Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH).Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.Based on the data in Table 1, which of the four patients most likely has central diabetes insipidus?
Answer(s): C
You're told that a normal value for urine osmolarity is 285 milli-osmoles per liter of H2O. Since ADH increases water reabsorption in the kidneys, patients with diabetes insipidus are expected to have a decreased urine osmolarity. And if normal is 285 milli-osmoles per liter of water, then based on the information in Table 1, you should have concluded that Patient A does not have diabetes insipidus. Patients B, C, and D, have a very low urine osmolarity prior to therapy, indicating that there is something wrong. To answer this question, you must have a good understanding of the mechanisms behind both central and nephrogenic diabetes insipidus.According to the passage, central diabetes insipidus is when ADH itself is either deficient in quantity or quality.Therefore, exogenous supplementation of ADH SHOULD alleviate the symptoms; that is, the kidneys should be able to concentrate urine, and therefore, urine osmolarity should greatly increase only AFTER ADH is administered. It should NOT increase after the 24-hour restriction of fluid intake because water is not being reabsorbed. If you look at the results of the four patients, you'll see only Patient C's urine osmolarity increased after ADH was administered. So, choice C is the right answer. In the case of nephrogenic diabetes insipidus it is the tubules themselves that are defective. Exogenous ADH would be ineffective as therapy since the patient's own ADH is sufficient in quality and quantity.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH).Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.Based on the data in Table 1, which of the four patients most likely has nephrogenic diabetes insipidus?
You're told that a normal value for urine osmolarity is 285 milli-osmoles per liter of H2O. Since ADH increases water reabsorption in the kidneys, patients with diabetes insipidus are expected to have a decreased urine osmolarity. And if normal is 285 milli-osmoles per liter of water, then based on the information in Table 1, you should have concluded that Patient A does not have diabetes insipidus. Patients B, C, and D, have a very low urine osmolarity prior to therapy, indicating that there is something wrong. To answer this question, you must have a good understanding of the mechanisms behind both central and nephrogenic diabetes insipidus.According to the passage, central diabetes insipidus is when ADH itself is either deficient in quantity or quality.Therefore, exogenous supplementation of ADH SHOULD alleviate the symptoms; that is, the kidneys should be able to concentrate urine, and therefore, urine osmolarity should greatly increase only AFTER ADH is administered. It should NOT increase after the 24-hour restriction of fluid intake because water is not being reabsorbed.
Just as the ingestion of nutrients is mandatory for human life, so is the excretion of metabolic waste products. One of these nutrients, protein, is used for building muscle, nucleic acids, and countless compounds integral to homeostasis. However, the catabolism of the amino acids generated from protein digestion produces ammonia, which, if not further degraded, can become toxic. Similarly, if the same salts that provide energy and chemical balance to cells are in excess, fluid retention will occur, damaging the circulatory, cardiac, and pulmonary systems.One of the most important homeostatic organs is the kidney, which closely regulates the excretion and reabsorption of many essential ions and molecules. One mechanism of renal function involves the secretion of antidiuretic hormone (ADH).Diabetes insipidus (DI), is the condition that occurs when ADH is ineffective. As a result, the kidneys are unable to concentrate urine, leading to excessive water loss. There are two types of DI central and nephrogenic. Central DI occurs when there is a deficiency in the quantity or quality of ADH produced. Nephrogenic DI occurs when the kidney tubules are unresponsive to ADH. To differentiate between these two conditions, a patient's urine osmolarity is measured both prior to therapy and after a 24-hour restriction on fluid intake. Exogenous ADH is then administered and urine osmolarity is measured again. The table below gives the results of testing on four patients. Assume that a urine osmolarity of 285 mOsm/L of H2O is normal.What is the most likely cause of Patient B's dilute urine before therapy?
Answer(s): A
Fluid restriction is the first step in the attempt to diagnose the pathology, if there is one, behind the inability to concentrate urine. Let's take a look at the results of therapy on Patient B. Patient B had a low urine osmolarity prior to the onset of therapy. However, following the restriction of fluid intake, there was a substantial increase in urine osmolarity, indicating that Patient B's dilute urine is a function of the amount of fluid ingested. If a lot of fluid is drunk during the day, then assuming the person's kidneys and ADH are both normal, the urine formed will be dilute. Likewise, if there is very little fluid drunk during the day, then the urine formed will be concentrated. Thus, the excessive intake of water seems to be the most likely explanation for the formation of dilute urine in Patient B. In fact, there are individuals who have a psychological condition in which they drink water excessively. This excessive intake causes the output of dilute urine. Simply restricting and observing fluid intake would enable the patient to concentrate urine. Fluid restriction had no effect on either Patient C or Patient D, indicating that they have a true pathology; so choices C and D are wrong. If Patient B was dehydrated, then the body's response would be to produce concentrated urine from the start, which was clearly not the case here since urine osmolarity was very low prior to therapy; therefore, choice B is also wrong.
