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Chapter: 06. Excretory System

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Check Point

Give one word answer.

Removal of nitrogenous wastes from body
Excretion
The artery that supplies blood to kidney
Renal artery
The bunch of capillaries inside the cup of kidney tubules
Glomerulus
Presence of glucose (sugar) in the urine represents
Diabetes (specifically Diabetes mellitus)
Ring of circular muscles around the opening of urethra
Sphincter (or sphincter muscle)
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Test Yourself

A. Multiple Choice Questions

Urea is produced from ammonia and carbon dioxide in (a) Kidneys (b) Glomerulus © Liver (d) Spleen
© Liver
Urine contains mainly (a) Glucose (b) Urea © Bile pigments (d) Salts
(b) Urea (Note: Urine is 95% water, 2.5% urea, and 2.5% other wastes. Among the options given, urea is the main dissolved solute/waste product.)
Kidneys are made up of fine tubular units called (a) Uriniferous tubules (b) Ureters © Afferent renal tubules (d) Collecting tubules
(a) Uriniferous tubules (also called nephrons)
Ultrafiltration of waste from blood takes place in (a) Nephron (b) Glomerulus © Collecting ducts (d) Ureter
(b) Glomerulus
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B. Assertion-Reason Type Questions

(a) Both Assertion [A] and Reason [R] are true. ​(b) Both Assertion [A] and Reason [R] are false. ​© Assertion [A] is true but Reason [R] is false. ​(d) Assertion [A] is false but Reason [R] is true.
Assertion [A]: Our body’s main waste products are ammonia and uric acid. ​Reason [R]: These nitrogenous products are poisonous and must be removed.
(d) Assertion [A] is false but Reason [R] is true. ​Explanation: In humans, the primary nitrogenous waste product is urea, while ammonia and uric acid are produced in much smaller quantities. Thus, the assertion is false. However, these nitrogenous products are indeed poisonous and must be removed, making the reason true.
Assertion [A]: Skin helps in excretion as its sweat glands remove excretory products. ​Reason [R]: Sweat glands remove excess of water from blood.
(a) Both Assertion [A] and Reason [R] are true. ​Explanation: The skin contributes to excretion because sweat glands eliminate excretory products like excess water, salts, and a small amount of urea. The reason is also true as sweat glands draw out excess water from the blood capillaries to form sweat.
Assertion [A]: Kidneys are bean-shaped structures located below the diaphragm. ​Reason [R]: Each kidney consists of a number of neurons.
© Assertion [A] is true but Reason [R] is false. ​Explanation: The kidneys are bean-shaped organs located in the abdominal cavity, which is below the diaphragm, making the assertion true. However, the functional units of kidneys are nephrons (uriniferous tubules), not neurons, making the reason false.
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C. Fill in the blanks with suitable words.

Bean-shaped organ in the body to remove nitrogenous wastes is called _________.
Kidney
Urea and uric acid are _________.
nitrogenous wastes (or excretory products)
The structural unit of kidney is _________.
nephron (or uriniferous tubule)
Artificial filtration of blood is carried out to remove _________.
nitrogenous wastes (or toxic wastes/urea)
Evaporation of sweat from skin has _________ effect.
cooling
In humans, carbon dioxide is excreted by _________.
lungs
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D. State whether these statements are true or false. If false, rewrite the correct form of statements.

Kidneys act as filters to remove waste from blood.
True
Urea from the body is excreted by sweat glands.
False. ​Correct form: Urea from the body is primarily excreted by the kidneys through urine, though trace amounts are excreted by sweat glands.
Sweat contains salt and water.
True
Ureters are long, coiled tubes in kidneys.
False. ​Correct form: Uriniferous tubules (or nephrons) are long, coiled tubes in kidneys. (Alternatively: Ureters are narrow tubes that carry urine from the kidneys to the urinary bladder.)
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E. Define the following.

Excretion
Excretion: The biological process of eliminating toxic metabolic waste substances (such as urea, uric acid, carbon dioxide, etc.) from the body of a living organism.
Nephron
Nephron: The microscopic structural and functional unit of the kidney, consisting of a cup-shaped Bowman’s capsule and a long coiled tubule, which filters blood and forms urine.
Osmoregulation
Osmoregulation: The process of regulating and maintaining the correct water balance and salt concentration in the body fluids of an organism.
Nitrogenous waste
Nitrogenous waste: Toxic by-products containing nitrogen (such as urea, uric acid, and ammonia) that are produced during the breakdown of proteins and amino acids.
Ultrafiltration
Ultrafiltration: The first step of urine formation in which blood is filtered under high pressure within the glomerulus, allowing water and small dissolved wastes to pass into the Bowman’s capsule while blood cells and large proteins are retained.
UTI
UTI (Urinary Tract Infection): A bacterial infection (commonly caused by the bacterium E. coli) that affects any part of the urinary tract, including the kidneys, ureters, urinary bladder, and urethra.
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F. Name the organ where following processes take place.

