Selina Concise Solutions for ICSE Class 10 Biology Chapter 7 The Excretory System Elimination Of Body Wastes

A. Multiple Choice Type:

Question 1. Excretion primarily involves
(a) removal of all byproducts during catabolism
(b) removal by products during anabolism
(c) removal of nitrogenous wastes
(d) throwing out excess water
Answer: (c) removal of nitrogenous wastes
In simple words: Excretion is mainly about getting rid of toxic nitrogen-containing waste chemicals that would poison our body if they stayed inside.

📝 Teacher's Note: Emphasize that while other options might be "waste removal," excretion specifically targets nitrogenous wastes like urea that are toxic. Use the analogy of a factory removing its most dangerous chemicals first.

🎯 Exam Tip: Remember "Excretion = Nitrogenous waste removal" - this is the defining characteristic that separates excretion from general waste disposal.

Question 2. Maximum amount of water from the glomerular filtrate is reabsorbed in
(a) proximal convoluted tubule
(b) descending limbs of loop of Henle
(c) ascending limb of loop of Henle
(d) distal convoluted tubule
Answer: (a) proximal convoluted tubule
In simple words: The proximal convoluted tubule is like the first and biggest "recycling station" that saves about 65% of the water from being lost as urine.

📝 Teacher's Note: Use percentages to help students remember - PCT reabsorbs about 65% of water, making it the clear winner. Compare it to sorting recyclables where the biggest bin comes first.

🎯 Exam Tip: "Proximal = Primary water saver" - remember that maximum reabsorption happens at the first major site, the PCT.

Question 3. Which one of the following in real sense is NOT an excretory activity?
(a) giving out carbon dioxide
(b) passing out faecal matter
(c) sweating
(d) Removal of urea
Answer: (b) passing out faecal matter
In simple words: Faecal matter is undigested food that never entered our body's metabolism, so removing it isn't excretion but just getting rid of leftovers.

📝 Teacher's Note: Clarify the difference between egestion (undigested food removal) and excretion (metabolic waste removal). Use the analogy of throwing away food packaging vs. disposing of factory waste.

🎯 Exam Tip: Remember that excretion only involves wastes produced BY the body's metabolism, not undigested materials that just passed through.

Question 4. In humans, urea is formed in
(a) ureter
(b) liver
(c) spleen
(d) kidney
Answer: (b) liver
In simple words: The liver is like a chemical factory that converts toxic ammonia from protein breakdown into less harmful urea, which is then sent to kidneys for removal.

📝 Teacher's Note: Stress that kidneys filter and remove urea, but liver produces it. Many students confuse the site of production with site of elimination. Use the factory-disposal analogy.

🎯 Exam Tip: "Liver makes it, kidney takes it" - this simple phrase helps distinguish between urea formation (liver) and elimination (kidney).

B. Very Short Answer Type:

Question 1. Name the following:
(a) The organ which produces urea
(b) The outer region of kidney containing the Bowman's capsule
(c) The tuft of capillaries inside the Bowman's capsule
(d) The part of kidney tubules where the term urine is first used for the fluid in it
(e) The vein in which urea concentration is maximum
Answer:
(a) Liver
(b) Cortex
(c) Glomerulus
(d) Collecting duct
(e) Renal artery (Renal vein has urea but renal artery has higher concentration of urea as compared to renal vein)
In simple words: These are key parts of the excretory system - liver makes urea, cortex filters it, glomerulus does the actual filtering, collecting duct finalizes urine, and renal artery brings the most urea-rich blood to kidneys.

📝 Teacher's Note: For part (e), explain the logic - renal artery brings "dirty" blood TO the kidney, so it has more urea than renal vein which carries "cleaned" blood away.

🎯 Exam Tip: For part (e), think logically - the artery bringing blood TO the kidney must have more waste than the vein taking cleaned blood away.

Question 2. Given below are two sets (a and b) of five terms each. Rewrite the terms in their correct order so as to be in logical sequence.
(a) Afferent arteriole, renal vein, capillary network, glomerulus, efferent arteriole.
(b) Renal artery, urethra, ureter, kidney, urinary bladder.
Answer:
(a) Afferent arteriole, glomerulus, efferent arteriole, capillary network, renal vein
(b) Renal artery, kidney, ureter, urinary bladder, urethra
In simple words: These show the path blood takes through kidney vessels and the path urine takes from kidney to outside the body.

