Assertion Reason Questions for Biology Chapter 22 Chemical Coordination and Integration

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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 : Failure of secretion of somatotropin from an early age causes dwarfism in the patient.
Reason : Somatotropin hormone stimulates the body growth and elongation of long bones.

Answer Answer: (a) The somatotropin (STH), also called growth hormone (GH) is secreted by the anterior lobe of pituitary gland. Somatotropin stimulates body growth by stimulating retention of proteins and calcium in the body, synthesis and deposition of proteins in tissues, growth and elongation of long bones, and proportionate growth of muscles and visceral organs. The failure of secretion of growth hormone from an early age stops the growth of long bones and of the body prematurely; this makes the patient dwarf and the condition is called dwarfism.

Q.2. Assertion: Neurohypophysis is under the direct regulation of the hypothalamus.
Reason: Neurohypophysis stores and releases two hormones called oxytocin and vasopressin which are actually synthesized by the hypothalamus.

Answer Answer: (c) Neurohypophysis also known as posterior pituitary stores and releases two hormones called oxytocin and vasopressin which are actually synthesized by the hypothalamus and are transported axonally to neurohypophysis. Therefore, the posterior pituitary is under the direct neural regulation of the hypothalamus.

Q.3. Assertion: Failure of secretion of hormone vasopressin causes diabetes mellitus in the patient.
Reason: Vasopressin increases the volume of urine by increasing the reabsorption of water from the urine.

Answer Answer: (d) Vasopressin or anti-diuretic hormone (ADH) reduces the volume of urine by increasing the reabsorption of water from the urine in the distal convoluted tubules, collecting tubules and collecting ducts in the kidney. It does so by rendering the walls of these tubules leads to diabetes insipidus (increased urination). Although the volume of urine is increased. No glucose appears in the urine of such patients.
Diabetes mellitus is a disease which is caused due to the failure of insulin hormone secretion by the pancreatic islets. The osmotic effect of glucose in the urine considerably increases the volume of urine, due to which thirst is also enhanced. In extreme cases, the patient suffers from coma and may die.

Q.4. Assertion : The person with diabetes insipidus feels thirsty.
Reason : A person with diabetes insipidus suffers from excess secretion of vasopressin.

Answer Answer: (c) Vasopressin or antidiuretic hormone is secreted by posterior pituitary gland. The deficiency of vaopressin results in a disorder known as diabetes insipidus. The main symptoms of diabetes insipidus are increase in thirst and increase in urination.

Q.5. Assertion : Diabetes insipidus is marked by excessive urination and too much thirst of water.
Reason : Anti-diuretic hormone (ADH) is secreted by the posterior lobe of pituitary gland.

Answer Answer: (b) Diabetes insipidus (DI) occurs when the kidneys are unable to conserve water as they perform their function of filtering blood. The amount of water conserved is controlled by antidiuretic hormone (ADH) also called vasopressin which is secreted by posterior lobe of pituitary gland. Diabetes inspidus is characterised by excessive urination and thirst. This problem appears due to the increase in permeability of collecting tubules.

Q.6. Assertion: Oxytocin is also known as Anti Diuretic hormone (ADH).
Reason: It can cause an increase in the renal reabsorption of water.

Answer Answer: (d) The hormone vasopressin (also known as antidiuretic hormone, ADH) reduces the volume of urine by increasing the reabsorption of water from the urine in the distal convoluted tubules, collecting tubules and collecting ducts in the kidney. It does so by rendering the walls of those tubules permeable to water. Failure of secretion of vasopressin leads to a reduced renal reabsorption of water and a consequent elimination of a large volume of very dilute (hypotonic) urine. Oxytocin is another hormone released by the posterior lobe of the pituitary gland. Oxytocin contracts the mammary glands, smooth muscles of uterus. Uterine contractions, stimulated by oxytocin at the end of pregnancy, help in the child-birth or parturition, hence also called birth hormone.

Q.7. Assertion: Melatonin influences the menstrual cycle, pigmentation and defense capability.
Reason: It plays an important role in the regulation of diurnal rhythm of our body.

Answer Answer: (b) Melatonin concentration in the blood follows a diurnal (day-night) cycle as it rises in the evening and through the night and drops to a low around noon. Because of this light mediated response, the pineal gland may act as a kind of ‘biological clock’ which may produce circadian rhythms (variations following a 24 hour cycle). In addition, melatonin also influences metabolism, pigmentation, the menstrual cycle as well as our defence capability.

Q.8. Assertion : The tadpoles become giant tadpoles when fed on thiourea.
Reason : Thiourea is an antithyroid substance.

Answer Answer: (a) The thyroid gland secretes thyroxine and triiodothyronine hormone. One of their functions is stimulation of tissue differentiation. Because of this action, they promote metamorphosis of tadpoles into adult frogs. Feeding of anti-thyroid substances like thiourea to tadpoles, delays their metamorphosis. As they continue to grow without metamorphosis, they become giant tadpoles.

