Excretory System is part of Biology. Below are notes on 10 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Accessory Excretory Organs: Role of Skin, Lungs, and Liver in Excretion

  • Accessory excretory organs assist the kidneys in waste elimination.
  • Skin (Sweat Glands): Excretes water, sodium chloride (NaCl), small amounts of urea, lactic acid, and trace minerals (e.g., magnesium, zinc) through sweat.
  • Lungs: Excrete gaseous wastes, mainly carbon dioxide (CO2), and water vapor via respiration.
  • Liver:
    • Metabolizes and detoxifies various substances (drugs, toxins).
    • Converts ammonia to less toxic urea (urea cycle).
    • Excretes bile pigments (bilirubin, biliverdin from hemoglobin breakdown), cholesterol, degraded steroid hormones, and certain drugs into bile, which is eliminated with feces.
  • Salivary glands are primarily involved in digestion and are not considered accessory excretory organs.

Artificial Kidney: Hemodialysis and Peritoneal Dialysis

  • Artificial Kidney (Dialysis): Procedure to remove nitrogenous waste products from the blood of patients with kidney failure.
  • Hemodialysis: Blood is drawn from an artery, pumped into a 'dialysing unit', and returned to a vein. Heparin is added to the blood to prevent clotting.
  • Dialysing Unit (Artificial Kidney): Consists of a long, coiled cellophane tube (acting as a semi-permeable membrane) surrounded by dialysing fluid.
  • Dialysing Fluid (Dialysate):
    • Composition: Has a composition almost identical to normal blood plasma, except it lacks nitrogenous wastes (e.g., urea, uric acid, creatinine).
    • Osmolarity: Iso-osmotic to blood plasma/body fluid.
    • Contains essential substances like glucose, salts, and amino acids in concentrations similar to blood to prevent their loss from the patient's blood.
  • Principle of Dialysis: Nitrogenous wastes diffuse from the patient's blood (high concentration) through the semi-permeable cellophane membrane into the dialysing fluid (low/zero concentration) due to a concentration gradient.
  • Peritoneal Dialysis: Dialysate is introduced into the patient's peritoneal cavity; the peritoneal membrane acts as the natural semi-permeable membrane for waste exchange from blood capillaries into the dialysate.

Common Disorders of Excretory System: Renal Calculi, Renal Failure, Nephritis

  • Renal calculi (kidney stones) are formed by the precipitation of various chemicals within the kidney.
  • The most common chemical compound found in human kidney stones is Calcium oxalate.
  • Other chemicals whose precipitation leads to kidney stone formation include Cystine and Uric acid.

Comparative Excretion: Overview of Excretory Structures in Different Animal Groups

  • Osmoconformers: Organisms whose body fluid osmolarity is approximately equal to that of their external environment; they do not actively regulate their internal osmolarity.
  • Hagfish are marine osmoconformers, maintaining an internal salt concentration similar to seawater.
  • Osmoregulators: Organisms that actively regulate the osmolarity of their body fluids to maintain a stable internal environment, independent of the external osmolarity.
  • Examples of osmoregulators include most bony fish (like Rohu), mammals (like Seals and Whales), and birds.

Human Excretory System: Gross Anatomy of Kidneys, Ureters, Bladder, and Urethra

  • Human Excretory System consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.
  • Kidneys are the primary excretory organs responsible for filtering blood, removing metabolic wastes (especially nitrogenous wastes like urea), and purifying blood.
  • Kidneys also maintain water-salt balance, acid-base balance, and help regulate blood pressure.
  • Ureters are tubes that carry urine from the kidneys to the urinary bladder.
  • Urinary Bladder is a muscular sac that temporarily stores urine.
  • Urethra is a tube that carries urine from the urinary bladder out of the body.
  • The correct sequence of urine flow in the human body is: Kidney → Ureter → Urinary Bladder → Urethra.

