CHAPTER 1 INTRODUCTION: EVOLUTION AND THE FOUNDATIONS OF

Suggested Answers and Teaching Tips

CHAPTER 1 INTRODUCTION: EVOLUTION AND THE FOUNDATIONS OF

BIOLOGY

Scientific Skills Exercise

Teaching objective: Students build scientific skills by interpreting data in a pair of bar graphs and relating the data to the biological system it came from.

Teaching tips: A version of this Scientific Skills Exercise can be assigned in Mastering Biology.

If this is the first exercise the students are doing related to interpreting graphs, then you will need to spend time reviewing independent and dependent variables. If the students are confused by having two independent variables on one graph, have them cover one set of data while they look at the other (for example, cover the “full moon” portion of graph A while analyzing the “no moon” portion of it).

In these graphs, there are no statistical significance values given for comparisons between treatments. In the original paper, there was a statistical difference between predation levels of light brown versus dark brown mice in light-colored soil enclosures with no moon and in dark- colored soil enclosures under a full moon. The other two combinations, light-colored soil under a full moon and dark-colored soil with no moon, had no statistically significant difference between light and dark mice.

Answers:

• (a) The independent variables for each graph are the coat color of the mice (light or dark

brown) and the presence or absence of moonlight (full moon or no moon). These are on the x- axis. Taking both graphs together, a third independent variable is the color of soil in the enclosure. (b) The dependent variable is the amount of predation, measured as the number of mice caught. The dependent variable is on the y-axis of the two graphs.

• (a) About 19. (b) About 12. (c) Based on the data, the mouse would be more likely to escape

on dark soil. This might be because in the moonlight, a dark mouse on light soil would be more noticeable than one on dark soil.

• (a) Under a full moon (12 were caught vs. 20 under no moon). (b) Under no moon (11 were

caught vs. 18 under a full moon).

• (a) Dark soil field with a full moon. (b) Light soil with no moon.

(Campbell Biology in Focus, 3e Urry, Lisa Cain, Michael Wasserman, Steven Minorsky, Peter Reece, Jane) (Solution Manual, For Complete File, Download link at the end of this File) 1 / 4

• (a) No moon plus dark brown coat had the highest predation level in the light soil enclosure

(38 mice were caught). (b) Full moon plus light brown coat had the highest predation level in the dark soil enclosure.

• Being on the contrasting soil is most deadly for both colors of mice.

• The total number of mice caught on moonlit nights was about 77, while the total caught on

nights without moonlight was about 95. This suggests that owls hunting on moonlit nights are slightly less successful than are owls hunting on nights without moonlight.

Interpret the Data

Figure 1.21 In the beach habitat, approximately 14 light models and 36 dark models were attacked. In the inland habitat, approximately 38 light models and 12 dark models were attacked.

Suggested Answers for End-of-Chapter Essay Questions

See the general information on grading short-answer essays and a suggested rubric at the beginning of this document.

• Scientific Inquiry

In this case, there are two groups of study mice with light or dark coat colors. The hypothesis is that the contrast of the coat color with the surroundings will have a direct effect on night predation. Therefore, in experiment A (light-colored soil), mice with light coats are the control group and the dark-coated ones, the study group. In the dark-colored soil experiment, mice with dark coats are the control group and the light-coated mice, the study group.

• Scientific Inquiry

Students are asked to use a PubMed search to identify an abstract of an article authored or co- authored by Hopi Hoekstra from 2016 forward. The range of abstracts from which students might choose will grow as the Hoekstra lab generates additional publications.

9. Focus on a Theme: Evolution

Sample key points:

• Darwin used reasoning based on observations to develop his theory of natural selection as a mechanism for evolution.

• His observations included:

• Heritable variations exist in each population.
• A population has more individuals than can be supported by the environment.
• Each species seems suited for its particular environment.

• He proposed that the best-adapted individuals in a population would outcompete others for resources and disproportionately survive and produce more offspring, leading to an increase in the adaptations seen in the population.

