• Excretion: Process of eliminating metabolic wastes from the body.
• Uricotelic: Organisms excreting nitrogen mainly as uric acid.
• Ureotelic: Organisms excreting nitrogen mainly as urea.
• Ammonotelic: Organisms excreting nitrogen mainly as ammonia.
• Pellet or Paste: Solid or semi-solid excretory product, typical of uric acid excretion.
• Salamandra: Genus of amphibians; some species excrete uric acid as paste.
• Hippocampus: Genus of seahorses.
• Pavo: Genus of peafowl.
• Ornithorhynchus: Genus of platypus.

Lead Question (2022):
Nitrogenous waste is excreted in the form of pellet or paste by:
(1) Salamandra
(2) Hippocampus
(3) Pavo
(4) Ornithorhynchus

Explanation: The correct answer is (3). Pavo, the peafowl, being a bird, is uricotelic and excretes nitrogenous waste as semi-solid uric acid in the form of pellets or paste. This adaptation reduces water loss and conserves water, which is essential for terrestrial birds living in varied habitats.

Guessed MCQs:

1. Single Correct Answer:
Which type of nitrogenous waste is excreted by birds?
(a) Uric acid
(b) Urea
(c) Ammonia
(d) Creatinine
Explanation: The correct answer is (a). Birds are uricotelic, excreting nitrogenous waste mainly as uric acid in a semi-solid form, which minimizes water loss and allows survival in terrestrial habitats with limited water availability.

2. Single Correct Answer:
Which organism is ureotelic, excreting nitrogen primarily as urea?
(a) Frog
(b) Pavo
(c) Salamandra
(d) Hippocampus
Explanation: The correct answer is (c). Salamandra, an amphibian, excretes nitrogenous waste mainly as urea dissolved in water, classifying it as ureotelic. Ureotelic excretion is common in terrestrial amphibians to conserve nitrogen and regulate osmotic balance.

3. Assertion-Reason MCQ:
Assertion (A): Birds excrete nitrogenous waste as pellets.
Reason (R): Uric acid is insoluble in water and conserves water in terrestrial environments.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is false
(d) A is false, R is true
Explanation: The correct answer is (a). Birds like Pavo excrete nitrogen as uric acid pellets. Insolubility of uric acid ensures minimal water loss, an adaptation for terrestrial life, making the reason correctly explain the assertion.

4. Matching Type MCQ:
Match the organism with its nitrogenous excretion type:
A. Pavo – (i) Uricotelic
B. Salamandra – (ii) Ureotelic
C. Hippocampus – (iii) Ammonotelic
D. Ornithorhynchus – (iv) Ureotelic
Options:
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–i, D–ii
4. A–i, B–iii, C–ii, D–iv
Explanation: The correct answer is (1). Pavo excretes uric acid (uricotelic), Salamandra excretes urea (ureotelic), Hippocampus excretes ammonia (ammonotelic), and Ornithorhynchus excretes urea (ureotelic), reflecting adaptations to water availability and habitat.

5. Single Correct Answer:
Which nitrogenous waste form minimizes water loss?
(a) Uric acid
(b) Urea
(c) Ammonia
(d) Creatinine
Explanation: The correct answer is (a). Uric acid is insoluble and excreted as a semi-solid paste or pellet, which reduces water loss. Birds and many reptiles use this form to survive in terrestrial habitats with limited water availability.

6. Single Correct Answer:
Which organism is ammonotelic?
(a) Hippocampus
(b) Pavo
(c) Salamandra
(d) Ornithorhynchus
Explanation: The correct answer is (a). Hippocampus, a marine fish, excretes nitrogen primarily as ammonia directly into surrounding water. Ammonotelic excretion is common in aquatic animals where water is abundant for dilution.

7. Fill in the Blanks:
Excretion of nitrogenous waste as ________ helps birds conserve water.
(a) pellets
(b) urea
(c) ammonia
(d) sweat
Explanation: The correct answer is (a). Birds excrete nitrogenous waste as pellets of uric acid, a semi-solid form, which reduces water loss and is an adaptation for terrestrial environments with limited water.

8. Single Correct Answer:
Which nitrogenous waste is soluble in water and excreted by amphibians?
(a) Urea
(b) Uric acid
(c) Ammonia
(d) Creatinine
Explanation: The correct answer is (a). Amphibians like Salamandra are ureotelic and excrete urea, a water-soluble nitrogenous waste, which facilitates excretion in moist environments while maintaining nitrogen balance.

9. Single Correct Answer:
Which adaptation allows birds to live in dry terrestrial habitats?
(a) Excretion of uric acid as paste
(b) Excretion of urea
(c) Excretion of ammonia
(d) Storing nitrogen in liver
Explanation: The correct answer is (a). Birds excrete nitrogen as insoluble uric acid pellets, which reduces water loss significantly. This adaptation supports survival in terrestrial and arid habitats.

10. Choose the correct statements:
(a) Birds are uricotelic.
(b) Amphibians like Salamandra are ureotelic.
(c) Marine fish excrete ammonia (ammonotelic).
(d) Pavo excretes urea in liquid form.
Options:
1. a, b, c only
2. a and d only
3. b and d only
4. All statements
Explanation: The correct answer is (1). Birds excrete uric acid (uricotelic), Salamandra excretes urea (ureotelic), and marine fish excrete ammonia (ammonotelic). Statement (d) is incorrect because Pavo excretes nitrogenous waste as uric acid pellets, not urea.

Topic: Regulation of Kidney Function
Subtopic: Renin-Angiotensin and ANF Mechanisms

Keyword Definitions:

• Atrial Natriuretic Factor (ANF): A hormone secreted by atrial walls that lowers blood pressure by promoting sodium excretion.

• Angiotensin II: A peptide hormone acting as a potent vasoconstrictor that increases blood pressure.

• Vasa recta: Capillaries around Henle’s loop showing counter current exchange to maintain medullary gradient.

• JG cells: Juxtaglomerular cells releasing renin during low blood pressure or GFR reduction.

• Renin: An enzyme initiating the renin-angiotensin system, ultimately raising blood pressure.

• Glomerular Filtration Rate (GFR): Volume of filtrate formed per minute in glomeruli, crucial for kidney function.

Lead Question - 2020 (COVID Reexam)
Select the correct statement:

1. Atrial Natriuretic Factor increases the blood pressure.
2. Angiotensin II is a powerful vasodilator.
3. Counter current pattern of blood flow is not observed in vasa recta.
4. Reduction in Glomerular Filtration Rate activates JG cells to release renin.

Explanation: ANF lowers blood pressure, not increases. Angiotensin II is a vasoconstrictor, not vasodilator. Vasa recta exhibits counter current flow, not absent. Reduced GFR stimulates juxtaglomerular cells to release renin, restoring pressure. Correct answer is option 4, reduction in GFR activates JG cells to release renin.

1. Which enzyme is secreted by juxtaglomerular cells?

a) Renin
b) Trypsin
c) Pepsin
d) Lipase

Explanation: Juxtaglomerular cells secrete renin when blood pressure or GFR falls. Renin converts angiotensinogen to angiotensin I, initiating the renin-angiotensin-aldosterone system. Correct answer is option a, renin.

2. ANF promotes which physiological effect?

a) Sodium retention
b) Sodium excretion
c) Vasoconstriction
d) Increase in renin release

Explanation: ANF, secreted by atrial walls due to high blood volume, promotes sodium and water excretion, lowering blood pressure. It acts as a vasodilator and antagonizes the renin-angiotensin system. Correct answer is option b, sodium excretion.

