Osmoregulation Practice Questions
40 free Osmoregulation practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is the most toxic nitrogenous waste requiring large amounts of water for its elimination?
- A Urea
- B Uric acid
- C Ammonia
- D Creatinine
Correct answer: Ammonia
Ammonia is highly toxic and readily soluble in water, requiring approximately 300-500 ml of water for every gram of nitrogen removed. It is generally excreted by diffusion across body surfaces or gill surfaces in aquatic animals.
The process of maintaining a constant internal osmotic pressure irrespective of the external environment is known as:
- A Homeostasis
- B Osmoconformation
- C Osmoregulation
- D Hemostasis
Correct answer: Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain homeostasis of the organism's water content. It keeps the organism's fluids from becoming too diluted or too concentrated.
Protonephridia or flame cells are the primary excretory structures in which of the following organisms?
- A Prawns and other crustaceans
- B Earthworms and annelids
- C Platyhelminthes
- D Insects and arthropods
Correct answer: Platyhelminthes
Protonephridia (flame cells) are specialized excretory and osmoregulatory organs found in flatworms like Planaria. They function primarily in ionic and fluid volume regulation.
Which segment of the nephron is impermeable to water but allows the transport of electrolytes actively or passively?
- A Ascending limb of Loop of Henle
- B Proximal Convoluted Tubule
- C Descending limb of Loop of Henle
- D Distal Convoluted Tubule
Correct answer: Ascending limb of Loop of Henle
The ascending limb of the Loop of Henle is impermeable to water. This segment plays a crucial role in making the medullary interstitium hyperosmotic by transporting electrolytes into the interstitial fluid.
The GFR (Glomerular Filtration Rate) in a healthy individual is approximately:
- A 125 mL/day
- B 125 mL/minute
- C 500 mL/minute
- D 180 mL/minute
Correct answer: 125 mL/minute
The GFR is the amount of filtrate formed by the kidneys per minute, which is about 125 mL/min. This totals to approximately 180 liters of filtrate produced per day.
Which hormone is released by the Atrial walls of the heart in response to an increase in blood pressure?
- A Aldosterone
- B ADH (vasopressin)
- C Renin
- D ANF (atrial natriuretic factor)
Correct answer: ANF (atrial natriuretic factor)
Atrial Natriuretic Factor (ANF) is released when blood pressure increases. It causes vasodilation and checks the Renin-Angiotensin mechanism to lower blood pressure.
The specialized capillary network that runs parallel to the Loop of Henle is called:
- A Peritubular network
- B Vasa recta
- C Glomerulus
- D Efferent arteriole
Correct answer: Vasa recta
The vasa recta is a U-shaped minute vessel of the peritubular capillary network that runs parallel to the Henle's loop. It plays a significant role in the counter-current mechanism to concentrate urine.
In which part of the nephron does maximum reabsorption of water and electrolytes (70-80%) occur?
- A Distal Convoluted Tubule (DCT)
- B Proximal Convoluted Tubule
- C Collecting Duct
- D Loop of Henle
Correct answer: Proximal Convoluted Tubule
The Proximal Convoluted Tubule (PCT) is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption. Nearly all essential nutrients and 70-80% of electrolytes and water are reabsorbed here.
Human kidneys can produce urine nearly _____ times concentrated than the initial filtrate formed.
- A 10
- B 100
- C 4
- D 2
Correct answer: 4
The counter-current mechanism involving the Loop of Henle and vasa recta helps maintain a concentration gradient in the medullary interstitium. This allows the human kidney to produce urine that is four times more concentrated (1200 mOsmol/L) than the initial filtrate (300 mOsmol/L).
Which of the following is NOT a constituent of sweat produced by sweat glands?
- A NaCl
- B Small amounts of urea
- C Lactic acid
- D Glucose in significant quantities
Correct answer: Glucose in significant quantities
Sweat produced by sweat glands is a watery fluid containing NaCl, small amounts of urea, and lactic acid. Glucose is typically not excreted through sweat in healthy individuals.
The condition of accumulation of urea in blood due to kidney failure is called:
- A Dysuria
- B Uremia
- C Ketonuria
- D Glycosuria
Correct answer: Uremia
Uremia is a clinical condition associated with fluid, electrolyte, and hormone imbalances and metabolic abnormalities, which develop in parallel with deterioration of renal function. It is characterized by high levels of urea in the blood.
