Excretion is the biological process by which animals remove metabolic wastes and maintain water, ion and acid-base balance.
Important Questions Class 11 Biology Chapter 16 help students practise excretory products and their elimination through definitions, processes and case-based questions.
Every cell produces waste during metabolism, but the body cannot allow ammonia, urea, excess salts, water or carbon dioxide to accumulate. Class 11 Biology Chapter 16 explains how animals remove nitrogenous wastes and how the human kidney forms urine through filtration, reabsorption and secretion. This chapter is important for the 2026-27 exam because it combines factual terms, labelled diagrams, flow-based processes and clinical conditions. Students should revise the nephron, GFR, JGA, ADH, counter current mechanism, micturition and dialysis carefully. These class 11 biology chapter 16 important questions are arranged by question type for faster board-style revision.
Key Takeaways
- nitrogenous wastes: Ammonia, urea and uric acid are the main nitrogenous wastes in animals.
- nephron: Each human kidney has nearly one million nephrons as functional units.
- GFR: A healthy person has a glomerular filtration rate of about 125 mL per minute.
- urine output: Humans form about 180 litres of filtrate daily, but release about 1 to 1.5 litres of urine.
Important Questions Class 11 Biology Chapter 16 Structure 2026-27
| Question Type |
Marks |
Best Answer Style |
| Objective type |
1 mark |
One term, one reason or correct option |
| Very short answer |
2 marks |
30-50 words with direct definition |
| Short answer |
3 marks |
50-80 words with labelled points |
| Long answer |
5 marks |
Process explanation with sequence |
| Case-based |
4 marks |
Concept, data clue and application |
Objective Type Questions from Important Questions Class 11 Biology Chapter 16
Objective questions from this chapter usually test waste types, excretory organs, nephron parts, GFR, hormones and disorders. Students should revise NCERT terms exactly because many options look similar.
Q1. Which nitrogenous waste is the most toxic?
- Urea
b. Uric acid
c. Ammonia
d. Creatinine
Answer: c. Ammonia
Ammonia is the most toxic nitrogenous waste and needs a large amount of water for elimination.
Q2. Which nitrogenous waste is least toxic?
- Ammonia
b. Urea
c. Uric acid
d. Carbon dioxide
Answer: c. Uric acid
Uric acid is least toxic and is removed with minimum water loss.
Q3. Animals that excrete ammonia are called:
- Ureotelic animals
b. Uricotelic animals
c. Ammonotelic animals
d. Osmoregulatory animals
Answer: c. Ammonotelic animals
Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic.
Q4. Mammals mainly excrete nitrogenous wastes as:
- Ammonia
b. Urea
c. Uric acid
d. Carbon dioxide
Answer: b. Urea
Mammals are ureotelic because they mainly excrete urea.
Q5. Birds and reptiles mainly excrete nitrogenous wastes as:
- Ammonia
b. Urea
c. Uric acid
d. Sodium chloride
Answer: c. Uric acid
Birds and reptiles are uricotelic animals.
Q6. The functional unit of the human kidney is:
- Neuron
b. Nephron
c. Alveolus
d. Villi
Answer: b. Nephron
Each kidney has nearly one million nephrons.
Q7. The Bowman’s capsule encloses the:
- DCT
b. PCT
c. Glomerulus
d. Collecting duct
Answer: c. Glomerulus
Glomerulus and Bowman’s capsule together form the renal corpuscle.
Q8. The first step of urine formation is:
- Secretion
b. Reabsorption
c. Glomerular filtration
d. Micturition
Answer: c. Glomerular filtration
Glomerular filtration is carried out by the glomerulus.
Q9. GFR in a healthy individual is approximately:
- 25 mL per minute
b. 75 mL per minute
c. 125 mL per minute
d. 250 mL per minute
Answer: c. 125 mL per minute
The kidneys form about 125 mL filtrate per minute.
Q10. Nearly how much filtrate is reabsorbed by renal tubules?
- 50 per cent
b. 70 per cent
c. 80 per cent
d. 99 per cent
Answer: d. 99 per cent
About 180 litres of filtrate forms daily, but only 1 to 1.5 litres urine is excreted.
Q11. Which hormone increases water reabsorption from the later parts of the tubule?