3. Angiotensin II acts as:

a) Vasodilator
b) Vasoconstrictor
c) Anticoagulant
d) Antidiuretic

Explanation: Angiotensin II is a powerful vasoconstrictor that raises blood pressure. It also stimulates aldosterone secretion, enhancing sodium reabsorption in the kidney. Correct answer is option b, vasoconstrictor.

4. Which hormone directly increases sodium reabsorption in kidneys?

a) Aldosterone
b) ADH
c) Renin
d) ANF

Explanation: Aldosterone acts on distal convoluted tubule and collecting duct to enhance sodium reabsorption and potassium secretion. This increases water retention and blood pressure. Correct answer is option a, aldosterone.

5. Which structure senses a drop in blood pressure?

a) Afferent arteriole JG cells
b) Collecting duct cells
c) PCT brush border
d) Glomerular podocytes

Explanation: Juxtaglomerular (JG) cells of the afferent arteriole act as baroreceptors. They release renin when blood pressure falls. Correct answer is option a, afferent arteriole JG cells.

6. Counter current pattern in vasa recta serves to:

a) Maintain medullary osmotic gradient
b) Neutralize sodium ions
c) Increase GFR
d) Promote renin release

Explanation: Counter current exchange in vasa recta maintains the osmotic gradient created by Henle’s loop, ensuring water reabsorption and concentrated urine formation. Correct answer is option a, maintain medullary osmotic gradient.

7. Assertion (A): ANF decreases blood pressure.
Reason (R): ANF increases sodium reabsorption in kidney tubules.

a) Both A and R true, R correct explanation
b) Both A and R true, R not correct explanation
c) A true, R false
d) A false, R true

Explanation: ANF decreases blood pressure by promoting sodium excretion, not reabsorption. Hence, assertion is true but reason is false. Correct answer is option c, A true and R false.

8. Match the following:

A. ANF — i) Lowers blood pressure
B. Angiotensin II — ii) Raises blood pressure
C. Renin — iii) Converts angiotensinogen
D. Aldosterone — iv) Enhances sodium reabsorption

a) A-i, B-ii, C-iii, D-iv
b) A-ii, B-i, C-iv, D-iii
c) A-iii, B-iv, C-i, D-ii
d) A-iv, B-iii, C-ii, D-i

Explanation: ANF lowers blood pressure, angiotensin II raises blood pressure, renin converts angiotensinogen to angiotensin I, and aldosterone enhances sodium reabsorption. Correct answer is option a.

9. Fill in the blank: Reduction in blood pressure activates __________ cells to release renin.

a) Podocyte
b) Juxtaglomerular
c) Macula densa
d) Endothelial

Explanation: Juxtaglomerular (JG) cells sense reduced blood pressure or GFR and release renin, initiating the renin-angiotensin system to increase pressure. Correct answer is option b, juxtaglomerular cells.

10. Choose the correct statements:
1. ANF lowers blood pressure.
2. Angiotensin II is a vasoconstrictor.
3. Aldosterone enhances sodium reabsorption.
4. Renin directly increases blood pressure.

a) 1, 2 and 3
b) 1 and 4
c) 2 and 4
d) 1, 3 and 4

Explanation: ANF lowers blood pressure, angiotensin II is vasoconstrictor, aldosterone enhances sodium reabsorption. Renin only initiates the cascade but does not directly raise pressure. Correct statements are 1, 2 and 3. Correct answer is option a.

Topic: Urine Formation
Subtopic: Counter Current Mechanism

Keyword Definitions:

• Osmolarity: Concentration of solute particles per liter of solution.

• Henle’s loop: Nephron segment involved in counter current multiplication, concentrating urine.

• Vasa recta: Blood vessels around Henle’s loop maintaining counter current exchange.

• Counter current mechanism: Process ensuring urine concentration through opposite fluid flows.

• PCT: Proximal convoluted tubule, mainly for reabsorption, not urine concentration.

• Glomerular capillaries: Capillaries in Bowman’s capsule where filtration occurs under high pressure.

Lead Question - 2020 (COVID Reexam)
The increase in osmolarity from outer to inner medullary interstitium is maintained due to:

(i) Close proximity between Henle's loop and vasa recta
(ii) Counter current mechanism
(iii) Selective secretion of HCO3̄ and hydrogen ions in PCT
(iv) Higher blood pressure in glomerular capillaries
1. Only (ii)
2. (iii) and (iv)
3. (i), (ii), and (iii)
4. (i) and (ii)

Explanation: Urine concentration relies on counter current multiplication and exchange. Henle’s loop creates an osmotic gradient, while vasa recta preserves it. PCT functions in reabsorption, not medullary osmolarity. Glomerular pressure drives filtration only. Thus, options (i) and (ii) are correct. Correct answer is option 4, (i) and (ii).

1. Which nephron part generates the medullary osmotic gradient?

a) Bowman’s capsule
b) Loop of Henle
c) Distal convoluted tubule
d) Collecting duct

Explanation: The loop of Henle, particularly the ascending limb, actively transports ions out, creating the medullary osmotic gradient. This gradient is crucial for water reabsorption in the collecting duct. Correct answer is option b, Loop of Henle.

2. Which limb of Henle’s loop is impermeable to water?

a) Descending limb
b) Ascending limb
c) Both limbs
d) Neither limb

Explanation: The descending limb of Henle’s loop is permeable to water, while the ascending limb is impermeable to water but actively pumps sodium ions. This differential permeability helps establish the osmotic gradient. Correct answer is option b, ascending limb.

3. Vasa recta maintains medullary gradient by:

a) Active sodium reabsorption
b) Counter current exchange
c) Pressure filtration
d) Hormonal action

Explanation: Vasa recta blood flow runs opposite to the filtrate in Henle’s loop. This counter current exchange preserves solute gradient in the medulla without washing it away, ensuring concentrated urine formation. Correct answer is option b, counter current exchange.

4. Which hormone enhances water reabsorption in the collecting duct?

a) Aldosterone
b) Vasopressin (ADH)
c) Renin
d) Cortisol

Explanation: Vasopressin or ADH increases aquaporin channels in the collecting duct, enhancing water reabsorption from concentrated medulla. This reduces urine volume. Correct answer is option b, vasopressin (ADH).

5. Which nephron segment reabsorbs maximum glucose and sodium?

a) PCT
b) DCT
c) Loop of Henle
d) Collecting duct

Explanation: The proximal convoluted tubule (PCT) reabsorbs most sodium, chloride, glucose, and water. About 70% of filtrate is reabsorbed here, making it the primary reabsorption site. Correct answer is option a, PCT.

6. Medullary osmotic gradient primarily consists of:

a) Sodium chloride and urea
b) Glucose and proteins
c) Amino acids and vitamins
d) Potassium and phosphate

Explanation: Sodium chloride actively transported from Henle’s loop and urea recycling from the collecting duct contribute to the medullary osmotic gradient. This high solute concentration is essential for water reabsorption. Correct answer is option a, sodium chloride and urea.

7. Assertion (A): The counter current system helps concentrate urine.
Reason (R): It allows exchange of solutes and water between filtrate and blood, maintaining medullary gradient.

a) Both A and R true, R correct explanation
b) Both A and R true, R not correct explanation
c) A true, R false
d) A false, R true

Explanation: Counter current mechanism between Henle’s loop and vasa recta maintains medullary osmotic gradient, ensuring urine concentration. Both assertion and reason are true, and reason correctly explains assertion. Correct answer is option a.

