NCERT Solutions for Class 11 Biology Chapter 16 PDF (FREE Download)
FAQs on NCERT Solutions for Class 11 Biology Chapter 16 Excretory Products and Their Elimination
1. What is the glomerular filtration rate (GFR) and how is it regulated in the human kidney as per NCERT Solutions for Class 11 Biology Chapter 16?
Glomerular Filtration Rate (GFR) refers to the volume of filtrate formed per minute by both kidneys, normally about 125 mL/min in adults. Regulation occurs via the juxtaglomerular apparatus (JGA) located between the afferent arteriole and distal convoluted tubule. When GFR decreases, JGA cells release renin, activating the renin-angiotensin mechanism, which restores GFR to normal by adjusting blood pressure and renal blood flow.
2. How does the process of micturition occur and what mechanisms are involved according to CBSE 2025–26 NCERT Solutions?
Micturition is the process of expelling urine from the urinary bladder. It involves the following steps:
- Bladder fills and stretches, activating stretch receptors
- Nerve signals sent to the spinal cord (reflex center)
- Motor neurons stimulate contraction of bladder smooth muscle and relaxation of urethral sphincter
- Urine is expelled voluntarily or involuntarily
3. Explain the countercurrent mechanism in the nephron for urine concentration, as detailed in Excretory Products and Their Elimination NCERT Solutions.
The countercurrent mechanism involves the loop of Henle and vasa recta. Filtrate flows in opposite directions in the descending and ascending limbs of Henle’s loop, while blood in the vasa recta flows counter to this. This arrangement maximizes reabsorption of water and sodium chloride, maintaining medullary osmolarity up to 1200 mOsm/L, thus allowing for the production of concentrated urine.
4. What are the main excretory products in humans, and how are they eliminated according to NCERT Solutions for Class 11 Chapter 16?
- Urea – main nitrogenous waste, excreted in urine via kidneys
- CO2 – eliminated by lungs during respiration
- Excess water and salts – excreted in urine and sweat
- Uric acid and creatinine – excreted through renal system
5. How do the liver, lungs, and skin function as accessory excretory organs in addition to the kidneys in Class 11 Biology Chapter 16?
Liver: Converts toxic ammonia to urea, produces bile pigments and excretes cholesterol.
Lungs: Expel carbon dioxide and small water vapors during breathing.
Skin: Eliminates water, salt, urea, and lactic acid via sweat glands. Sebaceous glands excrete lipids and sterols.
6. What is osmoregulation, and why is it important for excretory products and their elimination as per the CBSE curriculum?
Osmoregulation is the process of maintaining optimum water and electrolyte balance in body fluids. It is vital for homeostasis because it ensures the stability of internal environment, preventing dehydration or overhydration, and balances ions critical for cellular function.
7. Why do terrestrial animals generally excrete urea or uric acid but not ammonia, as discussed in NCERT Class 11 Biology Chapter 16 Solutions?
Ammonia is highly toxic and requires large amounts of water for excretion, which terrestrial animals cannot afford due to limited water availability. Therefore, they convert ammonia to less toxic urea (ureotelic) or uric acid (uricotelic) forms, which conserve water and prevent dehydration.
8. How does the juxtaglomerular apparatus (JGA) help control kidney function in excretion and elimination?
The juxtaglomerular apparatus (JGA) monitors blood pressure and sodium concentration in the kidney. When blood pressure or sodium declines, JGA cells release renin, starting the renin-angiotensin-aldosterone system, which increases blood pressure and sodium reabsorption to restore normal kidney filtration.
9. What is the significance of the proximal convoluted tubule in urine formation, based on Excretory Products and Their Elimination NCERT Solutions?
The proximal convoluted tubule (PCT) is the primary site in the nephron for the reabsorption of glucose, amino acids, water, and essential ions from the filtrate back into the blood, ensuring minimal loss of vital nutrients and contributing to the regulation of pH and blood volume.
10. What happens if GFR drops below normal, and how does the kidney respond according to the latest NCERT Solutions?
When GFR falls, the juxtaglomerular cells release renin, which activates the renin-angiotensin-aldosterone mechanism. This cascade raises blood pressure and enhances sodium and water reabsorption, restoring GFR to its normal range as per Class 11 NCERT.
11. How are urea, creatinine, and uric acid measured or detected as signs of kidney health according to CBSE Class 11 Biology curriculum?
Elevated levels of urea, creatinine, and uric acid in blood are detected through biochemical tests. Persistently high values may indicate kidney dysfunction or failure, as the kidneys are unable to filter and eliminate these wastes adequately. Monitoring these markers helps assess renal health.
12. Describe the role of antidiuretic hormone (ADH) in water reabsorption as per NCERT Solutions for Class 11 Biology Chapter 16.
Antidiuretic hormone (ADH), also called vasopressin, increases the permeability of the distal tubules and collecting ducts to water. This promotes water reabsorption from urine back into the blood, concentrating urine and maintaining body water balance as detailed in CBSE curriculum.
13. What would happen if the ascending limb of Henle's loop was permeable to water, contrary to NCERT Solution explanations?
If the ascending limb of Henle’s loop was permeable to water, it would disrupt the countercurrent multiplication mechanism, resulting in reduced medullary osmolarity and preventing the formation of concentrated urine. Water would move out along the entire loop, impairing the kidney's ability to conserve water.
14. Compare the excretory roles of lungs and skin based on the NCERT Solutions for Class 11 Chapter 16.
Lungs primarily eliminate carbon dioxide and a small amount of water vapor with each exhalation, which is essential for acid-base balance. Skin, by producing sweat, removes water, salts, urea, and lactic acid, aiding thermoregulation and minor excretion. Both serve as accessory excretory organs, but their waste types differ.
15. Why is the kidney considered the chief excretory organ in humans, as emphasized in Excretory Products and Their Elimination NCERT Solutions?
The kidney filters blood, removes the majority of metabolic wastes (especially urea), regulates electrolyte levels, maintains acid-base balance, and controls water content in the body. Its functions are vital and cannot be fully replaced by any other organ according to NCERT Solutions for Class 11 Biology Chapter 16.

