- Insulin
b. ADH
c. Thyroxine
d. Glucagon
Answer: b. ADH
ADH facilitates water reabsorption and prevents excess water loss.
Q12. The release of urine from the urinary bladder is called:
- Filtration
b. Reabsorption
c. Micturition
d. Dialysis
Answer: c. Micturition
Micturition is controlled by a neural reflex.
Q13. Assertion: Henle’s loop helps in concentrating urine.
Reason: Henle’s loop and vasa recta help maintain an osmotic gradient in the medulla.
- Both Assertion and Reason are true, and Reason explains Assertion
b. Both are true, but Reason does not explain Assertion
c. Assertion is true, Reason is false
d. Assertion is false, Reason is true
Answer: a. Both Assertion and Reason are true, and Reason explains Assertion
The counter current mechanism helps conserve water.
Q14. Assertion: ADH helps in producing concentrated urine.
Reason: ADH increases water reabsorption from the later parts of the tubule.
- Both Assertion and Reason are true, and Reason explains Assertion
b. Both are true, but Reason does not explain Assertion
c. Assertion is true, Reason is false
d. Assertion is false, Reason is true
Answer: a. Both Assertion and Reason are true, and Reason explains Assertion
ADH reduces water loss through urine.
Q15. Fill in the blank: Stone or insoluble mass of crystallised salts formed in the kidney is called ________.
Answer: renal calculi
Renal calculi are commonly called kidney stones.
Very Short Answer Questions from class 11 biology chapter 16 important questions
Very short answers in this chapter usually ask for definitions, names and direct functions. Write the term first, then add one fact from NCERT.
Q16. Define glomerular filtration rate.
Glomerular filtration rate is the amount of filtrate formed by the kidneys per minute. In a healthy person, GFR is approximately 125 mL per minute, which equals about 180 litres per day.
Q17. What is ammonotelism?
Ammonotelism is the process of excreting nitrogenous waste mainly as ammonia. Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic because ammonia can diffuse out easily in water.
Q18. What is meant by osmoregulation?
Osmoregulation is the regulation of water and ion concentration in body fluids. Excretory organs help maintain osmotic balance along with removal of nitrogenous wastes.
Q19. What is micturition?
Micturition is the process of releasing urine from the urinary bladder. It occurs through contraction of bladder muscles and relaxation of the urethral sphincter.
Q20. Name the excretory structures in flatworms and insects.
Flatworms have protonephridia or flame cells as excretory structures. Most insects, including cockroaches, have Malpighian tubules for excretion and osmoregulation.
Q21. What are renal columns?
Renal columns are extensions of the renal cortex between the medullary pyramids. They are also called columns of Bertini.
Q22. What is the role of podocytes?
Podocytes are epithelial cells of Bowman’s capsule. They form filtration slits, which help in the ultrafiltration of blood during urine formation.
Short Answer Questions from excretory products and their elimination class 11 important questions
Short answer questions from Chapter 16 often ask students to explain a part of the nephron or one step of urine formation. Use labelled points for better clarity.
Q23. Explain the three main steps of urine formation.
Urine formation class 11 includes three main steps.
- Glomerular filtration: Blood is filtered in the glomerulus.
- Reabsorption: Useful substances like glucose, amino acids, water and ions are reabsorbed.
- Secretion: H⁺, K⁺ and ammonia are secreted into the filtrate.
These steps help remove wastes and maintain body-fluid balance.
Q24. Distinguish between ammonotelic, ureotelic and uricotelic animals.
| Type |
Main waste |
Examples |
| Ammonotelic |
Ammonia |
Bony fishes, aquatic amphibians |
| Ureotelic |
Urea |
Mammals, many terrestrial amphibians |
| Uricotelic |
Uric acid |
Birds, reptiles, insects |
Ammonia needs maximum water, while uric acid needs minimum water.
Q25. Describe the structure of the human excretory system.
The human excretory system class 11 includes two kidneys, two ureters, a urinary bladder and a urethra.
Kidneys form urine by filtering blood. Ureters carry urine to the urinary bladder. The urinary bladder stores urine until micturition. The urethra releases urine outside the body.
Q26. What are the main parts of a nephron?
A nephron has two main parts: glomerulus and renal tubule.
