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Homework answers / question archive / Scientific Investigation Before going to lab, read the Introduction and Exercises 1 and 2

Scientific Investigation Before going to lab, read the Introduction and Exercises 1 and 2

Biology

Scientific Investigation

Before going to lab, read the Introduction and Exercises 1 and 2. Be prepared to answer all questions and contribute your ideas in a class discussion.

Laboratory Objectives

After completing this lab topic, you should be able to:

1. Identify and characterize questions that can be answered through scientific investigation.

2. Define hypothesis and explain what characterizes a good scientific hypothesis.

3. Identify and describe the components of a scientific experiment.

4. Summarize and present results in tables and graphs.

5. Discuss results and critique experiments.

6. Design a scientific experiment.

7. Interpret and communicate results.

Introduction

Biology is the study of the phenomena of life, and biological scientist’s researchers, teachers, and students—observe living systems and organisms, ask questions, and propose explanations for those observations. Scientific investigation is a way of testing those explanations. Science assumes that biological systems are understandable and can be explained by fundamental rules or laws. Scientific investigations share some common elements and procedures, which are referred to as the scientific method. Not all scientists follow these procedures in a strict fashion, but each of the elements is usually present. Science is a creative human endeavor that involves asking questions, making observations, developing explanatory hypotheses, and testing those hypotheses. Scientists closely scrutinize investigations in their field, and each scientist must present his or her work: at scientific meetings or in professional publications, providing evidence from observations and experiments that support the scientist’s explanations of biological phenomena. In this lab topic, you will not only review the process that scientists use to ask and answer questions about the living world, but you will develop the skills to conduct and critique scientific investigations. Like scientists, you will work in research teams in this laboratory and others, collaborating as you ask questions and solve problems. You will be investigating biology using the methodology of scientists, asking questions, proposing explanations, designing experiments, predicting results, collecting and analyzing data, and interpreting your results in light of your hypotheses.

EXERCISE 1

Questions and Hypotheses

This exercise explores the nature of scientific questions and hypotheses. Before going to lab, read the explanatory paragraphs and then be prepared to present your ideas in the class discussion.

Lab Study A. Asking Questions

Scientists are characteristically curious and creative individuals whose curiosity is directed toward understanding the natural world. They use their study of previous research or personal observations of natural phenomena as a basis for asking questions about the underlying causes or reasons for these phenomena. For a question to be pursued by scientists, the phenomenon must be well defined and testable. The elements must be measurable and controllable. There are limits to the ability of science to answer questions. Science is only one of many ways of knowing about the world in which we live. Consider, for example, this question: Do excessively high temperatures cause people to behave immorally? Can a scientist investigate this question? Temperature is certainly a well-defined, measurable, and controllable factor, but morality of behavior is not scientifically measurable. We probably could not even reach a consensus on the definition. Thus, there is no experiment that can be performed to test the question. Which of the following questions do you think can be answered scientifically?

1. Do kids who play violent video games commit more violence?

2. Did the consumption of seven cans of “energy drink” cause the heart attack of a motorcyclist in Australia?

3. Will increased levels of CO2 in the atmosphere stimulate the growth of woody vines, such as poison ivy and kudzu?

4. How effective are extracts of marigold and rosemary as insect repellents?

5. Should it be illegal to sell organs, such as a kidney, for transplant purposes?

How did you decide which questions can be answered scientifically?

Lab Study B. Developing Hypotheses

As questions are asked, scientists attempt to answer them by proposing possible explanations. Those proposed explanations are called hypotheses. A hypothesis tentatively explains something observed. It proposes an answer to a question. Consider question 4, preceding. One hypothesis based on this question might be “Marigold and rosemary extracts are more effective than DEET in repelling insects.” The hypothesis has suggested a possible explanation that compares the difference in efficacy between these plants extracts and DEET.

