Excretory Products and their Elimination — Practice Questions with Answers
30 free MCQs on Excretory Products and their Elimination with worked answers and explanations. Nitrogenous waste, kidney structure, urine formation in the nephron, and hormonal regulation of excretion.
Below are 30 practice questions on Excretory Products and their Elimination, sorted Easy → Hard. Tap “Show answer & explanation” under any question to check yourself. Want the full theory first? Read the Excretory Products and their Elimination notes.
Filtrate flows through four functionally distinct stages of the nephron: Bowman's capsule filters blood, the PCT reabsorbs most useful substances unconditionally, the Loop of Henle builds a concentration gradient via counter-current exchange, the DCT secretes selected substances, and the collecting duct performs the final ADH-controlled water reabsorption.
Easy — 10 questions
Q1.
The largest organ in the human body is:
A Liver
B Brain
C Skin
D Heart
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Answer: C. Skin
Why: The skin is the largest organ of the human body. It protects internal organs, regulates temperature, and senses the environment.
Q2.
The functional unit of the kidney is the:
A Glomerulus
B Ureter
C Nephron
D Bowman capsule
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Answer: C. Nephron
Why: The nephron is the structural and functional unit of the kidney. Each kidney has about 1 million nephrons.
Q3.
Urine is produced in the kidneys and flows to the bladder via:
A Urethra
B Ureter
C Renal vein
D Fallopian tube
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Answer: B. Ureter
Why: Urine flows from kidneys through ureters to the urinary bladder. From the bladder it exits through the urethra.
Q4.
The main excretory product of protein metabolism in humans is:
A Uric acid
B Urea
C Ammonia
D CO2
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Answer: B. Urea
Why: Urea is the main nitrogenous waste in humans, formed in the liver from ammonia (produced by deamination of amino acids).
Q5.
Which structure in the nephron is mainly responsible for filtering blood to form the initial filtrate?
A Collecting duct
B Glomerulus
C Loop of Henle
D Distal convoluted tubule
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Answer: B. Glomerulus
Why: The glomerulus, a network of capillaries within Bowman's capsule, filters blood under pressure to form the initial glomerular filtrate.
Q6.
Animals that excrete ammonia as their main nitrogenous waste are called:
A Uricotelic
B Aminotelic
C Ureotelic
D Ammonotelic
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Answer: D. Ammonotelic
Why: Ammonotelic animals, such as most bony fish, excrete nitrogenous waste mainly as ammonia, which requires large amounts of water for safe elimination.
Q7.
Birds and reptiles mainly excrete nitrogenous waste as:
A Urea
B Uric acid
C Ammonia
D Creatinine
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Answer: B. Uric acid
Why: Birds and reptiles are uricotelic, excreting nitrogenous waste mainly as uric acid, which is fairly insoluble and can be excreted with minimal water loss.
Q8.
Which of these is a paired excretory organ in humans, located on either side of the vertebral column?
A Liver
B Urinary bladder
C Kidney
D Pancreas
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Answer: C. Kidney
Why: Humans have a pair of bean-shaped kidneys located on either side of the vertebral column, behind the peritoneum, that filter blood and form urine.
Q9.
The process by which useful substances like glucose are taken back from the filtrate into the blood in the nephron is called:
A Micturition
B Reabsorption
C Secretion
D Filtration
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Answer: B. Reabsorption
Why: Reabsorption is the process, mainly occurring in the proximal convoluted tubule, by which useful substances such as glucose, amino acids, and water are returned from the filtrate to the blood.
Q10.
The expulsion of urine from the urinary bladder is known as:
A Osmoregulation
B Micturition
C Ultrafiltration
D Filtration
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Answer: B. Micturition
Why: Micturition is the process by which urine, stored in the urinary bladder, is voluntarily expelled from the body through the urethra.
Medium — 10 questions
Q11.
