Chapter 19: Excretory Products and Their Elimination – Long Answer Type Questions
CBSE Class 11 Biology Long 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: Long Answer Questions (LAQs)
- Answer Length: 120–150 words
- Exam Relevance: CBSE Class 11 Annual Examination, School & Periodic Assessments
Section A: Excretory System (Q1–Q9)
Q1. Explain excretion and its significance in humans.
Answer:
Excretion is the biological process by which metabolic waste products are eliminated from the body. In humans, metabolism produces nitrogenous wastes like urea, along with excess salts and water. Accumulation of these wastes can be toxic and interfere with normal cellular functions. Excretion helps maintain internal balance or homeostasis by regulating the composition of body fluids, including pH, osmotic pressure, and ion concentration. The kidneys play a major role by filtering blood and forming urine. Other organs like lungs, skin, and liver also assist in excretion. Thus, excretion is essential for survival and efficient functioning of the human body.
Q2. Describe the human excretory system with the functions of its parts.
Answer:
The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Kidneys are the main excretory organs that filter blood to remove nitrogenous wastes and regulate water and ion balance. Ureters transport urine from kidneys to the urinary bladder by peristaltic movements. The urinary bladder temporarily stores urine until it is expelled. The urethra carries urine out of the body during micturition. Together, these organs ensure efficient removal of wastes and maintenance of internal balance.
Q3. Describe the external and internal structure of the kidney.
Answer:
Kidneys are bean-shaped organs located in the abdominal cavity on either side of the vertebral column. Each kidney is protected by a fibrous capsule. Internally, the kidney is differentiated into an outer cortex and an inner medulla. The medulla contains renal pyramids whose tips open into the renal pelvis. The renal pelvis is a funnel-shaped cavity that collects urine and leads it into the ureter. Numerous nephrons present in cortex and medulla carry out urine formation. This structural organization supports efficient filtration and excretion.
Q4. What is a nephron? Describe its structure.
Answer:
A nephron is the structural and functional unit of the kidney responsible for urine formation. Each nephron consists of a renal corpuscle and a renal tubule. The renal corpuscle includes the glomerulus, a network of capillaries, and Bowman’s capsule surrounding it. The renal tubule consists of the proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct. These parts work together to filter blood, reabsorb useful substances, and secrete wastes, forming urine.
Q5. Differentiate between cortical and juxtamedullary nephrons.
Answer:
Cortical nephrons are located mainly in the cortex of the kidney and have short loops of Henle that extend only slightly into the medulla. They are more numerous and play a role in general filtration and reabsorption. Juxtamedullary nephrons are fewer in number but have long loops of Henle extending deep into the medulla. These nephrons are crucial for concentrating urine by maintaining the osmotic gradient through the counter current mechanism. Thus, both types complement each other in kidney function.
Q6. Explain the role of other organs in excretion besides kidneys.
Answer:
Besides kidneys, several organs assist in excretion. Lungs remove carbon dioxide and water vapour produced during respiration. The skin excretes sweat containing water, salts, and small amounts of urea through sweat glands. The liver converts toxic ammonia into urea and excretes bile pigments like bilirubin through bile. These organs collectively reduce the load on kidneys and help maintain metabolic balance. Hence, excretion in humans is a coordinated function involving multiple organs.
Q7. What are nitrogenous wastes? Name different types.
Answer:
Nitrogenous wastes are metabolic by-products formed during protein and nucleic acid metabolism. The main types are ammonia, urea, and uric acid. Ammonia is highly toxic and excreted by aquatic animals. Urea is moderately toxic and excreted by ureotelic animals like humans. Uric acid is least toxic and excreted by uricotelic animals. Humans primarily excrete urea through kidneys, making urea the chief nitrogenous waste.
Q8. Explain why humans are ureotelic organisms.
Answer:
Humans are called ureotelic organisms because urea is the primary nitrogenous waste excreted in urine. Urea is formed in the liver from ammonia and carbon dioxide. It is less toxic than ammonia and requires less water for elimination, making it suitable for terrestrial life. Kidneys efficiently remove urea from blood and excrete it in urine. This adaptation helps conserve water while safely eliminating nitrogenous wastes.
Q9. Describe renal calculi and uremia.
Answer:
Renal calculi, or kidney stones, are solid deposits formed by precipitation of salts such as calcium oxalate in the kidney. They can obstruct urine flow and cause severe pain. Uremia is a condition caused by accumulation of urea in blood due to kidney failure. It leads to toxicity and can be fatal if untreated. Both conditions highlight the importance of proper kidney function in waste elimination.
Section B: Urine Formation (Q10–Q18)
Q10. Explain the process of urine formation.
Answer:
Urine formation occurs through three main processes: glomerular filtration, selective reabsorption, and tubular secretion. In glomerular filtration, blood plasma is filtered under pressure in the glomerulus into Bowman’s capsule. Selective reabsorption occurs mainly in the PCT, where useful substances like glucose, amino acids, ions, and water are reabsorbed into blood. Tubular secretion occurs mainly in DCT, where substances like hydrogen and potassium ions are secreted into the tubule. These processes together form urine and regulate body balance.
Q11. Describe glomerular filtration and GFR.
