CHAPTER 2 THE CHEMICAL CONTEXT OF LIFE
Scientific Skills Exercise
Teaching objective: This exercise is designed to give students practice in figuring out what is
shown on a graph, how to describe the major trend(s) in the data, and extracting values from the
graph to calculate related information. The student is then led back to the biological context of
the data to draw a conclusion.
Teaching tips: A version of this Scientific Skills Exercise can be assigned in MasteringBiology.
Most students can look at a graph and describe the slope of the data line. However, many
struggle with writing out what the trend means in terms of the relationship between what was
In this example, students will need to make the additional mental step of reading the trend line
right to left, instead of left to right (the natural tendency), to reach a conclusion about the effect
of decreased carbonate ion concentration on calcification rate and reef growth.
Answers:
1. (a) The x-axis shows the concentration of carbonate ions in units of micromoles of carbonate
ions per kilogram of seawater. (b) The y-axis shows the calcification rate in units of millimoles
3. (a) If the seawater carbonate ion concentration was 270 µmol/kg, the calcification rate would
Interpret the Data
Table 2.1 As you probably know, the human body is made up in large part of water, H2O. The
atoms of oxygen in water, one per water molecule, likely account for the high percentage of
oxygen (65.0%) found in the human body.
Figure 2.19 The inland temperatures (100 F, 96 F, 106 F) are much higher than those along the
coast (73 F, 75 F, 72 F) because oceans are large bodies of water that can absorb or release heat,
moderating the climate nearer the coast.
Concept Check 2.5 #5 A liter of blood would contain 7.8 × 1013 molecules of ghrelin (1.3 ×
10 10 moles per liter × 6.02 × 1023 molecules per mole).
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
11. Scientific Inquiry
The complex shapes of biological molecules determine the great specificity with which they
interact with one another and form weak or strong bonds.
(a)
cell-surface molecules that are complementary in shape to sex attractant molecules
12. Focus on Evolution
It would be surprising if the percentages of naturally occurring elements in most organisms were
13. Focus on Organization
Sample key points:
covalent bonds of water molecules.
The partially charged regions of water molecules are attracted to oppositely charged ions.
Sample top-scoring answer:
Water is the solvent of life, a function emerging from the polar covalent bonds of water
molecules. A water molecule consists of an oxygen atom bonded to two hydrogen atoms. Due to
r to the oxygen at the
14. Synthesize Your Knowledge
forms due to both cohesion of water molecules within the column and the surface tension along
the sides of the column. Adhesion, cohesion, and surface tension are possible because of