The renal tubule begins with Bowman’s capsule. It continues as PCT, Henle’s loop, DCT and collecting duct. Glomerulus with Bowman’s capsule forms the renal corpuscle.
Q27. Explain the role of PCT in urine formation.
PCT is lined by brush border epithelium, which increases surface area for reabsorption.
It reabsorbs nearly all essential nutrients and 70 to 80 per cent of electrolytes and water. It also helps maintain pH and ionic balance by secreting hydrogen ions and ammonia.
Q28. Explain the role of DCT in urine formation.
DCT performs conditional reabsorption of sodium ions and water.
It also reabsorbs bicarbonate ions. DCT selectively secretes hydrogen ions, potassium ions and ammonia to maintain pH and sodium-potassium balance in blood.
Q29. What is the importance of JGA in kidney function?
JGA regulates glomerular filtration rate class 11 through renin release.
When GFR falls, JG cells release renin. Renin helps increase glomerular blood flow and restores GFR. This makes JGA important in kidney function and blood pressure regulation.
Q30. Describe the role of liver, lungs and skin in excretion.
Lungs remove carbon dioxide and water. The liver excretes bile pigments, cholesterol, degraded steroid hormones, vitamins and drugs through bile.
Skin removes small amounts of urea, lactic acid and salts through sweat. Sebaceous glands eliminate sterols, hydrocarbons and waxes through sebum.
Long Answer Questions from Important Questions Class 11 Biology Chapter 16
Long answers from this chapter usually ask for full processes. Add sequence, structures and function terms clearly.
Q31. Explain urine formation in humans.
Urine formation class 11 takes place in nephrons through filtration, reabsorption and secretion.
- Glomerular filtration: Blood enters the glomerulus through the afferent arteriole. Glomerular blood pressure filters plasma into Bowman’s capsule. Plasma proteins usually do not pass into the filtrate.
- Reabsorption: Useful substances are reabsorbed from the filtrate into blood. Glucose, amino acids, sodium ions and water are reabsorbed in different parts of the renal tubule.
- Secretion: Tubular cells secrete hydrogen ions, potassium ions and ammonia into the filtrate. This helps maintain ionic and acid-base balance.
- Concentration: Henle’s loop, vasa recta and collecting duct help concentrate urine by conserving water.
A healthy adult releases about 1 to 1.5 litres of urine per day.
Q32. Explain the counter current mechanism class 11.
The counter current mechanism class 11 explains how the kidney produces concentrated urine.
The flow of filtrate in the two limbs of Henle’s loop is in opposite directions. Blood flow in the two limbs of vasa recta is also in opposite directions. This arrangement helps maintain an osmotic gradient in the medulla.
The gradient increases from about 300 mOsmol/L in the cortex to about 1200 mOsmol/L in the inner medulla. Sodium chloride and urea mainly create this gradient.
Water moves out from the collecting duct because of this gradient. As a result, urine becomes concentrated.
Human kidneys can produce urine nearly four times more concentrated than the initial filtrate.
Q33. Describe the regulation of kidney function.
Kidney function is regulated by hormonal feedback involving the hypothalamus, JGA and heart.
When body fluid volume falls, osmoreceptors stimulate the hypothalamus. ADH is released from the neurohypophysis. ADH increases water reabsorption from later parts of the tubule and reduces water loss.
When GFR falls, JG cells release renin. Renin activates the renin-angiotensin mechanism. Angiotensin II increases blood pressure and GFR. It also stimulates aldosterone release, which increases sodium and water reabsorption.
The heart releases ANF when atrial blood flow increases. ANF causes vasodilation and lowers blood pressure.
These mechanisms balance GFR, blood pressure and water levels.
Q34. Explain the structure of the nephron with functions of its parts.
The nephron is the structural and functional unit of the kidney.
- Glomerulus: It is a tuft of capillaries formed by the afferent arteriole. It filters blood.
- Bowman’s capsule: It surrounds the glomerulus and receives the filtrate.
- PCT: It reabsorbs essential nutrients, water and electrolytes. It also secretes hydrogen ions and ammonia.
- Henle’s loop: It helps maintain medullary osmolarity and concentrates the filtrate.
- DCT: It allows conditional reabsorption of sodium ions and water. It also secretes hydrogen and potassium ions.
- Collecting duct: It reabsorbs large amounts of water and helps produce concentrated urine.