Electromagnetic radiation from space constantly bombards the earth. Most wavelengths are absorbed by the atmosphere; however, there are two "windows" of nonabsorption through which significant amounts of radiation reach the ground. The first transmits ultraviolet and visible light, as well as infrared light or heat; the second transmits radio waves. As a result, terrestrial organisms have evolved a number of pigments that interact with light in various ways: some capture light energy, some provide protection from light-induced damage, and some serve camouflage or signaling purposes.Among these compounds are many conjugated polyenes, which play important roles as photoreceptors. For every chemical compound, there are certain wavelengths of light whose quanta possess exactly the correct amount of energy to raise electrons from their ground state to higher-energy orbitals. For most organic compounds, these wavelengths are in the UV range. However, conjugated double bond systems stabilize the electrons, so that they can be excited by lower-frequency photons with wavelengths in the visible spectrum. Such a pigment, known as a chromophore, will then transmit the "subtraction color," a color complementary to the one absorbed. For instance, carotene, a hydrocarbon compound with eleven conjugated double bonds, absorbs blue light and transmits orange. The wavelength that is absorbed generally increases with the number of conjugated bonds; rings and side-chains also affect wavelength.Among the many biological molecules that are affected by light is DNA, the genetic material of living organisms. DNA absorbs ultraviolet light, and may be damaged by UVC (< 280 nm) and UVB (280-315 nm). UVA (315-400 nm) and visible light can actually repair light-induced damage to DNA by a process called photorepair. For this reason, UVA, which also stimulates tanning, was once considered beneficial. However, there is now increasing evidence that UVA can damage skin.The electrons that give color to a carotene molecule are found in:
Answer(s): B
Double bonds, like the ones in carotene, consist of one sigma bond, formed by the overlap of two sp2 orbitals, and one bond, formed by the overlap of perpendicular p orbitals. It is the latter, the bond, that is stabilized by the conjugated polyene system. This conjugation makes the electrons able to be excited by lower frequencies of light. Choice A, s orbitals, is wrong because the electrons which give conjugated bonds their stability, are not in s orbitals. The other two choices are wrong because carbon and hydrogen, which are the main or only components of organic molecules like carotene, don't have d and f orbitals.
Electromagnetic radiation from space constantly bombards the earth. Most wavelengths are absorbed by the atmosphere; however, there are two "windows" of nonabsorption through which significant amounts of radiation reach the ground. The first transmits ultraviolet and visible light, as well as infrared light or heat; the second transmits radio waves. As a result, terrestrial organisms have evolved a number of pigments that interact with light in various ways: some capture light energy, some provide protection from light-induced damage, and some serve camouflage or signaling purposes. Among these compounds are many conjugated polyenes, which play important roles as photoreceptors. For every chemical compound, there are certain wavelengths of light whose quanta possess exactly the correct amount of energy to raise electrons from their ground state to higher-energy orbitals. For most organic compounds, these wavelengths are in the UV range. However, conjugated double bond systems stabilize the electrons, so that they can be excited by lower-frequency photons with wavelengths in the visible spectrum. Such a pigment, known as a chromophore, will then transmit the "subtraction color," a color complementary to the one absorbed. For instance, carotene, a hydrocarbon compound with eleven conjugated double bonds, absorbs blue light and transmits orange. The wavelength that is absorbed generally increases with the number of conjugated bonds; rings and side-chains also affect wavelength.Among the many biological molecules that are affected by light is DNA, the genetic material of living organisms. DNA absorbs ultraviolet light, and may be damaged by UVC (< 280 nm) and UVB (280-315 nm). UVA (315-400 nm) and visible light can actually repair light-induced damage to DNA by a process called photorepair. For this reason, UVA, which also stimulates tanning, was once considered beneficial. However, there is now increasing evidence that UVA can damage skin.Two pigments are identical except for the lengths of their conjugated polyene chains. The first transmits yellow light and the second red. What can be said about the sizes of the chromophores?
For each compound, the light that's transmitted is complementary in color to the light absorbed; thus, the first chromophore must absorb violet light and the second must absorb green light. Violet light has a shorter wavelength than green, meaning it has a higher energy. You're told that longer chromophores generally absorb longer-wavelength light than shorter ones, so the one that absorbs the green light, and therefore has a red color, must be the longer one. This makes B correct and A and D incorrect. Even though you know one pigment is longer, there's no basis for concluding that it is a dimer (meaning a compound made up of two identical subunits), so choice C is definitely wrong.
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