Answer:
Glomerular filtration is the first step of urine formation. Blood enters the glomerulus under high pressure, forcing plasma into Bowman’s capsule. The filtrate resembles plasma but lacks proteins and blood cells. The glomerular filtration rate (GFR) is the volume of filtrate formed per minute by both kidneys. In a healthy adult, GFR is about 125 mL per minute. GFR is an important indicator of kidney function and is regulated by blood pressure and hormones.
Q12. Explain selective reabsorption with examples.
Answer:
Selective reabsorption is the process by which useful substances are reabsorbed from the filtrate into the blood. It occurs mainly in the proximal convoluted tubule. Glucose, amino acids, sodium ions, and large amounts of water are reabsorbed actively or passively. This process ensures that essential substances are not lost in urine. Different segments of the nephron reabsorb substances according to the body’s needs, helping maintain homeostasis.
Q13. What is tubular secretion? Explain its role.
Answer:
Tubular secretion is the active transfer of substances from blood into the renal tubules. It occurs mainly in the distal convoluted tubule. Substances like hydrogen ions, potassium ions, and ammonia are secreted. Tubular secretion helps regulate pH, maintain ionic balance, and remove additional wastes from blood. It complements filtration and reabsorption, ensuring precise control over urine composition.
Q14. Explain the role of loop of Henle in urine concentration.
Answer:
The loop of Henle plays a crucial role in concentrating urine. The descending limb is permeable to water, allowing water reabsorption, while the ascending limb is impermeable to water but actively transports salts. This creates an osmotic gradient in the medulla. The gradient enables reabsorption of water from the collecting ducts, resulting in concentrated urine. This mechanism conserves water in the body.
Q15. Describe the counter current mechanism.
Answer:
The counter current mechanism operates between the loop of Henle and the vasa recta. The flow of filtrate in opposite directions maintains a high osmotic gradient in the medulla. Sodium and chloride ions are actively transported in the ascending limb, while water moves out of the descending limb. Vasa recta preserves this gradient. This mechanism is essential for producing concentrated urine and conserving water.
Q16. Explain the role of collecting duct in urine formation.
Answer:
The collecting duct receives filtrate from several nephrons. It plays an important role in determining final urine concentration. Under the influence of antidiuretic hormone (ADH), water is reabsorbed from the collecting duct. This concentrates urine and reduces urine volume. In the absence of ADH, less water is reabsorbed, producing dilute urine.
Q17. Why are proteins absent in normal urine?
Answer:
Proteins are absent in normal urine because they are large molecules that cannot pass through the glomerular filtration membrane. The filtration barrier selectively allows small molecules to pass while retaining proteins and blood cells in blood. Presence of proteins in urine indicates kidney damage.
Q18. Explain micturition.
Answer:
Micturition is the process of expelling urine from the urinary bladder. When the bladder fills, stretch receptors send signals to the spinal cord, initiating the micturition reflex. It involves contraction of bladder muscles and relaxation of urethral sphincter. In humans, it is under voluntary control.
Section C: Regulation of Kidney Function (Q19–Q25)
Q19. Explain hormonal regulation of kidney function.
Answer:
Kidney function is regulated by several hormones. Antidiuretic hormone (ADH) increases water reabsorption in collecting ducts, producing concentrated urine. Aldosterone increases sodium reabsorption and potassium excretion, regulating electrolyte balance. Atrial natriuretic factor (ANF) reduces sodium reabsorption, lowering blood volume and pressure. These hormones ensure proper regulation of body fluids and blood pressure.
Q20. Describe the juxtaglomerular apparatus (JGA).
Answer:
The juxtaglomerular apparatus is a specialized structure formed by DCT cells, afferent arteriole, and glomerulus. It regulates blood pressure and glomerular filtration rate. When blood pressure falls, JGA releases renin, activating mechanisms that raise blood pressure and restore GFR.
Q21. Explain the role of renin–angiotensin system.
Answer:
The renin–angiotensin system regulates blood pressure and kidney function. Renin released by JGA converts angiotensinogen into angiotensin, which increases blood pressure and aldosterone secretion. This enhances sodium and water reabsorption, restoring normal blood volume.
Q22. What is dialysis? Describe hemodialysis.
Answer:
Dialysis is an artificial method of removing wastes from blood when kidneys fail. In hemodialysis, blood is passed through a dialyzer containing a semipermeable membrane. Wastes diffuse into dialysis fluid and purified blood returns to the body.
Q23. Explain kidney transplantation.
Answer:
Kidney transplantation involves replacing a failed kidney with a healthy donor kidney. It restores normal kidney function but requires tissue matching and immunosuppressive drugs to prevent rejection.
Q24. Why is water balance important for the body?
Answer:
Water balance maintains blood volume, osmotic pressure, and proper cellular functions. Kidneys regulate water balance by adjusting urine concentration under hormonal control.
Q25. How do kidneys help maintain homeostasis?
Answer:
Kidneys maintain homeostasis by removing wastes, regulating water and electrolyte balance, maintaining blood pH, and controlling blood pressure.
NCERT & CBSE Compliance Note
✔ Strictly based on NCERT Class 11 Biology
✔ Answer length maintained (120–150 words)
✔ Framework-aligned and exam-focused
✔ Ideal for CBSE Class 11 board examinations