The DCTs of many nephrons open into collecting ducts.
Q35. Explain disorders of excretory system class 11.
Disorders of excretory system class 11 include uremia, renal calculi and glomerulonephritis.
Uremia occurs when urea accumulates in blood due to kidney malfunction. It is harmful and may lead to kidney failure. Hemodialysis can remove urea from the blood using an artificial kidney.
Renal calculi are stones or insoluble masses of crystallised salts formed inside the kidney. They can block urine flow and cause pain.
Glomerulonephritis is inflammation of the glomeruli. It affects filtration and kidney function.
In acute renal failure, kidney transplantation may be needed. A healthy kidney from a donor is transplanted into the patient.
Case-Based Questions from class 11 biology chapter 16 excretory products and their elimination
Case-based questions usually combine a small clinical or experimental situation with kidney function. Identify the process first, then explain the reason.
Q36. Case Study: Low water intake and concentrated urine
A student drinks very little water during summer. By evening, the urine volume decreases and the urine becomes darker. The body tries to conserve water through hormonal regulation.
Q36(a). Which hormone helps conserve water?
The hormone is ADH.
ADH increases water reabsorption from the later parts of the renal tubule.
Q36(b). Which organ releases ADH?
ADH is released from the neurohypophysis.
The hypothalamus stimulates its release when body fluid volume falls.
Q36(c). Why does urine become concentrated?
More water is reabsorbed from the filtrate.
This reduces urine volume and increases urine concentration.
Q37. Case Study: Fall in GFR
A patient has reduced glomerular blood flow. The kidney responds by activating a specialised region near the afferent arteriole and DCT. This region releases renin and helps restore GFR.
Q37(a). Name the specialised region.
The specialised region is JGA.
JGA means juxta glomerular apparatus.
Q37(b). Which substance is released by JG cells?
JG cells release renin.
Renin helps activate the renin-angiotensin mechanism.
Q37(c). How does this help the kidney?
It increases glomerular blood pressure and restores GFR.
This supports normal filtration.
Q38. Case Study: Artificial kidney
A patient has high urea levels in blood due to kidney failure. Blood is passed through a dialysing unit after adding heparin. Nitrogenous wastes move out into the dialysis fluid.
Q38(a). Name the condition caused by urea accumulation in blood.
The condition is uremia.
It occurs when kidneys fail to remove urea properly.
Q38(b). Name the process used to remove urea.
The process is hemodialysis.
It removes urea from blood through a dialysing unit.
Q38(c). Why does urea move into dialysis fluid?
Dialysis fluid lacks nitrogenous wastes.
So, urea moves from blood to dialysis fluid along the concentration gradient.
Diagram-Based Questions from human excretory system class 11
Diagram questions from this chapter usually focus on kidney structure, nephron structure and urine formation. Label the diagram first, then explain the function.
Q39. Draw a labelled diagram of the human excretory system and mention its parts.
The human excretory system includes:
- Pair of kidneys
- Pair of ureters
- Urinary bladder
- Urethra
Kidneys form urine. Ureters carry urine to the urinary bladder. The urinary bladder stores urine. The urethra releases urine outside the body.
Q40. Draw a labelled diagram of a nephron and mark its main regions.
A nephron diagram should show:
- Bowman’s capsule
- Glomerulus
- PCT
- Henle’s loop
- DCT
- Collecting duct
- Afferent arteriole
- Efferent arteriole
- Peritubular capillaries
- Vasa recta
The diagram should show that PCT, DCT and renal corpuscle lie in the cortex, while Henle’s loop extends into the medulla.
Chapter-Wise Revision for Important Questions for Class 11 Biology Chapter 16
Important questions for class 11 biology chapter 16 should be revised through three layers: definitions, processes and regulation. Definitions help in 1-mark and 2-mark questions. Processes help in 3-mark and 5-mark answers.
Students should first revise nitrogenous wastes and excretory organs across animals. Then they should move to human kidney structure, nephron parts and urine formation.
After this, the regulation topics should be practised. ADH, JGA, renin-angiotensin mechanism and ANF are commonly tested because they connect kidney function with blood pressure and water balance.
Finally, students should revise disorders like uremia, renal calculi and glomerulonephritis. These topics help answer clinical and case-based questions.
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