Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.
Q.1. Assertion : Aquatic mammals like whales and seals are said to be ureotelic animals.
Reason : It is because of the fact that their main nitrogenous waste product is urea.
AnswerAnswer: (a) Ureotelism is defined as the urinary elimination of nitrogen mainly as urea. Aquatic mammals like whales and seals are said to be ureotelic animals because their major nitrogenous waste product is urea. As a matter of fact, ammonia is the basic nitrogenous catabolite of protein but since ammonia is highly toxic to the animals, therefore, its concentration must be kept very low in the blood.
Q.2. Assertion: Sharks are said to be ammonotelic animals.
Reason: Sharks have a ability to retain considerable amounts of ammonia in vertebrates.
AnswerAnswer: (d) Sharks are ureotelic, they are not ammonotelic animals. Ureotelic animals excrete urea instead of ammonia as the major nitrogenous waste product. These include man and all other mammals, terrestrial and semi-aquatic amphibians such as toads and frogs, cartilaginous fishes (elasmobranchs) such as sharks and sting rays. Sharks need to avoid water loss from body, thus they cannot excrete ammonia, as it requires enough water to be eliminated. In order to retain so much urea in their blood, their blood osmotic pressure approaches that of sea water. This minimises water loss from their body to adjust to the concentrated saline water of the sea.
Q.3. Assertion: Ammonia should be removed from the body as rapidly as it is formed.
Reason: In water, ammonia is insoluble.
AnswerAnswer: (c) Ammonia is a type of the basic nitrogenous catabolite of proteins, that is highly soluble in water and highly toxic to the animal. Therefore, its concentration must be kept very low in the blood. Due to this ammonia should be removed as rapidly from the body as it is formed. A large volume of water is required by the animals to dissolve ammonia and remove it from the body. So, its elimination in urine involves considerable loss of water from the body.
Q.4. Assertion: Both ammonia and urea are excreted by earthworms.
Reason: Excretion in earthworm depends on the environment.
Q.5. Assertion: In birds and reptiles, main excretory product is the combined form of urine and faeces.
Reason: Birds and reptiles consists no separate chamber for excretion of urine and faeces.
AnswerAnswer: (a) In birds and reptiles, ureters and the rectum open into a common sac is known as the cloaca (as there is no chamber for urine and faces) for these two that stores both, and reabsorbs water from them and ultimately excretes these white and brownish black material along with aqueous fluid.
Q.6. Assertion: Comparative to uric acid, urea is a more toxic excretory substance.
Reason: Birds and insects are uricotelic animals.
AnswerAnswer: (b) Urea is more toxic than uric acid and less toxic to ammonia.
Ammonia > Urea > Uric acid
Urea formation takes place in kidneys.
Q.7. Assertion: The primary excretory organ in vertebrates is referred to as liver.
Reason: Liver helps kidneys urine secretion.
AnswerAnswer: (d) In vertebrates, accessory excretory organs are the lungs, liver and skin are referred as because besides the urinary system, these organs also participate in the removal of waste products from the body. The liver helps in the excretion of cholesterol, bile pigments (bilirubin and biliverdin), inactivated products of steroid hormones, some vitamins and many drugs. These are carried by the bile to the intestine and are eliminated with the faeces. It has no role in urine secretion.
Q.8. Assertion : Urinary bladder and ureters are lined by transitional epithelium.
Reason : Ureters carry the urine to urinary bladder where it is stored temporarily.
AnswerAnswer: (b) Urinary bladder and ureters of excretory system are lined by transitional epithelium because it is a stretchable epithelium, hence the urinary bladder and ureters may be considerably stretched without getting torn when they are filled with urine. Ureters are thin muscular tubes which emerge from the hilum of each kidney. Urine enters the ureters from the renal pelvis and is conducted along the ureters by peristaltic waves on their walls. Ureters from both the kidneys finally open into urinary bladder which is a hollow muscular sac. In this way urine from both the kidneys is drained into the urinary bladder which stores it temporarily.
Q.9. Assertion : In vertebrates, the liver is also referred as an accessory excretory organ.
Reason : Liver helps kidneys in the secretion of urine.
AnswerAnswer: (c) In vertebrates, the lungs, liver & skin are referred as accessory excretory organs because besides the urinary system these organs also participate in the removal of waste products from the body. The liver is the principal organ for the excretion of cholesterol, bile pigments (bilirubin and biliverdin) and inactivated products of steroid hormones, some vitamins and many drugs. It secretes these substances in the bile and indirectly helps by formation of urea through amino acids in ornithine cycle. They are carried by the bile to the intestine and are ultimately eliminated with the faeces. It has no role in secretion of urine.
Q.10. Assertion : If human urine is allowed to stand for some time, it smells strongly of ammonia.
Reason : Main constituent of human urine is ammonia. [AIIMS 2013]
AnswerAnswer: (c) Urea is the chief nitrogenous constituent of human urine, though it possesses small amount of ammonia. But when the urine is allowed to stand for sometime, bacterial degradation occurs and it leads to the production of ammonia from urine, and thus smells strongly
Q.11. Assertion : Kidneys maintain the osmotic concentration of the blood.
Reason : Kidneys eliminate either hypotonic or hypertonic urine according to the need of the body.
AnswerAnswer: (a) Kidneys play an essential role in maintaining the concentration and osmotic pressure of blood. When water intake of an aminal is very high, the urine excreted has to be hypotonic i.e., dilute and lower in osmotic pressure than their blood in order to remove the excess of water contrary to this, when there is a threat of excessive water loss from the body; the urine needs to be hypertonic more concentrated and higher in osmotic pressure than their blood, to reduce the loss of water with urine. In this way, the osmotic concentration of the blood is maintained.
Q.12. Assertion : During physiology of excretion, deamination does not take place in liver.
Reason : Deamination is a process to make use of excess of amino acids which cannot be incorporated into protoplasm. [AIIMS 2001]
AnswerAnswer: (d) Deamination is the process of converting amino acid to keto acid with the release of NH3. It occurs in the liver.
Q.13. Assertion: According to their relative position in the cortex, nephrons are of two types cortical and juxtamedullary.
Reason: Juxtamedullary nephrons have short loop of Henle whereas cortical nephrons have long loop of Henle.
AnswerAnswer: (c) The nephrons are of two types on the basis of location. In majority of nephrons, the loop of Henle is too short, that extends only little into the medulla. These nephrons are called cortical nephrons and form 85% of the total nephrons. In some of the nephrons, the loop of Henle is very long and runs deep into the medulla. these nephrons are called juxtamedullary nephrons ehich form 15% of the total nephrons.
Q.14. Assertion: In cortical nephrons, vasa recta is absent or highly reduced.
Reason: Cortical nephrons are mainly concerned with concentration of urine.
AnswerAnswer: (c) Cortical nephrons are situated in the renal cortex and consists of short loop of Henle and no vasa recta. Hence, they are not involved in concentration of urine. They control plasma volume when water supply is normal.
Q.15. Assertion: Homeostasis is a process of maintaining a constant internal environment.
Reason: Kidneys are excretory and homeostatic organs.
AnswerAnswer: (b) The term homeostasis (homeios same; stasis = standing) was introduced by Walter Cannon in 1932. It maintains the stability of the cell environment and this way provides the organism with a degree of independence of the environment; in order to achieve stability, mammals have two kidneys that perform excretory fuction and maintain urea level in blood.
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