Chapter 19: Excretory Products and Their Elimination – Short Answer Type Questions
CBSE Class 11 Biology Short Answer Questions – Excretory Products and Their Elimination (NCERT)
Course & Examination Details
- Course: CBSE Class 11 Biology
- Prescribed By: Central Board of Secondary Education
- Based On: NCERT
- Unit: Unit V – Human Physiology
- Chapter: Chapter 19 – Excretory Products and Their Elimination
- Question Type: Short Answer Questions (SAQs)
- Answer Length: 60–80 words
- Exam Relevance: CBSE Class 11 Annual Exam, Unit Tests, Periodic Assessments
Section A: Excretory System (Q1–Q18)
Q1. Define excretion and explain its importance.
Answer:
Excretion is the process of removal of metabolic waste products from the body. It is essential to prevent accumulation of toxic substances like urea and excess salts, which can disrupt cellular activities. Excretion helps maintain internal balance, or homeostasis, by regulating water, ion concentration, and pH of body fluids.
Q2. Why are humans called ureotelic organisms?
Answer:
Humans are called ureotelic because they excrete nitrogenous waste mainly in the form of urea. Urea is less toxic than ammonia and requires moderate water for elimination, making it suitable for terrestrial life.
Q3. Name the organs of the human excretory system and state their functions.
Answer:
The human excretory system includes kidneys, ureters, urinary bladder, and urethra. Kidneys filter blood and form urine, ureters transport urine to the bladder, the bladder stores urine temporarily, and the urethra expels urine outside the body.
Q4. Describe the location of kidneys in humans.
Answer:
The kidneys are bean-shaped organs located in the abdominal cavity on either side of the vertebral column. The right kidney is slightly lower than the left due to the presence of the liver.
Q5. Explain the internal structure of the kidney.
Answer:
Internally, the kidney has an outer cortex and an inner medulla. The medulla contains renal pyramids that open into the renal pelvis, which collects urine and leads it into the ureter.
Q6. What is a nephron? Mention its significance.
Answer:
A nephron is the structural and functional unit of the kidney. It filters blood and forms urine through filtration, reabsorption, and secretion, thereby maintaining fluid and ionic balance.
Q7. Describe the structure of a nephron briefly.
Answer:
A nephron consists of a renal corpuscle made of glomerulus and Bowman’s capsule, followed by a renal tubule including PCT, loop of Henle, DCT, and collecting duct.
Q8. Differentiate between cortical and juxtamedullary nephrons.
Answer:
Cortical nephrons are located mainly in the cortex and have short loops of Henle. Juxtamedullary nephrons have long loops extending deep into the medulla and play a major role in urine concentration.
Q9. What is the role of afferent and efferent arterioles?
Answer:
The afferent arteriole brings blood into the glomerulus, while the efferent arteriole carries blood away. Their diameter difference maintains high pressure for effective filtration.
Q10. Explain the function of ureters.
Answer:
Ureters transport urine from kidneys to the urinary bladder through peristaltic movements, ensuring continuous flow of urine.
Q11. What is renal pelvis and its function?
Answer:
Renal pelvis is a funnel-shaped cavity that collects urine from collecting ducts and channels it into the ureter.
Q12. What is tissue fluid and how is it related to excretion?
Answer:
Tissue fluid is derived from blood plasma and surrounds body cells. It facilitates exchange of wastes, which are later removed by blood and excretory organs.
Q13. Name any two nitrogenous wastes excreted by humans.
Answer:
Urea and uric acid are nitrogenous wastes excreted by humans, mainly through kidneys.
Q14. How does the skin help in excretion?
Answer:
Skin excretes sweat containing water, salts, and small amounts of urea through sweat glands, aiding in excretion and temperature regulation.
Q15. State one excretory function of lungs.
Answer:
Lungs excrete carbon dioxide and water vapour produced during cellular respiration.
Q16. What is uremia?
Answer:
Uremia is a condition caused by accumulation of urea in blood due to kidney failure, leading to serious health problems.
Q17. Define renal calculi.
Answer:
Renal calculi are kidney stones formed due to precipitation of salts like calcium oxalate in the kidney.
Q18. What is glomerulonephritis?
Answer:
Glomerulonephritis is inflammation of glomeruli that reduces filtration efficiency of kidneys.
Section B: Urine Formation (Q19–Q34)
Q19. Describe glomerular filtration.
Answer:
Glomerular filtration is the first step of urine formation where blood plasma is filtered under pressure in the glomerulus. The filtrate enters Bowman’s capsule and lacks proteins and blood cells.
Q20. What is glomerular filtration rate (GFR)?
Answer:
GFR is the volume of filtrate formed per minute by kidneys. In a healthy adult, it is about 125 mL per minute.