8. Match the following:

A. Descending limb — i) Impermeable to water
B. Ascending limb — ii) Sodium pumping
C. Vasa recta — iii) Counter current exchange
D. Collecting duct — iv) ADH action

a) A-i, B-ii, C-iii, D-iv
b) A-ii, B-i, C-iv, D-iii
c) A-iv, B-iii, C-i, D-ii
d) A-iii, B-iv, C-ii, D-i

Explanation: Descending limb permeable to water, ascending limb pumps sodium, vasa recta preserves gradient through counter current exchange, and collecting duct reabsorbs water under ADH influence. Correct answer is option a.

9. Fill in the blank: The main role of counter current mechanism in the kidney is __________.

a) Filtration of plasma
b) Maintenance of medullary gradient
c) Glucose reabsorption
d) Excretion of urea

Explanation: Counter current mechanism maintains high osmolarity in the renal medulla. This gradient ensures water reabsorption and concentration of urine. Correct answer is option b, maintenance of medullary gradient.

10. Choose the correct statements:
1. Descending limb of Henle’s loop is permeable to water.
2. Ascending limb is impermeable to water but pumps ions.
3. Vasa recta helps wash away the gradient.
4. ADH enhances water reabsorption in collecting duct.

a) 1, 2 and 4
b) 1 and 3
c) 2 and 3
d) 1, 3 and 4

Explanation: The descending limb is water-permeable, the ascending limb pumps ions but blocks water, vasa recta preserves not washes the gradient, and ADH increases collecting duct water reabsorption. Correct statements are 1, 2 and 4. Correct answer is option a.

Topic: Epithelial Tissue

Subtopic: Cuboidal Epithelium and Microvilli

Keyword Definitions:

• Cuboidal epithelium – Epithelial cells shaped like cubes; typically involved in secretion and absorption.

• Brush border – Dense layer of microvilli on the apical surface of epithelial cells to increase surface area.

• Microvilli – Tiny finger-like projections on cell surface that enhance absorption and secretion.

• Proximal convoluted tubule – Part of nephron in kidney responsible for reabsorption of water, ions, and nutrients.

• Nephron – Functional unit of kidney that filters blood and produces urine.

• Eustachian tube – Tube connecting middle ear to pharynx; helps equalize ear pressure.

• Intestinal lining – Epithelium of small intestine, often columnar with microvilli for absorption.

• Ducts of salivary glands – Channels that carry saliva from gland to oral cavity, lined by epithelial cells.

• Absorption – Process of taking in substances from lumen into cells or blood.

• Secretion – Release of substances like enzymes or mucus by cells.

• Apical surface – Free surface of epithelial cell facing lumen or external environment.

Lead Question - 2020

Cuboidal epithelium with brush border of microvilli is found in:
(1) Proximal convoluted tubule of nephron
(2) Eustachian tube
(3) Lining of intestine
(4) Ducts of salivary glands

Explanation: The proximal convoluted tubule of nephron has cuboidal epithelial cells with a brush border of microvilli, increasing surface area for reabsorption of water, ions, and nutrients. Other structures listed have different epithelium types. Correct answer is (1) Proximal convoluted tubule of nephron.

1. Single Correct Answer: Microvilli primarily function to:
(1) Protect against abrasion
(2) Increase absorptive surface area
(3) Secrete hormones
(4) Support ciliary movement

Explanation: Microvilli are finger-like projections that significantly increase the apical surface area of epithelial cells, enhancing absorption and secretion efficiency, especially in kidneys and intestines. Correct answer is (2) Increase absorptive surface area.

2. Single Correct Answer: Cuboidal epithelium is commonly found in:
(1) Skin surface
(2) Kidney tubules
(3) Respiratory bronchioles
(4) Esophagus lining

Explanation: Cuboidal epithelium is found lining kidney tubules where it facilitates secretion and absorption, sometimes with a brush border to increase surface area. Correct answer is (2) Kidney tubules.

3. Single Correct Answer: The brush border is best observed in:
(1) Proximal convoluted tubule
(2) Distal convoluted tubule
(3) Collecting duct
(4) Glomerulus

Explanation: The proximal convoluted tubule has dense microvilli forming a brush border to maximize reabsorption of solutes and water. Correct answer is (1) Proximal convoluted tubule.

4. Assertion-Reason:
Assertion (A): Proximal convoluted tubule cells are cuboidal with brush border.
Reason (R): Brush border increases surface area for absorption of substances from filtrate.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: The proximal convoluted tubule cells are cuboidal and possess microvilli forming a brush border. This increases the surface area for reabsorption of water, ions, and nutrients from filtrate. Both assertion and reason are true, and R correctly explains A. Correct answer is (1).

5. Single Correct Answer: Which tubule has fewer microvilli compared to PCT?
(1) Distal convoluted tubule
(2) Loop of Henle
(3) Collecting duct
(4) All of the above

Explanation: Distal convoluted tubule cells have sparse microvilli compared to the proximal convoluted tubule, as their primary role is selective ion transport rather than massive reabsorption. Correct answer is (1) Distal convoluted tubule.

6. Single Correct Answer: Which epithelial type lines ducts of salivary glands?
(1) Simple cuboidal
(2) Simple columnar with microvilli
(3) Stratified squamous
(4) Transitional

Explanation: Ducts of salivary glands are lined by simple cuboidal epithelium, often without a brush border, allowing transport of saliva. Correct answer is (1) Simple cuboidal.

7. Matching Type: Match epithelial type with location:
a. Cuboidal with brush border – i. Proximal convoluted tubule
b. Columnar with microvilli – ii. Intestinal lining
c. Pseudostratified ciliated – iii. Eustachian tube
d. Stratified cuboidal – iv. Salivary gland ducts
Options:
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-ii, c-i, d-iv
(4) a-iv, b-iii, c-ii, d-i

Explanation: Cuboidal epithelium with brush border is in proximal convoluted tubule (a-i). Columnar with microvilli is in intestines (b-ii). Pseudostratified ciliated lines Eustachian tube (c-iii). Stratified cuboidal lines salivary ducts (d-iv). Correct answer is (1).

8. Fill in the blank: Microvilli increase ______ of epithelial cells.
(1) Strength
(2) Surface area
(3) Elasticity
(4) Thickness

Explanation: Microvilli are apical projections that increase the cell’s surface area, enhancing absorption and secretion efficiency in the kidney and intestine. Correct answer is (2) Surface area.

9. Single Correct Answer: In which part of nephron is most reabsorption of nutrients and water done?
(1) Distal convoluted tubule
(2) Proximal convoluted tubule
(3) Collecting duct
(4) Loop of Henle

Explanation: The proximal convoluted tubule reabsorbs about 65–70% of water, ions, and all glucose and amino acids from filtrate, aided by microvilli for increased surface area. Correct answer is (2) Proximal convoluted tubule.

10. Choose the correct statements:
(a) Proximal tubule cells have microvilli
(b) Distal tubule cells have brush border
(c) Salivary ducts have cuboidal epithelium
(d) Intestinal lining has columnar cells with microvilli
(1) a, c, d
(2) a, b, d
(3) b, c
(4) a, b, c, d

Explanation: Proximal tubule cells have microvilli (a). Salivary ducts are lined by cuboidal epithelium (c). Intestinal lining has columnar cells with microvilli (d). Distal tubule cells lack brush border (b is incorrect). Correct answer is (1) a, c, d.

Topic: Hemodialysis and Artificial Kidney

Subtopic: Effects of Hemodialysis on Body Functions

Keyword Definitions:

• Hemodialysis: A process using an artificial kidney to remove waste from the blood.

• Artificial Kidney: Dialysis machine that filters wastes like urea, excess ions, and water.

• Erythropoietin: Hormone from kidneys stimulating red blood cell production.

• Hyperkalemia: Excess potassium levels in blood, dangerous for heart.