Glomerular filtration rate (GFR) refers to:
A Volume of urine excreted from the bladder per hour
B Volume of blood filtered by glomeruli per minute (normal ~125 mL/min)
C Rate at which sodium and water are reabsorbed in the proximal tubule
D Concentration of glucose spilling into urine during hyperglycemia
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Answer: B. Volume of blood filtered by glomeruli per minute (normal ~125 mL/min)
Why: GFR = volume of fluid filtered from glomerular capillaries into Bowman's capsule per minute. Normal ~125 mL/min (180 L/day). Key kidney function indicator.
Q12.
Antidiuretic hormone (ADH) acts on the:
A Glomerulus to increase the overall rate of filtration
B Collecting duct to increase water reabsorption
C Loop of Henle specifically, bypassing the collecting duct
D Urinary bladder directly, increasing its muscular tone
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Answer: B. Collecting duct to increase water reabsorption
Why: ADH (vasopressin) increases water permeability of collecting duct and distal tubule by inserting aquaporin channels. More water reabsorbed, concentrated urine produced.
Q13.
Reabsorption of glucose and amino acids from the filtrate occurs mainly in the:
A Distal convoluted tubule
B Loop of Henle
C Collecting duct
D Proximal convoluted tubule
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Answer: D. Proximal convoluted tubule
Why: The proximal convoluted tubule (PCT) reabsorbs almost all of the filtered glucose and amino acids, along with most Na+, K+ and water.
Q14.
The process of tubular secretion in the nephron mainly helps to:
A Filter plasma proteins out of the blood at Bowman's capsule in general clinical practice
B Maintain ionic and acid-base balance by adding H+ and K+ to the filtrate
C Concentrate filtrate as it enters Bowman's capsule in most reference accounts
D Reabsorb filtered glucose back into the peritubular blood as frequently documented
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Answer: B. Maintain ionic and acid-base balance by adding H+ and K+ to the filtrate
Why: Tubular secretion moves substances such as H+, K+ and ammonia from peritubular capillaries into the filtrate, helping maintain ionic and acid-base balance.
Q15.
Ammonia is converted to urea mainly in the:
A Liver
B Kidney
C Lungs
D Pancreas
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Answer: A. Liver
Why: Ammonia produced from protein metabolism is converted to the less toxic urea in the liver via the ornithine cycle, then transported to kidneys for excretion.
Q16.
Animals that excrete nitrogenous waste mainly as uric acid are called:
A Ammonotelic
B Aminotelic
C Ureotelic
D Uricotelic
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Answer: D. Uricotelic
Why: Uricotelic animals (birds, reptiles, insects) excrete uric acid, which requires little water and can be removed as a semi-solid paste, conserving water.
Q17.
The high osmolarity in the medullary interstitium of the kidney is mainly maintained by the:
A Counter-current flow in the loop of Henle and vasa recta
B Renal artery and renal vein together in typical laboratory settings
C Proximal convoluted tubule reabsorbing salts as generally observed
D Glomerulus and Bowman's capsule together under normal conditions
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Answer: A. Counter-current flow in the loop of Henle and vasa recta
Why: The counter-current arrangement of the loop of Henle and vasa recta progressively increases osmolarity towards the inner medulla, enabling concentrated urine formation.
Q18.
A decrease in blood pressure or blood volume stimulates the release of which hormone to help restore them?
A Aldosterone
B Insulin
C Atrial natriuretic factor
D Calcitonin
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Answer: A. Aldosterone
Why: Low blood pressure activates the renin-angiotensin system, leading to aldosterone release, which increases Na+ and water reabsorption to raise blood volume and pressure.
Q19.
Compared to the glomerular filtrate, the urine that finally leaves the body is much more concentrated mainly because of:
A Reabsorption of most filtered water along the tubules and collecting duct
B Secretion of extra water into the filtrate by the tubules according to most studies
C Filtration of plasma proteins at the glomerulus under usual circumstances
D A rise in glomerular filtration rate during the day in the majority of documented cases
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Answer: A. Reabsorption of most filtered water along the tubules and collecting duct
Why: About 99% of the glomerular filtrate is reabsorbed along the tubules and collecting duct, mainly as water, concentrating the small remaining volume into urine.
