Textbook Questions
to accompany
Principles of Life, Second Edition
Hillis • Sadava • Hill • Price
Chapter 2: Reconstructing and Using Phylogenies
Concept Checkpoint Questions
Concept 2.1 Atomic Structure Is the Basis for Life’s Chemistry
1. What is the arrangement of protons, neutrons, and electrons in an atom?
2. Sketch the electron shell configuration of a sodium atom (symbol Na), which has 11 protons. According to the octet rule, what would be the simplest way for a sodium atom to achieve electron stability?
3. Many elements have isotopes, which are rare variants of the element with additional neutrons in the nucleus. Deuterium is an isotope of hydrogen that has one neutron (normal hydrogen has no neutrons). Does the neutron change the chemical reactivity of deuterium, compared with normal hydrogen? Explain why or why not.
Concept 2.2 Atoms Interact and From Molecules
1. How do variations in electronegativity result in the unequal sharing of electrons in polar molecules?
2. Some functional groups (see Figure 2.7) can either donate or accept hydrogen bonds with other molecules, acting either as a donor (like the oxygen in a water molecule) or as an acceptor (like the hydrogens in a water molecule). For each of the following, is it an H-bond donor, acceptor, both, or neither?
3. Here is the structure of the molecule glycine:
a. What are the functional groups on this molecule? What is the R group to which they are attached? Is the R group hydrophilic or hydrophobic? Explain.
b. Draw two glycine molecules and show how they can be linked by a condensation reaction.
4. The boiling point (the temperature at which a liquid vaporizes) of water (H2O) is 100°C, whereas the boiling point of methane (CH4) is –161°C. Explain this difference in terms of hydrogen bonding between molecules.
Concept 2.3 Carbohydrates Consist of Sugar Molecules
1. Draw the chemical structure of a disaccharide formed from two glucose monosaccharides.
2. Examine the glucose molecule shown in Figure 2.9. What are the functional groups on the molecule?
3. Notice the large number of hydrogen bonding groups present in the linear structure of cellulose (see Figure 2.10A). Why is this structure so strong?
4. Some sugars have other functional groups in addition to those typically present. Draw the structure of the amino sugar glucosamine, which has an amino group bonded at carbon 2 of glucose. Would this molecule be more or less polar than glucose? Explain why.
Concept 2.4 Lipids Are Hydrophobic Molecules
1. What is the difference between fats and oils?
2. Why are phospholipids amphipathic, and how does this result in a lipid bilayer membrane?
3. If fatty acids are carefully put onto the surface of water, they form a single molecular layer. If the mixture is then shaken vigorously, the fatty acids will form round structures called micelles. Explain these observations.
Concept 2.5 Biochemical Changes Involve Energy
1. Describe the forms of energy used, and the changes in energy, that are involved in using the food energy in a candy bar to decide to go for a walk and to do the walking”.
2. What is the difference between anabolism and catabolism? Between endergonic and exergonic reactions?
3. Predict whether these situations are endergonic or exergonic, and explain your reasoning:
a. The formation of a phospholipid bilayer membrane
b. Turning on a TV set
Apply the Concept Questions
Concept 2.2 Atoms Interact and Form Molecules,
1. The concepts of chemical bonding and electronegativity (see Table 2.2) allow us to predict whether a molecule will be polar or nonpolar, and how it will interact with water. Typically, a difference in electronegativity greater than 0.5 will result in polarity. For each of the bonds below, indicate:
1. Whether the bond is polar or nonpolar
2. If polar, which is the d+ end
3. How a molecule with the bond will interact with water (hydrophilic or hydrophobic)
N—H C—H C=O C—N
O—H C—C H—H O—P
Concept 2.5 Biochemical Changes Involve Energy, p. 34
1. For each reaction, would you expect DG to be positive or negative?
2. Which reactions will be spontaneous? Explain your answer.
Analyze the Data Questions
Analyze the Data 2.1: Miller and Urey Synthesized Preioic Molecules in an Experimental Atmosphere
The following data show the amount of energy impinging on Earth in different forms.
A. Only a small fraction of the sun’s energy is ultraviolet light (less than 250 nm). What is the rest of the solar energy?
B. The molecules CH4, H2O, NH3, and CO2 absorb light at wavelengths less than 200 nm. What fraction of total solar radiation is in this range?
C. Instead of electric discharges, what other sources of energy could be used in these experiments?