What is the function of Antidiuretic Hormone (ADH) / Vasopressin?
- A Decreases water reabsorption from DCT and collecting duct
- B Increases water reabsorption from DCT and collecting duct
- C Causes vasodilation of renal arterioles
- D Inhibits Aldosterone release from adrenal cortex
Correct answer: Increases water reabsorption from DCT and collecting duct
ADH is released from the neurohypophysis in response to an increase in body fluid osmolarity. It facilitates water reabsorption from the latter parts of the tubule (DCT and collecting duct), thereby preventing diuresis.
The Juxtaglomerular Apparatus (JGA) is formed by cellular modifications in which two structures?
- A Loop of Henle and Efferent arteriole
- B PCT and Afferent arteriole
- C DCT and Afferent arteriole
- D Bowman's capsule and Glomerulus
Correct answer: DCT and Afferent arteriole
JGA is a sensitive region formed by cellular modifications in the Distal Convoluted Tubule and the afferent arteriole at the location of their contact. A fall in GFR activates JG cells to release renin.
Which nitrogenous waste is excreted in the form of pellet or paste with a minimum loss of water?
- A Uric acid
- B Hippuric acid
- C Urea
- D Ammonia
Correct answer: Uric acid
Uricotelic animals like reptiles, birds, and land snails excrete uric acid. It is the least toxic and requires very little water for elimination, allowing it to be excreted as a semi-solid paste.
The osmolarity of the filtrate increases as it moves down the descending limb of the Loop of Henle because:
- A The descending limb is permeable to electrolytes
- B The descending limb is permeable to water
- C The descending limb is impermeable to water
- D Active transport of sodium drives concentrating
Correct answer: The descending limb is permeable to water
The descending limb of the Loop of Henle is permeable to water but almost impermeable to electrolytes. As the filtrate moves down, water exits the tubule into the hyperosmotic interstitium, concentrating the filtrate.
Renin converts ______ in the blood to ______.
- A Angiotensinogen to Angiotensin I
- B Angiotensin I to Angiotensin II
- C Angiotensinogen to Aldosterone
- D Angiotensin II to Atrial Natriuretic Factor
Correct answer: Angiotensinogen to Angiotensin I
Renin is an enzyme secreted by JG cells that converts angiotensinogen (a plasma protein) into angiotensin I. Angiotensin I is later converted to angiotensin II by Angiotensin Converting Enzyme (ACE).
Glycosuria and Ketonuria in urine are indicative of which disease?
- A Nephritis
- B Diabetes Mellitus
- C Renal Calculi
- D Diabetes Insipidus
Correct answer: Diabetes Mellitus
The presence of glucose (glycosuria) and ketone bodies (ketonuria) in urine is a classic diagnostic indicator of Diabetes Mellitus, where insulin deficiency leads to high blood sugar levels.
What happens to the GFR when the afferent arteriole diameter increases (vasodilation) relative to the efferent arteriole?
- A GFR decreases
- B GFR rises significantly
- C GFR remains constant
- D Filtration stops
Correct answer: GFR rises significantly
Widening the afferent arteriole allows more blood to enter the glomerulus, increasing the glomerular hydrostatic pressure. This results in an increase in the rate of filtration (GFR).
Sebaceous glands eliminate certain substances like ______ through sebum.
- A Urea and lactic acid
- B Sterols, hydrocarbons and waxes
- C NaCl, water and ammonia
- D Amino acids and fatty acids
Correct answer: Sterols, hydrocarbons and waxes
Sebaceous glands help in the elimination of sterols, hydrocarbons, and waxes through sebum. This secretion also provides a protective oily covering for the skin.
The epithelial cells of Bowman's capsule called podocytes are arranged in an intricate manner to leave some minute spaces called:
- A Fenestrae
- B Filtration slits
- C Vasa recta
- D Glomerular gaps
Correct answer: Filtration slits
Podocytes are the inner wall cells of the Bowman's capsule. They possess foot processes that create filtration slits (slit pores) through which the blood is filtered into the capsule space.
Which of the following best defines osmoregulation in living organisms?
