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Excretory Products and Their Elimination – CBSE NCERT Study Resources

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11th

11th - Biology

Excretory Products and Their Elimination

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Overview of the Chapter: Excretory Products and Their Elimination

This chapter explores the mechanisms by which living organisms eliminate nitrogenous wastes and maintain osmotic balance. It covers the structure and function of excretory organs in humans, the process of urine formation, and disorders related to the excretory system.

Excretion: The biological process of removal of harmful metabolic wastes from the body.

Types of Excretory Products

Different organisms excrete nitrogenous wastes in various forms:

  • Ammonia: Highly toxic, requires large amounts of water for elimination (e.g., aquatic animals).
  • Urea: Less toxic, excreted by mammals, amphibians, and some marine fishes.
  • Uric Acid: Least toxic, excreted in paste-like form by birds and reptiles.

Human Excretory System

The human excretory system consists of:

  • Kidneys: Bean-shaped organs that filter blood and produce urine.
  • Ureters: Tubes that carry urine from kidneys to the urinary bladder.
  • Urinary Bladder: Stores urine temporarily.
  • Urethra: Releases urine from the body.

Nephron: The functional unit of the kidney, responsible for filtration, reabsorption, and secretion.

Process of Urine Formation

Urine formation involves three key steps:

  1. Glomerular Filtration: Blood is filtered in the glomerulus, forming filtrate.
  2. Reabsorption: Essential substances (glucose, amino acids, water) are reabsorbed in renal tubules.
  3. Secretion: Additional wastes (H+, K+, ammonia) are secreted into the filtrate.

Regulation of Kidney Function

Kidney function is regulated by:

  • Hormonal Control: Antidiuretic hormone (ADH), aldosterone, and atrial natriuretic peptide (ANP).
  • Neural Control: Sympathetic nervous system adjusts blood flow to kidneys.

Disorders of the Excretory System

Common disorders include:

  • Uremia: Accumulation of urea in blood due to kidney failure.
  • Renal Calculi: Formation of kidney stones.
  • Glomerulonephritis: Inflammation of glomeruli.

Dialysis: A medical procedure to filter blood artificially in case of kidney failure.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Define excretion.
Answer:
Definition: Elimination of metabolic wastes like urea and CO2.
Question 2:
Name the primary excretory organ in humans.
Answer:

Our textbook shows kidneys as the primary excretory organ.

Question 3:
What is glomerular filtration rate (GFR)?
Answer:
Definition: Volume of filtrate formed by kidneys per minute (~125 mL/min).
Question 4:
Identify the structural and functional unit of the kidney.
Answer:

We studied nephrons as the functional unit of kidneys.

Question 5:
List two nitrogenous wastes excreted by humans.
Answer:
  • Urea
  • Uric acid
Question 6:
Which hormone regulates water reabsorption in kidneys?
Answer:

Antidiuretic hormone (ADH) controls water reabsorption.

Question 7:
What causes the yellow color of urine?
Answer:

Urochrome pigment gives urine its yellow color.

Question 8:
Name the blood vessel bringing blood to the glomerulus.
Answer:

Afferent arteriole supplies blood to glomerulus.

Question 9:
Define osmoregulation.
Answer:
Definition: Maintenance of water and solute balance in body fluids.
Question 10:
Which part of nephron has microvilli for absorption?
Answer:

Proximal convoluted tubule contains microvilli.

Question 11:
What is renal calculi commonly called?
Answer:

Kidney stones are termed renal calculi.

Question 12:
Name the muscular tubes carrying urine to bladder.
Answer:

Ureters transport urine from kidneys to bladder.

Question 13:
Which enzyme helps in RAAS mechanism?
Answer:

Renin initiates the RAAS pathway.

Question 14:
What is micturition?
Answer:
Definition: Process of expelling urine from the bladder.
Question 15:
Name the structural and functional unit of the kidney.
Answer:

The structural and functional unit of the kidney is the nephron. It consists of a glomerulus and a renal tubule, which filter blood and form urine.

Question 16:
What is the role of podocytes in the kidney?
Answer:

Podocytes are specialized cells in the glomerulus that form filtration slits. They prevent large molecules like proteins from entering the Bowman's capsule during ultrafiltration.

Question 17:
Define glomerular filtration rate (GFR).
Answer:

Glomerular filtration rate (GFR) is the volume of filtrate formed by both kidneys per minute (approx. 125 mL/min in humans). It indicates kidney efficiency.

Question 18:
Why is the loop of Henle critical in urine concentration?
Answer:

The loop of Henle creates a high osmolarity gradient in the medulla by countercurrent mechanism, enabling water reabsorption in the collecting duct for concentrated urine.

Question 19:
Name the hormone that regulates water reabsorption in the kidneys.
Answer:

Antidiuretic hormone (ADH) or vasopressin regulates water reabsorption in the collecting duct by increasing its permeability.

Question 20:
What is the function of the juxtaglomerular apparatus (JGA)?
Answer:

The JGA regulates glomerular filtration rate (GFR) and blood pressure by releasing renin in response to low blood flow or sodium levels.

Question 21:
How does the proximal convoluted tubule (PCT) contribute to urine formation?
Answer:

The PCT reabsorbs 70-80% of filtrate, including glucose, amino acids, and ions, via active and passive transport, maintaining pH and electrolyte balance.

Question 22:
What causes the dark yellow color of urine in dehydration?
Answer:

Dark yellow urine results from concentrated urochrome pigment due to reduced water content, as the kidneys conserve water under dehydration.