📝 Teacher's Note: Draw simple flow diagrams on the board to show these sequences. For blood flow, emphasize the filtration occurs between afferent and efferent arterioles.

🎯 Exam Tip: Think of logical flow - blood goes IN (afferent), gets filtered (glomerulus), goes OUT (efferent), and urine follows gravity downward from kidney to exit.

Question 3. In each one of the following sets of body parts or substances or processes, pick out the one item which overall includes the remaining four.
(a) Glomerular filtrate, bowman's capsule, ultrafiltration, glomerulus, blood plasma.
(b) skin, liver, lungs, kidney, excretion
(c) ADH, Water, pituitary, osmoregulation, urine
(d) CO2, bile pigments, water, excretion, urea.
Answer:
(a) Ultrafiltration
(b) Excretion
(c) Osmoregulation
(d) Excretion
In simple words: These are the "umbrella terms" that include all the other items as parts or examples of the bigger process.

📝 Teacher's Note: Help students identify the "umbrella concept" by asking "Which term can include all others as its components or examples?" Use concept mapping to show relationships.

🎯 Exam Tip: Look for the broadest term that can encompass all others as its parts, examples, or components - usually the process name rather than specific structures.

C. Short Answer Type:

Question 1. Write down the functional activity of the following parts,
(a) Glomerulus .....................
(b) Henle's loop ................
(c) Ureter ........................
(d) Renal artery ................
(e) Urethra ......................
Answer:
(a) Glomerulus is involved in the process of ultrafiltration. The liquid part of the blood which is plasma including urea, salts, glucose filters out from the glomerulus into the renal tubule.
(b) Henle's loop is involved in reabsorption of water and sodium ions.
(c) Ureter carries urine to the urinary bladder by ureteral peristalsis.
(d) Renal artery supplies blood to the kidney.
(e) Urethra is involved in the process of micturition i.e. expelling urine out of the body.
In simple words: Each part has a specific job - glomerulus filters blood, Henle's loop saves water and salts, ureter transports urine, renal artery supplies blood, and urethra expels urine.

📝 Teacher's Note: Use the analogy of a water treatment plant where each component has a specific function. Emphasize that peristalsis in ureters is like squeezing a tube of toothpaste.

🎯 Exam Tip: Remember one key function per structure - filtration, reabsorption, transport, supply, and expulsion respectively.

Question 2. Why is excretion necessary? Name the common excretory substance in our body.
Answer: Excretion helps in removing toxic wastes from our body and it also plays an important role in osmoregulation i.e. the maintenance of the homeostasis of the body. Carbon dioxide, water, nitrogenous compounds such as urea, uric acid and excess salts are some common excretory products.
In simple words: Excretion is like taking out the garbage - it removes poisonous waste chemicals and helps maintain the right balance of water and salts in our body.

📝 Teacher's Note: Connect excretion to homeostasis concept. Explain that accumulation of metabolic wastes would be like never taking out garbage - eventually toxic and harmful.

🎯 Exam Tip: Always mention both functions of excretion - waste removal AND osmoregulation. List at least 3-4 excretory products for full marks.

Question 3. What is a uriniferous tubule? How does it function?
Answer: A uriniferous tubule also known as the kidney tubule is the structural and functional unit of the kidney. It takes in impure blood from the renal artery and removes wastes in the form of urine. It also provides a larger surface area for reabsorption of salts and water.
In simple words: A uriniferous tubule is like a tiny filtration and recycling unit in the kidney that cleans blood and makes urine while saving useful substances.

📝 Teacher's Note: Compare nephron structure to a miniature water treatment plant with different zones for filtration, reabsorption, and waste concentration.

🎯 Exam Tip: Define it as the "structural and functional unit" and mention its dual role - filtration AND reabsorption.

Question 4. Why is it necessary to maintain a normal osmotic concentration of the blood?
Answer: Maintaining a normal osmotic concentration in the body means regulating the percentage of water and salts. If this regulation mechanism fails we either end up losing vital salts and water or may accumulate unwanted salts and excess water in our body.
In simple words: It's like keeping the right recipe of water and salt in our blood - too much or too little of either can make our cells sick or stop working properly.