Mechanism of Urine Formation: Glomerular Filtration Rate (GFR) and Ultrafiltration

  • Urine formation in human beings occurs in three main sequential steps: Glomerular Filtration, Tubular Reabsorption, and Tubular Secretion, followed by the formation of concentrated urine.
  • 1. Glomerular Filtration (Ultrafiltration):
    • Site: Glomerulus (tuft of capillaries) and Bowman's capsule.
    • Mechanism: Blood is filtered under pressure, forming 'glomerular filtrate' or 'ultrafiltrate'.
    • Filtration Membrane: Composed of three layers: the endothelium of glomerular blood vessels, the basement membrane, and the podocytes of Bowman's capsule.
    • Filtrate Composition: Contains water, glucose, amino acids, urea, uric acid, creatinine, and salts. (Hence, ammonia, uric acid, water, and sugar ARE filtered).
    • Substances NOT Filtered: Large molecules like proteins, fats, and blood cells (RBCs, WBCs, platelets) due to their size.
    • Glomerular Filtration Rate (GFR): Volume of filtrate formed by both kidneys per minute; normal GFR is approximately 125 ml/min (180 liters/ day) in adults.
    • Blood Processing: Kidneys receive about 1100-1200 ml of blood per minute (approx. 20-25% of cardiac output). While all blood passes through the kidneys, only a fraction of the plasma (~20%) is filtered into Bowman's capsule.
  • 2. Tubular Reabsorption: Selective reabsorption of essential substances (e.g., 99% of water, glucose, amino acids, Na+, etc.) from the filtrate back into the blood. Occurs mainly in the Proximal Convoluted Tubule (PCT), Loop of Henle, Distal Convoluted Tubule (DCT), and Collecting Duct.
  • 3. Tubular Secretion: Secretion of waste products (e.g., H+, K+, ammonia, creatinine, certain drugs) from the blood into the filtrate. Helps maintain ionic and acid-base balance of body fluids. Occurs in PCT, DCT, and Collecting Duct.
  • Formation of Concentrated Urine: The final stage, primarily regulated by the countercurrent mechanism (involving the Loop of Henle and vasa recta) and the action of Antidiuretic Hormone (ADH), to conserve water and produce concentrated urine.

Mechanism of Urine Formation: Selective Reabsorption in Renal Tubules

Urine formation in the nephron occurs in 1. three main sequential steps: Ultrafiltration, Selective Reabsorption, and Tubular Secretion. Ultrafiltration: Occurs in the glomerulus and 2. Bowman's capsule, where blood is filtered to form a protein-free filtrate (glomerular filtrate). Selective Reabsorption: Occurs along the 3. renal tubules (PCT, Loop of Henle, DCT, and collecting duct), where useful substances are reabsorbed from the filtrate back into the peritubular capillaries. Nearly 100% of essential nutrients, including 4. all glucose and most amino acids, are actively reabsorbed in the Proximal Convoluted Tubule (PCT). Reabsorbed substances (e.g., glucose) are 5. returned to the bloodstream via the peritubular capillaries, which eventually drain into the renal venules and the renal vein. Tubular Secretion: Occurs in the renal tu6. bules, where waste products, excess ions (e.g., K+, H+), and other substances are actively secreted from the blood in the peritubular capillaries into the filtrate. After waste removal and reabsorption, clean7. er blood leaves the kidney and returns to systemic circulation through the renal vein.

Microscopic Structure of Kidney: Detailed Anatomy of Nephron (Bowman's capsule, Glomerulus, Renal Tubules)

  • Nephron: Structural & functional unit of the kidney.
  • Each nephron has two main parts: Renal Corpuscle (Malpighian body) and Renal Tubule.
  • Renal Corpuscle: Site of blood filtration.
    • Glomerulus: A tuft of capillaries formed by afferent arteriole. Filters blood.
    • Bowman's Capsule: A double-walled cup-like structure that encloses the glomerulus. Site of ultrafiltration.
  • Renal Tubule: Continues from Bowman's capsule.
    • Proximal Convoluted Tubule (PCT): Highly coiled segment.
    • Loop of Henle: Hairpin-shaped structure, has descending and ascending limbs.
    • Distal Convoluted Tubule (DCT): Highly coiled segment, opens into a collecting duct.