Question 23:
Differentiate between ureters and urethra.
Answer:
  • Ureters: Carry urine from kidneys to bladder.
  • Urethra: Expels urine from bladder to outside.
Question 24:
What is the significance of aldosterone in kidney function?
Answer:

Aldosterone increases sodium reabsorption and potassium excretion in the distal convoluted tubule (DCT), regulating blood pressure and electrolyte balance.

Question 25:
Why is ammonia not a common nitrogenous waste in humans?
Answer:

Ammonia is highly toxic and requires large water for excretion. Humans convert it to less toxic urea via the ornithine cycle in the liver.

Question 26:
Name the condition caused by the accumulation of uric acid crystals in joints.
Answer:

Gout is caused by uric acid crystal deposition in joints, leading to inflammation and pain, often due to metabolic disorders.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
What is the role of podocytes in the nephron?
Answer:

Podocytes are specialized cells in the Bowman's capsule that wrap around the glomerular capillaries. They form filtration slits to prevent large molecules like proteins from entering the filtrate.

Question 2:
How does ADH regulate water reabsorption in the kidneys?
Answer:

Antidiuretic hormone (ADH) increases water permeability in the collecting duct by inserting aquaporins, reducing urine volume and concentrating it when the body is dehydrated.

Question 3:
What is the significance of the counter-current mechanism in the kidney?
Answer:

The counter-current mechanism in the loop of Henle maintains a high osmotic gradient in the medulla, enabling efficient water reabsorption and concentrated urine formation.

Question 4:
List two nitrogenous wastes excreted by humans.
Answer:
  • Urea (formed in the liver from ammonia)
  • Uric acid (from nucleic acid metabolism)
Question 5:
Why is the proximal convoluted tubule (PCT) called the major reabsorption site?
Answer:

The PCT reabsorbs 70-80% of filtrate components like glucose, amino acids, and electrolytes through active and passive transport, making it the primary reabsorption site.

Question 6:
Differentiate between micturition and urination.
Answer:

Micturition is the reflex process of emptying the bladder, while urination is the voluntary act of expelling urine. Both terms are often used interchangeably.

Question 7:
What happens if the juxtaglomerular apparatus (JGA) is damaged?
Answer:

Damage to the JGA disrupts renin secretion, impairing blood pressure regulation and sodium balance via the renin-angiotensin system.

Question 8:
Explain the term renal threshold for glucose.
Answer:

The renal threshold for glucose (180 mg/dL) is the maximum blood glucose level the kidneys can fully reabsorb. Excess glucose spills into urine, as seen in diabetes.

Question 9:
How does aldosterone influence kidney function?
Answer:

Aldosterone enhances sodium reabsorption and potassium excretion in the distal convoluted tubule, regulating blood pressure and electrolyte balance.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of podocytes in the formation of glomerular filtrate.
Answer:

Podocytes are specialized cells in the Bowman's capsule that wrap around the glomerular capillaries. They have foot-like extensions called pedicels that create filtration slits. These slits act as a fine sieve, allowing small molecules like water, glucose, and ions to pass into the glomerular filtrate while blocking larger proteins and blood cells. This selective filtration ensures efficient urine formation.

Question 2:
Describe the counter-current mechanism in the loop of Henle and its significance.
Answer:

The counter-current mechanism involves the flow of filtrate in opposite directions in the ascending and descending limbs of the loop of Henle.

1. The descending limb is permeable to water but not ions, leading to water loss and concentrated filtrate.
2. The ascending limb actively pumps out Na+ and Cl-, making the medulla hypertonic.

This mechanism maintains a high osmotic gradient in the medulla, enabling water reabsorption in the collecting duct and production of concentrated urine.

Question 3:
Differentiate between ureotelic and uricotelic excretion with examples.
Answer:
  • Ureotelic organisms excrete nitrogenous waste as urea (e.g., humans, mammals). Urea is less toxic and requires moderate water for excretion.
  • Uricotelic organisms excrete waste as uric acid (e.g., birds, reptiles). Uric acid is non-toxic and excreted as a semi-solid paste, conserving water.

Ureotelism is adaptive for terrestrial life with moderate water availability, while uricotelism is suited for water-scarce environments.

Question 4:
What is the importance of the juxtaglomerular apparatus (JGA) in kidney function?
Answer:

The JGA is a specialized structure where the afferent arteriole contacts the distal convoluted tubule.

1. It regulates glomerular filtration rate (GFR) by releasing renin when blood pressure drops.
2. Renin triggers the RAAS pathway, increasing Na+ reabsorption and blood volume.

Thus, JGA maintains kidney efficiency and systemic blood pressure.

Question 5:
Explain the process of tubular secretion and its role in urine formation.
Answer:

Tubular secretion is the active transport of substances like H+, K+, and drugs from blood into the filtrate in the renal tubules.

1. It occurs mainly in the proximal convoluted tubule and collecting duct.
2. Helps in maintaining acid-base balance (by secreting H+) and eliminating toxins.

This step fine-tunes urine composition alongside filtration and reabsorption.

Question 6:
How does ADH regulate water reabsorption in the kidney?
Answer:

Antidiuretic hormone (ADH) is released by the posterior pituitary when the body is dehydrated.

1. ADH binds to receptors on the collecting duct cells, increasing their permeability to water.
2. This allows more water to be reabsorbed into the bloodstream, reducing urine volume and making it more concentrated.

ADH thus helps maintain blood pressure and osmolality by conserving water during water scarcity.

Question 7:
Explain the process of tubular secretion in urine formation.
Answer:

Tubular secretion is the active transport of substances like H+ ions, K+ ions, and creatinine from the blood into the renal tubule.

1. It occurs mainly in the distal convoluted tubule and collecting duct.
2. This process helps in maintaining pH balance, electrolyte levels, and removing excess toxins.