A scientifically useful hypothesis must be testable and falsifiable (able to be proved false). To satisfy the requirement that a hypothesis be falsifiable, it must be possible that the test results do not support the explanation. In our example, the experiment might be to spray one arm with plant extracts and the other with DEET. Then place both arms in a chamber with mosquitoes. If mosquitoes bite both arms with equal frequency or the DEET arm has fewer bites, then the hypothesis has been falsified. Even though the hypothesis can be falsified, it can never be proved true. The evidence from an investigation can only provide support for the hypothesis. In our example, if there are fewer bites on the arm with plant extracts than on the DEET-treated arm, then the hypothesis has not been proved, but has been supported by the evidence. Other explanations still must be excluded, and new evidence from additional experiments and observations might falsify this hypothesis at a later date. In science seldom does a single test provide results that clearly support or falsify a hypothesis. In most cases, the evidence serves to modify the hypothesis or the conditions of the experiment. Science is a way of knowing about the natural world (Moore, 1993) that involves testing hypotheses or explanations. The scientific method can be applied to the unusual and the commonplace. You use the scientific method when you investigate why your once-white socks are now blue. Your hypothesis might be that your blue jeans and socks were washed together, an assertion that can be tested through observations and experimentation. Students often think that controlled experiments are the only way to test a hypothesis. The test of a hypothesis may include experimentation, additional observations, or the synthesis of information from a variety of sources. Many scientific advances have relied on other procedures and information to test hypotheses. For example, James Watson and Francis Crick developed a model that was their hypothesis for the structure of DNA. Their model could only be supported if the accumulated data from a number of other scientists were consistent with the model. Actually, their first model (hypothesis) was falsified by the work of Rosalind Franklin. Their final model was tested and supported not only by the ongoing work of Franklin and Maurice Wilkins but also by research previously published by Erwin Chargaff and others. Watson and Crick won the Nobel Prize for their scientific work. They did not perform a controlled experiment in the laboratory but tested their powerful hypothesis through the use of existing evidence from other research. Methods other than experimentation are acceptable in testing hypotheses. Think about other areas of science that require comparative observations and the accumulation of data from a variety of sources, all of which must be consistent with and support hypotheses or else be inconsistent and falsify hypotheses.

The information in your biology textbook is often thought of as a collection of facts, well understood and correct. It is true that much of the knowledge of biology has been derived through scientific investigations, has been thoroughly tested, and is supported by strong evidence. However, scientific knowledge is always subject to novel experiments and new technology, any aspect of which may result in modification of our ideas and a better understanding of biological phenomena. The structure of the cell membrane is an example of the self-correcting nature of science. Each model of the membrane has been modified as new results have negated one explanation and provided support for an alternative explanation.

Application

Before scientific questions can be answered, they must first be converted to hypotheses, which can be tested. For each of the following questions, write an explanatory hypothesis. Recall that the hypothesis is a statement that explains the phenomenon you are interested in investigating.

1. Does supplemental feeding of birds at backyard feeders affect their reproductive success?

2. Do preschool boys in coed classes develop better verbal skills than boys in all-male classes?

Scientists often propose and reject a variety of hypotheses before they design a single test. Discuss with your class which of the following statements would be useful as scientific hypotheses and could be investigated using scientific procedures. Give the reason for each answer by stating whether it could possibly be falsified and what factors are measurable and controllable.

1. The use of pesticides in farming causes deformities in nearby frog populations.

2. Sea turtles are more likely to hatch during a new moon.

3. Drinking two or three cups of coffee a day reduces the risk of heart disease in women.

4. Manatees and elephants share a common ancestor.

5. Organic food is healthier than conventionally produced food.

EXERCISE 2

Designing Experiments to Test Hypotheses

The most creative aspect of science is designing a test of your hypothesis that will provide unambiguous evidence to falsify or support a particular explanation. Scientists often design, critique, and modify a variety of experiments and other tests before they commit the time and resources to perform a single experiment. In this exercise, you will follow the procedure for experimentally testing hypotheses, but it is important to remember that other methods, including observation and the synthesis of other sources of data, are acceptable in scientific investigations. An experiment involves defining variables, outlining a procedure, and determining controls to be used as the experiment is performed. Once the experiment is defined, the investigator predicts the outcome of the experiment based on the hypothesis.