Regulation of Kidney Function: Hormonal (RAAS, ADH, ANP) and Neural Control

  • Renin-Angiotensin-Aldosterone System (RAAS):
    • Stimulus: Low glomerular blood pressure/volume, low Na+ concentration in macula densa, sympathetic stimulation.
    • JG (Juxtaglomerular) cells secrete Renin into blood.
    • Renin converts Angiotensinogen (from liver) to Angiotensin I.
    • ACE (Angiotensin Converting Enzyme) in lungs converts Angiotensin I to Angiotensin II.
    • Angiotensin II effects:
      • Potent vasoconstrictor: Increases blood pressure and GFR.
      • Stimulates Aldosterone release from adrenal cortex.
      • Stimulates ADH release from posterior pituitary.
      • Increases Na+ reabsorption in PCT.
      • Increases thirst.
    • Aldosterone effects:
      • Increases Na+ and water reabsorption in DCT and collecting duct.
      • Increases K+ and H+ secretion into filtrate.
      • Increases blood volume and pressure.
  • Antidiuretic Hormone (ADH) / Vasopressin:
    • Source: Hypothalamus (produced), Posterior Pituitary (released).
    • Stimulus: Increased ECF osmolarity (dehydration), decreased blood volume/pressure.
    • Action: Increases water permeability of DCT and collecting duct by inserting aquaporins.
    • Effect: Increases water reabsorption, decreases urine volume, increases urine concentration, restores blood volume/pressure.
  • Atrial Natriuretic Peptide (ANP):
    • Source: Atrial walls of heart.
    • Stimulus: High blood volume/pressure, stretching of atria.
    • Action:
      • Vasodilation of afferent arteriole, vasoconstriction of efferent arteriole (increases GFR).
      • Inhibits Renin release, Aldosterone release, and ADH release.
      • Inhibits Na+ reabsorption in collecting duct.
    • Effect: Increases Na+ and water excretion (natriuresis and diuresis), decreases blood volume and pressure.
  • Neural Control (Sympathetic Nervous System):
    • Strong sympathetic stimulation (e.g., severe hemorrhage, intense exercise) causes vasoconstriction of afferent arterioles.
    • Effect: Decreases renal blood flow and GFR, conserving blood volume.
  • Kidney Regulation of pH Balance:
    • Maintains blood pH by secreting H+ ions into the filtrate.
    • Reabsorbs bicarbonate (HCO3-) ions from the filtrate back into the blood.
    • Generates new bicarbonate ions.
    • This process removes excess acid (H+) from the body and conserves buffer (HCO3-).

Types of Excretory Wastes and Modes of Excretion

  • Kidneys are a part of the excretory system in human beings, primarily for waste removal.
  • Types of Nitrogenous Wastes:
    • Ammonia: Most toxic; requires large water for excretion (ammonotelism, e.g., aquatic animals).
    • Urea: Less toxic than ammonia; requires moderate water for excretion (ureotelism, e.g., mammals including humans, amphibians).
    • Uric Acid: Least toxic; requires minimal water for excretion (uricotelism, e.g., birds, reptiles like lizards, insects, land snails).
  • Urea Production & Excretion:
    • Urea is primarily produced in the liver.
    • It is formed from the metabolism of proteins (specifically amino acids).
    • Urea is removed from the blood by the kidneys.
    • A healthy adult human excretes approximately 2-2.5 gm of urea per day.
    • Bacterial decomposition of urea, e.g., in spilled urine, produces ammonia, causing a foul smell.
  • Urine Characteristics:
    • The yellow color of urine is due to the pigment Urochrome.
    • Bloody urine is known as Hematuria.
    • Dark yellow urine can indicate dehydration.
    • Colourless urine can indicate overhydration.
    • The urine of a diabetic patient contains glucose.

14. Nervous System

Practice MCQs: Excretory System

Accessory Excretory Organs: Role of Skin, Lungs, and Liver in Excretion

  1. Blood flows against gravity is prevented from flowing back by

    Asked in: Forest Officer (RFO) 2018

    1. the extremely low-pressure of venous blood
    2. valves
    3. movements in the surrounding muscles
    4. narrowing down veins by the contraction of the muscle layer comprising their walls
    Show answer

    Answer: B. valves

    The circulatory system has specialized mechanisms to ensure efficient blood flow, especially in veins where blood pressure is lower and faces the pull of gravity. BPSC Prelims Exam-63rd Sweat is a mechanism for thermoregulation and excretion. It contains various dissolved substances from the body, including minerals and trace elements.