Tubular secretion ensures the final composition of urine is adjusted to meet the body's needs.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the counter-current mechanism in the nephron and its role in urine concentration. How does it exemplify biological efficiency?
Answer:
Theoretical Framework

The counter-current mechanism involves the flow of filtrate in opposite directions in the loop of Henle and vasa recta, creating a concentration gradient in the medulla. Our textbook shows this maximizes water reabsorption.

Evidence Analysis
  • The descending limb is permeable to water but not ions, concentrating filtrate.
  • The ascending limb actively pumps out NaCl, diluting filtrate.
  • Vasa recta maintain the gradient via counter-current exchange.
Critical Evaluation

This mechanism reduces energy expenditure by 70% compared to passive diffusion, as per NCERT data. Desert mammals like kangaroo rats exemplify its efficiency.

Question 2:
Compare ammonotelism, ureotelism, and uricotelism with examples. Why do terrestrial animals prefer ureotelism?
Answer:
Theoretical Framework

Nitrogenous waste excretion evolves based on habitat: ammonotelism (aquatic), ureotelism (terrestrial), and uricotelism (birds/reptiles).

Evidence Analysis
  • Ammonia (toxic, soluble) in bony fish.
  • Urea (less toxic) in mammals like humans.
  • Uric acid (non-toxic, paste) in birds.
Critical Evaluation

Ureotelism balances water conservation (1g urea needs 50ml water) and toxicity. Our textbook cites camel adaptations as evidence.

Question 3:
Describe the renin-angiotensin mechanism during low blood pressure. How does it integrate with the excretory system?
Answer:
Theoretical Framework

The renin-angiotensin system (RAS) regulates blood pressure and fluid balance. Juxtaglomerular cells release renin when BP drops.

Evidence Analysis
  • Renin converts angiotensinogen to angiotensin I.
  • ACE enzymes in lungs form angiotensin II.
  • Causes vasoconstriction and aldosterone release.
Critical Evaluation

NCERT highlights RAS increases Na+ reabsorption, raising blood volume. Patients with kidney disease often exhibit RAS overactivity.

Question 4:
Analyze the autoregulation of GFR via myogenic and tubuloglomerular feedback. Why is precise GFR control vital?
Answer:
Theoretical Framework

GFR is maintained at ~125ml/min through autoregulation involving afferent arteriole adjustments and macula densa signals.

Evidence Analysis
  • Myogenic response: Arteriole constricts if BP rises.
  • Tubuloglomerular feedback: Macula densa detects NaCl levels.
  • ATP/adenosine mediates feedback.
Critical Evaluation

Prevents kidney damage from hypertension while ensuring waste removal. NCERT cites GFR fluctuations beyond 10% as pathological.

Question 5:
Critically evaluate hemodialysis as an artificial kidney technology. What are its limitations compared to renal transplantation?
Answer:
Theoretical Framework

Hemodialysis filters blood externally using semipermeable membranes, mimicking nephron function.

Evidence Analysis
  • Removes urea/creatinine via diffusion.
  • Requires 3-4 weekly sessions (4hrs each).
  • Anticoagulants prevent clotting.
Critical Evaluation

While life-saving, it lacks hormonal functions (no erythropoietin). NCERT states transplants restore 90% function vs. 15% by dialysis.

Question 6:
Explain the process of urine formation in the human kidney with emphasis on the role of nephrons. Include the three main steps involved.
Answer:

The process of urine formation in the human kidney involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. These steps occur in the functional unit of the kidney called the nephron.

1. Glomerular Filtration: This occurs in the glomerulus, where blood is filtered under high pressure. Water, salts, glucose, and urea pass through the glomerular membrane into the Bowman's capsule, forming the filtrate. Larger molecules like proteins and blood cells remain in the blood.

2. Tubular Reabsorption: The filtrate moves through the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). Essential substances like glucose, amino acids, and ions (Na+, K+) are reabsorbed into the blood. Water is reabsorbed in the collecting duct under the influence of ADH (Antidiuretic Hormone).

3. Tubular Secretion: Waste products like urea, creatinine, and excess ions (H+, K+) are actively secreted into the tubule from the blood. This helps maintain electrolyte balance and pH.

The final urine is concentrated in the collecting duct and excreted via the ureter, bladder, and urethra. Nephrons play a crucial role in maintaining homeostasis by regulating water and solute balance.

Question 7:
Describe the mechanism of counter-current exchange in the kidney and its significance in urine concentration. Support your answer with a well-labeled diagram.
Answer:

The counter-current mechanism in the kidney is essential for concentrating urine and conserving water. It involves two key processes: counter-current multiplier (in the loop of Henle) and counter-current exchanger (in the vasa recta).

1. Counter-Current Multiplier:
The descending limb of the loop of Henle is permeable to water but not ions, causing water to move out, concentrating the filtrate.
The ascending limb is impermeable to water but actively pumps out Na+ and Cl-, diluting the filtrate.
This creates a gradient where the medulla becomes hypertonic, aiding water reabsorption.

2. Counter-Current Exchanger:
The vasa recta (blood capillaries) run parallel to the loop of Henle.
As blood flows down, it loses water and gains solutes, becoming concentrated.
As blood flows up, it gains water and loses solutes, maintaining the medullary gradient.

Significance:
- Enables the kidney to produce concentrated urine, conserving water.
- Maintains osmotic balance in the body.
- Regulates blood pressure and volume.

Diagram (Description):
A well-labeled diagram should include:
- Loop of Henle (descending and ascending limbs)
- Vasa recta (blood flow direction)
- Medullary gradient (increasing osmolarity towards the inner medulla)
- Arrows showing ion and water movement.