Read the following description of a scientific investigation of the effects of sulfur dioxide on soybean reproduction. Then in Lab Study A you will determine the types of variables involved, and in Lab Study B, the experimental procedure for this experiment and for others.

INVESTIGATION OF THE EFFECT OF SULFUR DIOXIDE ON SOYBEAN REPRODUCTION

Agricultural scientists were concerned about the effect of air pollution, sulfur dioxide in particular, on soybean production in fields adjacent to coal powered power plants. Based on initial investigations, they proposed that sulfur dioxide in high concentrations would reduce reproduction in soybeans. They designed an experiment to test this hypothesis (Figure 1). In this experiment, 48 soybean plants, just beginning to produce flowers, were divided into two groups, treatment and no treatment. The 24 treated plants were divided into four groups of 6. One group of 6 treated plants was placed in a fumigation chamber and exposed to 0.6 ppm (parts per million) of sulfur dioxide for 4 hours to simulate sulfur dioxide emissions from a power plant. The experiment was repeated on the remaining three treated groups. The no treatment plants were divided similarly into four groups of 6. Each group in turn was placed in a second fumigation chamber and exposed to filtered air for 4 hours. Following the experiment, all plants were returned to the green house. When the beans matured, the number of bean pods, the number of seeds per pod, and the weight of the pods were determined for each plant.

Lab Study A. Determining the Variables

Read the description of each category of variable; then identify the variable described in the preceding investigation. The variables in an experiment must be clearly defined and measurable. The investigator will identify

Figure 1.

Experimental design for soybean experiment. The experiment was repeated four times. Soybeans were fumigated for 4 hours and define dependent, independent, and controlled variables for a particular experiment.

 

The Dependent Variable

Within the experiment, one variable will be measured or counted or observed in response to the experimental conditions. This variable is the dependent variable. For the soybeans, several dependent variables are measured, all of which provide information about reproduction. What are they?

The Independent Variable

The scientist will choose one variable, or experimental condition, to manipulate. This variable is considered the most important variable by which to test the investigator's hypothesis and is called the independent variable. What was the independent variable in the investigation of the effect of sulfur dioxide on soybean reproduction? Can you suggest other variables that the investigator might have changed that would have had an effect on the dependent variables?

Although other factors, such as light, temperature, time, and fertilizer, might affect the dependent variables, only one independent variable is usually chosen. Why is it important to have only one independent variable?

Why is it acceptable to have more than one dependent variable?

The Controlled Variable

Consider the variables that you identified as alternative independent variables. Although they are not part of the hypothesis being tested in this investigation, they would have significant effects on the outcome of this experiment. These variables must, therefore, be kept constant during the course of the experiment. They are known as the controlled variables. The underlying assumption in experimental design is that the selected independent variable is the one affecting the dependent variable. This is only true if all other variables are controlled. What are the controlled variables in this experiment? What variables other than those you may have already listed can you now suggest?

Lab Study B. Choosing or Designing the Procedure

The procedure is the stepwise method, or sequence of steps, to be performed for the experiment. It should be recorded in a laboratory notebook before initiating the experiment, and any exceptions or modifications should be noted during the experiment. The procedures may be designed from research published in scientific journals, through collaboration with colleagues in the lab or other institutions, or by means of one’s own novel and creative ideas. The process of outlining the procedure includes determining control treatment(s), levels of treatments, and numbers of replications.

Level of Treatment

The value set for the independent variable is called the level of treatment. For this experiment, the value was determined based on previous research and preliminary measurements of sulfur dioxide emissions. The scientists may select a range of concentrations from no sulfur dioxide to an extremely high concentration. The levels should be based on knowledge of the system and the biological significance of the treatment level. In some experiments, however, independent variables represent categories that do not have a level of treatment (for example, gender). What was the level of treatment in the soybean experiment?

Replication

Scientific investigations are not valid if the conclusions drawn from them are based on one experiment with one or two individuals. Generally, the same procedure will be repeated several times (replication), providing consistent results. Notice that scientists do not expect exactly the same results inasmuch as individuals and their responses will vary. Results from replicated experiments are usually averaged and may be further analyzed using statistical tests. Describe replication in the soybean experiment.