  2. Which organ is not related to the function of excretion?

    Asked in: APPSC Draughtman 2008

    1. Sweat gland
    2. Kidney
    3. Salivary gland
    4. Lung
    Show answer

    Answer: C. Salivary gland

    Kidneys, sweat glands, and lungs are significant organs involved in excretion, whereas salivary glands are primarily involved in digestion.

Artificial Kidney: Hemodialysis and Peritoneal Dialysis

  1. In dialysis for kidney failure patients, the dialysing fluid is iso-osmotic to

    Asked in: UPSC CISF AC EXE 2018

    1. Blood
    2. Urine
    3. Water
    4. Body fluid
    Show answer

    Answer: A. Blood

    - Dialysis is a process that filters waste products and excess fluid from the blood when the kidneys are unable to perform these functions. - The dialysing fluid, or dialysate, is a sterile solution that is separated from the patient's blood by a semi-permeable membrane (the dialyser or peritoneum). - The dialysate is carefully formulated to have an osmotic pressure similar to that of normal blood plasma (making it iso-osmotic to blood) to prevent damage to blood cells and large shifts in fluid balance. - Waste products like urea and creatinine, which are in high concentration in the patient's blood, diffuse across the membrane into the dialysate where their concentration is low. - Excess electrolytes in the blood can also be removed, and necessary electrolytes added to the blood from the dialysate, facilitating balance. - Water removal (ultrafiltration) is typically achieved by creating a pressure gradient or sometimes by adding glucose to the dialysate to increase its osmotic pressure slightly compared to blood, but the base solution is iso-osmotic.

Common Disorders of Excretory System: Renal Calculi, Renal Failure, Nephritis

  1. The "Stones" formed in human kidney consist mostly of :

    Asked in: HPPSC HPAS Prelims 2013 · UPPCS Prelims 2000

    1. Calcium oxalate
    2. Sodium acetate
    3. Magnesium sulphate
    4. Calcium alone
    Show answer

    Answer: A. Calcium oxalate

    Calcium oxalate is the most common chemical composition of kidney stones formed in humans.

  2. Most kidney stones are composed of :

    Asked in: HPPSC HPAS Prelims 2021

    1. Calcium carbonate
    2. Calcium oxalate
    3. Magnesium carbonate
    4. Magnesium oxalate
    Show answer

    Answer: B. Calcium oxalate

    Calcium oxalate is the most common chemical compound found in kidney stones.

  3. मानव वृक्क में बनने वाले पत्थर (स्टोन) में मुख्यतः क्या होता है ?

    Asked in: HPPSC HPAS Prelims 2013

    1. कै lÐशयम ऑक्सजेलिेट
    2. सोlल्डियम ऐसीटेट
    3. मैग्नीlशयम सÐफे ट
    4. अके लिा कै lÐशयम
    Show answer

    Answer: A. कै lÐशयम ऑक्सजेलिेट

    मानवि विृक्क (lकल्डिनी) में बनने विालिे अlधकांश पत्थर (Öटोन) कै lÐशयम ऑक्सजेलिेट (Calcium oxalate) से बने होते हैं। यह आहार में कै lÐशयम और ऑक्सजेलिेट की उच्च मात्रा के कारण बन सकते हैं, खासकर अगर तरलि पदाथर्त का सेविन कम हो।

  4. Kidney stones are formed by the Precipitation of the following chemicals I. Cystine II. Oxalate III. Uric acid IV. Sodium

    Asked in: TNPSC CS Prelims 2021

    1. I and II
    2. I, II and III
    3. III and IV
    4. I, II, III and IV
    Show answer

    Answer: B. I, II and III

    The primary chemicals that commonly precipitate to form kidney stones include calcium oxalate (the most common type), uric acid, and cystine. These substances can crystallize when their concentration in urine is high or when there are imbalances in urine composition.

  5. The major chemical compound found in human kidney stones is

    Asked in: UPPCS Prelims 1998

    1. Uric acid
    2. Calcium carbonate
    3. Calcium oxalate
    4. Calcium sulphate
    Show answer

    Answer: C. Calcium oxalate

    Calcium oxalate is the most prevalent chemical compound found in human kidney stones.

