Unformatted text preview: BSC 2010 Quiz #2 Key Spring 2014 The average on Quiz #2 was an 78.4%/78.3% (secs 007/8 and 003/4 respectively). I have included comments for each question below. If you missed any items, please take a careful look and stop by my office if you still have questions. You will see these problems or ones like them on the first exam! A good exercise is to write out WHY the wrong answers are wrong, as I did for #7 and #8 below. It is not enough to merely memorize facts; you must be able to APPLY what you know. Success depends upon attending the LECTURE, taking thorough NOTES, STUDYING them each week, and seeking out HELP when you are unclear on a topic. 1. Which of the following organisms are classified as eukaryotes? (Please consult the evolutionary tree diagram from the slides and Chapter 1!) plants protists archaea plants and protists plants, protists, and archaea What characteristics do ALL of these organisms share (as they are common to all living things)? By what process did this diversity of life on earth originate? Be sure you are aware of the ‘three questions’ about this process that we discussed in lecture. 2. Hypothetically speaking, which subatomic particle(s) of an atom could be altered in number without changing the identity of the atom (or which element it is)? neutrons protons protons or electrons electrons or neutrons electrons, neutrons, or protons Recall that the identity of an atom depends upon the number of protons (only!). If you missed this, please review the first three sub-‐sections of section 2.2 (subatomic particles through isotopes) and the second subsection in section 2.3 (ionic bonds). 3. Phosphorus VIOLATES the 'octet rule' in biological molecules by _____. forming less than eight covalent bonds forming more than eight covalent bonds having less than eight electrons in its valence shell after covalent bonding having more than eight electrons in its valence shell after covalent bonding NOT forming covalent bonds The octet rule says that atoms react chemically in order to obtain 8 electrons in their outer shell. However, some atoms like hydrogen and phosphorus are exceptions to this rule. Since P has 5 electrons in its outer shell, we would expect it to form 3 covalent bonds to acquire 3 more electrons. Instead, it forms 5 covalent bonds. Since each covalent bond contains two electrons, P has 10 electrons in its outer shell. 4. When an oxygen atom and a hydrogen atom form a covalent bond, _____ is produced. a nonpolar covalent bond a polar covalent bond a hydrogen bond a van der Waals interaction an unstable bond A hydrogen atom that is covalently bonded to oxygen COULD go on to form a hydrogen bond, but that doesn’t mean it will. Read the questions carefully so that you are clear about what they are saying; then choose the most direct answer to the question. 5. Which of the following types of chemical bonds and interactions are relatively WEAK in cells? hydrogen bonds ionic bonds covalent bonds hydogen bonds and ionic bonds hydogen bonds, ionic bonds, and covalent bonds Why are ‘ionic bonds’ not strong within cells? This question is ‘right out of the lecture’. J 6. In order for a hydrogen atom to be capable of hydrogen bonding, what is required? The hydrogen must be covalently bonded (to any atom). The hydrogen must NOT be covalently bonded. The hydrogen must be covalently bonded to a strongly electronegative atom. The hydrogen must be covalently bonded to an atom of similar electronegativity. The hydrogen must be part of a water molecule. If you had difficulty with this question, please review the third subsection in section 2.3 (hydrogen bonds). 7. Which of the following DOES NOT apply to biological weak interactions? They can be broken. True; for example, when the two strands of a DNA molecule come apart. They can occur between different molecules. Examples of intermolecular weak interactions include a reactant and it’s enzyme, a hormone and it’s receptor, and DNA wrapped around histone proteins. They can occur within a single molecule. An example of an intramolecular weak interaction is the weak interactions that help hold together receptor’s 3-‐D shape. In fact, most proteins contain such interactions. They do not have functional relevance to cells. Obviously they are critical to cellular function! More than one answer listed here. Rather than trying to identify the answer that ‘DOES NOT’, simply eliminate all of the answers that ‘DO APPLY’. This topic was discussed exclusively in lecture. 8. Which of the following statements about sp3 hybridization is CORRECT? It occurs when certain atoms form hydrogen bonds. Has nothing to do with hydrogen bonding. It occurs when atoms are not bonded to other atoms. Actually, it occurs as a direct result of covalent bonding. It occurs with carbon atoms, but not oxygen atoms. It occurs with carbon, oxygen, and nitrogen (why not H?). So, the shape of biomolecules will greatly depend on this concept! It involves the formation of four new p orbitals. No: one s and three p orbitals combine, and four new orbitals form. It involves the formation of four new sp3 hybrid orbitals. Correct; the four old orbitals are replaced by four new ones—each an sp3 hybrid orbital. 9. Which of the following weak interactions involves nonpolar molecules or nonpolar parts of molecules? hydrogen bonds ionic bonds van der Walls interactions hydrophobic interactions both van der Walls interactions and hydrophobic interactions So two of the four weak interactions discussed involve polar/charged molecules, and two of the interactions involve nonpolar/uncharged molecules. 10. Chemical equilibrium is the point in a chemical reaction when _____. all the reactants have been changed to products the reaction has completely stopped there are equal concentrations of reactants and products the speed of the forward reaction is equal to the speed of the reverse reaction the meaning of this term varies for different reactions Although the concentrations of reactants and products are not equal, what CAN we say about them at equilibrium? ...
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