Control

The experimental design includes control in which the independent variable is held at an established level or is omitted. The control or control treatment serves as a benchmark that allows the scientist to decide whether the predicted effect is really due to the independent variable. In the case of the soybean experiment, what was the control treatment?

What is the difference between the control and the controlled variables discussed previously?

Lab Study C. Making Predictions

The investigator never begins an experiment without a prediction of its outcome. The prediction is always based on the particular experiment designed to test a specific hypothesis. Predictions are written in the form of if/then statements: “If the hypothesis is true, then the results of the experiment will be .. .”; for example, “if extracts of marigold and rosemary are more effective than DEET in repelling insects, then there will be fewer bites on the arm sprayed with the plant extract compared to the arm sprayed with DEET after a 5-minute exposure to mosquitoes.” Making a prediction provides a critical analysis of the experimental design. If the predictions are not clear, the procedure can be modified before beginning the experiment. For the soybean experiment, the hypothesis was: “Exposure to sulfur dioxide reduces reproduction.” What should the prediction be? State your prediction.

To evaluate the results of the experiment, the investigator always returns to the prediction. If the results match the prediction, then the hypothesis is supported. If the results do not match the prediction, then the hypothesis is falsified. Either way, the scientist has increased knowledge of the process being studied. Many times the falsification of a hypothesis can provide more information than confirmation since the ideas and data must be critically evaluated in light of new information. In the soybean experiment, the scientist may learn that the prediction is true (sulfur dioxide does reduce reproduction at the concentration tested). As a next step, the scientist may now wish to identify the particular level at which the effect is first demonstrated.

Return to Exercise 1 and review your hypotheses for the numbered questions. Consider how you might design an experiment to test the first hypothesis. For example, you might count the number of eggs per nest or count the number of chicks successfully raised in the summer. The prediction might be:

If supplemental feeding of birds at backyard feeders increases their reproductive success (a restatement of the hypothesis), then there will be more eggs per nest for birds with supplemental feeding compared to birds who receive no supplemental feeding (predicting the results from the experiment).

Now consider an experiment you might design to test the second hypothesis. How will you measure “better verbal skills”?

 

State a prediction for this hypothesis and experiment. Use the if/then format.

The actual test of the prediction is one of the great moments in research. No matter the results, the scientist is not just following a procedure but truly testing a creative explanation derived from an interesting question.

Discussion

1. From this exercise, list the components of scientific investigations from asking a question to carrying out an experiment.

2. From this exercise, list the variables that must be identified in designing an experiment.

3. What are the components of an experimental procedure?

 

 EXERCISE 3

Designing an Experiment

Materials

Meter sticks or yard sticks

Short metric rulers (approximately 30 cm or 1 foot)

Cloth metric measuring tapes or cotton string

Calipers (optional)

Calculators

Introduction

The shape of an organism depends in part on the relative growth rates of different body parts during development. The terms allometry and allometric growth are used when describing the changing relative rates of growth. Specifically, allometry is the phenomenon whereby parts of an organism grow at different rates, or the disproportionate growth of a part in relation to the entire organism. This can be observed in humans as seen in Figure 2, an illustration of differential growth rates. Notice in this figure, in which the newborn and adult are scaled to the same height, that the head is larger in proportion to the body length in a newborn than in an adult.

Allometric growth contrasts with isometric growth when two parts grow at the same rate. This takes place when proportions between body parts remain constant as the organism grows. You can imagine this type of growth by taking a photo of the baby in Figure 2 and simply enlarging it as it grows to an adult. For example, if the arms and legs of a human grow isometric ally, then their lengths will be the same relative to the body in a newborn as in an adult.