Comparative Excretion: Overview of Excretory Structures in Different Animal Groups

  1. Which one of the following animals is an osmoconformer?

    Asked in: POST GRADUATE TEACHER (PGT) 2018

    1. Hagfish
    2. Seal
    3. Whale
    4. Rohu
    Show answer

    Answer: A. Hagfish

    Seals, whales, and Rohu (a freshwater fish) are osmoregulators. They actively control their internal osmotic pressure to maintain homeostasis, which is different from their external environment.

Human Excretory System: Gross Anatomy of Kidneys, Ureters, Bladder, and Urethra

  1. Which one of the following is the correct sequence of organs that occur in the path of urine flow in human body?

    Asked in: UPSC CDS 1 2020

    1. Kidney, ureter, urinary bladder, urethra
    2. Kidney, urinary bladder, ureter, urethra
    3. Kidney, ureter, urethra, urinary bladder
    4. Urinary bladder, kidney, urethra, ureter
    Show answer

    Answer: A. Kidney, ureter, urinary bladder, urethra

    The correct sequence of organs in the path of urine flow is: Kidney $\rightarrow$ Ureter $\rightarrow$ Urinary Bladder $\rightarrow$ Urethra. Any other order would be incorrect based on the physiological process of urine formation, transport, storage, and elimination.

  2. The excretory system of human beings does not include -

    Asked in: Asst. Engineer Comb. Comp. Exam 2018

    1. Pair of kidneys
    2. Pair of eyes
    3. Pair of ureters
    4. Urinary bladder
    Show answer

    Answer: B. Pair of eyes

    The human excretory system comprises organs that filter waste products from the blood and eliminate them from the body. The primary organs are the kidneys, which produce urine. The urine then travels through the ureters to the urinary bladder for storage and is eventually expelled from the body through the urethra.

  3. Which of the following organs is used in the purification of blood in human body?

    Asked in: Assistant Engineer (Civil) 2018 19 2018

    1. Liver
    2. Kidney
    3. Spleen
    4. Lungs
    Show answer

    Answer: B. Kidney

    Understanding the basic functions of major human organs, particularly those involved in waste removal and blood processing, is fundamental to biology and health science.

  4. In human body, kidney is responsible

    Asked in: COMBINED STATE AGRICULTURAL SER‐ VICES (PRE.) EXAM 2024

    1. For excretion
    2. For nutrition
    3. For transportation of blood
    4. For respiration
    Show answer

    Answer: A. For excretion

    The kidneys are vital organs of the excretory system. They also play roles in regulating blood pressure, electrolyte balance, and red blood cell production.

  5. Which organ in humans filters nitrogenous waste from blood?

    Asked in: lower devision clerk 2025

    1. Liver
    2. Kidney
    3. Heart
    4. Lungs
    Show answer

    Answer: B. Kidney

    Kidneys play a crucial role in maintaining the body's fluid and electrolyte balance, as well as filtering blood.

  6. Which part of our body filters the dirty blood ?

    Asked in: Rakshak 2023

    1. Heart
    2. Lung
    3. Ureter
    4. Kidney
    Show answer

    Answer: D. Kidney

    Kidneys act as the body's natural filters, removing metabolic waste products and excess substances from the blood.

Mechanism of Urine Formation: Glomerular Filtration Rate (GFR) and Ultrafiltration

  1. Generally through kidney which of the following is not filtered ?

    Asked in: MPSC CS Prelims 2013

    1. Ammonia
    2. Uric acid
    3. Water
    4. Sugar
    Show answer

    Answer: D. Sugar

    - Glomerular filtration allows small molecules from blood into the renal tubules. - Large molecules like proteins and blood cells are not filtered. - Substances like water, ions, urea, uric acid, ammonia, and glucose are filtered. - Filtered substances undergo reabsorption and/or secretion in the tubules before final excretion as urine.

  2. Arrange the following in order with respect to the urine formation in human beings : A. Formation of concentrated urine B. Tubular reabsorption C. Glomerular filtration D. Tubular secretion Choose the correct order : A) A, C, B, D B) C, B, D, A C) B, A, D, C D) A, D, B, C

    Asked in: TSPSC Group 1 Prelims 2023

    1. A, C, B, D
    2. C, B, D, A
    3. B, A, D, C
    4. A, D, B, C
    Show answer

    Answer: B. C, B, D, A

    Urine formation is a vital process for filtering waste products from the blood and maintaining homeostasis in the body, occurring in the nephrons of the kidneys through filtration, reabsorption, and secretion.