Question 8:
Explain the process of urine formation in the human kidney with emphasis on the role of nephrons.
Answer:

The process of urine formation in the human kidney involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. Each step is crucial for maintaining homeostasis by removing waste while retaining essential substances.

Glomerular filtration occurs in the glomerulus, where blood pressure forces water, salts, glucose, and urea out of the blood into the Bowman's capsule. This forms the filtrate.

Tubular reabsorption takes place in the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). Essential substances like glucose, amino acids, and ions are reabsorbed into the blood.

Tubular secretion occurs in the DCT and collecting duct, where additional wastes like creatinine and excess H+ ions are secreted into the filtrate.

The nephron's counter-current mechanism in the loop of Henle ensures water conservation by creating a concentration gradient in the medulla. Finally, the filtrate becomes urine, which is stored in the urinary bladder before excretion.

Question 9:
Describe the role of the kidneys in maintaining the pH balance of blood. Include the mechanisms involved.
Answer:

The kidneys play a vital role in regulating blood pH (around 7.4) through two key mechanisms: reabsorption of bicarbonate (HCO3-) and excretion of hydrogen ions (H+).

Reabsorption of bicarbonate: In the PCT, HCO3- combines with H+ to form H2CO3, which breaks down into CO2 and H2O. CO2 diffuses back into cells, reforming HCO3-, which re-enters the blood to buffer acidity.

Excretion of H+ ions: Excess H+ is secreted into the DCT and collecting duct via Na+/H+ exchangers and H+ ATPase pumps. These ions combine with phosphate (HPO42-) or ammonia (NH3) to form excretable compounds like NH4+.

Additionally, the kidneys adjust the production of new HCO3- to replace lost buffers. This dual action ensures blood pH remains stable despite metabolic fluctuations.

Question 10:
Explain the process of urine formation in the human kidneys, highlighting the role of nephrons and associated mechanisms.
Answer:

The process of urine formation in the human kidneys involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. These processes occur in the functional units of the kidneys called nephrons.

1. Glomerular Filtration:
Blood enters the glomerulus through the afferent arteriole, where high pressure forces water, ions, glucose, and urea out of the blood into the Bowman's capsule. This fluid is called the glomerular filtrate. Larger molecules like proteins and blood cells remain in the blood.

2. Tubular Reabsorption:
The filtrate moves through the proximal convoluted tubule (PCT), where essential substances like glucose, amino acids, and ions (Na+, K+) are reabsorbed into the blood. Water is reabsorbed in the loop of Henle and distal convoluted tubule (DCT) through osmosis.

3. Tubular Secretion:
In the DCT and collecting duct, waste products like urea, creatinine, and excess ions (H+, K+) are actively secreted into the filtrate from the blood. This helps maintain pH and electrolyte balance.

The final urine is concentrated in the collecting duct under the influence of antidiuretic hormone (ADH), which regulates water reabsorption. The urine then passes through the ureters to the bladder for storage and eventual elimination.

Additional Points:
The counter-current mechanism in the loop of Henle ensures efficient water and ion reabsorption. The kidneys also play a role in maintaining blood pressure through the renin-angiotensin system.

Question 11:
Explain the process of urine formation in the human kidneys, highlighting the role of nephrons and associated structures.
Answer:

The process of urine formation in the human kidneys involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. Each step is crucial for maintaining homeostasis by removing waste while retaining essential substances.

1. Glomerular Filtration: This occurs in the glomerulus, a network of capillaries in the Bowman's capsule. Blood pressure forces water, salts, glucose, and urea out of the blood into the Bowman's capsule, forming the filtrate. Larger molecules like proteins and blood cells remain in the blood.

2. Tubular Reabsorption: The filtrate moves through the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). Essential substances like glucose, amino acids, and ions (Na+, K+) are actively or passively reabsorbed into the blood. Water is reabsorbed in the collecting duct under the influence of ADH (antidiuretic hormone).

3. Tubular Secretion: In the DCT and collecting duct, excess ions (K+, H+) and toxins like creatinine are actively secreted into the filtrate to maintain electrolyte and pH balance.

The final urine, now concentrated, passes through the ureters to the bladder for storage and eventual elimination. This process ensures waste removal while conserving vital nutrients and water.

Value-added note: The countercurrent mechanism in the loop of Henle and vasa recta enhances water reabsorption, making urine hypertonic. This adaptation is vital for water conservation in terrestrial animals.

Question 12:
Explain the process of urine formation in the human kidney, highlighting the role of nephrons. Include the three main steps involved and the significance of each step.
Answer:

The process of urine formation in the human kidney involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. These steps occur in the functional unit of the kidney called the nephron.

1. Glomerular Filtration:
This occurs in the glomerulus, where blood is filtered under high pressure. The glomerular filtrate contains water, glucose, salts, urea, and other small molecules. Larger molecules like proteins and blood cells are retained in the blood. This step is crucial for removing waste products from the bloodstream.

2. Tubular Reabsorption:
In the proximal convoluted tubule (PCT), essential substances like glucose, amino acids, and ions are reabsorbed back into the blood. Water is also reabsorbed in the loop of Henle and distal convoluted tubule (DCT). This step ensures that useful substances are not lost in urine.

3. Tubular Secretion:
In the DCT and collecting duct, additional waste products like excess ions (K+, H+) and drugs are actively secreted into the filtrate. This step helps in maintaining the body's pH and electrolyte balance.

The nephron plays a vital role in maintaining homeostasis by regulating the composition and volume of blood. The final urine formed is concentrated in the collecting duct and excreted via the ureter, bladder, and urethra.