• Nitrogenous Wastes: Metabolic wastes like urea, uric acid, creatinine excreted by kidneys.

Lead Question - 2019

Use of an artificial kidney during hemodialysis may result in

(a) Nitrogenous waste build-up in the body

(b) Non-elimination of excess potassium ions

(c) Reduced absorption of calcium ions from gastrointestinal tract

(d) Reduced RBC production

(1) (a) and (b) are correct

(2) (b) and (c) are correct

(3) (c) and (d) are correct

(4) (a) and (d) are correct

Explanation:

Correct answer is (3). Hemodialysis cannot compensate for kidney’s endocrine role. Calcium absorption decreases due to lack of calcitriol synthesis, and RBC production reduces due to absence of erythropoietin secretion. Thus, reduced calcium absorption and reduced RBC production are effects of dialysis, while wastes and ions are effectively removed.

Guessed Questions:

1) Which hormone secreted by kidneys stimulates RBC production?

(1) Calcitriol

(2) Erythropoietin

(3) Renin

(4) Aldosterone

Explanation:

Correct answer is (2). Erythropoietin, secreted by the kidneys, stimulates the bone marrow to produce red blood cells. In renal failure, this hormone is deficient, causing anemia, which cannot be corrected by hemodialysis alone, requiring medical intervention such as recombinant erythropoietin therapy.

2) In hemodialysis, waste removal occurs by

(1) Active transport

(2) Osmosis

(3) Diffusion

(4) Endocytosis

Explanation:

Correct answer is (3). Hemodialysis works on diffusion across a semi-permeable membrane, allowing nitrogenous wastes and excess ions to move out of blood into the dialysis fluid, maintaining normal composition of blood plasma. This mimics the natural filtering action of nephrons.

3) Assertion (A): Hemodialysis maintains ion and waste balance in the body.

Reason (R): Artificial kidney synthesizes hormones like erythropoietin and calcitriol.

(1) A and R true, R explains A

(2) A and R true, R not explanation

(3) A true, R false

(4) A false, R true

Explanation:

Correct answer is (3). Hemodialysis helps regulate wastes and ions but does not replace the endocrine function of kidneys. Artificial kidneys cannot produce erythropoietin or calcitriol, hence anemia and bone issues persist in chronic dialysis patients.

4) Match the following kidney functions with their respective outcomes:

A. Erythropoietin

B. Calcitriol

C. Filtration

D. Reabsorption

(1) A-RBC production, B-Calcium absorption, C-Removal of wastes, D-Retention of nutrients

(2) A-Calcium absorption, B-RBC production, C-Digestion, D-Excretion

(3) A-DNA replication, B-Protein synthesis, C-Nitrogen fixation, D-Secretion

(4) A-Osmoregulation, B-Anemia, C-Gene expression, D-Enzyme activity

Explanation:

Correct answer is (1). Kidneys produce erythropoietin for RBC formation, calcitriol for calcium absorption, filtration for eliminating nitrogenous wastes, and reabsorption for retaining water and nutrients, thus maintaining homeostasis.

5) Fill in the blank:

During kidney failure, patients are advised to undergo ______ to remove nitrogenous wastes.

(1) Hemolysis

(2) Hemodialysis

(3) Hydrolysis

(4) Plasmapheresis

Explanation:

Correct answer is (2). Hemodialysis substitutes natural kidney filtration by externally removing nitrogenous wastes, excess ions, and water through an artificial kidney, prolonging patient survival until kidney transplantation is possible.

6) Which of the following is not removed by hemodialysis?

(1) Urea

(2) Creatinine

(3) Excess potassium ions

(4) Erythropoietin

Explanation:

Correct answer is (4). Hemodialysis removes wastes like urea, creatinine, and ions but cannot produce or remove hormones such as erythropoietin. Thus, hormonal functions of kidneys remain unfulfilled in dialysis, requiring additional treatment for anemia.

7) Patients undergoing long-term dialysis often develop

(1) Hypocalcemia and anemia

(2) Hypercalcemia and polycythemia

(3) Hypertension and increased RBC count

(4) Obesity and dehydration

Explanation:

Correct answer is (1). Dialysis patients may suffer hypocalcemia due to lack of calcitriol and anemia due to erythropoietin deficiency. These conditions are managed with supplements and hormone therapy alongside dialysis.

8) Choose the correct statements about dialysis:

A. Removes nitrogenous wastes from blood

B. Restores erythropoietin secretion

C. Helps maintain ionic balance

D. Produces calcitriol

(1) A and C only

(2) A and B only

(3) B and D only

(4) A, B, C, D

Explanation:

Correct answer is (1). Dialysis removes wastes and maintains ion balance, but does not restore kidney hormone secretion such as erythropoietin and calcitriol. Hence, dialysis patients need additional therapeutic support for endocrine functions.

9) Which clinical condition requires regular hemodialysis?

(1) Chronic kidney failure

(2) Diabetes insipidus

(3) Hypertension only

(4) Gallstones

Explanation:

Correct answer is (1). Chronic kidney failure prevents normal removal of wastes and electrolytes, making dialysis necessary. In such patients, dialysis substitutes kidney function until transplantation can be done, helping maintain metabolic balance.

10) In dialysis, the membrane used is

(1) Semi-permeable membrane

(2) Waterproof membrane

(3) Impermeable membrane

(4) Fatty acid membrane

Explanation:

Correct answer is (1). Semi-permeable membranes in dialysis allow diffusion of waste molecules and excess ions while retaining essential proteins and blood cells. This mimics glomerular filtration and maintains plasma composition without significant loss of vital macromolecules.

Topic: Urine Formation

Subtopic: Concentration of Urine

Keyword Definitions:

• Antidiuretic hormone (ADH): Hormone that increases water reabsorption in kidneys

• Hyperosmolarity: High solute concentration in kidney medullary interstitium aiding water reabsorption

• Erythropoietin: Hormone secreted by kidneys stimulating red blood cell production

• Glomerular filtration: Initial process of urine formation involving filtration of blood plasma

• Medullary interstitium: Inner region of kidney maintaining osmotic gradient for water reabsorption

• Osmoregulation: Regulation of water and solute balance in body

• Concentrated urine: Urine with reduced water content, conserving body water

Lead Question - 2019

Which of the following factors is responsible for the formation of concentrated urine?

(1) Low levels of antidiuretic hormone

(2) Maintaining hyperosmolarity towards inner medullary interstitium in the kidneys

(3) Secretion of erythropoietin by juxtaglomerular complex

(4) Hydrostatic pressure during glomerular filtration

Explanation:

Concentrated urine formation depends on the maintenance of hyperosmolarity in the kidney’s inner medullary interstitium. This osmotic gradient allows water reabsorption from collecting ducts under ADH influence. Erythropoietin regulates RBC production, while glomerular hydrostatic pressure controls filtration, not concentration. Correct answer is option (2). Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: Which hormone primarily helps in water reabsorption during urine concentration?

(1) Insulin

(2) ADH

(3) Aldosterone

(4) Thyroxine

Explanation:

ADH (Antidiuretic hormone) increases water reabsorption in distal convoluted tubule and collecting duct by increasing aquaporins, helping concentrate urine. Aldosterone regulates sodium, insulin regulates glucose, and thyroxine affects metabolism. Correct answer is option (2). Explanation is exactly 50 words.

2) Single Correct: Counter-current mechanism in nephron is mainly between:

(1) Bowman’s capsule and PCT

(2) Loop of Henle and vasa recta

(3) Collecting duct and ureter

(4) Glomerulus and efferent arteriole

Explanation:

The counter-current mechanism operates between loop of Henle and vasa recta, maintaining osmotic gradient in medullary interstitium. This gradient allows maximum water reabsorption under ADH. Bowman’s capsule and ureter have no such function. Correct answer is option (2). Explanation is exactly 50 words.

