1. High blood glucose triggers cells in the pancreas to release the hormone insulin, which lowers blood glucose levels. Type 2 diabetes occurs when cells no longer respond to insulin. The blood glucose levels of several diabetic rats are measured and the rats are then fed a highcarbohydrate meal. Which statement explains how a rat s blood glucose levels will most likely be affected by the high-carbohydrate meal? (A) The rat s blood glucose level will increase after eating, which will cause insulin levels to rise until blood glucose decreases below the pre-meal level. This answer suggests the student may understand that an increase in blood glucose causes insulin to be released and that insulin normally results in blood glucose levels declining, but does not understand how insulin resistance, which is caused by type 2 diabetes, affects cells by preventing them from taking up the excess glucose in the blood. (B) The rat s blood glucose level will increase after eating and, after the rat is given an insulin injection, will quickly decrease to the pre-meal level. This answer suggests the student may understand that blood glucose will increase after a meal, but does not understand how insulin resistance, which is caused by type 2 diabetes, affects this feedback system by preventing cells from taking in the excess glucose in the blood. (C) The rat s blood glucose level will increase for several hours after eating, and then will gradually decrease over several hours to the pre-meal level. This answer suggests the student may understand that blood glucose levels will increase after eating, but does not understand that insulin levels will increase rapidly after eating and remain higher than pre-meal levels for several hours because body cells will not respond to insulin and, even after a long period of time, will not take in the excess glucose in the blood. (D) The rat s blood glucose level will increase after eating and, even after the rat is given an insulin injection, will remain higher than the pre-meal level. Page 1 of 5
This answer suggests the student understands that the normal response to insulin is for cells to uptake excess glucose in the blood, which results in lowering of blood glucose levels, and that insulin-target cells are unresponsive to insulin in organisms with type 2 diabetes. 2. When the concentration of solutes in the blood (blood osmolarity) is high, the pituitary gland releases antidiuretic hormone (ADH). ADH stimulates the kidneys to reabsorb water in order to increase blood volume and decrease blood osmolarity. A person takes a long hike on a hot day without water. At the end of the day, the hiker drinks enough water to replace what was lost during the hike. Which statement explains the most likely physiological response that the hiker s body will experience after drinking the water? (A) The pituitary gland will secrete ADH because drinking water will cause blood volume to increase, and an increased blood volume will cause the pituitary gland to release more ADH in a positive feedback loop. This answer suggests the student may understand that drinking water increases blood volume, but does not understand that an increased blood volume will reduce the secretion of ADH through a negative feedback loop. (B) The pituitary gland will stop secreting ADH because drinking water will cause blood volume to increase, and an increased blood volume will cause the pituitary gland to stop releasing ADH in a negative feedback loop. This answer suggests the student understands that drinking water causes blood volume to increase and decreases blood osmolarity, which reduces and/or stops the secretion of ADH through a negative feedback loop. (C) The increased blood volume will prevent the release of ADH and cause the kidneys to excrete less water in a negative feedback loop. Page 2 of 5
This answer suggests the student may understand that secretion of ADH is regulated by a negative feedback loop, but does not understand that the kidneys will excrete more water, not less, as the increased blood volume prevents the release of ADH. (D) The high blood volume will increase the release of ADH and cause the kidneys to increase reabsorption of water in a positive feedback loop. This answer suggests the student may understand that drinking water increases blood volume, but does not understand that the release of ADH is controlled via a negative feedback loop and the release of ADH stops once blood volume increases. 3. While the initial release of oxytocin, the hormone that triggers the onset of childbirth, is not fully understood, scientists do know that high levels of the hormone estrogen lead to the formation of receptors for the oxytocin on the uterus late in pregnancy. Oxytocin causes the uterus to contract, and uterine contractions stimulate the pituitary gland to release more oxytocin. Which statement best explains how the uterus and the pituitary gland work together during childbirth? (A) Uterine contractions signal the pituitary gland to release more oxytocin via a negative feedback loop, which causes the frequency and intensity of uterine contractions to be maintained at a constant rate until birth occurs. This answer suggests the student may understand that there is a feedback mechanism between the uterus and the pituitary gland, but does not understand that more oxytocin is released by the pituitary gland as uterine contractions increase via a positive feedback loop and that the frequency and intensity of the contractions increase as a result. (B) Uterine contractions cause the pituitary gland to release oxytocin via a negative feedback loop, which increases the frequency and intensity of uterine contractions until birth occurs. This answer suggests the student may understand that there is a feedback mechanism between the uterus and the pituitary gland that causes the frequency and intensity of uterine contractions to increase, but does not recognize that the increased release of oxytocin is accomplished via a positive feedback loop. Page 3 of 5
(C) Oxytocin causes uterine contractions, which cause the pituitary gland to secrete more oxytocin and cause more uterine contractions via a positive feedback loop, which increases the frequency and intensity of the contractions until birth occurs. This answer suggests the student understands that oxytocin stimulates uterine contractions and that uterine contractions stimulate the pituitary gland to release more oxytocin via a positive feedback loop, and this causes the frequency and intensity of uterine contractions to increase until birth. (D) Oxytocin is released only in response to uterine contractions via a positive feedback loop, which causes the frequency and intensity of uterine contractions to be consistent until birth occurs. This answer suggests the student may understand that there is a positive feedback loop between the uterus and the pituitary gland, but does not understand that the positive feedback loop results in more oxytocin being released by the pituitary gland, which causes the frequency and intensity of uterine contractions to increase until birth. 4. An allergy is caused when a person s immune system overreacts to a normally harmless substance, such as plant pollen, dust, or pet dander. Substances that trigger an allergic reaction are called allergens. An allergic reaction is triggered when the immune system recognizes an allergen as foreign and tries to destroy it by releasing histamines, much like it would if it encountered a harmful virus or bacteria. Histamines cause localized swelling, and result in allergy symptoms such as itchy eyes, a runny nose, and sneezing. Which statement best explains how an allergen causes an allergic reaction? (A) The initial exposure to the allergen causes a negative feedback mechanism in the immune system to become overactive and leads to the release of histamines that destroy immune cells. This answer suggests the student may understand that allergic reactions are caused by an overactive immune system, but does not understand that the release of histamines is caused by a positive feedback mechanism, or that histamines destroy allergens, not immune cells. Page 4 of 5
(B) Prolonged exposure to the allergen interferes with a negative feedback loop in the immune system, which results in the immune system releasing histamines more aggressively with increased allergen exposure. This answer suggests the student may understand that the immune system releases histamines in response to an allergen, but does not understand that the allergen does not interfere with the feedback mechanism involved in the immune response, that the feedback mechanism is enhanced by presence of an allergen, or that the feedback mechanism is positive and not negative. (C) Repeated exposure to the allergen interferes with a positive feedback loop in the immune system, which results in the immune system reacting less aggressively with increased allergen exposure. This answer suggests the student may understand that an allergic response involves a positive feedback mechanism occurring in the immune system, but does not understand that the immune system becomes more active with repeated exposure and releases more histamines via the positive feedback loop. (D) The initial exposure of the allergen causes a positive feedback mechanism in the immune system to become overactive and leads to the release of histamines in an attempt to destroy the allergen. This answer suggests the student understands that an allergic reaction is an immune system response that causes overactivity in a positive feedback loop in which histamines are released in an attempt to destroy allergens. Page 5 of 5