Question 13:
Explain the process of urine formation in the human kidneys, highlighting the role of nephrons. Include a brief note on the counter-current mechanism.
Answer:

The process of urine formation in the human kidneys involves three main steps: glomerular filtration, tubular reabsorption, and tubular secretion. Nephrons, the functional units of the kidney, play a crucial role in this process.

1. Glomerular Filtration: Blood enters the glomerulus under high pressure, forcing water, salts, glucose, and urea into the Bowman's capsule. This filtrate is called glomerular filtrate.

2. Tubular Reabsorption: Essential substances like glucose, amino acids, and ions are reabsorbed in the proximal convoluted tubule (PCT), loop of Henle, and distal convoluted tubule (DCT). Water is reabsorbed in the collecting duct.

3. Tubular Secretion: Waste products like creatinine and excess ions are actively secreted into the tubule for excretion.

The counter-current mechanism in the loop of Henle and vasa recta helps maintain a concentration gradient in the medulla, enabling water reabsorption. This mechanism ensures efficient urine concentration and water conservation.

Question 14:
Describe the role of the liver, lungs, and skin in excretion. How do these organs complement the excretory function of the kidneys?
Answer:

While the kidneys are the primary excretory organs, the liver, lungs, and skin also play vital roles in excretion and homeostasis.

1. Liver: The liver detoxifies harmful substances like ammonia by converting it into urea (via the ornithine cycle). It also excretes bile pigments (bilirubin) derived from hemoglobin breakdown into the intestines.

2. Lungs: They remove carbon dioxide (a metabolic waste) and small amounts of water vapor during exhalation. This helps maintain blood pH.

3. Skin: Sweat glands excrete water, salts (NaCl), and small amounts of urea through sweat, aiding in thermoregulation and waste removal.

These organs complement the kidneys by:

  • Processing toxins before they reach the kidneys (liver).
  • Removing gaseous wastes that kidneys cannot handle (lungs).
  • Providing an alternative excretory route during excessive heat or water retention (skin).
Together, they ensure efficient elimination of diverse waste products from the body.

Question 15:
Explain the process of ultrafiltration in the nephron and describe how the glomerular filtration rate (GFR) is regulated. Provide a labeled diagram of the nephron showing the site of ultrafiltration.
Answer:

Ultrafiltration is the first step in urine formation, occurring in the glomerulus of the nephron. The afferent arteriole brings blood to the glomerulus, where high pressure forces water, ions, glucose, and small molecules out of the blood into the Bowman's capsule. This filtrate is called the glomerular filtrate.

The glomerular filtration rate (GFR) is regulated by:

  • Autoregulation: The juxtaglomerular apparatus (JGA) monitors filtrate flow and adjusts arteriole diameter to maintain GFR.
  • Hormonal control: Antidiuretic hormone (ADH) and aldosterone fine-tune water and electrolyte reabsorption.
  • Neural control: Sympathetic nerves can constrict arterioles to reduce GFR during stress.

Here’s a simple labeled diagram of the nephron showing the glomerulus (site of ultrafiltration):

[Diagram: Nephron structure with labels: Glomerulus, Bowman’s capsule, Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule, Collecting duct]

Question 16:
Describe the counter-current mechanism in the kidney and explain its significance in urine concentration. How does the vasa recta contribute to this process?
Answer:

The counter-current mechanism is a key process in the kidney that concentrates urine by maintaining a high osmotic gradient in the medullary interstitium. It involves two components:

  • Counter-current multiplier (Loop of Henle): The descending limb is permeable to water but not ions, while the ascending limb actively pumps out Na+ and Cl−, creating a gradient.
  • Counter-current exchanger (vasa recta): The vasa recta (capillaries around the Loop of Henle) maintain the gradient by slowing blood flow and passively exchanging ions and water.

Significance: This mechanism allows the kidney to produce concentrated urine, conserving water in the body. The vasa recta prevents the washout of the medullary gradient by acting as a passive exchange system.

For example, in dehydration, ADH increases water reabsorption in the collecting duct, utilizing this gradient to form concentrated urine.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A patient with chronic kidney disease shows reduced urine output and high urea levels. Explain the role of nephrons in filtration and how dysfunction leads to these symptoms.
Answer:
Case Deconstruction

Nephrons filter blood via glomerular filtration, reabsorb nutrients, and secrete wastes. Dysfunction reduces filtration efficiency.

Theoretical Application
  • Damaged nephrons impair urea excretion, raising blood levels.
  • Reduced GFR (glomerular filtration rate) decreases urine output.
Critical Evaluation

Our textbook shows nephron damage is irreversible, aligning with the patient's chronic symptoms. Dialysis mimics filtration, proving nephron centrality.

Question 2:
Compare aquatic and terrestrial organisms' nitrogen excretion strategies. Why might a fish excrete ammonia while a bird excretes uric acid?
Answer:
Case Deconstruction

Ammonia is toxic but water-soluble, while uric acid is less toxic but energy-intensive.

Theoretical Application
  • Fish use water to dilute ammonia (ammonotelism).
  • Birds conserve water via uricotelism, needing less hydration.
Critical Evaluation

We studied how habitat dictates excretion: aquatic animals prioritize solubility, while terrestrial ones minimize water loss, as seen in NCERT examples.

Question 3:
Analyze how loop of Henle and ADH regulate urine concentration. Use desert mammals as an example.
Answer:
Case Deconstruction

The loop creates an osmotic gradient; ADH increases water reabsorption in collecting ducts.

