Chapter 6: Human Body: Excretory System class 7 icse

 

Let Us Practice

A. Choose the correct option

1. Which of the following is not an excretory organ?
• Answer: (c) small intestine (The small intestine absorbs digested food; the large intestine eliminates solid waste, and lungs, kidneys, and skin excrete metabolic wastes).
2. Which one of the following is a correctly matched pair?
• Answer: (d) Renal artery - carries blood with waste from heart to the kidneys

3. A kidney is divided into three parts and they are:
• Answer: (a) cortex, medulla and pelvis
4. It is the state of steady internal conditions maintained by a living organism:
• Answer: (b) homeostasis
5. Observe the picture and label its parts:
• (Looking at the labels on the diagram: I points to the outer layer cortex, II points to the inner medulla, III points to the cap-like adrenal gland, and IV points to the funnel-shaped pelvis)
• Answer: (a) I – cortex, II – medulla, III – Adrenal gland, IV – Pelvis

B. Fill in the blanks

1. Excretion is the process of removing waste from the body.
2. A chemical that comes from break down of amino acids is urea.
3. The major organ of the excretory system is the kidney, which removes urea and other wastes.
4. Urine is a watery fluid that contains urea and other wastes.
5. Nephrons are tiny filtering units found inside the kidney, which remove waste from the blood and forms urine.
6. Thermoregulation means maintaining steady internal temperature. (Alternatively, Homeostasis if referring broadly to steady internal balance).

C. Define the following

1. Homeostasis: The self-regulating process by which an organism maintains a stable and steady internal environment despite changes in external conditions.
2. Urinary bladder: A thin, muscular, elastic sac-like organ that temporarily stores urine before it is expelled from the body[cite: 3, 5].
3. Urinary system: An organ system consisting of the kidneys, ureters, urinary bladder, and urethra, responsible for filtering blood and expelling liquid metabolic waste as urine.

 

D. Short-answer questions

1. Name the different excretory organs in the human body.
• Kidneys, lungs, skin, and liver (and the large intestine aids in solid waste removal).

 

2. What is the function of a nephron?
• Nephrons are the structural and functional units of the kidney that filter blood to remove metabolic wastes like urea, excess salts, and water to form urine.

 

3. Fill in the table:

Organ	Excretes what?	In what form?
Lungs	(a) Carbon dioxide and water vapour	(b) Gas / Exhaled air
Kidney	(c) Urea, uric acid, and excess salts	(d) Urine (liquid)
Skin	(e) Excess water, salts, and traces of urea	(f) Sweat (perspiration)

4. How will the blood in the renal artery be different from the blood in the renal vein with respect to excretory waste?
• The blood in the renal artery contains high concentrations of metabolic waste products (like urea and excess salts) coming to the kidneys for purification. In contrast, the blood leaving the kidney through the renal vein is purified and has significantly lower levels of these waste products.

 

5. Urine production varies on a daily basis. Which of the following, as per you, will cause an increase or decrease in the quantity of urine produced?
• (a) A hot and dry day: Decrease (more water is lost as sweat)
• (b) A cold day: Increase (very little sweating occurs)
• (c) Drinking a litre of water a day: Decrease (1 litre is low intake, prompting water conservation)
• (d) Strenuous exercise with much sweating: Decrease (water is lost through perspiration)

E. Long-answer questions

1. Explain the role of kidneys in the urinary system of human beings.
• Role:
• Filtration: They continuously filter blood via millions of microscopic nephrons, removing harmful toxins, excess urea, and uric acid.
• Osmoregulation: They regulate the water and salt balance (electrolytes) in body fluids to ensure homeostasis.
• pH & Blood Pressure Regulation: They help maintain blood pH and secrete renin to control blood pressure.

 

2. Write in short about disorders of the urinary system.
• Kidney Stones (Renal Calculi): Hard deposits of calcium or uric acid crystals that lodge in the kidneys or ureters, causing intense pain, blockage of urine, and sometimes blood in urine.
• Urinary Tract Infection (UTI): Bacterial infection (most commonly E. coli) causing pain and burning during urination, frequent urge to urinate, and inflammation of the urethra or bladder.

 

3. Draw a well-labelled diagram of the human urinary system and explain the functions of the ureters and urethra.
• Diagram: Sketch two bean-shaped kidneys, two narrow tubes (ureters) connecting each kidney to a central sac (urinary bladder), and a narrow outlet tube (urethra) at the bottom.
• Function of Ureters: Muscular tubes that propel urine from the renal pelvis of each kidney down into the bladder by peristaltic contractions.
• Function of Urethra: A duct that carries stored urine from the bladder out of the body during urination (micturition).

 

4. Are excretion and egestion the same? Why?
• No, they are different:
• Excretion is the removal of metabolic chemical wastes (such as urea and carbon dioxide) produced inside cells during biochemical processes.
• Egestion is the discharge of undigested, unabsorbed food material (faeces) from the alimentary canal through the anus.

 

F. Case based questions

I. Ravi's Case Study (Kidney Stones)

1. What is the most common cause of kidney stone formation?
• Answer: (b) Dehydration and high salt/mineral concentration in urine
2. The severe pain experienced by Ravi was most likely due to:
• Answer: (b) Stone blocking the ureter
3. Which of the following can help prevent the formation of kidney stones?
• Answer: (c) Drinking plenty of water
4. Which structure does a kidney stone pass through after leaving the kidney?
• Answer: (c) Ureter → → Bladder → → Urethra

 

II. Healthy Kidneys Comprehension Questions

1. Which one of the following do not help in keeping our kidneys healthy?
• Answer: (c) eating junk food
2. Why must we avoid eating health supplements to keep our kidneys healthy?
• Answer: Unnecessary or excessive health supplements (along with excessive painkillers) put extra stress on the kidneys to filter out high chemical/mineral concentrations, which can cause long-term kidney damage.
3. What type of food we should eat to keep our kidneys healthy?
• Answer: A balanced diet low in salt, sugar, and processed foods, accompanied by plenty of fresh water.

C. Word Search Puzzle

• Clue Solutions:
1. The process of removing wastes from the body: EXCRETION[cite: 2, 5]
2. A major organ of the excretory system which removes urea and other wastes: KIDNEY
3. A watery fluid waste that contains urea: URINE[cite: 2, 3, 5]
4. A sac-like muscular organ that stores urine: BLADDER[cite: 3, 5]
5. Body covering that has excretory function: SKIN[cite: 2, 5]
6. Excretory waste of lungs: CARBON DIOXIDE (or WATER) (In grid: SWEAT and URETER are also prominently present)

 

• Grid Coordinates / Placement:

• EXCRETION: Row 1, columns 5 to 13 (horizontal: E-X-C-R-E-T-I-O-N)
• KIDNEY: Row 4, columns 4 to 9 (horizontal: K-I-D-N-E-Y)
• URINE: Row 7, columns 3 to 7 (horizontal: U-R-I-N-E)
• SKIN: Row 5, columns 3 to 6 (horizontal: S-K-I-N)
• BLADDER: Found diagonally or vertically across middle columns.
• SWEAT: Row 9, columns 3 to 7 (horizontal: S-W-E-A-T)
• URETER: Row 8, columns 7 to 12 (horizontal: U-R-E-T-E-R)