 

 

Table 1

Average (50th percentile) Body Part Sizes for Newborn (38 Weeks Gestation)

North American Humans, Both Sexes

Body Part

Description of Measurement

Size(cm)(rounded to nearest 0.5)

Length/Height

From sole of foot to top of head

48

Head circumference

Head at largest diameter

33

Upper Limb (total arm)

From shoulder joint to tip of middle finger

20

Hand length

From wrist to tip of middle finger

6

Span

Between fingertips of middle finger with arms outstretched

51

Lower Limb (total leg)

From sole of foot to joint where leg meets hip laterally

18

Crown rump length

In seated position, from top of head to surface of a flat-bottom chair or bench

33

Foot length

Measure from heel to toe standing on a tape measure

7.5

(Data from Hall et al., 2007)

In the following exercise you will collect data to compare ratios of height to selected body parts for newborns with the same ratios in students (your-selves). This should provide information to determine if selected body parts grow allometrically or isometrically in humans. In the process you will practice designing experiments, collecting data, and processing that data. The data for newborns are given in Table 1. These data are taken from Hall et al. (2007), a handbook of physical measurements for health professionals.

In your research teams, examine Table 1 and take a few minutes to discuss several specific questions that you can ask about growth rates (allometric, isometric) of body parts in relation to height in humans. Choose two body parts and write your questions in the margin of the lab manual. Discuss with your teammates a testable hypothesis for each question. Choose one question and hypothesis to add to a class list recorded by the instructor.

 

  1. The class decides on two body parts to be compared with total height. For each, the class selects a question and hypothesis and then develops the experimental design for each body part. They then predict the results of the experiments. The same two body parts and height are measured by all teams.

Record the body parts and the corresponding questions chosen by the class.

Hypothesis

Record a hypothesis for each of the questions chosen by the class.

 

The Experiment

In this experiment you will compare the ratios of height to selected body parts in newborns and students. As a class, design your experiment. Describe how you will measure each selected body part for each team member. Include data collection and analysis. To determine height to body part ratio (H/BP), students may self-report their height. Be sure all teams understand the protocol.

What is the dependent variable in your experiments?

What is the independent variable?

Controlled variables:

Control:

Level of treatment:

Replication:

Prediction

Predict the results of each experiment based on your hypotheses (if/then). Write two predictions based on the two body parts chosen.

Performing the Experiment

Following the procedures established by your class for each body part, perform the experiment.

Results

1. List the first body part chosen in the title for Table 2a.

2. Record results for each member of your team for the first body part in Table 2a. (Remember, to convert inches to cm, multiply by 2.54.)

3. Calculate H/BP ratios for each member of your team.

4. Record data for newborns from Table 1 for the first body part.

5. Calculate the H/BP ratio for newborns.

6. Follow the same procedure for the second body part chosen, and record all data in Table 2b.

7. Record ratios for every student in Table 3.

8. Determine the class average for H/BP and record in Table 3.

 Table 2a

Height to ---------- Ratio for Students and Newborns

 

Subject

Height

Body Part Size

H/BP Ratio

Team Member 1

 

 

 

Team Member 2

 

 

 

Team Member 3

 

 

 

Team Member 4

 

 

 

Newborns

 

 

 

 

Table 2b

Height to ---------- Ratio for Students and Newborns

 

Subject

Height (cm)

Body Part Size (cm)

H/BP Ratio

Team Member 1

 

 

 

Team Member 2

 

 

 

Team Member 3

 

 

 

Team Member 4

 

 

 

Newborns

 

 

 

 

Table 3

Ratios of heights Two body parts for each student.

Student#

1

2

3

4

5

6

7

8

9

10

11

12

Body Part #1

 

 

 

 

 

 

 

 

 

 

 

 

Body Part #2

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3, continued

Student#

13

14

15

16

17

18

19

20

21

22

23

24

Average Ratio

Body Part #1

 

 

 

 

 

 

 

 

 

 

 

 

 

Body Part #2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Presenting and Analyzing Results

Once the data are collected, they must be organized and summarized so that scientists can determine if the hypothesis has been supported or falsified. In this exercise, you will design tables and graphs, the letter are also called figures. Table and figures have two primary functions. They are used (1) to help you analyze and interpret your results and (2) to enhance the clarity with which you present the work to a reader or viewer.

