The Chemical Context of Life Chapter 2 The Chemical Context of Life Questions prepared by William Wischusen Louisiana State University Jung Choi Georgia Institute of Technology

A patient is diagnosed with anemia resulting from iron deficiency A patient is diagnosed with anemia resulting from iron deficiency. What is the best way to supplement the patient’s diet with iron? The patient should add fine metallic iron filings to his morning cereal. The patient should periodically suck on rusty nails. The patient should cook with a cast-iron skillet and eat vegetables with high iron content, such as spinach. The patient should eat more red meat. Answer c should increase the uptake of iron into the patient’s body and red blood cells. Answer d may also help, but may have other undesirable effects such as increased fat and cholesterol intake. Choice a will be ineffective, as the reduced (metallic) form of iron is not available to cells; choice b is only marginally better, and unpleasant. This question could lead to a discussion about biologically active forms (ionization states) of the elements. Based on Concept 2.1 on essential elements and Concept 2.3 on ionization. 2

Based on the periodic table shown here, which elements will most likely form an ionic bond? Na and Cl, and Li and F C and O N and O Si and Cl all of the above Answer: a is the best choice This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. 3

Based on the periodic table shown here, which elements will most likely form a polar covalent bond? Na and Cl C and O, and N and O Si and Cl, and H and H all of the above none of the above Answer: b is the best choice This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. 4

Based on the periodic table shown here, which elements will most likely form a covalent bond? Na and Cl C and O N and O Si and Cl H and H Answer: e is the best choice This question is aimed at Concept 2.3. It should lead to a discussion of the basic concepts of electronegativity and types of bonds. One way to change this question would be to add C and H as a choice. This could be used to lead into a more detailed discussion. 5

What do elements with atomic numbers 6, 14, and 22 have in common? same number of electrons same atomic mass same valence and will form the same number of covalent bonds all of the above none of the above Answer: c This question focuses on Concept 2.2. It highlights the fact that these elements have the same basic structures and therefore the same basic properties. 6

Living systems differ from nonliving systems in that living systems are composed largely of unusual elements. living systems are composed largely of elements with large (high) atomic numbers. living systems contain large percentages (greater than 10%) of nine elements. living systems combine simple elements in unique combinations. Answer: d This question focuses on the chemical differences between living and nonliving systems. It should generate discussion about the differences. 7

The surface of a planet with life (a biosphere) would differ from the surface of a planet with no living organisms in that the planet with a biosphere would have unusual elements. the surface of the planet with a biosphere would have more elements with large (high) atomic numbers. the surface of the planet with a biosphere would contain large percentages of nine elements. the surface of the planet with a biosphere would have molecules that combine simple elements in unique combinations. Answer: d This is an alternate form of the previous question on the chemical differences between living and nonliving systems. It should generate discussion about how to detect life on other planets, such as Mars. 8

Water is a polar molecule because of the presence of ___________ bonds. ionic covalent polar covalent hydrogen More than one of the above options is correct. Answer: c This question focuses on the properties that result from different bonding patterns in molecules. 9

The force of the chemical bond (the attraction between the different elements) is an electrical attraction. is a unique chemical attraction. results from the sharing of electrons. results from atoms filling their outermost valence shell. Answer: a This question focuses on understanding the force that holds atoms together in molecules. Answers c and d are potentially correct but do not answer the question in terms of what creates the attraction. 10

Which of the following observations would distinguish between the alternative hypotheses that geckos walk on vertical surfaces via either hydrogen bonding or van der Waals interactions? Geckos can walk up dry surfaces. Geckos can walk up smooth glass surfaces—silicon dioxide is a polar, hydrophilic compound. Geckos can walk up smooth plastic surfaces— plastics are hydrophobic. Answer: c This was indeed one of the tests used to verify that van der Waals interactions allow geckos to walk up walls. Both polar and nonpolar (hydrophobic) compounds can have atoms with asymmetric electron distributions, required for van der Waals interactions. Geckos have difficulty with surfaces made of compounds like trifluoroethylene (Teflon), which have atoms with symmetric electron distributions. 11