Question 1

Selenocysteine is an amino acid that gets incorporated into proteins that serve as antioxidants. Evidence points to a need for a minimum daily dose of selenium of 55 $\mu$10g. How many moles of selenocysteine (C₃H₇NO₂Se, 168 g/mol) can be synthesized using this amount of selenium?

Accepted Answer

The answer of Selenocysteine is an amino acid that gets...

Question 2

Selenium can substitute for sulfur in the amino acid cysteine to make the amino acid selenocysteine because ________

Accepted Answer

Both sulfur and selenium have six valence electrons and can form two covalent bonds. Therefore, they have the same valence electron configuration, making it possible for selenium to substitute for sulfur in the amino acid cysteine.

Question 3

The concentration of Li in the human body is approximately 30 ng/g body mass. How many milligrams of Li are there in a person weighing 170 lb? 1 lb = 454 g

Accepted Answer

The answer of The concentration of Li in the human...

Question 4

Fluoridation to prevent tooth decay replaces ________ with fluoride in hydroxyapatite.

Accepted Answer

Fluoridation to prevent tooth decay involves replacing the hydroxide ions in hydroxyapatite (the mineral form of calcium phosphate that makes up tooth enamel) with fluoride ions. This process creates a more decay-resistant material called fluorapatite.

Question 5

Selenium is an ultratrace element that is essential for life. It is used in the synthesis of ________, which is ________.

Accepted Answer

Selenium is used in the synthesis of selenocysteine, an amino acid.

Question 6

Copper is a trace metal in the human body with a typical concentration of 110 mg in 75 kg of body mass. What is this concentration in units of parts per million (ppm)?

Accepted Answer

To find the concentration in ppm, use the formula: (mass of solute/mass of solution) * 10^6. Here, (110 mg / 75,000,000 mg) * 10^6 = 1.5 ppm.

Question 7

The active site of an enzyme typically contains ________

Accepted Answer

The active site of an enzyme typically contains a transition metal. Transition metals such as zinc, iron, and copper are commonly found in the active site of enzymes and are important for catalysis.

Question 8

Chromium is an ultratrace metal in the human body with a typical concentration of 5.0 mg in
75 kg of body mass. What is this concentration in units of parts per billion (ppb)?

Accepted Answer

The answer of Chromium is an ultratrace metal in the...

Question 9

The release of radioactive cesium-137 into the environment by the nuclear accident at Chernobyl produced a health hazard because cesium ions can substitute for ________ in plants, making them unsafe for human consumption.

Accepted Answer

Cesium ions (Cs⁺) can substitute for potassium ions (K⁺) in plants because they have similar chemical properties, making the plants unsafe for human consumption.

Question 10

A radioactive isotope that emits the shortest range particles and therefore would be a good choice for implantation therapy most likely decays via ________

Accepted Answer

Alpha particles have the shortest range and highest energy deposition among the given options. This makes them an ideal choice for implantation therapy, where a radioactive source is implanted close to the target tissue to minimize damage to surrounding healthy tissue. Beta particles, positrons, gamma rays, and X-rays all have longer ranges and may cause damage to healthy tissue before reaching the intended target.

Question 11

Barium is a nonessential element in the human body, but some organisms build exoskeletons using barium sulfate, which has a K_sp of 1.1 * 10^-¹⁰ at 25°C. What is the mass of barium in 1.0 L of a saturated solution of barium sulfate at 25°C?

Accepted Answer

The solubility product (Ksp) of barium sulfate is used to calculate the concentration of barium ions in a saturated solution. The Ksp expression for BaSO4 is [Ba²⁺][SO₄²⁻] = 1.1 * 10⁻¹⁰. Since the solution is saturated, [Ba²⁺] = [SO₄²⁻] = s, where s is the solubility. Solving for s gives s = √(1.1 * 10⁻¹⁰) = 1.05 * 10⁻⁵ M. The molar mass of Ba is 137.33 g/mol, so the mass of Ba in 1.0 L is 1.05 * 10⁻⁵ mol/L * 137.33 g/mol = 1.44 mg.

Question 12

An enzyme catalyzes the decomposition of hydrogen peroxide at 20°C. The activation energy for the uncatalyzed reaction is 75.3 kJ/mol. The activation energy for the catalyzed reaction is 29.3 kJ/mol. By what factor is the rate of the reaction increased by the enzyme? Use the Arrhenius equation, which is given below, to determine the ratio of rate constants, k_catalyzed/k_uncatalyzed. (R = 8.315 J / (mol K)) $k = A \exp \left( - \frac { E _ { a } } { R T } \right)$

Accepted Answer

The answer of An enzyme catalyzes the decomposition of hydrogen...