  3. Which of the following is correct ?

    Asked in: UPPCS Prelims 1994

    1. All the blood in the body is absorbed through the kidneys.
    2. All the blood in the body passes through the kidneys.
    3. All the blood in the body is filtered through the kidneys.
    4. All the blood in the body is made through the kidneys..
    Show answer

    Answer: B. All the blood in the body passes through the kidneys.

    The kidneys receive a large portion of the body's blood supply (about 20-25% of the cardiac output) at rest. This blood flows through the kidneys as part of the circulatory system. Over time, the entire volume of blood in the body passes through the kidneys multiple times per day for processing.

Mechanism of Urine Formation: Selective Reabsorption in Renal Tubules

  1. In the nephron of man, what is the correct sequence of urine formation ?

    Asked in: MPSC CS Prelims 2019

    1. Selective reabsorption, tubular secretion and ultrafiltration
    2. Ultrafiltration, tubular secretion and selective reabsorption
    3. Ultrafiltration, selective reabsorption and tubular secretion
    4. Tubular secretion, selective reabsorption and ultrafiltration
    Show answer

    Answer: C. Ultrafiltration, selective reabsorption and tubular secretion

    Urine formation is a three-step process involving filtration of blood from the glomerulus into Bowman's capsule (ultrafiltration), reabsorption of essential substances from the filtrate back into the blood, and secretion of waste products from the blood into the filtrate. These steps occur sequentially along the different parts of the nephron.

  2. With reference to the work of human kidney, consider the following statements: After the waste is removed in the kidney, the cleaner blood is sent back through renal artery. From Bowman’s capsule, the filtered liquid passes through tiny tubes where much of the glucose is reabsorbed and sent back to the blood in the renal vein. Which of these statements is/the correct?

    Asked in: UPPCS Prelims 2003

    1. Only 1
    2. Only 2
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Answer: B. Only 2

    - Blood enters the kidney via the renal artery and leaves via the renal vein. - Filtration occurs in the glomerulus within Bowman's capsule. - Reabsorption of useful substances like glucose happens in the renal tubules. - Reabsorbed substances return to the blood circulating around the tubules, which drains into the renal vein.

Microscopic Structure of Kidney: Detailed Anatomy of Nephron (Bowman's capsule, Glomerulus, Renal Tubules)

  1. Which part of nephron of the human kidney is responsible for filtration of blood for excretion ?

    Asked in: UPSC NDA 2 2024

    1. Collecting duct
    2. Renal vein
    3. Ureter
    4. Bowman's capsule
    Show answer

    Answer: D. Bowman's capsule

    The nephron is the functional unit of the kidney. It consists of the renal corpuscle (Glomerulus and Bowman's capsule) and the renal tubule. The renal corpuscle is where the initial step of urine formation, glomerular filtration, takes place.

  2. Nephron is related to which organ of the body?

    Asked in: Assistant Auditor (Direct) 2021

    1. Nervous system
    2. Pulse
    3. Liver
    4. None of the above
    Show answer

    Answer: D. None of the above

    Nephrons are microscopic structures within the kidneys that perform the essential functions of filtration, reabsorption, and secretion to form urine.

Regulation of Kidney Function: Hormonal (RAAS, ADH, ANP) and Neural Control

  1. Kidneys are helping to maintain pH balance by which of the following ?

    Asked in: MPSC CS Prelims 2014

    1. Adding hydrogen ions to filtrate
    2. Removal of hydrogen ions from blood
    3. Dissolving calcium and sodium ions in blood
    4. Removing carbonate ions from blood
    Show answer

    Answer: A. Adding hydrogen ions to filtrate

    The kidneys are crucial organs for regulating the body's internal environment, including blood pH. They do this by controlling the excretion of acids and bases and regulating bicarbonate levels.

Types of Excretory Wastes and Modes of Excretion

  1. Which one of the following statements is correct?

    Asked in: UPSC CDS 1 2019

    1. Urea is produced in liver.
    2. Urea is produced in blood.
    3. Urea is produced from digestion of starch.
    4. Urea is produced in lung and kidney.
    Show answer

    Answer: A. Urea is produced in liver.