Sample top-scoring answer:

Based on many observations of different species, Darwin proposed his theory that evolution by means of natural selection accounts for both the unity and diversity of life on Earth. He noticed that variations existed among the individuals in a population and that these variations seemed to 2 / 4

be heritable. He also saw that populations could grow larger than could be supported by the resources around them. Finally, he observed that species (like the different species of finches) seemed to suit their environment. He proposed that the best-suited individuals in a population would survive and reproduce more successfully that those less adapted to their environment, and he called this “natural selection.” In Darwin’s view, this mechanism could account for both the unity and diversity of features among species. The descent of organisms from a common ancestor explains similar features, while the force of natural selection in different environments accounts for differences between organisms.

10. Focus on a Theme: Information

Common ancestry explains this observation. The thousand-some-odd genes shared by humans and prokaryotes originated in early prokaryotes. They have been retained, with some modification, over the billions of years of eukaryotic evolution. These genes no doubt code for proteins and RNAs whose functions are essential for survival—for example, the genes that code for ribosomal RNA, which is important for protein synthesis in both prokaryotes and eukaryotes.

• Synthesize Your Knowledge

It’s difficult to pick out this gecko against the background of the tree trunk, because the gecko itself looks like mossy bark. This coloration likely makes it harder for the gecko to be seen by predators, thus enhancing its survival. This cryptic coloration pattern probably evolved over generations. The members of a gecko population that more closely resembled their background would have been less visible to predators, thus more likely to survive, reproduce, and leave offspring. The offspring would inherit the genes that generated the mossy bark coloration, and the offspring that blended in better would survive better and reproduce more successfully. Over generations, the coloration would become a closer and closer match to the tree bark. (The mossy leaf-tailed gecko is endemic to Madagascar, meaning it is found only there and nowhere else in the world. Many endemic species live in Madagascar. This is because it is an island with land features and climatic factors that have allowed evolution of many species in isolation.)

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 Mastering Biology.

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 reported on one axis relative to the other axis. Thus, while a student may respond that the data line has a positive slope, they may also respond that a higher calcification rate results in a higher carbonate ion concentration. Helping them sort out dependent and independent variables should 3 / 4

clear up the problem. Visual learners will benefit from drawing a mock-up of 1 square meter of the reef, with dots in the water to represent carbonate ions and arrows to indicate calcification.

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:

• (a) The x-axis shows the concentration of CO

3 -2 (carbonate) ions in units of micromoles (µmol) of CO 3 -2 per kilogram of seawater. (b) The y-axis shows the calcification rate in units of millimoles of CaCO

• accumulated per square meter of reef per day. (c) Carbonate ion

concentration is the independent variable. (d) Calcification rate is the dependent variable.

• The data show that the rate of calcification is positively related to the concentration of CO

3 -2 in the seawater. As the concentration of CO 3 -2 increases, the rate of calcification increases.

• If the seawater CO

3 -2 concentration was 270 µmol/kg, the calcification rate would be approximately 19 mmol CaCO 3/m 2 · day. It would take 1 square meter of reef approximately 1.6 days to accumulate 30 mmol of CaCO

• [(30 mmol of CaCO3/m

2

• / (19 mmol CaCO3/m

2 · day) = 1.6 days].

• (a) The final step of the process shown in Figure 2.25, the rate of conversion of CO

3 2- and Ca 2+ into CaCO3, is measured in this experiment. (b) The results do support the hypothesis that increased concentration of atmospheric CO

• could lead to slower growth of coral reefs. It

supports it because, according to the chemistry shown in Figure 2.25, more CO

• entering the

ocean will push the reactions toward formation of more HCO 3

• (bicarbonate) ions, decreasing the

amount of CO 3 2- available for formation of CaCO3. The results in the graph show that, under the experimental conditions, the lower the concentration of CO 3 2-, the lower the rate of calcification, and thus the slower the growth of coral reefs. (As an example, if you do the same calculation as in question 3 for a CO 3 -2 concentration of 250 µmol/kg, you will see it takes 2.5 days instead of 1.6 days to accumulate the same amount of calcium carbonate at this lower CO 3 -2 concentration. )

Interpret the Data

Table 2.1 As you probably know, the human body is made up in large part of water, H 2O. 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 × 10 13 molecules of ghrelin (1.3 × 10 –10 moles per liter × 6.02 × 10 23 molecules per mole).

• / 4