Question 13

Urease is an enzyme that catalyzes the decomposition of urea to ammonia and carbon dioxide. The rate constant for the uncatalyzed reaction is 4.0*10^-¹¹/s at 22°C. Urease increases the rate constant to a value of 8.0 *10^-⁵/s. Use the Arrhenius equation, which is given below, to determine the difference in the activation energies E_uncatalyzed - E_catalyzed. (R = 8.315 J / (mol K)) $k = A \exp \left( - \frac { E _ { a } } { R T } \right)$

Accepted Answer

The answer of Urease is an enzyme that catalyzes the...

Question 14

Selenium, an ultratrace element, is used in the synthesis of selenocysteine, which is ________

Accepted Answer

Selenium is used in the synthesis of an amino acid called selenocysteine, making option A the correct answer. Selenocysteine is commonly found in proteins involved in antioxidant defense and thyroid hormone metabolism. It also plays a role in regulating the immune system and gene expression.

Question 15

Adding fluoride ions to toothpaste and drinking water converts the mineral in tooth enamel, hydroxyapatite, to fluoroapatite. This conversion is beneficial in preventing tooth decay because fluoroapatite ________

Accepted Answer

Fluoroapatite is less soluble at acidic pH levels, which helps prevent tooth decay.

Question 16

Hydroxyapatite, which is a component of tooth enamel, is very insoluble in water. For the following reaction, K_sp = 2.3 *10^-⁵⁹. Ca₅(PO₄)₃(OH)(s) $\rightleftarrows$Ca₅(PO₄)₃⁺(aq) + OH^-(aq) What is the molar concentration of Ca₅(PO₄)₃⁺ when the pH of the mouth is 4.0?

Accepted Answer

K_sp = [Ca₅(PO₄)₃⁺][OH^-] = 2.3 * 10^-59[OH^-] = 10^-4 M (from pH = 4)[Ca₅(PO₄)₃⁺] = K_sp/[OH^-] = 2.3 * 10^-59 / 10^-4 = 2.3 * 10^-49 M

Question 17

Radioactive ⁹⁰Sr can substitute for ________ in the human body.

Accepted Answer

The human body requires calcium (Ca) for various physiological functions including bone health and muscle contraction. Since radioactive strontium (Sr) has similar chemical and physical properties to calcium, it can potentially substitute for calcium in the body. Therefore, option B (Ca²⁺) is the best choice for the substitution.

Question 18

Iodine's role is very specific. It is incorporated into a hormone, ________, that regulates energy production and use.

Accepted Answer

Iodine is incorporated into thyroxine hormone, which regulates energy production and use. None of the other options mentioned are related to iodine's role in hormone production.

Question 19

Chromium is an ultratrace metal in the human body. The typical concentration is 5.0 mg in 70.0 kg of body mass. This concentration can be expressed as ________

Accepted Answer

To convert from mg/kg to ppm or ppb, we need to divide the mass of chromium (in mg) by the total mass of the body (in kg) and multiply by 1,000,000 for ppm or 1,000,000,000 for ppb.

For this problem, we have 5.0 mg of chromium in 70.0 kg of body mass:

5.0 mg / 70.0 kg = 0.0000714 mg/kg

To convert to ppm or ppb:

0.0000714 mg/kg x 1,000,000 = 0.0714 ppm or
0.0000714 mg/kg x 1,000,000,000 = 71.4 ppb

Therefore, the answer is A) 0.071 ppm or 71 ppb.

Question 20

Adding fluoride ions to toothpaste and drinking water to prevent tooth decay is effective because fluoride ________

Accepted Answer

Fluoride ions reduce the solubility of tooth enamel at low pH, making teeth less susceptible to acid attacks from bacteria that produce acid as a byproduct of sugar fermentation. This helps to prevent tooth decay.

Quiz 22: Life and the Periodic Table

Selenocysteine is an amino acid that gets incorporated into proteins that serve as antioxidants. Evidence points to a need for a minimum daily dose of selenium of 55 $\mu$ 10g. How many moles of selenocysteine (C₃H₇NO₂Se, 168 g/mol) can be synthesized using this amount of selenium?

Selenium can substitute for sulfur in the amino acid cysteine to make the amino acid selenocysteine because ________

The concentration of Li in the human body is approximately 30 ng/g body mass. How many milligrams of Li are there in a person weighing 170 lb? 1 lb = 454 g

Fluoridation to prevent tooth decay replaces ________ with fluoride in hydroxyapatite.

Selenium is an ultratrace element that is essential for life. It is used in the synthesis of , which is .

Copper is a trace metal in the human body with a typical concentration of 110 mg in 75 kg of body mass. What is this concentration in units of parts per million (ppm) ?

The active site of an enzyme typically contains ________

Chromium is an ultratrace metal in the human body with a typical concentration of 5.0 mg in 75 kg of body mass. What is this concentration in units of parts per billion (ppb) ?

The release of radioactive cesium-137 into the environment by the nuclear accident at Chernobyl produced a health hazard because cesium ions can substitute for ________ in plants, making them unsafe for human consumption.