Lab Study A. Tables

You have collected data from your experiment in the form of a list of numbers that may appear at first glance to have little meaning. Look at your data. How could you organize the data set to make it easier to interpret? You could average the data set for each treatment, but even averages can be rather uninformative. Could you use a summary table to convey the data (in this case, averages)?

Table 4 is an example of a table using data averages of the number of seeds per pod and number of pods per plant as the dependent variables and exposure to sulfur dioxide as the independent variable. Note that the number of replicates and the units of measurement are provided in the table title.

Tables are used to present results that have a few too many data points. They are also useful for displaying several dependent variables and when the quantitative values rather than the trends are the focus. For example, average number of bean pods, average number of seeds per pod, and average weight of pods per plant for treated and untreated plants could all be presented in one table.

The following guidelines will help you construct a table.

  • All values of the same kind should read down the column, not across a row. Include only data that are important in presenting the results and for further discussion.
  • Information and results that are not essential (for example: test-tube number, simple calculations, or data with no differences) should be omitted.
  • The headings of each column should include units of measurement, if appropriate.
  •  Tables are numbered consecutively throughout a lab report or scientific paper. For example: Table 4 would be the fourth table in your report.
  • The title, which is located at the top of the table, should be clear and concise, with enough information to allow the table to be understandable apart from the text. Capitalize the first and important words in the title. Do not capitalize articles (a, an, the), short prepositions, and conjunctions. The title does not need a period at the end.
  • Refer to each table in the written text. Summarize the data and refer to the table; for example, “The plants treated with sulfur dioxide produced an average of 1.96 seeds per pod (Table 4).” Do not write, “See the results in Table 4.”
  • If you are using a database program, such as Excel, you should still sketch your table on paper before constructing it on the computer.

Table 4

Effects of 4-Hour Exposure to 0.6 ppm Sulfur Dioxide on Average Seed and Pod Production in Soybeans (24 Replicates)

Treatment

Seeds per POD

Pods per plant

Control

3.26

16

SO2

1.96

13

 

Application

1. Using the student average data from Table 3, design a table to present the results for students in your class for H/BP for each body part measured. Include in your table ratios for newborns.

2. Label this Table 5. Compose a title for your table. Refer to the guidelines in the previous section of this lab topic for composing titles.

Lab Study B. Figures

Graphs, diagrams, drawings, and photographs are all called figures. The results of an experiment usually are presented graphically, showing the relationships among the independent and dependent variable(s). A graph or figure provides a visual summary of the results. Often, characteristics of the data are not apparent in a table but may become clear in a graph. By looking at a graph, then, you can visualize the effect that the independent variable has on the dependent variable and detect trends in your data. Making a graph may be one of the first steps in analyzing your results.

The presentation of your data in a graph will assist you in interpreting and communicating your results. In the final steps of a scientific investigation, you must be able to construct a logical argument based on your results that either supports or falsifies your starting hypothesis. Your graph should be accurately and clearly constructed, easily interpreted, and well annotated.

The following guidelines will help you to construct such a graph.

  • Use graph paper and a ruler to plot the values accurately. If using a database program, you should first sketch your axes and data points before constructing the figure on the computer.
  • The independent variable is graphed on the x axis (horizontal axis, or abscissa), and the dependent variable, on the y axis (vertical axis, or ordinate).
  • The numerical range for each axis should be appropriate for the data being plotted. Generally, begin both axes of the graph at zero (the extreme left corner). Then choose your intervals and range to maximize the use-of the graph space. Choose intervals that are logically spaced and therefore will allow easy interpretation of the graph, for example, intervals of 5s or 10s. To avoid generating graphs with wasted space, you may signify unused graph space by two perpendicular tic marks between the zero and your lowest number on one or both axes.
  • Label the axes to indicate the variable and the units of measurement. Include a legend if colors or shading is used to indicate different aspects of the experiment.
  • Choose the type of graph that best presents your data. Line graphs and bar graphs are most frequently used. The choice of graph type depends on the nature of the variable being graphed.
  • Compose a title for your figure, and write it below your graph. Figures should be numbered consecutively throughout a lab report or scientific paper. Each figure is given a caption or title that describes its contents, giving enough information to allow the figure to be self-contained. Capitalize only the first word in a figure title and place a period at the end.