Q20.
Atrial Natriuretic Factor (ANF) is released by the heart in response to:
A Low sodium concentration in the blood under most conditions studied
B Increased blood volume stretching the atrial wall
C A drop in overall blood volume as widely reported
D A drop in systemic blood pressure in standard reference material
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Answer: B. Increased blood volume stretching the atrial wall
Why: Increased blood volume stretches the atria, triggering ANF release, which dilates blood vessels and reduces blood pressure, acting as a check on the renin-angiotensin system.
Hard — 10 questions
Q21.
The juxtaglomerular apparatus (JGA) controls blood pressure by:
A Increasing the filtration surface area of glomerular capillaries on demand quickly in many documented cases
B Macula densa sensing tubular flow and releasing renin from JG cells when blood pressure drops (RAAS activation)
C Synthesizing aldosterone directly within the nephron for rapid sodium retention purposes according to conventional understanding
D Selectively blocking the passage of plasma proteins across Bowman's capsule membrane in routine practice overall
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Answer: B. Macula densa sensing tubular flow and releasing renin from JG cells when blood pressure drops (RAAS activation)
Why: JGA: senses low blood pressure or low Na+ in tubule. Macula densa cells signal JG cells to secrete renin, activating RAAS (angiotensin II → aldosterone → Na+/water retention → BP rise).
Q22.
The counter-current multiplier in the loop of Henle:
A It filters plasma proteins out of the blood as it enters the glomerulus using size-selective podocyte slits rather than any salt-gradient mechanism in the medulla
B Creates a hyperosmotic medullary gradient by active NaCl transport in thick ascending limb, enabling concentrated urine production
C It reabsorbs all filtered glucose completely via SGLT transporters in the descending limb, a transporter and nephron segment actually responsible for glucose, not osmotic gradient formation
D It synthesizes and releases the enzyme renin into the afferent arteriole, a hormone-secreting function carried out by granular cells, not the loop of Henle itself
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Answer: B. Creates a hyperosmotic medullary gradient by active NaCl transport in thick ascending limb, enabling concentrated urine production
Why: Counter-current multiplier: thick ascending limb actively pumps NaCl without water (impermeable to water). This concentrates medullary interstitium. Descending limb (permeable to water) loses water. Together they create an osmotic gradient to concentrate urine.
Q23.
The renin-angiotensin-aldosterone system (RAAS) chain is:
A Renin cleaves angiotensinogen to Ang I, ACE converts to Ang II, Ang II stimulates aldosterone secretion from adrenal cortex
B Renin is converted directly into aldosterone by hepatic liver enzymes without any intermediate steps under most conditions encountered
C Aldosterone secreted by the adrenal cortex stimulates juxtaglomerular cells to release more renin as frequently observed in practice
D ACE inhibitors bind angiotensin II receptors directly to amplify overall RAAS signaling activity in many documented cases
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Answer: A. Renin cleaves angiotensinogen to Ang I, ACE converts to Ang II, Ang II stimulates aldosterone secretion from adrenal cortex
Why: RAAS: renin (from JG cells) cleaves angiotensinogen to angiotensin I. ACE (in lungs) converts Ang I to Ang II. Ang II: vasoconstricts + stimulates aldosterone (zona glomerulosa) → Na+/water retention.
Q24.