A radioactive isotope that emits the shortest range particles and therefore would be a good choice for implantation therapy most likely decays via ________

Barium is a nonessential element in the human body, but some organisms build exoskeletons using barium sulfate, which has a K_sp of 1.1 * 10^-¹⁰ at 25°C. What is the mass of barium in 1.0 L of a saturated solution of barium sulfate at 25°C?

Selenium, an ultratrace element, is used in the synthesis of selenocysteine, which is ________

Adding fluoride ions to toothpaste and drinking water converts the mineral in tooth enamel, hydroxyapatite, to fluoroapatite. This conversion is beneficial in preventing tooth decay because fluoroapatite ________

Hydroxyapatite, which is a component of tooth enamel, is very insoluble in water. For the following reaction, K_sp = 2.3 *10^-⁵⁹. Ca₅(PO₄) ₃(OH) (s) $\rightleftarrows$ Ca₅(PO₄) ₃⁺(aq) + OH^-(aq) What is the molar concentration of Ca₅(PO₄) ₃⁺ when the pH of the mouth is 4.0?

Radioactive ⁹⁰Sr can substitute for ________ in the human body.

Iodine's role is very specific. It is incorporated into a hormone, ________, that regulates energy production and use.

Chromium is an ultratrace metal in the human body. The typical concentration is 5.0 mg in 70.0 kg of body mass. This concentration can be expressed as ________

Adding fluoride ions to toothpaste and drinking water to prevent tooth decay is effective because fluoride ________

Quiz 22: Life and the Periodic Table

Selenocysteine is an amino acid that gets incorporated into proteins that serve as antioxidants. Evidence points to a need for a minimum daily dose of selenium of 55 μ\muμ 10g. How many moles of selenocysteine (C3H7NO2Se, 168 g/mol) can be synthesized using this amount of selenium?

Selenium can substitute for sulfur in the amino acid cysteine to make the amino acid selenocysteine because ________

The concentration of Li in the human body is approximately 30 ng/g body mass. How many milligrams of Li are there in a person weighing 170 lb? 1 lb = 454 g

Fluoridation to prevent tooth decay replaces ________ with fluoride in hydroxyapatite.

Selenium is an ultratrace element that is essential for life. It is used in the synthesis of ________, which is ________.

Copper is a trace metal in the human body with a typical concentration of 110 mg in 75 kg of body mass. What is this concentration in units of parts per million (ppm) ?

The active site of an enzyme typically contains ________

Chromium is an ultratrace metal in the human body with a typical concentration of 5.0 mg in 75 kg of body mass. What is this concentration in units of parts per billion (ppb) ?

The release of radioactive cesium-137 into the environment by the nuclear accident at Chernobyl produced a health hazard because cesium ions can substitute for ________ in plants, making them unsafe for human consumption.

A radioactive isotope that emits the shortest range particles and therefore would be a good choice for implantation therapy most likely decays via ________

Barium is a nonessential element in the human body, but some organisms build exoskeletons using barium sulfate, which has a Ksp of 1.1 * 10-10 at 25°C. What is the mass of barium in 1.0 L of a saturated solution of barium sulfate at 25°C?

Selenium, an ultratrace element, is used in the synthesis of selenocysteine, which is ________

Adding fluoride ions to toothpaste and drinking water converts the mineral in tooth enamel, hydroxyapatite, to fluoroapatite. This conversion is beneficial in preventing tooth decay because fluoroapatite ________

Hydroxyapatite, which is a component of tooth enamel, is very insoluble in water. For the following reaction, Ksp = 2.3 *10-59. Ca5(PO4) 3(OH) (s) ⇄\rightleftarrows⇄ Ca5(PO4) 3+(aq) + OH-(aq) What is the molar concentration of Ca5(PO4) 3+ when the pH of the mouth is 4.0?

Radioactive 90Sr can substitute for ________ in the human body.

Iodine's role is very specific. It is incorporated into a hormone, ________, that regulates energy production and use.

Chromium is an ultratrace metal in the human body. The typical concentration is 5.0 mg in 70.0 kg of body mass. This concentration can be expressed as ________

Adding fluoride ions to toothpaste and drinking water to prevent tooth decay is effective because fluoride ________

Selenocysteine is an amino acid that gets incorporated into proteins that serve as antioxidants. Evidence points to a need for a minimum daily dose of selenium of 55 $\mu$ 10g. How many moles of selenocysteine (C₃H₇NO₂Se, 168 g/mol) can be synthesized using this amount of selenium?

Selenium is an ultratrace element that is essential for life. It is used in the synthesis of , which is .

Barium is a nonessential element in the human body, but some organisms build exoskeletons using barium sulfate, which has a K_sp of 1.1 * 10^-¹⁰ at 25°C. What is the mass of barium in 1.0 L of a saturated solution of barium sulfate at 25°C?

Radioactive ⁹⁰Sr can substitute for ________ in the human body.