Theoretical Application
  • Desert rodents have longer loops for maximal water retention.
  • ADH release rises in dehydration, concentrating urine.
Critical Evaluation

Our textbook shows kangaroo rats survive without water, proving the loop’s efficiency. ADH’s role is validated by diuretic drugs blocking it.

Question 4:
A diabetic patient has glucose in urine (glycosuria). Link this to tubular maximum and kidney function.
Answer:
Case Deconstruction

Normally, kidneys reabsorb all glucose via tubular maximum (Tm). Excess glucose exceeds Tm.

Theoretical Application
  • High blood glucose saturates transporters, causing glycosuria.
  • This signals uncontrolled diabetes, as per NCERT.
Critical Evaluation

We studied Tm’s limit (180 mg/dL). Glycosuria confirms hyperglycemia, emphasizing the kidney’s role as a diagnostic tool.

Question 5:
A patient exhibits symptoms like proteinuria and edema. Based on our study of glomerular filtration, explain the possible malfunction and its consequences.
Answer:
Case Deconstruction

The symptoms suggest impaired glomerular filtration, likely due to damage in the podocytes or basement membrane, allowing proteins to leak into urine.

Theoretical Application
  • Healthy glomeruli prevent large molecules like proteins from filtering.
  • Damage disrupts the selective permeability, causing proteinuria.
Critical Evaluation

Edema results from reduced blood osmotic pressure due to protein loss, as per Starling’s forces. This aligns with our textbook’s explanation of nephrotic syndrome.

Question 6:
Compare countercurrent mechanism in the kidney with a desert mammal’s adaptation. How does this ensure water conservation?
Answer:
Case Deconstruction

Both systems maximize water reabsorption. The loop of Henle creates a concentration gradient, while desert mammals have longer loops.

Theoretical Application
  • In kidneys, the countercurrent multiplier concentrates urine.
  • Desert mammals like kangaroo rats excrete highly concentrated urine.
Critical Evaluation

This parallels our study of osmoregulation, where structural adaptations enhance efficiency, as seen in NCERT examples.

Question 7:
A student argues that aldosterone and ADH function identically. Critically analyze this claim with evidence.
Answer:
Case Deconstruction

While both regulate water balance, aldosterone targets Na+ reabsorption, whereas ADH increases water permeability.

Theoretical Application
  • Aldosterone acts via distal tubules, ADH via collecting ducts.
  • ADH responds to blood osmolarity; aldosterone to blood volume.
Critical Evaluation

Our textbook highlights their synergistic but distinct roles, disproving the claim.

Question 8:
Why might a diabetic patient show glycosuria? Relate this to the renal threshold concept.
Answer:
Case Deconstruction

High blood glucose exceeds the renal threshold (~180 mg/dL), overwhelming tubular reabsorption capacity.

Theoretical Application
  • Normally, all glucose is reabsorbed via SGLT transporters.
  • In diabetes, excess glucose spills into urine.
Critical Evaluation

This confirms our study of transport maximum, where saturation leads to excretion, as in NCERT Case Study 1.

Question 9:
A patient exhibits symptoms like proteinuria and edema. Based on our study of kidney disorders, analyze the possible condition and its physiological impact.
Answer:
Case Deconstruction

The symptoms suggest nephrotic syndrome, where damaged glomeruli leak proteins into urine. Proteinuria reduces blood osmotic pressure, causing edema.

Theoretical Application
  • Glomerular filtration barrier impairment leads to albumin loss.
  • Reduced plasma albumin lowers oncotic pressure, triggering fluid retention.
Critical Evaluation

Our textbook shows similar cases where steroid therapy reduces inflammation. A 2022 study highlights diet modifications to manage protein loss.

Question 10:
Compare countercurrent mechanism in the kidney with thermoregulation in marine mammals. Use two adaptive examples.
Answer:
Case Deconstruction

Both processes maintain gradients—countercurrent in nephrons for urine concentration, and in marine mammals to conserve heat.

Theoretical Application
  • Kidney: Henle’s loop creates osmotic gradient for water reabsorption.
  • Marine mammals: Arterial-venous networks minimize heat loss.
Critical Evaluation

We studied how desert rodents use similar mechanisms. A 2023 paper notes parallels in energy efficiency.

Question 11:
A student argues that diuretics only affect blood pressure. Critically evaluate this claim with evidence from kidney function.
Answer:
Case Deconstruction

Diuretics primarily reduce blood volume by increasing urine output, but also alter electrolyte balance.

Theoretical Application
  • Loop diuretics inhibit Na+-K+-2Cl− symport in Henle’s loop.
  • Thiazides target distal tubules, affecting Na+ reabsorption.
Critical Evaluation

Our textbook shows side effects like hypokalemia. A 2021 study links prolonged use to renal impairment.

Question 12:
Analyze how ADH and aldosterone synergistically regulate water reabsorption during dehydration.
Answer:
Case Deconstruction

ADH increases aquaporin-2 channels in collecting ducts, while aldosterone enhances Na+ reabsorption in DCT.

Theoretical Application
  • ADH action concentrates urine by water retention.
  • Aldosterone raises osmotic gradient for passive water uptake.
Critical Evaluation

We studied cases where imbalance causes diabetes insipidus. Research shows caffeine inhibits ADH, exacerbating dehydration.

Question 13:
Compare ureotelic and uricotelic excretion with examples. How does habitat influence this adaptation?
Answer:
Case Deconstruction

Ureotelic organisms (e.g., humans) excrete nitrogen as urea, while uricotelic ones (e.g., birds) excrete uric acid.