📝 Teacher's Note: Use examples of what happens when osmotic balance is disturbed - dehydration, edema, cell swelling or shrinkage. Connect to real-life situations like sports drinks.

🎯 Exam Tip: Explain both consequences - losing vital substances OR accumulating harmful excess. Mention that cells need specific concentrations to function.

Question 5. If you donate one kidney to a needy patient, would it cause any harm to you? Give reason.
Answer: If one kidney is donated to a needy patient, the other kidney alone is sufficient for removing wastes or excretion. Thus, the donor can live a normal life.
In simple words: One healthy kidney can do the job of two because kidneys have extra capacity - like having two engines when you only need one to fly the plane.

📝 Teacher's Note: Explain the concept of functional reserve in kidneys. One kidney can increase its filtration capacity to compensate. Use analogies of backup systems.

🎯 Exam Tip: Emphasize that kidneys have reserve capacity and one kidney can adapt to handle the full workload of excretion.

Question 6. In summer the urine is slightly thicker than in winter explain the reason.
Answer: During summer, a considerable part of water is lost through perspiration so the kidneys have to reabsorb more water from the urine. This makes the urine thicker in summer than in winters.
In simple words: In summer we sweat more, losing water, so kidneys save more water by making more concentrated (thicker) urine.

📝 Teacher's Note: Connect this to water balance in the body. When water is lost through sweating, kidneys compensate by conserving water. Relate to students' experience of darker urine on hot days.

🎯 Exam Tip: Link sweating in summer to water loss, which triggers kidneys to reabsorb more water, making urine more concentrated.

Question 7. Differentiate between the following pairs of terms:
(a) Bowman's capsule and malpighian capsule.
(b) Renal cortex and renal medulla
(c) Renal pelvis and renal papilla
(d) Urea and urine
(e) Excretion and katabolism
Answer:
(a) Bowman's capsule is a thin walled cup containing the glomerulus. This Bowman's capsule along with the glomerulus is known as malpighian capsule.
(b) The renal cortex is the outer darker region of the kidney whereas the renal medulla is the inner lighter region of the kidney.
(c) Renal pelvis is the expanded front end of the ureter in the kidney whereas the renal papilla is the apex of the renal pyramid which projects into the pelvis.
(d) Urea is the chief excretory product which is excreted in the form of urine whereas urine is the filtrate left after reabsorption and tubular secretion which contains 95% water and 5% solid wastes.
(e) Excretion is the process of removal of chemical wastes especially nitrogenous wastes from the body. Catabolism on the other hand is the set of metabolic pathways which break down molecules into smaller units and release energy.
In simple words: These pairs show the difference between parts and wholes, locations, structures, waste forms, and different body processes.

📝 Teacher's Note: Use diagrams to show anatomical differences. For (a), explain that malpighian capsule = Bowman's capsule + glomerulus. For (e), catabolism produces wastes that excretion removes.

🎯 Exam Tip: For each pair, identify the key distinguishing feature - structure vs. combined unit, location, position, chemical vs. solution, removal vs. breakdown.

Question 8. Name the main nitrogenous metabolic waste excreted out by mammals including humans.
Answer: Urea, creatinine, uric acid
In simple words: These are the main nitrogen-containing waste chemicals that mammals need to get rid of to avoid poisoning.

📝 Teacher's Note: Explain that these come from protein metabolism. Urea is the major one, while creatinine comes from muscle metabolism and uric acid from nucleic acid breakdown.

🎯 Exam Tip: Remember the "big three" nitrogenous wastes - urea (major), creatinine (from muscles), uric acid (from DNA/RNA).

Question 9. Match the terms in Column I with those in Column II and write down the matching pairs.
Answer:
Column I - Column II
(a) Bowman's Capsule - Glomerulus
(b) Contains more CO2 and less urea - Renal Vein
(c) Anti-diuretic hormone - Regulates amount of water excreted
(d) Contains more urea - Renal artery
In simple words: These matches show the relationships between kidney structures and their contents or functions.