- A Removal of nitrogenous wastes from the body
- B Maintenance of internal water and ion balance
- C Regulation of core body temperature
- D Control of blood glucose levels by hormones
Correct answer: Maintenance of internal water and ion balance
Osmoregulation refers to maintaining a constant internal environment with respect to water and salts. It ensures proper cellular function despite external fluctuations.
Freshwater fishes constantly gain water by osmosis. How do they primarily maintain osmotic balance?
- A By drinking large amounts of water to dilute salts
- B By producing large volumes of dilute urine
- C By excreting excess salts through feces
- D By reducing glomerular filtration rate
Correct answer: By producing large volumes of dilute urine
Freshwater fishes excrete excess water as dilute urine to maintain osmotic balance. This prevents swelling of body cells due to continuous water influx.
Which structure in the human kidney plays a major role in concentrating urine?
- A Glomerulus
- B Proximal convoluted tubule
- C Bowman's capsule
- D Loop of Henle
Correct answer: Loop of Henle
The Loop of Henle establishes a concentration gradient in the medulla. This gradient allows water reabsorption and results in concentrated urine.
Marine fishes tend to lose water to their environment. Which adaptation helps them counter this problem?
- A Excretion of dilute urine with low salt content
- B Active absorption of water through the skin surface
- C Drinking seawater and excreting excess salts
- D Reduced kidney function and lower urine output
Correct answer: Drinking seawater and excreting excess salts
Marine fishes drink seawater to compensate for water loss. Excess salts are actively excreted through gills and kidneys.
Which hormone regulates water reabsorption in the distal convoluted tubule and collecting duct?
- A Aldosterone
- B Insulin
- C ADH (antidiuretic hormone)
- D Thyroxine
Correct answer: ADH (antidiuretic hormone)
ADH increases the permeability of distal tubules and collecting ducts to water. This leads to increased water reabsorption and concentrated urine.
Which nitrogenous waste is excreted by mammals and requires more water for elimination?
- A Ammonia
- B Urea
- C Uric acid
- D Bile
Correct answer: Urea
Mammals are ureotelic and excrete urea as the main nitrogenous waste. Urea is less toxic than ammonia but requires water for elimination.
Ammonotelic animals are typically found in which environment?
- A Dry desert habitats
- B Open marine habitats
- C Freshwater aquatic habitats
- D Moist terrestrial habitats
Correct answer: Freshwater aquatic habitats
Ammonotelic animals excrete ammonia, which is highly toxic and requires large amounts of water. This is feasible in freshwater environments.
Which of the following animals is uricotelic?
- A Human
- B Frog
- C Bird
- D Bony fish
Correct answer: Bird
Birds excrete nitrogenous waste mainly as uric acid. Uric acid conserves water and is suitable for terrestrial and aerial life.
What is the main role of aldosterone in osmoregulation?
- A Promote water reabsorption without affecting electrolytes
- B Increase sodium reabsorption and potassium excretion
- C Reduce glomerular filtration rate by constricting afferent arterioles
- D Inhibit urine formation by blocking tubular secretion
Correct answer: Increase sodium reabsorption and potassium excretion
Aldosterone, secreted by the adrenal cortex, promotes sodium reabsorption and potassium excretion in the distal convoluted tubule and collecting duct. Water follows sodium osmotically, helping maintain blood volume and osmotic balance.
Which part of the nephron is primarily involved in selective reabsorption?
- A Glomerulus, where high pressure drives filtration
- B Bowman's capsule, which collects the filtrate
- C Proximal convoluted tubule
- D Renal pelvis, which channels urine to the ureter
Correct answer: Proximal convoluted tubule
The proximal convoluted tubule (PCT) is primarily responsible for selective reabsorption. It reabsorbs most of the filtered water, glucose, amino acids, and ions through active and passive transport mechanisms, retaining essential substances for the body.
Why are desert mammals able to survive with minimal water intake?
- A They excrete dilute urine to flush out toxins efficiently
- B They lack a Loop of Henle and rely on skin for water retention
- C They produce highly concentrated urine
- D They excrete ammonia directly through specialized skin glands
Correct answer: They produce highly concentrated urine
Desert mammals have exceptionally long Loops of Henle that create a steep osmotic gradient in the renal medulla, enabling maximum water reabsorption. This results in highly concentrated urine, minimizing water loss in arid environments.
