Previous year questions: Excretory Products and their Elimination
Excretory Products and their Elimination36 min readLesson 6 of 6
These ten questions come from the NCERT Exemplar chapter on excretory products and their elimination, the only official previous year source available for Class 11 Biology. The set covers the site of filtration, the pH of urine, uremia, vasopressin, the counter current mechanism, the abbreviations used in this chapter, the excretory structures, the renin-angiotensin mechanism, dialysis and micturition. Marks follow the book convention: 1 mark MCQ, 2 marks very short answer, 3 marks short answer and 5 marks long answer. Each heading quotes the Exemplar chapter and question number.
Q1 (NCERT Exemplar, 1 mark; Chapter 19, Multiple Choice 2)
Filtration of the blood takes place at which site?
Answer: Filtration happens at the malpighian body, that is, at the glomerulus together with Bowman's capsule. The proximal convoluted tubule, distal convoluted tubule and collecting ducts do reabsorption and secretion, but the pressure driven filtering of plasma occurs only in the renal corpuscle.
Q2 (NCERT Exemplar, 1 mark; Chapter 19, Multiple Choice 5)
The pH of human urine is approximately what?
Answer: The printed key is option c, pH 6. The textbook describes human urine as slightly acidic, near pH 6.0, and the exemplar answer key confirms 6. Option 6.5 is only an approximation and is not the printed answer, while 7 and 7.5 would be neutral or alkaline. Do not confuse this with blood pH, which is about 7.4.
Q3 (NCERT Exemplar, 1 mark; Chapter 19, Multiple Choice 10)
The condition of accumulation of urea in the blood is termed what?
Answer: Accumulation of urea in the blood is uremia. Renal calculi are stones inside the kidney and glomerulonephritis is inflammation of the glomeruli, while ketonuria is the appearance of ketone bodies in the urine. Uremia is the one that describes urea in the blood and it can progress to kidney failure. The word uremia names the blood condition, not the urine, which is why it is the correct choice.
Q4 (NCERT Exemplar, 1 mark; Chapter 19, Multiple Choice 11)
Which one of the following is also known as antidiuretic hormone?
Answer: Vasopressin is the antidiuretic hormone. It is released from the neurohypophysis under the control of the hypothalamus and it increases water reabsorption in the later parts of the tubule. Oxytocin, adrenaline and calcitonin have other functions and do not act as ADH.
Q5 (NCERT Exemplar, 1 mark; Chapter 19, Multiple Choice 14)
Which mechanism allows us to produce concentrated or dilute urine?
Answer: The counter current mechanism of the loop of Henle and the vasa recta is the mechanism that allows concentrated or dilute urine to be produced. Reabsorption in the PCT and DCT and the collecting duct adjust the final composition, but the ability to concentrate the urine depends on the medullary gradient built by the counter current arrangement.
Q6 (NCERT Exemplar, 2 marks; Chapter 19, Very Short Answer 5)
What is the excretory structure in amoeba?
Answer: Amoeba uses a contractile vacuole as its excretory and osmoregulatory structure. The vacuole collects excess water and dissolved wastes from the cytoplasm and discharges them out of the cell, which keeps the water and ion balance of the single cell steady.
Q7 (NCERT Exemplar, 2 marks; Chapter 19, Very Short Answer 6)
The following abbreviations are used in the context of excretory functions. What do they stand for: ANF, ADH, GFR and DCT?
Answer: ANF stands for atrial natriuretic factor, ADH for antidiuretic hormone, GFR for glomerular filtration rate, and DCT for distal convoluted tubule. ANF is released when blood flow to the atria rises and it lowers blood pressure; ADH raises water reabsorption; GFR is the volume of filtrate formed per minute; and the DCT is the segment that makes the conditional reabsorption of sodium and water.
Q8 (NCERT Exemplar, 3 marks; Chapter 19, Short Answer 2)
What is the role played by renin-angiotensin in the regulation of kidney function?