📝 Teacher's Note: Emphasize the logic - Bowman's capsule contains glomerulus, renal vein has less waste (cleaned blood), ADH controls water retention, renal artery brings waste-rich blood.

🎯 Exam Tip: Think about function and flow - what contains what, what has more/less waste, and what controls what process.

Question 10. In a nephron, the .............. flows through the .............. under great pressure. The reason for this great pressure is that the .............. (outgoing) .............. is narrower than the .............. (incoming). This high pressure causes the.............. part of the blood to filter out from the .............. into the renal capsule.
Answer: In a nephron, the blood flows through the glomerulus under great pressure. The reason for this great pressure is that the efferent (outgoing) arteriole is narrower than the afferent (incoming). This high pressure causes the liquid part of the blood to filter out from the glomerulus into the renal capsule.
In simple words: Blood gets squeezed through a narrow exit after entering through a wide entrance, creating pressure that forces liquid and small particles to filter out.

📝 Teacher's Note: Use the analogy of a garden hose with a narrow nozzle - pressure builds up when the exit is smaller than the entrance, forcing filtration.

🎯 Exam Tip: Remember the pressure concept - wider entrance (afferent) + narrower exit (efferent) = high pressure = filtration of liquid blood components.

Long Answer Type

Question 1. Define the following terms:
(a) Ultrafiltration (b) Micturition
(c) Renal pelvis (d) urea
(e) Osmoregulation
Answer:
(a) Ultrafiltration - The process of the filtration of blood in the glomerulus under great pressure during which the liquid part of the blood i.e. plasma along with urea, glucose, amino acids and other substances enter the renal tubule.
(b) Micturition: The process of expelling urine out of the body through urethra by opening the sphincter muscles passing of urine involving relaxation of sphincter muscles between the urinary bladder and urethra.
(c) Renal pelvis - Renal pelvis is the expanded front end of the ureters into the kidney.
(d) Urea - A nitrogenous waste produced primarily in the liver due to the break down dead protein remains and extra amino acids.
(e) Osmoregulation - It is a process of maintaining the blood composition of the body i.e. the normal osmotic concentration of water and salts in the body.
In simple words: These are key terms about how kidneys filter blood and remove waste - like a cleaning factory that sorts good stuff from bad stuff.

📝 Teacher's Note: Use the analogy of a water filter at home - just like it removes impurities from water, kidneys filter blood. Start with ultrafiltration (the main filtering) then move to other processes.

🎯 Exam Tip: Remember that urea is made in the LIVER but removed by the KIDNEYS. This distinction often confuses students in exams.

Question 2. Explain the terms ultrafiltration and selective absorption
Answer:
Ultrafiltration
Ultrafiltration involves filtration of the blood which takes place in the glomerulus. The blood containing urea from the afferent arteriole enters the glomerulus under high pressure. The high pressure is created because the efferent arteriole is narrower than the afferent arteriole. The high pressure causes the liquid part of the blood to filter out from the glomerulus into the renal tubule. This filtrate is known as 'glomerular filtrate'.

Glomerular filtrate consists of water, urea, salts, glucose and other plasma solutes. Blood corpuscles, proteins and other large molecules remain behind in the glomerulus. Therefore the blood which is carried away by the efferent arteriole is relatively thick.

Selective absorption
The Glomerular filtrate entering the renal tubule contains a lot of usable materials such as glucose and sodium. As this filtrate passes down the renal tubule, a lot of water along with these usable materials is reabsorbed. Such reabsorption is called 'selective absorption'. The reabsorption occurs only to the extent that the normal concentration of the blood is undisturbed.
In simple words: Ultrafiltration is like forcing water through a strainer under pressure, and selective absorption is like picking up the good stuff that was accidentally thrown away.

📝 Teacher's Note: Use a tea strainer analogy - ultrafiltration is like forcing tea through the strainer, selective absorption is like collecting the tea leaves you actually want to keep.

🎯 Exam Tip: Always mention that the efferent arteriole is NARROWER than afferent - this creates the high pressure needed for filtration.