Which mechanism helps maintain a high osmotic gradient in the renal medulla?
- A Ultrafiltration
- B Counter-current mechanism
- C Active transport in glomerulus
- D Diffusion in Bowman's capsule
Correct answer: Counter-current mechanism
The counter-current mechanism involves the hairpin loop of Henle and the vasa recta running in opposite directions. This arrangement builds and maintains a high osmotic gradient in the renal medulla, which is essential for concentrating urine via ADH-regulated water reabsorption in the collecting duct.
Which ion is actively secreted into the tubular fluid during acid-base balance regulation?
- A Sodium
- B Chloride
- C Hydrogen
- D Calcium
Correct answer: Hydrogen
Hydrogen ions are actively secreted into the tubular fluid to regulate blood pH. This helps maintain acid-base balance.
What happens to ADH secretion when the body is dehydrated?
- A It decreases
- B It remains unchanged throughout dehydration
- C It increases, enhancing water reabsorption
- D It stops completely after prolonged dehydration
Correct answer: It increases, enhancing water reabsorption
During dehydration, rising plasma osmolarity is detected by osmoreceptors in the hypothalamus, which triggers increased ADH secretion from the posterior pituitary. ADH enhances water reabsorption in the collecting duct, reducing urine output and restoring normal hydration.
Which structure carries blood away from the glomerulus?
- A Renal vein
- B Renal artery
- C Afferent arteriole
- D Efferent arteriole
Correct answer: Efferent arteriole
The efferent arteriole carries blood away from the glomerulus. It is narrower than the afferent arteriole, which creates back-pressure that maintains high glomerular filtration pressure. Blood then flows from the efferent arteriole into the peritubular capillaries surrounding the nephron.
Which of the following correctly matches an animal with its osmoregulatory strategy?
- A Human – ammonotelic
- B Bird – ureotelic in all stages
- C Fish – uricotelic
- D Reptile – uricotelic
Correct answer: Reptile – uricotelic
Reptiles excrete uric acid and are classified as uricotelic. Uric acid is nearly insoluble and can be excreted as a semi-solid paste with minimal water loss, making this strategy highly advantageous in dry terrestrial habitats.
Which hormone is secreted by the adrenal cortex and influences electrolyte balance?
- A ADH (antidiuretic hormone)
- B Aldosterone
- C Epinephrine
- D Calcitonin
Correct answer: Aldosterone
Aldosterone is secreted by the adrenal cortex (zona glomerulosa). It acts on the distal convoluted tubule and collecting duct to promote sodium reabsorption and potassium excretion, indirectly regulating water balance and blood pressure.
Why is uric acid considered an advantage for birds and reptiles?
- A Initial filtration of blood under pressure in the glomerulus
- B Active reabsorption of glucose in the proximal tubule
- C Maintenance of medullary osmotic gradient
- D Secretion of erythropoietin and renin into circulation
Correct answer: Maintenance of medullary osmotic gradient
The vasa recta are the long, hairpin-shaped capillaries that run parallel to the loop of Henle. By flowing in the opposite direction (counter-current), they exchange solutes and water in a way that preserves the steep osmotic gradient of the renal medulla, which is essential for concentrating urine.
Which factor directly increases glomerular filtration rate?
- A A decrease in systemic blood pressure reducing perfusion
- B An increase in plasma protein concentration raising oncotic pressure
- C Increase in glomerular blood pressure
- D Constriction of the afferent arteriole limiting blood inflow
Correct answer: Increase in glomerular blood pressure
Glomerular filtration rate (GFR) is directly driven by the net filtration pressure across the glomerular membrane. An increase in glomerular blood (hydrostatic) pressure overcomes the opposing capsular and oncotic pressures, enhancing the rate of filtrate formation.
Which of the following best describes the role of vasa recta?
- A Filtration of blood
- B Reabsorption of glucose
- C Maintenance of medullary osmotic gradient
- D Secretion of hormones
Correct answer: Maintenance of medullary osmotic gradient
Vasa recta helps maintain the osmotic gradient in the renal medulla. It prevents dilution of the gradient while allowing nutrient exchange.