Theoretical Application
  • Urea requires water for excretion, making it suitable for terrestrial mammals.
  • Uric acid is water-insoluble, conserving water in arid habitats or egg-laying species.
Critical Evaluation

We studied how osmoregulation drives these adaptations, with desert reptiles also being uricotelic to minimize water loss.

Question 14:
Analyze how loop of Henle and vasa recta create a counter-current multiplier system. Include a diagrammatic explanation.
Answer:
Case Deconstruction

The loop of Henle establishes an osmotic gradient, while vasa recta maintains it via counter-current flow.

Theoretical Application
  • Descending limb reabsorbs water, concentrating filtrate.
  • Ascending limb pumps out NaCl, diluting filtrate.
[Diagram: Loop and vasa recta showing gradient]Critical Evaluation

Our textbook highlights how this system enables urine concentration, critical for water conservation in mammals.

Question 15:
A diabetic patient has high glucose in urine. Link this to tubular maximum and transporters in nephrons.
Answer:
Case Deconstruction

Excess blood glucose exceeds the tubular maximum for reabsorption, leading to glycosuria.

Theoretical Application
  • Proximal convoluted tubule uses SGLT transporters for glucose uptake.
  • When transporters saturate (~180 mg/dL), glucose spills into urine.
Critical Evaluation

We studied how uncontrolled diabetes overwhelms this mechanism, exemplifying the nephron’s role in maintaining blood homeostasis.

Question 16:

Rahul, a 16-year-old boy, was diagnosed with renal calculi (kidney stones) after experiencing severe pain in his lower back. His doctor advised him to increase his water intake and avoid certain foods.

a) What are the possible reasons for the formation of renal calculi in Rahul's case?
b) How does increased water intake help in preventing renal calculi?

Answer:

a) Possible reasons for renal calculi formation in Rahul include:

  • High intake of calcium, oxalates, or uric acid through diet (e.g., spinach, nuts, or meat).
  • Inadequate water intake leading to concentrated urine.
  • Genetic predisposition or metabolic disorders affecting mineral balance.

b) Increased water intake helps by:

  • Diluting urine, reducing the concentration of stone-forming minerals like calcium oxalate.
  • Promoting frequent urination, which flushes out small crystals before they grow into larger stones.
  • Maintaining proper kidney function and preventing urine stagnation.

Note: Rahul should also avoid excessive salt and animal protein to minimize recurrence.

Question 17:

Priya observed that her urine was darker and had a strong odor after a long workout session. She also noticed reduced urine output that day.

a) Explain why Priya's urine became concentrated post-exercise.
b) How does the antidiuretic hormone (ADH) regulate urine concentration in such situations?

Answer:

a) Priya's urine became concentrated due to:

  • Excessive sweating during exercise, leading to water loss and reduced blood volume.
  • The body's attempt to conserve water by reabsorbing more of it in the kidney tubules, resulting in less urine output.

b) Role of ADH:

  • ADH is released by the pituitary gland when the body is dehydrated.
  • It increases the permeability of the collecting duct in the nephron, allowing more water reabsorption.
  • This reduces urine volume and makes it more concentrated, maintaining osmoregulation.

Note: Priya should rehydrate with electrolytes to restore fluid balance.

Question 18:

Rahul, an 11th-grade student, noticed that his urine output decreased significantly after a day of intense sports. His friend suggested it might be due to dehydration. Based on this case:

  • Explain the role of ADH (Antidiuretic Hormone) in regulating urine output.
  • How does dehydration affect the functioning of the kidneys?
Answer:

ADH (Antidiuretic Hormone) plays a crucial role in regulating urine output by controlling water reabsorption in the kidneys. It is released by the posterior pituitary gland when the body is dehydrated or when blood osmolarity increases. ADH makes the walls of the collecting ducts in the nephrons more permeable to water, allowing more water to be reabsorbed into the bloodstream. This reduces urine volume and concentrates the urine.


During dehydration, the body conserves water to maintain homeostasis. The kidneys respond by:

  • Reducing the glomerular filtration rate (GFR) to minimize water loss.
  • Increasing water reabsorption in the proximal convoluted tubule and collecting duct under the influence of ADH.
  • Producing highly concentrated urine to excrete waste with minimal water loss.

Thus, Rahul's decreased urine output is a protective mechanism to prevent further water loss during dehydration.

Question 19:

Priya observed that her grandfather, a diabetic patient, had glucose in his urine during a routine test. The doctor explained it was due to a condition called glycosuria.

  • What is the normal process of glucose reabsorption in the nephron?
  • Why does glycosuria occur in diabetic patients?
Answer:

In a healthy nephron, glucose is filtered out of the blood in the glomerulus and enters the renal tubule. Normally, all the filtered glucose is reabsorbed in the proximal convoluted tubule (PCT) through active transport using sodium-glucose symporters. This ensures no glucose is lost in the urine.


Glycosuria occurs in diabetic patients because:

  • High blood glucose levels (hyperglycemia) exceed the reabsorption capacity of the PCT.
  • The transporters become saturated, leading to glucose spillage into the urine.
  • This is a sign of uncontrolled diabetes, where the kidneys cannot reabsorb all the excess glucose.

Thus, Priya's grandfather's condition indicates poorly managed blood sugar levels, requiring medical attention.

Question 20:

Rahul, a 11th-grade student, noticed his grandfather frequently visiting the washroom and feeling excessively thirsty. Upon consulting a doctor, he was diagnosed with diabetes insipidus. The doctor explained that this condition affects the kidneys and their ability to concentrate urine.

Based on this case:

  • Explain the role of ADH in urine concentration.
  • How does the deficiency of ADH lead to the symptoms observed in Rahul's grandfather?
Answer:

ADH (Antidiuretic Hormone) plays a crucial role in regulating water reabsorption in the kidneys. It is produced by the hypothalamus and released by the posterior pituitary gland.