Ultrafiltration and formation of urine
Kidneys (specifically in the nephrons)
Transport of urine from kidney
Ureters
Temporary storage of urine
Urinary bladder
Formation of sweat
Skin (specifically in the sweat glands)
Formation of urea
Liver
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G. Match the columns.

Column A
Column B
1. Excretion
(a) Loss of salt
2. Uriniferous tubule
(b) Sugar in urine
3. Sweat gland
© During summer
4. Excessive sweat
(d) Kidney
5. Diabetes
(e) Ultrafiltration
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Matching Pairs:
1. Excretion matches with (d) Kidney
2. Uriniferous tubule matches with (e) Ultrafiltration
3. Sweat gland matches with © During summer
4. Excessive sweat matches with (a) Loss of salt
5. Diabetes matches with (b) Sugar in urine
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H. Answer these questions.

What is excretion?
Excretion is the process by which toxic metabolic wastes (like urea, uric acid, and carbon dioxide) produced during various chemical reactions inside cells are removed from the body of an organism.
Name excretory organs in human body. What does each one of them excrete?
The primary excretory organs and their excretory products in humans are:
Kidneys: Excrete water, urea, uric acid, and excess salts in the form of urine.
Skin (Sweat glands): Excrete excess water, salts (like sodium chloride), and small amounts of urea in the form of sweat.
Lungs: Excrete carbon dioxide and water vapour during exhalation.
Liver: Excretes bile pigments, toxins, and synthesizes urea (which is transported via blood to the kidneys for final excretion).
Name the three steps in urine formation.
The three steps in urine formation are:
Ultrafiltration: Filtering water and nitrogenous wastes under pressure from blood capillaries in the glomerulus into the Bowman’s capsule.
Reabsorption: Reabsorbing useful materials (like glucose, amino acids, salts, and water) back into the blood as the filtrate moves down the nephron tubule.
Secretion: Actively transporting remaining salts and urea from blood capillaries into the tubule to form the final urine.
Name the excretory units found in kidney. What happens within each unit?
The excretory units found in the kidney are called nephrons (or uriniferous tubules). Within each nephron:
Blood enters the glomerulus, where ultrafiltration takes place, filtering out wastes and water into the Bowman’s capsule.
The filtrate flows through the coiled tubule, where reabsorption of essential substances (glucose, water, amino acids) takes place back into the blood.
Additional wastes are secreted into the tubule, leaving behind a fluid called urine, which is then collected and sent out of the kidney.
Draw a labelled diagram of renal excretory system of man.
Note: Students should draw the diagram based on Fig. 6.2. The diagram must clearly show and label:
Two kidneys (bean-shaped structures)
Renal artery and Renal vein
Two ureters (narrow tubes carrying urine downwards)
Urinary bladder (muscular bag-like structure in the lower abdomen)
Urethra and Urinary opening
Draw labelled diagram of V.S. of kidney.
Note: Students should draw the vertical cross-section diagram of the kidney based on Fig. 6.3. The diagram must label:
Renal cortex (the outer region)
Renal pyramids / Medulla (the inner region)
Renal pelvis (the central cavity leading into the ureter)
Ureter
Describe symptoms of urinary tract infection.
The symptoms of a Urinary Tract Infection (UTI) include:
A strong, frequent, and sudden urge to urinate.
Cloudy, dark, or strange-smelling urine.
A painful or burning sensation during urination.
Fever, chills, or back pain if the infection spreads up to the kidneys.
What is the need for excretion?
Excretion is needed because cells constantly perform biochemical reactions that generate toxic waste products such as carbon dioxide, ammonia, and other nitrogenous compounds. If allowed to accumulate, these substances:
Can prove highly toxic and damage cells.
Will alter the stable internal environment of cells.
Will disrupt the essential ionic and water balance within cells.
What is the basic difference between waste products and excretory products?
Waste products are any unusable or unwanted substances produced during metabolic processes in the body. Excretory products are a specific category of metabolic wastes that cannot be safely stored inside the body due to their toxicity and must be eliminated.
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I. Case-based Questions

What is the role of cellophane tubes in artificial kidney?
Cellophane tubes act as a selectively permeable membrane. Their tiny pores allow small waste molecules (like urea, uric acid, and excess ions) to pass out of the blood and into the dialysing solution, while preventing larger, essential blood cells and proteins from escaping.
What type of products diffuse out of the blood into the water bath?
Waste products like urea, uric acid, excess salts (ions), and excess glucose diffuse out of the blood into the water bath.
What do you mean by dialysis?
Dialysis is the medical process of filtering and purifying blood using an artificial kidney machine to remove toxic nitrogenous wastes when a person’s kidneys are damaged or non-functional.
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Critical Thinking (ThinkZone)

We take more water in summer but excrete less volume of urine. On the other hand, we drink less water in winter and produce more urine. Why?
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