The Line Graph

Line graphs show changes in the quantity of the chosen variable and emphasize the rise and fall of the values over their range. Use a line graph to present continuous quantitative data. For example, changes in the dependent variable, soybean weight, measured over time would be depicted best in a line graph.

  • Plot data as separate points.
  • Whether to connect the dots or draw a best fit curve depends on the type of data and how they were collected. To show trends, draw smooth curves or straight lines to fit the values plotted for any one data set. Connect the points dot to dot when emphasizing meaningful changes in values on the x axis.
  • If more than one set of data is presented on a graph, use different colors or symbols and provide a key or legend to indicate which set is which.
  • A boxed graph, instead of one with only two sides, makes it easier to see the values on the right side of the graph.

Note the features of a line graph in Figure 3, which shows the decline in smoking by high school seniors since 1998.

The Bar Graph

Bar graphs are constructed following the same principles as for line graphs, except that vertical bars, in a series, are drawn down to the horizontal axis. Bar graphs are often used for data that represent separate or discontinuous groups or nonnumerical categories, thus emphasizing the discrete differences between the groups. For example, a bar graph might be used to depict differences in number of seeds per pod for treated and untreated soybeans. Bar graphs are also used when the values on the x axis are numerical but grouped together. These graphs are called histograms.

Note the features of a bar graph in Figure 4, which shows the increase of diabetes in older citizens of three racial groups.

You will be asked to design graphs throughout this laboratory manual. Remember, the primary function of the figure is to present your results in the clearest manner to enhance the interpretation and presentation of your data.

Application

1. Using data from your experiments and the grid provided on the next page, design a bar graph that shows the relationship between the dependent and independent variables for both body parts. Discuss with your teammates how to design one figure so that it includes the data for the independent variable for each experiment.

a. What was the independent variable for each experiment? On which axis would you graph this?

b. What was the dependent variable? Write this on the appropriate axis.

2. Add a legend to your figure to distinguish newborn and student ratios.

3. Draw, label, and compose a title for your figure.

4. Imagine an experiment similar to the one you have performed where it would be appropriate to use a line graph.

Exercise 5

Interpreting and communicating Results

The last component of a scientific investigation is to interpret the results and discuss their implications in light of the hypothesis and supporting literature. The investigator studies the results, including the table and figures and determine if the hypothesis has been supported or falsified. If the hypothesis has been falsified, the investigator must suggest alternate hypothesis for testing. If the hypothesis has been supported, the investigator suggest additional experiments to strengthen the hypothesis, using the same or alternate methods.

Scientists will thoroughly investigate a scientific question, testing hypotheses, collecting data, and analyzing results. In the early stages of a scientific study, scientists review the scientific literature relevant to their topic. They continue to review related published research as they interpret their results and develop conclusions. The final phase of a scientific investigation is the communication of the results to other scientists. Preliminary results may be presented within a laboratory research group and at scientific meetings where the findings can be discussed. Ultimately, the completed project is presented in the form of a scientific paper that is reviewed by scientists within the field and published in a scientific journal. The ideas, procedures, results, analyses, and conclusions of all scientific investigations are critically scrutinized by other scientists. Because of this, science is sometimes described as self-correcting, meaning that errors that may occur are usually discovered within the scientific community. Scientific communication, whether spoken or written, is essential to science. During this laboratory course, you often will be asked to present and interpret your results at the end of the laboratory period. Additionally, you will write components of a scientific paper for many lab topics.

Application

1. Using your tables and figures, analyze your results. What relationships are apparent between variables? Look for trends in your figures and tables. Discuss your conclusions with your group.

2. Write a summary statement for your experiments incorporating evidence from your results. Use your results to support or falsify your hypotheses. Be prepared to present your conclusions to the class.

3. Critique your experiment. What weaknesses do you see in the experiment? Suggest improvements.

Weaknesses in Experiment

Improvement

1.

 

2.

 

3.

 

4.