1. Role of ADH in urine concentration: ADH increases the permeability of the collecting ducts and distal convoluted tubules in the nephron to water. This allows more water to be reabsorbed back into the bloodstream, leading to concentrated urine and reduced water loss.


2. Effect of ADH deficiency: In diabetes insipidus, ADH is either insufficient or ineffective. Without ADH, the kidneys cannot reabsorb water efficiently, leading to:

  • Production of large volumes of dilute urine (polyuria).
  • Excessive thirst (polydipsia) due to dehydration caused by water loss.

This explains Rahul's grandfather's frequent urination and thirst.

Question 21:

Priya conducted an experiment where she compared the urine samples of two individuals: one who drank 1 liter of water and another who consumed 1 liter of a salty soup. She observed that the second individual produced less urine but with a higher solute concentration.

Based on this scenario:

  • Explain the physiological mechanism behind the difference in urine output.
  • Name the part of the nephron primarily responsible for this adjustment.
Answer:

The difference in urine output is due to the body's osmoregulation mechanism, which maintains water and electrolyte balance.


1. Physiological mechanism: The salty soup increased the osmolarity of the blood, detected by osmoreceptors in the hypothalamus. This triggers:

  • Release of ADH from the pituitary gland.
  • ADH increases water reabsorption in the kidneys, reducing urine volume but increasing its concentration.

2. Part of the nephron involved: The collecting duct is primarily responsible for this adjustment, as it becomes more permeable to water under the influence of ADH, allowing water to be reabsorbed into the bloodstream.


In contrast, the person who drank plain water had lower blood osmolarity, leading to reduced ADH release and more dilute urine.

Question 22:

Rahul, a 11th-grade student, noticed that his urine output decreased significantly after a long football match under the sun. His friend told him it was due to dehydration. Based on this case:

  • Explain the role of ADH (Antidiuretic Hormone) in regulating urine output during dehydration.
  • How does the kidney respond to reduced water levels in the body?
Answer:

When the body is dehydrated, the hypothalamus detects increased blood osmolarity and signals the pituitary gland to release ADH (Antidiuretic Hormone).


ADH acts on the kidney's collecting ducts, making them more permeable to water. This allows more water to be reabsorbed into the bloodstream, reducing urine output and conserving water.


The kidney responds by:

  • Increasing water reabsorption in the proximal convoluted tubule and loop of Henle.
  • Reducing the volume of urine produced to maintain blood pressure and hydration.

This mechanism ensures the body retains essential fluids during dehydration, preventing further water loss.

Question 23:

Priya observed that her grandfather, a diabetic patient, had frequent urination and excessive thirst. The doctor explained it was due to improper kidney function.

  • How does diabetes mellitus affect kidney function and urine composition?
  • Why does excessive glucose in urine lead to increased urine output?
Answer:

In diabetes mellitus, high blood glucose levels exceed the renal threshold, causing glucose to appear in urine (glycosuria).


The kidney is affected because:

  • Excess glucose in the filtrate reduces water reabsorption in the proximal tubule, leading to osmotic diuresis.
  • Increased urine output (polyuria) occurs as glucose draws more water into the urine.

Excessive glucose in urine leads to increased urine output because:

  • Glucose acts as an osmotic agent, preventing water reabsorption in the nephron.
  • The body tries to eliminate excess glucose by producing more urine, causing dehydration and thirst (polydipsia).

This condition highlights the importance of kidney function in maintaining glucose balance.

Question 24:

Rahul, a 11th-grade student, noticed his grandfather experiencing frequent urination and excessive thirst. Upon consulting a doctor, he was diagnosed with diabetes mellitus. The doctor explained that this condition affects the kidneys.

Based on this case:

  • Explain how diabetes mellitus can lead to increased urine output.
  • Describe the role of ADH in normal urine concentration and how its function might be impaired in this condition.
Answer:

Increased urine output in diabetes mellitus: In diabetes mellitus, high blood glucose levels exceed the renal threshold, leading to glucosuria (glucose in urine). This causes osmotic diuresis, where water follows glucose into the urine, increasing urine output (polyuria).


Role of ADH and its impairment: Antidiuretic hormone (ADH) normally acts on the collecting ducts of nephrons to promote water reabsorption, concentrating urine. In uncontrolled diabetes, chronic high glucose levels may damage kidney tubules or disrupt ADH sensitivity, reducing water reabsorption and exacerbating polyuria.


Value-added note: Prolonged polyuria can lead to dehydration, triggering excessive thirst (polydipsia), a classic symptom of diabetes.

Question 25:

During a school trip to a village, Priya observed farmers using urea as a fertilizer. Her teacher explained that urea is a nitrogenous waste excreted by humans.

Based on this scenario:

  • Compare the ureotelic and uricotelic modes of excretion in animals, giving one example of each.
  • Justify why humans excrete urea instead of uric acid despite its toxicity.
Answer:

Comparison:

  • Ureotelic animals (e.g., humans, mammals) excrete urea, which is soluble in water and requires moderate water for elimination.
  • Uricotelic animals (e.g., birds, reptiles) excrete uric acid as a semi-solid paste, conserving water—an adaptation for arid environments.

Justification for urea excretion in humans: Urea is less toxic than ammonia (needing less water for dilution) and more energy-efficient to synthesize than uric acid. Humans, with access to water and efficient liver function, can detoxify ammonia into urea via the ornithine cycle.


Application: Urea’s solubility allows its excretion via urine, while uric acid’s insolubility would risk kidney stone formation in humans.

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