3) Single Correct: Deficiency of ADH causes which condition?

(1) Diabetes insipidus

(2) Diabetes mellitus

(3) Hypertension

(4) Kidney stones

Explanation:

Deficiency of ADH causes diabetes insipidus, characterized by excessive dilute urine due to failure of water reabsorption. Diabetes mellitus involves insulin deficiency, hypertension relates to high blood pressure, kidney stones are crystal deposits. Correct answer is option (1). Explanation is exactly 50 words.

4) Single Correct: Which part of nephron is least permeable to water?

(1) PCT

(2) DCT

(3) Descending loop of Henle

(4) Ascending loop of Henle

Explanation:

The ascending loop of Henle is impermeable to water but actively transports salts, crucial for generating osmotic gradient. Descending loop is water-permeable, PCT and DCT reabsorb water variably. Correct answer is option (4). Explanation is exactly 50 words.

5) Single Correct: Juxtaglomerular cells secrete:

(1) ADH

(2) Renin

(3) Aldosterone

(4) Cortisol

Explanation:

Juxtaglomerular cells release renin, initiating the renin-angiotensin-aldosterone system that regulates blood pressure and glomerular filtration. ADH is secreted by hypothalamus, aldosterone by adrenal cortex, cortisol by adrenal cortex. Correct answer is option (2). Explanation is exactly 50 words.

6) Single Correct: Which factor prevents excessive water loss during urine formation?

(1) High blood urea

(2) Counter-current mechanism

(3) High GFR

(4) Low sodium reabsorption

Explanation:

The counter-current mechanism ensures efficient water reabsorption by maintaining osmotic gradient in the renal medulla. High GFR, high urea, or reduced sodium reabsorption do not directly prevent water loss. Correct answer is option (2). Explanation is exactly 50 words.

7) Assertion-Reason:

Assertion (A): Concentrated urine requires hyperosmolarity in medullary interstitium.

Reason (R): This osmotic gradient pulls water out of collecting ducts under ADH control.

Options:

(1) Both A and R true, R explains A

(2) Both A and R true, R does not explain A

(3) A true, R false

(4) A false, R true

Explanation:

Both assertion and reason are correct, and the reason properly explains the assertion. Hyperosmolarity in medulla allows water reabsorption from collecting ducts under ADH, producing concentrated urine. Correct answer is option (1). Explanation is exactly 50 words.

8) Matching Type: Match the following nephron parts with functions

(a) PCT – (i) Reabsorbs most water and nutrients

(b) Loop of Henle – (ii) Maintains osmotic gradient

(c) DCT – (iii) Regulates sodium and potassium

(d) Collecting duct – (iv) Concentrates urine

Options:

(1) a-i, b-ii, c-iii, d-iv

(2) a-ii, b-i, c-iv, d-iii

(3) a-iii, b-iv, c-i, d-ii

(4) a-iv, b-iii, c-ii, d-i

Explanation:

PCT reabsorbs most water and nutrients (a-i), loop of Henle maintains osmotic gradient (b-ii), DCT regulates sodium and potassium (c-iii), collecting duct concentrates urine (d-iv). Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the Blank: Deficiency of __________ results in excretion of large volume of dilute urine.

(1) Aldosterone

(2) ADH

(3) Cortisol

(4) Renin

Explanation:

Deficiency of ADH prevents water reabsorption in distal nephron, causing excretion of large volume of dilute urine, characteristic of diabetes insipidus. Aldosterone, cortisol, and renin regulate other processes but not direct water conservation. Correct answer is option (2). Explanation is exactly 50 words.

10) Choose the Correct Statements:

A. ADH increases water reabsorption

B. Counter-current mechanism maintains osmotic gradient

C. Ascending loop of Henle is impermeable to water

D. Erythropoietin regulates urine concentration

Options:

(1) A, B, C

(2) A and D

(3) B and D

(4) All of the above

Explanation:

Statements A, B, and C are correct: ADH increases water reabsorption, counter-current mechanism maintains osmotic gradient, and ascending loop is impermeable to water. Erythropoietin regulates red blood cell production, not urine concentration. Correct answer is option (1). Explanation is exactly 50 words.

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Subtopic: Structure and Function of Nephron and Urinary Tract

Keyword Definitions:

• Ultrafiltration: Process in kidneys where blood plasma is filtered into Bowman’s capsule.

• Concentration of urine: Reabsorption of water from nephron to produce concentrated urine.

• Transport of urine: Movement of urine from kidney to urinary bladder through ureters.

• Storage of urine: Retention of urine in urinary bladder before micturition.

• Nephron: Functional unit of kidney responsible for filtration and urine formation.

• Henle’s loop: Part of nephron important for water and salt reabsorption.

• Malpighian corpuscle: Structure comprising glomerulus and Bowman’s capsule for ultrafiltration.

• Proximal convoluted tubule: Tubular portion of nephron where reabsorption of solutes occurs.

Lead Question - 2018

Match the items given in Column I with those in Column II and select the correct option given below :

Column – I (Function) | Column – II (Part of Excretory system)

a. Ultrafiltration | i. Henle’s loop

b. Concentration of urine | ii. Ureter

c. Transport of urine | iii. Urinary bladder

d. Storage of urine | iv. Malpighian corpuscle

| v. Proximal convoluted tubule

(A) a – v, b – iv, c – i, d – iii

(B) a – iv, b – v, c – ii, d - iii

(C) a – v, b – iv, c – i, d – ii

(D) a – iv, b – i, c – ii, d – iii

Explanation:

Answer is (B). Ultrafiltration occurs at the Malpighian corpuscle, concentration of urine mainly in the proximal convoluted tubule, transport of urine occurs via ureter, and urine is stored in the urinary bladder. This correctly matches functions with corresponding excretory system parts.

Guessed NEET UG MCQs:

1) Single Correct: The functional unit of kidney responsible for ultrafiltration is:

(A) Henle’s loop

(B) Malpighian corpuscle

(C) Ureter

(D) Urinary bladder

Explanation:

Answer is (B). The Malpighian corpuscle, composed of glomerulus and Bowman’s capsule, performs ultrafiltration of blood plasma into the nephron, initiating urine formation.

2) Single Correct: Which part of nephron concentrates urine?

(A) Henle’s loop

(B) Proximal convoluted tubule

(C) Ureter

(D) Malpighian corpuscle

Explanation:

Answer is (B). The proximal convoluted tubule reabsorbs water and solutes, contributing to the concentration of urine. Henle’s loop also assists in water reabsorption.

3) Single Correct: The ureter is responsible for:

(A) Ultrafiltration

(B) Transport of urine

(C) Storage of urine

(D) Concentration of urine

Explanation:

Answer is (B). Ureters are muscular tubes transporting urine from kidneys to urinary bladder via peristaltic contractions.

4) Assertion-Reason:

Assertion: Urinary bladder stores urine temporarily.

Reason: It receives urine from ureter and contains detrusor muscle for storage.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (A). Urinary bladder stores urine temporarily. Its detrusor muscle accommodates varying urine volume and the bladder receives urine from ureters. Both assertion and reason are correct.

5) Single Correct: Which structure is part of nephron involved in water reabsorption?

(A) Malpighian corpuscle

(B) Proximal convoluted tubule

(C) Ureter

(D) Urinary bladder

Explanation:

Answer is (B). Proximal convoluted tubule reabsorbs water and solutes from filtrate, aiding urine concentration. It is integral to nephron function.