Aquaporin-2 channels in collecting duct are regulated by:
A ADH binding directly to the AQP2 channel pore to physically widen its overall diameter according to conventional understanding
B ADH-stimulated PKA phosphorylation of AQP2, causing vesicle fusion with apical membrane (more water channels inserted)
C Aldosterone-driven upregulation of sodium channels located on the basolateral membrane surface in routine practice
D Renin-mediated cleavage of angiotensinogen occurring within the collecting duct lumen region overall in most cases
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Answer: B. ADH-stimulated PKA phosphorylation of AQP2, causing vesicle fusion with apical membrane (more water channels inserted)
Why: ADH (vasopressin) binds V2 receptors in collecting duct → Gs → adenylyl cyclase → cAMP → PKA → phosphorylates AQP2. Phospho-AQP2 vesicles fuse with apical membrane, inserting more water channels.
Q25.
ADH (vasopressin) acts on the kidney to conserve water mainly by:
A Stimulating renin release from nearby juxtaglomerular cells
B Raising glomerular filtration rate to filter more blood plasma
C Raising water permeability of the distal tubule and collecting duct
D Blocking sodium reabsorption within the proximal tubule
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Answer: C. Raising water permeability of the distal tubule and collecting duct
Why: ADH increases water permeability of the distal convoluted tubule and collecting duct by promoting insertion of aquaporin channels, allowing more water reabsorption and concentrated urine formation.
Q26.
The descending limb of the loop of Henle is relatively impermeable to which substance, a key feature of the counter-current mechanism?
A Glucose dissolved in the filtrate
B Water
C Urea, but not other ions
D Sodium and chloride ions
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Answer: D. Sodium and chloride ions
Why: The descending limb is permeable to water but largely impermeable to Na+ and Cl-, while the ascending limb is impermeable to water but actively transports out Na+ and Cl-, together creating the medullary osmotic gradient.
Q27.
If the afferent arteriole of a glomerulus constricts, the most direct effect on kidney function would be:
A A rise in glomerular filtration rate from higher blood flow
B No change, since arteriole diameter does not affect filtration
C A surge of glucose being secreted directly into urine
D A fall in glomerular filtration rate from reduced blood flow
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Answer: D. A fall in glomerular filtration rate from reduced blood flow
Why: Constriction of the afferent arteriole reduces blood flow and pressure within the glomerular capillaries, lowering the glomerular filtration rate.
Q28.
Urea recycling between the collecting duct and the loop of Henle contributes to the kidney's concentrating ability mainly by:
A Adding to medullary osmolarity, which aids water reabsorption from the duct
B Reducing sodium reabsorption mainly along the nephron
C Pumping water out of the collecting duct without any osmotic gradient
D Diluting the medullary interstitium to limit water loss
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Answer: A. Adding to medullary osmolarity, which aids water reabsorption from the duct
Why: Urea diffuses out of the collecting duct into the medullary interstitium and is recycled back into the loop of Henle, contributing to the high medullary osmolarity that drives water reabsorption from the collecting duct.
Q29.
In uremia, a condition associated with kidney failure, urea accumulates in the blood mainly because:
A The liver has stopped producing urea from ammonia
B The urinary bladder fails to store urine properly
C Urea is being overproduced by the pancreas instead
D The kidneys cannot filter and excrete urea efficiently
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Answer: D. The kidneys cannot filter and excrete urea efficiently
Why: Uremia results from impaired kidney function, in which urea and other nitrogenous wastes are not adequately filtered out of the blood, leading to their accumulation and potential toxicity.
Q30.
During hemodialysis, a patient's blood is passed through a dialysing fluid that has a composition similar to plasma but lacking nitrogenous wastes, mainly so that:
A Red blood cells pass freely into the dialysing fluid in most observed cases
B Nitrogenous wastes diffuse out down their gradient while useful solutes stay
C Plasma proteins diffuse out of the blood into the fluid in standard reference material
D Water is pumped into the blood from the dialysing fluid under most conditions studied
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Answer: B. Nitrogenous wastes diffuse out down their gradient while useful solutes stay
Why: Because the dialysing fluid lacks nitrogenous wastes, these substances diffuse out of the blood down their concentration gradient across the dialysis membrane, while essential solutes at similar concentrations are retained in the blood.