Q.9. Assertion: Thyroid hormones promote physical growth and development of mental faculties.
Reason: Hypothyroidism in adults causes retarded sexual development.

Answer Answer: (b) Thyroid hormones stimulate protein synthesis and, therefore, promote growth of the body tissues (physical development). They also regulate the development of mental faculties. Hyperthyroidism in adults causes myxoedema. This disease is characterized by puffy appearance due to accumulation of fat in the subcutaneous tissue because of low metabolic rate. The patient lacks alertness, intelligence and initiative. He also suffers from slow heart beat, low body temperature and retarded sexual development.

Q.10. Assertion : Hormone calcitonin has antagonistic effect to that of parathormone.
Reason : Calcitonin decreases blood calcium level while parathormone increases blood calcium level.

Answer Answer: (a) Calcitonin or thyrocalcitonin is secreted by parafollicular cells of thyroid stroma. It retards bone dissolution and stimulates excretion of calcium in urine. Thus, it lowers calcium level in extra cellular fluid (ECF). Parathormone is secreted by chief cells of parathyroid gland and is also known as Collip’s hormone. It maintains blood calcium level by increasing its absorption from food in intestine and its reabsorption from nephrons in the kidney. Maintenance of proper calcium level is in fact, a combined function of parathormone and calcitonin. When calcium level falls below normal parathormone maintains it by promoting its absorption, reabsorption and also by demineralisation of bones. When blood calcium level exceeds above normal then calcitonin hormone increases excretion of calcium in urine

Q.11. Assertion: PTH is a hypercalcemic hormone.
Reason: It stimulates the process of bone resorption.

Answer Answer: (a) Parathyroid hormone (PTH) increases the Ca2+ levels in the blood. PTH acts on bones and stimulates the process of bone resorption (dissolution/demineralisation). PTH also stimulates reabsorption of Ca2+ by the renal tubules and increases Ca2+ absorption from the digested food. It is, thus, clear that PTH is a hypercalcemic hormone, i.e., it increases the blood Ca2+ levels. Along with calcitonin, it plays a significant role in calcium balance in the body.

Q.12. Assertion: Immune response of old persons become weak.
Reason: Thymus degenerates in old individuals.

Answer Answer: (a) Thymus plays a major role in the development of the immune system. This gland secretes the peptide hormones called thymosins. Thymosins play a major role in the differentiation of T-lymphocytes, which provide cell-mediated immunity. In addition, thymosins also promote production of antibodies to provide humoral immunity. Thymus is degenerated in old individuals resulting in a decreased production of thymosins. As a result, the immune responses of old persons become weak.

Q.13. Assertion: Adrenal medulla is called the gland for ‘fight, fright and flight’.
Reason: The hormones adrenaline and noradrenaline help the body to combat against stress and emergency conditions.

Answer Answer: (a) Adrenaline or epinephrine dilates (widens) arterioles in the skeletal muscles and constricts (narrows) those in the skin and abdominal viscera. It increases the rate and force of heart beats and arterial blood pressure by enhancing the cardiac output. Adrenaline relaxes the smooth muscles of gastro-intestinal tract, and urinary bladder and bronchioles and contracts the sphincters of gastrointestinal tract and bladder. It increases blood sugar and blood lactic acid levels and also increases heat production, metabolic rate and body temperature. Noradrenaline or norepinephrine constricts arterioles in general or increases the total peripheral resistance against the flow of blood. The coordinated actions of both adrenaline and noradrenaline, thus help the body to react under stress conditions.

Q.14. Assertion: Adrenal medullary hormones help in combating stress.
Reason: Both adrenaline and noradrenaline act on same organs and produce similar effects.

Answer Answer: (b) The adrenal medulla secretes two hormones called adrenaline or epinephrine and noradrenaline or norepinephrine. Adrenaline and noradrenaline are rapidly secreted in response to stress of any kind and during emergency situations and are called emergency hormones or hormones of fight. These hormones increase alertness, pupillary dilation, piloerection, sweating, etc. Both the hormones increase the heart beat, the strength of heart contraction and the rate of respiration. They also stimulate the breakdown of glycogen resulting in an increased concentration of glucose in blood. In addition, they also stimulate the breakdown of lipids and proteins. Both the hormones act on the same organs and produce similar effects on them e.g., accelerate heart beat, raise blood pressure, slow peristalsis, etc.

Q.15. Assertion: Adrenal cortex is not vital for survival and may be removed without subsequently
leading to death.
Reason: It secretes a number of steroid hormones which have only cummulative effects on the hormones of other glands.

Answer Answer: (d) The outer part of adrenal gland is called adrenal cortex. This part of adrenal is vitally important for life and its destruction or removal kills the animal. It secretes a number of steroid hormones which are broadly classified into three groups, viz. glucocorticoids, mineralocorticoids and sex corticoids. Glucocorticoids regulate the metabolisms of carbohydrate, fats and proteins. Mineralocorticoids regulate the balance of water and electroytes in our body. Sex corticoids stimulate the development of external sex characters.

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