Answer: A fall in glomerular blood flow or pressure, or in the GFR, makes the JG cells of the juxtaglomerular apparatus release renin. Renin turns angiotensinogen in the blood into angiotensin I, and angiotensin I is turned into angiotensin II. Angiotensin II is a strong vasoconstrictor, so the pressure inside the glomerulus rises and the GFR comes back up. The same hormone tells the adrenal cortex to release aldosterone, and aldosterone makes the distal tubule take back more sodium and water, which lifts the pressure and the GFR still further. The sequence is the renin-angiotensin mechanism, and ANF from the heart is its natural brake.
Q9 (NCERT Exemplar, 3 marks; Chapter 19, Short Answer 5)
What is the procedure advised for the correction of extreme renal failure? Give a brief account of it.
Answer: The procedure is haemodialysis with an artificial kidney. Blood is drained from a convenient artery and an anticoagulant such as heparin is added so that it does not clot. The blood is pumped into a dialysing unit that contains a coiled cellophane tube surrounded by dialysing fluid, and the fluid has the same composition as plasma except that it contains no nitrogenous wastes. Waste substances such as urea diffuse out of the blood through the cellophane into the fluid, and the cleaned blood is returned to the body. Dialysis removes the wastes that the failed kidneys cannot remove, so the patient has to be dialysed repeatedly until a transplant is possible. The dialysing fluid is renewed so that the waste concentration stays low and diffusion continues, and the flow of blood and fluid is arranged so that the two never mix. That separation matters, because mixing would let the wastes return to the blood.
Q10 (NCERT Exemplar, 5 marks; Chapter 19, Long Answer 3)
Explain briefly micturition and the disorders of the excretory system.
Answer: Urine made in the nephrons travels down the collecting ducts into the renal pelvis, then along the ureters to the urinary bladder, which stores it until the central nervous system gives a voluntary signal. The signal begins when stretch receptors in the wall of the full bladder send impulses to the central nervous system. Motor messages then arrive at the bladder, the smooth muscle of the bladder contracts and the urethral sphincter relaxes at the same time, so urine passes out. This process is micturition and the neural circuit is the micturition reflex. An adult human passes about 1 to 1.5 litres of urine a day, and the urine is slightly acidic with a pH near 6.0.
The main disorders are uremia, renal calculi, glomerulonephritis and gout. Uremia is the accumulation of urea in the blood because the kidneys are failing, and it can be treated by haemodialysis. Renal calculi are stones formed when salts crystallise inside the kidney. Glomerulonephritis is inflammation of the glomeruli, which disturbs filtration. Gout is the accumulation of uric acid crystals in the joints. Urine analysis also detects glycosuria, the presence of glucose in the urine, and ketonuria, the presence of ketone bodies, and both are usually signs of diabetes mellitus.
Answer habits for this set
Three habits carry most of the marks here. First, whenever the question is about a process, write the steps in order and name the structure at each step: for filtration, the three layers and the slit pores; for concentration, the two limbs of the loop and the two limbs of the vasa recta; for micturition, the stretch receptors, the central nervous system, the bladder muscle and the sphincter. Second, quote the numbers that the book prints, because examiners look for them: 125 mL per minute, 180 litres per day, 300 to 1200 mOsmol per litre, 25 to 30 g of urea per day, 1 to 1.5 litres of urine per day. Third, keep the hormonal answers in separate loops: ADH for water, renin-angiotensin-aldosterone for sodium and pressure, and ANF as the brake on the renin loop. A diagram of the nephron with the sites of filtration, reabsorption and secretion marked is quick to draw and it earns marks even when the words are short. Finally, keep the vocabulary of the chapter exact, because a single wrong term spoils an otherwise correct answer: filtration is not the same as reabsorption, the renal pelvis is not a pyramid, and the loop of Henle does not sit in the cortex. A short revision of the labelled nephron and kidney diagrams before the exam is the fastest way to fix all of these terms at once.