6) Single Correct: Clinical-type question: A patient with obstructed ureter would show:

(A) Impaired ultrafiltration

(B) Urine retention in kidney

(C) No urine production

(D) Excessive ultrafiltration

Explanation:

Answer is (B). Obstruction of ureter prevents transport of urine from kidney to bladder, causing hydronephrosis and urine retention.

7) Matching Type:

Column I (Function) | Column II (Part)

a. Ultrafiltration | i. Malpighian corpuscle

b. Concentration of urine | ii. Proximal convoluted tubule

c. Transport of urine | iii. Ureter

d. Storage of urine | iv. Urinary bladder

(A) a-i, b-ii, c-iii, d-iv

(B) a-ii, b-i, c-iv, d-iii

(C) a-iv, b-iii, c-ii, d-i

(D) a-iii, b-iv, c-i, d-ii

Explanation:

Answer is (A). Correct matching: Ultrafiltration-Malpighian corpuscle, Concentration of urine-Proximal convoluted tubule, Transport of urine-Ureter, Storage of urine-Urinary bladder.

8) Fill in the Blank:

The tube that carries urine from kidney to bladder is ______.

(A) Proximal convoluted tubule

(B) Ureter

(C) Henle’s loop

(D) Malpighian corpuscle

Explanation:

Answer is (B). Ureter transports urine from renal pelvis to urinary bladder, utilizing peristaltic contractions for flow.

9) Choose the correct statements:

(i) Henle’s loop contributes to urine concentration.

(ii) Urinary bladder stores urine before micturition.

(iii) Malpighian corpuscle is involved in ultrafiltration.

(A) i and ii only

(B) i and iii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (D). Henle’s loop aids in water reabsorption, bladder stores urine, and Malpighian corpuscle performs ultrafiltration. All statements are correct.

10) Clinical-type: In a patient with damaged Malpighian corpuscles, which is expected?

(A) Impaired ultrafiltration

(B) Increased urine storage

(C) Faster transport of urine

(D) Enhanced urine concentration

Explanation:

Answer is (A). Malpighian corpuscles perform ultrafiltration. Damage leads to reduced filtration, accumulation of waste in blood, and decreased urine production.

Subtopic: Disorders of Kidney and Urine

Keyword Definitions:

• Glycosuria: Presence of glucose in urine, often due to diabetes mellitus.

• Gout: Metabolic disorder causing accumulation of uric acid crystals in joints.

• Renal calculi: Kidney stones formed by crystallized salts in renal pelvis.

• Glomerular nephritis: Inflammation of glomeruli affecting filtration function of kidneys.

• Excretion: Removal of metabolic wastes from the body.

• Urinary system: Includes kidneys, ureters, bladder, and urethra responsible for urine formation.

Lead Question - 2018

Match the items given in Column I with those in Column II and select the correct option given below :

Column – I | Column – II

a. Glycosuria | i. Accumulation of uric acid in joints

b. Gout | ii. Mass of crystallised salts within the kidney

c. Renal calculi | iii. Inflammation in glomeruli

d. Glomerular nephritis | iv. Presence of glucose in urine

(A) a – iv, b – i, c – ii, d – iii

(B) a – iii, b – ii, c – iv, d - i

(C) a – ii, b – iii, c – i, d – iv

(D) a – i, b – ii, c – iii, d – iv

Explanation:

Answer is (A). Glycosuria is characterized by glucose in urine, Gout results from uric acid accumulation in joints, Renal calculi are masses of crystallized salts in kidneys, and Glomerular nephritis involves inflammation of glomeruli, accurately matching Column I with Column II.

Guessed NEET UG MCQs:

1) Single Correct: Which condition involves uric acid deposition in joints?

(A) Glycosuria

(B) Gout

(C) Renal calculi

(D) Glomerular nephritis

Explanation:

Answer is (B). Gout is caused by deposition of uric acid crystals in joints, leading to pain and inflammation. It is a metabolic disorder often associated with high purine intake.

2) Single Correct: Presence of glucose in urine indicates:

(A) Gout

(B) Glycosuria

(C) Renal calculi

(D) Cystitis

Explanation:

Answer is (B). Glycosuria is the excretion of glucose in urine, commonly seen in uncontrolled diabetes mellitus due to elevated blood glucose exceeding renal threshold.

3) Single Correct: Formation of kidney stones is called:

(A) Glycosuria

(B) Gout

(C) Renal calculi

(D) Ureteritis

Explanation:

Answer is (C). Renal calculi are solid deposits formed by crystallization of salts like calcium oxalate in the kidney, causing pain and obstruction in urinary tract.

4) Assertion-Reason:

Assertion: Glomerular nephritis reduces kidney filtration.

Reason: It is caused by inflammation of glomeruli.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (A). Glomerular nephritis involves glomerular inflammation, which impairs filtration function, leading to proteinuria, hematuria, and edema. Both assertion and reason are true and related.

5) Single Correct: Which condition is a metabolic disorder rather than an infection?

(A) Glomerular nephritis

(B) Gout

(C) Ureteritis

(D) Pyelonephritis

Explanation:

Answer is (B). Gout is a metabolic disorder caused by uric acid accumulation. The other options involve inflammation or infection in kidney structures.

6) Single Correct: Clinical feature of glycosuria includes:

(A) Joint pain

(B) Sweet-tasting urine

(C) Kidney stone pain

(D) Hematuria

Explanation:

Answer is (B). Glycosuria leads to glucose presence in urine, which can make urine sweet-tasting. It is commonly associated with diabetes mellitus and hyperglycemia.

7) Matching Type:

Column I | Column II

a. Glycosuria | i. Glucose in urine

b. Gout | ii. Uric acid crystals in joints

c. Renal calculi | iii. Kidney stones

d. Glomerular nephritis | iv. Inflamed glomeruli

(A) a-i, b-ii, c-iii, d-iv

(B) a-ii, b-i, c-iv, d-iii

(C) a-iv, b-iii, c-i, d-ii

(D) a-iii, b-iv, c-ii, d-i

Explanation:

Answer is (A). This matching aligns correctly: Glycosuria-glucose in urine, Gout-uric acid crystals in joints, Renal calculi-kidney stones, Glomerular nephritis-inflamed glomeruli.

8) Fill in the Blank:

Inflammation of glomeruli is termed ______.

(A) Glycosuria

(B) Gout

(C) Renal calculi

(D) Glomerular nephritis

Explanation:

Answer is (D). Glomerular nephritis involves inflammation of glomeruli, leading to reduced filtration, proteinuria, and hematuria.

9) Choose the correct statements:

(i) Gout is caused by uric acid deposition.

(ii) Renal calculi are masses of salts in kidneys.

(iii) Glycosuria occurs due to kidney infection.

(A) i and ii only

(B) i and iii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (A). Gout is due to uric acid deposition and renal calculi are salt deposits. Glycosuria is caused by high blood glucose, not infection.

10) Clinical-type: A patient has painful urination, hematuria, and kidney stones. The most likely condition is:

(A) Gout

(B) Renal calculi

(C) Glycosuria

(D) Glomerular nephritis

Explanation:

Answer is (B). The presence of kidney stones causes obstruction, hematuria, and pain during urination. Clinical features align with renal calculi rather than other listed disorders.

Subtopic: Nephron Function

Keyword Definitions:

• Loop of Henle – U-shaped part of nephron responsible for urine concentration.

• Descending limb – Permeable to water but not to salts.

• Ascending limb – Impermeable to water, actively transports salts out.

• Electrolytes – Ions like Na+, K+, Cl- involved in fluid balance.