Q21. Explain selective reabsorption.
Answer:
Selective reabsorption is the process by which essential substances like glucose, amino acids, ions, and water are reabsorbed from filtrate into blood, mainly in PCT.
Q22. Why is PCT important in urine formation?
Answer:
PCT reabsorbs most of the filtered glucose, amino acids, sodium ions, and water, making it crucial for maintaining body balance.
Q23. What is tubular secretion?
Answer:
Tubular secretion involves active transport of substances like hydrogen, potassium, and ammonia from blood into renal tubules to regulate pH and ion balance.
Q24. Role of loop of Henle in urine formation.
Answer:
The loop of Henle establishes an osmotic gradient in the medulla, essential for concentrating urine and conserving water.
Q25. Explain counter current mechanism.
Answer:
Counter current mechanism operates between loop of Henle and vasa recta, maintaining osmotic gradient that allows reabsorption of water from collecting ducts.
Q26. Why is ascending limb impermeable to water?
Answer:
The ascending limb actively transports salts but does not allow water movement, helping build medullary osmotic gradient.
Q27. What is the role of collecting duct?
Answer:
The collecting duct reabsorbs water under hormonal control and carries concentrated urine towards renal pelvis.
Q28. Name substances normally present in urine.
Answer:
Urine normally contains urea, uric acid, creatinine, excess salts, and water.
Q29. How does kidney help in maintaining pH balance?
Answer:
Kidneys regulate blood pH by selective reabsorption and secretion of hydrogen and bicarbonate ions.
Q30. Why is urine concentrated in desert mammals?
Answer:
Desert mammals have long loops of Henle and efficient counter current mechanism, allowing them to conserve water by producing concentrated urine.
Q31. What is micturition?
Answer:
Micturition is the process of expelling urine from the urinary bladder through the urethra under voluntary control.
Q32. How is urine formation linked to blood pressure?
Answer:
Changes in blood pressure affect GFR; low pressure reduces filtration, while high pressure increases urine formation.
Q33. What happens if reabsorption fails?
Answer:
Failure of reabsorption leads to loss of essential nutrients and water in urine, disturbing homeostasis.
Q34. Why are proteins absent in normal urine?
Answer:
Proteins are too large to pass through glomerular membrane and are retained in blood during filtration.
Section C: Regulation of Kidney Function (Q35–Q50)
Q35. Role of ADH in kidney function.
Answer:
ADH increases water reabsorption in collecting ducts, reducing urine volume and producing concentrated urine.
Q36. Source of ADH.
Answer:
ADH is secreted by the posterior pituitary gland.
Q37. Explain the function of aldosterone.
Answer:
Aldosterone increases sodium reabsorption and potassium excretion in renal tubules, regulating electrolyte balance.
Q38. What is atrial natriuretic factor (ANF)?
Answer:
ANF is a hormone released by atria of heart that promotes sodium excretion, lowering blood volume and pressure.
Q39. Define juxtaglomerular apparatus (JGA).
Answer:
JGA is a specialized structure near the glomerulus that regulates GFR and blood pressure.
Q40. What is the function of renin?
Answer:
Renin helps regulate blood pressure by activating the renin–angiotensin system.
Q41. How does JGA respond to low blood pressure?
Answer:
JGA releases renin, which increases blood pressure and restores normal GFR.
Q42. What is dialysis?
Answer:
Dialysis is an artificial process to remove wastes from blood when kidneys fail to function properly.
Q43. Explain hemodialysis briefly.
Answer:
In hemodialysis, blood is passed through a dialyzer where wastes diffuse into dialysis fluid before returning to body.
Q44. Why is kidney transplantation preferred over dialysis?
Answer:
Kidney transplantation restores normal renal function and offers a permanent solution compared to repeated dialysis.
Q45. What is renal failure?
Answer:
Renal failure is loss of kidney function leading to accumulation of wastes in blood.
Q46. How does liver assist excretion?
Answer:
Liver converts ammonia into urea and excretes bile pigments, aiding excretion.
Q47. Role of lungs in maintaining acid-base balance.
Answer:
Lungs regulate blood pH by controlling carbon dioxide elimination.
Q48. What is diuresis?
Answer:
Diuresis is increased urine output due to reduced ADH secretion.
Q49. Why is water balance important for the body?
Answer:
Water balance maintains blood volume, osmotic pressure, and proper cellular functioning.
Q50. How do kidneys maintain homeostasis?
Answer:
Kidneys maintain homeostasis by regulating waste removal, water balance, electrolyte concentration, and blood pH.
NCERT & CBSE Compliance Note
✔ Strictly based on NCERT Class 11 Biology
✔ Answer length maintained at 60–80 words
✔ Framework-aligned and exam-oriented
✔ Ideal for CBSE Class 11 board exams