Question 3. What is dialysis? Under what condition is it carried out?
Answer:
Dialysis involves the use of artificial kidney or a dialysis machine. The patient's blood is from the radial artery is led through the machine where excess salts and urea is removed. The purified blood is then returned to a vein in the same arm.

Dialysis is carried out in case of failure of both the kidneys. In case there is a permanent damage, then the dialysis is to be repeated for about 12 hours twice a week.
In simple words: Dialysis is like using an artificial kidney machine when your real kidneys stop working properly.

📝 Teacher's Note: Emphasize that dialysis is needed only when BOTH kidneys fail - one working kidney can sustain life. Show students how the machine works like an external filter.

🎯 Exam Tip: Remember the frequency - 12 hours twice a week for permanent damage. This specific detail is often asked in exams.

Structured / Application / Skill Type

Question 1. Look at the figure given below, it is a section of human kidney as seen from the front.
(a) Is it the left kidney or the right one? Give reason in support of your answer.
(b) Is it a longitudinal section or a cross-section?
(c) Name the parts numbered 1-5
(d) which area/part (give its name and the number given on the diagram) contains the following respectively:
(i) malpighian capsule
(ii) The pyramids
(iii) Freshly collected urine
Answer:
(a) The image shown can be left or right kidney. As the right kidney is slightly lower than the left one, so we need to have the images of both the kidneys for comparison.
(b) It is a longitudinal section of the kidney.
(c) 1-renal artery, 2-renal vein, 3-ureter, 4-cortex, 5-pelvis
(d) (i) 4/cortex
(ii) medulla
(iii) 5/pelvis
In simple words: The kidney diagram shows how blood enters, gets cleaned, and waste leaves as urine through different parts.

📝 Teacher's Note: Point out that the cortex (outer region) contains the filtering units, medulla (middle) has collecting tubes, and pelvis (inner) collects final urine.

🎯 Exam Tip: Remember the flow direction: artery brings blood IN, vein takes blood OUT, ureter takes urine DOWN to bladder.

Question 2. Given alongside is the figure of certain organs and associated parts in the human body. Study the same and answer the questions that follow:
(a) Name all the organ systems shown completely or even partially
(b) name the parts numbered 1 to 5
(c) Name the structural and functional unit of the part marked '1'
(d) name the two main organic constituents of the fluid that flows down the part labelled '3'
(e) Name the two major steps involved in the formation of the fluid that passes down the part labelled '3'
Answer:
(a) Excretory system and Circulatory system.
(b) 1-kidney, 2-renal artery, 3-ureter, 4-urinary bladder, 5-urethra
(c) Nephron
(d) Urea and ammonia
(e) Ultrafiltration and selective reabsorption
In simple words: This shows how the kidney connects to other organs to clean blood and remove liquid waste from the body.

📝 Teacher's Note: Trace the path with students: blood enters kidney → gets filtered → clean blood returns → waste becomes urine → travels down ureter → stored in bladder → exits through urethra.

🎯 Exam Tip: Don't confuse ureter (tube from kidney to bladder) with urethra (tube from bladder to outside). Remember: ureter = kidney to bladder, urethra = bladder to exit.

Question 3. The following diagram represents a mammalian kidney tubule (nephron) and its blood supply.
Parts indicated by the guidelines 1 to 8 are as follows:
1. Afferent arteriole from renal artery
2. efferent arteriole
3. Bowman's capsule
4. Glomerulus;
5. Proximal convoluted tubule with blood capillaries;
6. Distal convoluted tubule with blood capillaries;
7. collecting tubule;
8. U-shaped loop of Henle
Study the diagram and answer the question that follow:
(a) where does ultrafiltration take place?
(b) Which structure contains the lowest concentration of urea?
(c) Which structure contains the highest concentration of urea?
(d) Which structure (normally) contains the lowest concentration of glucose?
(e) where is most water reabsorbed?
Answer:
(a) 4/Glomerulus
(b) 2/Efferent arteriole
(c) 1/Afferent arteriole from renal artery
(d) 7/Collecting tubule
(e) 5/Proximal convoluted tubule with blood capillaries
In simple words: The nephron works like a filtration assembly line - waste gets concentrated as it moves through, while useful stuff gets reabsorbed back into blood.