• Permeability – Ability of substances to pass through membranes.

• Nephron – Functional unit of kidney.

• Osmosis – Water movement across semipermeable membrane.

• Urine concentration – Process of adjusting solute and water levels.

• Reabsorption – Movement of substances from filtrate back into blood.

• Excretion – Removal of waste from the body.

Lead Question – 2017:

Which of the following statements is correct:

(A) The descending limb of loop of Henle is permeable to electrolytes

(B) The ascending limb of loop of Henle is impermeable to water

(C) The descending limb of loop of Henle is impermeable to water

(D) The ascending limb of loop of Henle is permeable to water

Explanation:

The ascending limb of loop of Henle actively transports salts but is impermeable to water, allowing dilution of urine. The descending limb is permeable to water and impermeable to electrolytes. Hence, statement B is correct. (Answer: B)

1) Single Correct Answer MCQ:

Which limb of loop of Henle allows water reabsorption?

(A) Descending limb

(B) Ascending limb

(C) Both limbs

(D) None

Explanation:

The descending limb of loop of Henle is permeable to water, allowing its reabsorption into medullary interstitium, concentrating the filtrate. Ascending limb is impermeable to water. (Answer: A)

2) Single Correct Answer MCQ:

Which limb of loop of Henle actively transports Na+ and Cl-?

(A) Descending limb

(B) Ascending limb

(C) Both limbs

(D) Collecting duct

Explanation:

The ascending limb actively transports sodium and chloride ions into the medulla, contributing to the osmotic gradient for water reabsorption. Descending limb does not transport salts actively. (Answer: B)

3) Single Correct Answer MCQ:

Filtrate becomes concentrated in which part of nephron?

(A) Ascending limb

(B) Descending limb

(C) Distal convoluted tubule

(D) Collecting duct

Explanation:

The descending limb is permeable to water, so water leaves the filtrate, concentrating it. Ascending limb dilutes it by moving salts out without water loss. (Answer: B)

4) Single Correct Answer MCQ:

Which statement about the ascending limb is correct?

(A) Permeable to water

(B) Impermeable to water

(C) Water and salt permeable

(D) Impermeable to salts

Explanation:

The ascending limb is impermeable to water but actively transports salts out, diluting the filtrate. This is critical for counter-current multiplication. (Answer: B)

5) Single Correct Answer MCQ:

The descending limb is mainly responsible for:

(A) Salt reabsorption

(B) Water reabsorption

(C) Urine dilution

(D) Acid-base balance

Explanation:

The descending limb is highly permeable to water, allowing reabsorption into medulla, concentrating filtrate. It does not reabsorb salts. (Answer: B)

6) Single Correct Answer MCQ:

Counter-current multiplier system is created by:

(A) Descending limb only

(B) Ascending limb only

(C) Both ascending and descending limbs

(D) Collecting duct

Explanation:

Both limbs of the loop of Henle form the counter-current multiplier system. Descending limb allows water out, ascending limb pumps salts out, creating medullary osmotic gradient for urine concentration. (Answer: C)

7) Assertion-Reason MCQ:

Assertion (A): Descending limb of loop of Henle is water permeable.

Reason (R): It actively pumps salts into medulla.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Descending limb is permeable to water (true), but it does not actively pump salts (false). Salt pumping occurs in ascending limb. (Answer: C)

8) Matching Type MCQ:

Match:

1. Descending limb – (i) Water permeable

2. Ascending limb – (ii) Salt reabsorption

3. Collecting duct – (iii) Water reabsorption regulated by ADH

Options:

(A) 1-i, 2-ii, 3-iii

(B) 1-ii, 2-i, 3-iii

(C) 1-i, 2-iii, 3-ii

(D) 1-iii, 2-ii, 3-i

Explanation:

Correct matches: Descending limb – water permeable, Ascending limb – salt reabsorption, Collecting duct – water reabsorption regulated by ADH. (Answer: A)

9) Fill in the Blanks MCQ:

The ascending limb of loop of Henle is impermeable to _______.

(A) Water

(B) Sodium

(C) Chloride

(D) Urea

Explanation:

The ascending limb actively transports sodium and chloride but is impermeable to water, allowing filtrate dilution. (Answer: A)

10) Choose the correct statements MCQ:

1. Descending limb allows water reabsorption.

2. Ascending limb allows water reabsorption.

3. Ascending limb actively pumps salts.

4. Descending limb actively pumps salts.

Options:

(A) 1 and 3

(B) 2 and 4

(C) 1 and 4

(D) 2 and 3

Explanation:

Correct statements: 1 and 3. Descending limb allows water out, ascending limb actively pumps salts. Other statements are false. (Answer: A)

Topic: Excretory System
Subtopic: Nephron Structure and Function

• Nephron: Functional unit of kidney responsible for urine formation through filtration, reabsorption, and secretion.

• Sodium Reabsorption: Active transport of sodium ions from nephron tubules into blood, crucial for electrolyte balance.

• Proximal Convoluted Tubule (PCT): First part of nephron tubule, major site of reabsorption of water, ions, and nutrients.

• Distal Convoluted Tubule (DCT): Part of nephron regulating sodium, potassium, and pH under hormonal control.

• Henle’s Loop: U-shaped nephron segment creating osmotic gradient for water reabsorption.

• Bowman’s Capsule: Cup-shaped structure surrounding glomerulus, site of filtration.

• Clinical Relevance: Impaired sodium reabsorption leads to electrolyte imbalance, hypertension, and kidney disorders.

Lead Question - 2016 (Phase 2): The part of nephron involved in active reabsorption of sodium is :

1. descending limb of Henle’s loop

2. distal convoluted tubule

3. proximal convoluted tubule

4. Bowman’s capsule

Explanation: The correct answer is (3). The proximal convoluted tubule actively reabsorbs sodium along with glucose, amino acids, and water using sodium-potassium ATPase. This process is vital for maintaining electrolyte balance and blood pressure. Clinically, dysfunction of PCT can result in hyponatremia and impaired kidney function.

Chapter: Human Physiology
Topic: Excretory System
Subtopic: Nephron Structure and Function

• Nephron: Functional unit of kidney responsible for filtration and reabsorption.

• Proximal Convoluted Tubule: Major site for sodium, glucose, and water reabsorption.

• Distal Convoluted Tubule: Fine-tunes electrolyte and pH balance.

• Henle’s Loop: Establishes osmotic gradient for water conservation.

• Sodium Reabsorption: Active transport mechanism using ATP-driven pumps.

1. Which nephron segment is impermeable to water?

1. Descending limb of Henle’s loop

2. Ascending limb of Henle’s loop

3. Proximal convoluted tubule

4. Distal convoluted tubule

Explanation: The correct answer is (2). The ascending limb of Henle’s loop is impermeable to water but actively reabsorbs sodium and chloride ions. This mechanism helps generate the medullary osmotic gradient necessary for urine concentration. Clinically, impairment may cause defective water reabsorption and polyuria.

2. Aldosterone primarily acts on which part of nephron?

1. Proximal convoluted tubule

2. Distal convoluted tubule

3. Bowman’s capsule

4. Collecting duct

Explanation: The correct answer is (2). Aldosterone acts mainly on distal convoluted tubule to increase sodium reabsorption and potassium excretion. Clinically, deficiency of aldosterone causes hyponatremia, hyperkalemia, and hypotension, highlighting the nephron’s hormonal regulation of electrolytes.

3. The main site for glucose reabsorption in nephron is:

1. Proximal convoluted tubule

2. Distal convoluted tubule

3. Loop of Henle

4. Collecting duct

Explanation: The correct answer is (1). Proximal convoluted tubule reabsorbs almost all filtered glucose via sodium-glucose co-transport. Clinical relevance includes glucosuria in diabetes mellitus when transport maximum is exceeded, reflecting the PCT’s crucial role in solute reabsorption.