    Urea is primarily synthesized in the liver through the urea cycle.

  2. The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of

    Asked in: UPSC CDS 2 2017

    1. urea into sulphur dioxide
    2. sugar into carbon dioxide
    3. lipids into methane
    4. urea into ammonia
    Show answer

    Answer: D. urea into ammonia

    The enzymatic decomposition of urea by bacteria yields ammonia and carbon dioxide.

  3. Urea is produced by metabolism of

    Asked in: UPSC CDS 2 2022

    1. Proteins
    2. Carbohydrates
    3. Lipids
    4. Both Proteins and Carbohydrates
    Show answer

    Answer: A. Proteins

    - Urea is produced from the breakdown of amino acids, which are the building blocks of proteins. When proteins are consumed in excess of the body's needs or when tissues are broken down, the amino groups from amino acids are removed (deamination). These amino groups are converted into ammonia, which is toxic. The liver then converts ammonia into urea through the urea cycle. - Carbohydrates and lipids are primarily metabolized for energy, producing carbon dioxide and water as waste products, not significant amounts of nitrogenous waste like urea.

  4. The urine sample of a diabetic patient contains :

    Asked in: HPPSC HPAS Prelims 2011

    1. Sucrose
    2. Fructose
    3. Glucose
    4. All of the above
    Show answer

    Answer: C. Glucose

    Glucose is found in the urine of diabetic patients when blood glucose levels are elevated beyond the kidney's reabsorptive capacity.

  5. The kidneys in human beings are a part of system for

    Asked in: MPPSC CS Prelims 2017 · WBCS Main Paper 4 2021

    1. nutrition
    2. transportation
    3. excretion
    4. respiration
    Show answer

    Answer: C. excretion

    The kidneys are the primary organs of the excretory system in human beings. Their main function is to filter waste products, excess water, and electrolytes from the blood to form urine. This process removes metabolic wastes like urea and creatinine from the body, maintaining homeostasis. Nutrition involves the intake and processing of food. Transportation is primarily the function of the circulatory system. Respiration involves gas exchange (oxygen and carbon dioxide).

  6. Which of the following matches is correct ?

    Asked in: MPSC CS Prelims 2015

    1. Dark yellow urine — Melanuria
    2. Colourless urine — Dehydration
    3. Bloody urine — Hematuria
    4. Greenish urine — Consumption of beet
    Show answer

    Answer: C. Bloody urine — Hematuria

    Hematuria is the medical term for blood in the urine.

  7. In humans, urea is mainly formed from the metabolism of which one of the following components of food ?

    Asked in: UPSC CAPF 2023

    1. Fatty acids
    2. Vitamins
    3. Amino acids
    4. Glucose
    Show answer

    Answer: C. Amino acids

    Amino acids, derived from protein digestion, contain nitrogen. The liver converts this excess nitrogen into urea for excretion.

  8. The yellow colour of Urine is due to the presence of:

    Asked in: APPSC Draughtman 2008

    1. Urochromem
    2. Blood
    3. Cholesterol
    4. Bile
    Show answer

    Answer: A. Urochromem

    The normal yellow colour of urine is primarily due to the presence of a pigment called urobilin. Urobilin is a byproduct of the breakdown of hemoglobin, processed via bilirubin in the liver and gut. The term "urochrome" is an older, more general term often used to refer to the pigment responsible for the yellow colour of urine.

  9. Urea is removed from the blood by the:

    Asked in: APPSC Draughtman 2008

    1. Kidneys
    2. Lungs
    3. Large Intestine
    4. Spleen
    Show answer

    Answer: A. Kidneys

    The kidneys are responsible for filtering blood and removing urea to produce urine.

  10. On an average, urea excreted by a healthy adult human per day is - 10-15 milligram - 2-2.5 gram

    Asked in: Protection Officer 2022

    1. 10-15 mg
    2. 150-200 mg
    3. 2-2.5 gm
    4. 25-30 gm
    Show answer

    Answer: C. 2-2.5 gm

    Urea is the primary nitrogenous waste product excreted by mammals, formed in the liver from the breakdown of amino acids. The kidneys filter urea from the blood and excrete it in urine. The amount can vary based on diet and hydration.