📝 Teacher's Note: Explain that urea concentration increases as blood moves through the nephron because urea stays while water gets reabsorbed. Glucose should be completely reabsorbed normally.

🎯 Exam Tip: Remember that efferent arteriole has LOWEST urea because most waste has been filtered out already. Afferent has HIGHEST because it's bringing waste-rich blood.

Question 4. Given alongside is a highly simplified (but also somewhat wrong) diagram of the human kidney cut open longitudinally. Answer the questions that follow.
(a) Define excretion
(b) Name the functional units of the kidneys.
(c) Why does the cortex of the kidney show a dotted appearance?
(d) Mention two functions of the kidney.
(e) Write two differences in the composition of the blood flowing through the blood vessels, 'A' and 'B'[There is an error in the diagram. Can you identify it?]
Answer:
(a) The process of removal of chemical wastes especially nitrogenous waste from the body is known as excretion.
(b) Nephrons
(c) As the cortex region contains numerous nephrons or kidney tubules, therefore, it shows a dotted appearance.
(d) Kidneys help in removing wastes or excretion and osmoregulation.
(e) The blood vessel 'B' is renal artery and the blood vessel 'A' is renal vein.
So the blood vessel 'B' contains oxygenated blood with high concentration of urea and glucose whereas the blood vessel 'A' contains deoxygenated blood with low concentration of urea and glucose as compared to renal artery.
In simple words: Excretion is getting rid of body waste, and kidneys are made of millions of tiny filters called nephrons that clean the blood.

📝 Teacher's Note: The dotted appearance is like looking at a sponge - millions of tiny holes (nephrons) give it that texture. Emphasize that each dot represents a filtering unit.

🎯 Exam Tip: Always mention NITROGENOUS waste in excretion definition. Remember that renal artery brings dirty blood (high urea), renal vein takes clean blood (low urea).

Question 5. Study the diagram given alongside and then answer the questions that follow:
(a) Name the region in the kidney where the above structure is present?
(b) Name the parts labelled 1, 2, 3 and 4.
(c) Name the stages involved in the formation of urine
(d) What is the technical term given to the process occurring in 2 and 3? Briefly describe the process.
Answer:
(a) Cortex
(b) 1-Afferent arteriole, 2-Glomerulus, 3-Bowman's capsule, 4-Efferent arteriole
(c) Ultrafiltration and selective reabsorption
(d) Ultrafiltration. The high pressure in the glomerulus forces the liquid part of blood (plasma) along with dissolved substances like urea, glucose, salts through the walls into Bowman's capsule, forming glomerular filtrate.
In simple words: This shows the filtering part of a nephron where blood gets squeezed under pressure to separate waste from useful substances.

📝 Teacher's Note: Use the analogy of squeezing a wet sponge - the pressure forces liquid out but keeps the solid parts inside. This happens in the glomerulus.

🎯 Exam Tip: Remember that ultrafiltration happens specifically between glomerulus (2) and Bowman's capsule (3). The pressure difference is key to the process.

Solution 5:
Answer:
(a) The structure is a Bowman's capsule, which is part of the nephron. The Bowman's capsule is found in the cortex of the kidney.
(b) 1 - Afferent arteriole
2 - Glomerulus
3 - Bowman's capsule
4 - Efferent arteriole
(c) Urine formation occurs in two steps - ultrafiltration and reabsorption.
(d) The process occurring in 2 and 3 is known as ultrafiltration.
In the glomerulus, the blood flows under high pressure because of the narrow lumen of the capillary network of the glomerulus. This forces most of the components (both waste and useable materials) of the blood out of the capillaries. This process of the filtration of blood under high pressure in the Bowman's capsule is known as ultrafiltration.
In simple words: The kidney filters blood like a coffee filter - high pressure pushes blood through tiny holes in the glomerulus, separating waste and useful materials in the Bowman's capsule through ultrafiltration.

📝 Teacher's Note: Use the analogy of a coffee filter or strainer to help students visualize ultrafiltration. Emphasize that both useful and waste materials are filtered out initially, making reabsorption necessary.

🎯 Exam Tip: Always mention "high pressure" and "narrow lumen" when explaining ultrafiltration - these are key terms examiners look for in nephron function questions.