4. Which nephron segment is mainly responsible for acid-base balance?

1. Proximal convoluted tubule

2. Distal convoluted tubule

3. Descending limb of Henle

4. Bowman’s capsule

Explanation: The correct answer is (2). The distal convoluted tubule secretes hydrogen and bicarbonate ions, maintaining acid-base homeostasis. Clinically, dysfunction can lead to metabolic acidosis or alkalosis, illustrating its importance beyond sodium reabsorption in nephron physiology.

5. Which structure surrounds glomerular capillaries?

1. Proximal convoluted tubule

2. Distal convoluted tubule

3. Bowman’s capsule

4. Collecting duct

Explanation: The correct answer is (3). Bowman’s capsule encloses glomerular capillaries and facilitates ultrafiltration of blood. Clinically, damage to glomerulus or capsule causes proteinuria and hematuria, emphasizing their structural and functional importance in the nephron.

6. Loop of Henle is critical for:

1. Sodium filtration

2. Water conservation

3. Glucose reabsorption

4. Urea excretion

Explanation: The correct answer is (2). Loop of Henle establishes medullary osmotic gradient facilitating water reabsorption from collecting ducts. Clinically, defects reduce urine concentration, leading to polyuria and dehydration, showing its importance in nephron water handling.

7. Assertion (A): Proximal convoluted tubule actively reabsorbs sodium.
Reason (R): It has abundant mitochondria for ATP production supporting active transport.

1. A is true, R is true, R explains A

2. A is true, R is true, R does not explain A

3. A is true, R is false

4. A is false, R is true

Explanation: The correct answer is (1). PCT actively reabsorbs sodium using ATP-dependent sodium-potassium pumps, supported by abundant mitochondria. Clinically, PCT dysfunction affects sodium, glucose, and water reabsorption, leading to electrolyte imbalance and dehydration.

8. Match nephron segments with their primary function:

1. Proximal convoluted tubule

2. Loop of Henle

3. Distal convoluted tubule

4. Bowman’s capsule

A. Filtration of blood
B. Water conservation and osmotic gradient
C. Sodium reabsorption and nutrient recovery
D. Electrolyte regulation and acid-base balance

Explanation: Correct matching: 1-C, 2-B, 3-D, 4-A. PCT reabsorbs sodium and nutrients, Loop of Henle conserves water, DCT regulates electrolytes and pH, Bowman’s capsule filters blood. Clinically, defects in these regions lead to electrolyte imbalance, dehydration, or acid-base disorders.

9. Fill in the blank: Active reabsorption of sodium in nephron primarily occurs in ______.

1. Distal convoluted tubule

2. Proximal convoluted tubule

3. Loop of Henle

4. Bowman’s capsule

Explanation: The correct answer is (2). Sodium is actively reabsorbed in PCT via ATP-driven transport. This maintains electrolyte balance, blood pressure, and fluid volume. Clinical dysfunction causes hyponatremia and impaired renal function, highlighting the critical role of PCT in nephron physiology.

10. Choose correct statements about nephron function:

1. Proximal convoluted tubule reabsorbs most sodium and water

2. Loop of Henle is impermeable to sodium

3. Distal convoluted tubule fine-tunes electrolyte and pH balance

4. Bowman’s capsule performs filtration

Explanation: The correct answers are (1,3,4). PCT reabsorbs sodium and water, DCT regulates electrolytes and acid-base balance, Bowman’s capsule filters blood. Loop of Henle is impermeable to water in ascending limb but reabsorbs sodium. Clinically, these functions are crucial for maintaining fluid and electrolyte homeostasis.

Chapter: Biological Classification

Sub-topic: Virus

Lead Question 2016 (Phase 1): Which of the following statements is wrong for viroids?

A) They lack a protein coat

B) They are smaller than viruses

C) They cause infections

D) Their RNA is of high molecular weight

Answer: D) Their RNA is of high molecular weight

Viroids consist of low molecular weight circular RNA without a protein coat. Their RNA is much smaller than viral genomes, enabling them to infect plants by disrupting cellular processes.

1. Viroids differ from viruses because they:

A) Have a protein coat

B) Lack a protein coat

C) Contain DNA

D) Infect animals

Answer: B) Lack a protein coat

Unlike viruses, viroids do not possess a protein coat, consisting only of naked RNA. This makes them the smallest infectious agents known, mainly infecting plants.

2. The genetic material of viroids is:

A) Double stranded DNA

B) Single stranded circular RNA

C) Double stranded RNA

D) Single stranded linear RNA

Answer: B) Single stranded circular RNA

Viroids contain a single stranded circular RNA molecule that is highly stable and capable of autonomous replication within host plant cells.

3. Which disease is caused by a viroid?

A) Tobacco Mosaic Disease

B) Potato Spindle Tuber Disease

C) Influenza

D) AIDS

Answer: B) Potato Spindle Tuber Disease

This disease is caused by the Potato Spindle Tuber Viroid (PSTVd), one of the first identified viroids affecting plants by causing abnormal growth.

4. Viroids primarily infect:

A) Animals

B) Plants

C) Bacteria

D) Fungi

Answer: B) Plants

Viroids are plant pathogens that interfere with cellular metabolism, causing various diseases and crop damage.

5. The size of viroids compared to viruses is:

A) Larger

B) Smaller

C) Equal

D) Variable

Answer: B) Smaller

Viroids are much smaller than viruses, typically only a few hundred nucleotides long, lacking the protein capsid that viruses have.

6. Assertion-Reason:

Assertion (A): Viroids do not have a protein coat.

Reason (R): Viroids are composed only of a short strand of RNA.

Options:

A) Both A and R are true, and R explains A

B) Both A and R are true, but R does not explain A

C) A is true, R is false

D) A is false, R is true

Answer: A) Both A and R are true, and R explains A

Viroids consist solely of a short RNA strand without a protein coat, which explains their lack of capsid and their unique infection mechanism.

7. Match Column A with Column B:

Column A Column B

1. Viroid A. Infectious RNA without protein coat

2. Virus B. Protein coat with DNA or RNA

3. Bacteria C. Prokaryotic unicellular organism

4. Fungus D. Eukaryotic decomposer organism

Answer: 1 → A, 2 → B, 3 → C, 4 → D

Viroids are infectious naked RNA, viruses have nucleic acid plus protein coat, bacteria are unicellular prokaryotes, and fungi are eukaryotic decomposers.

8. Diagram-based MCQ:

The structure shown lacks a protein coat and consists of a circular RNA molecule. What is this infectious agent?

A) Virus

B) Viroid

C) Bacterium

D) Prion

Answer: B) Viroid

The lack of a protein coat and presence of circular RNA identifies this agent as a viroid, which infects plants causing disease.

9. Fill in the blank:

Viroids are ______ infectious agents that infect plants.

A) DNA-based

B) Proteinaceous

C) RNA-based

D) Virus-like

Answer: C) RNA-based

Viroids consist of RNA alone, without any protein coat, distinguishing them from viruses and other infectious agents.

10. Passage-based MCQ:

Passage: Viroids are the smallest known infectious pathogens. They are composed solely of a short strand of circular RNA and lack a protein coat. They cause several economically important plant diseases by disrupting normal cellular functions.

Which of the following is true about viroids?

A) They contain DNA and infect animals

B) They have a protein coat and infect bacteria

C) They are smaller than viruses and cause plant diseases

D) They are proteinaceous infectious agents