 

5.

 

 

4. Suggest additional and modified hypotheses that might be tested in the future. Briefly describe your next experiment.

5. Briefly describe the four major parts of a scientific paper. What is the abstract? What information is found in a References Cited section? What sections of a scientific paper always include references?

Reviewing Your Knowledge

1. Review the major components of an experiment by matching the following terms to the correct definition: control, controlled variables, and level of treatment, dependent variable, replication, procedure, prediction, hypothesis, and independent variable.

a. Variables that are kept constant during the experiment (variables not being manipulated)

b. Tentative explanation for an observation

c. What the investigator varies in the experiment (for example, time, pH, temperature, concentration)

d. Process used to measure the dependent variable

e. Appropriate values to use for the independent variable

f. Treatment that eliminates the independent variable or sets it at a standard value

g. What the investigator measures, counts, or records; what is being affected in the experiment

h. Number of times the experiment is repeated

i. Statement of the expected results of an experiment based on the hypothesis

2. Identify the dependent and independent variables in the following investigations. (Circle the dependent variable and underline the independent variable.)

a. Scientists investigating the effects of increased temperatures on plants in urban environments measured the size of ragweed flowers in Baltimore city lots and rural fields.

 

b. Scientists determined the abundance of apple aphids on leaves of 120 apple trees on 5 days in October. The autumn leaf color of the apple trees varied with 40 red trees, 40 yellow trees, and 40 green trees.

c. Synapse number and level of synaptic proteins in the brains of fruit flies are measured during wakeful periods and periods of sleep.

3. Suggest a control treatment for each of the following experiments.

a. Geneticists are studying the inheritance of “wolfman syndrome,” where the body and face are covered with dark hair. They studied three families in which 16 individuals had the syndrome. They discovered DNA deletions in four genes in each of the 16 persons.

Control treatment:

b. Nutrition experts investigate if eating yogurt every day will reduce gum disease.

Control treatment:

c. The number of T-lymphocytes are counted in the blood of vultures that feed on carcasses of livestock treated with antibiotics.

Control treatment:

4. In a recent study of 10,000 women (Velicer et al., 2004) scientists reported that women who had breast cancer had a history of heavier antibiotic use than women who did not have breast cancer. What possible explanations for this correlation can you suggest?

5. What is the essential feature of science that makes it different from other ways of understanding the natural world?

Applying Your Knowledge

Interpreting Graphed and Tabular Data

1. The use of DDT for malaria control stopped being funded by the World Health Organization (WHO) in the 1980s. The World Bank required a ban on DDT for developing countries seeking loans. At the same time there has been an increase in resistance by the malarial parasite to the most common antimalarial drugs. Since 2001, WHO has allowed the spraying of DDT in Africa on interior walls to kill mosquitoes. Review the graph in Figure 5 and information provided and then answer the following questions.

What is the independent variable?

What is the dependent variable?

Why was a bar graph selected to present these data? Could the authors have used a line graph?

Write a statement summarizing the results. Specifically address trends from 1972~1992; 1995-2000; and 2000-2004.

Figure 5.

 

Malaria cases in South Africa before, during, and after banned DDT spraying. (After Opar, 2006) Figure from The Return of DDT by A. Opar from SEED © 2006 Ali Rights reserved. Used by permission and protected by the Copyright Laws of the United States.

Figure 6.

 

The relationship of beak depth in ground finches and the maximum hardness of seeds they can crack. Adapted from B. R. Grant and P. R. Grant. 2003. “What Darwin's Finches Can Teach us About the Evolutionary Origin and Regulation of Biodiversity,” BioScience, vol. 53, pp. 965-975.

Figure 7.

Evolutionary change in beak depth in the population of the medium ground finch on the Galapagos

Island of Daphne Major. The carets indicate the means for the population. Adapted from B. R. Grant and P. R. Grant. 2003. “What Darwin's Finches Can Teach us About the Evolutionary Origin and Regulation of Biodiversity,” BioScience, vol. 53, pp. 965-975.

2. Rosemary and Peter Grant have studied the Galapagos finches on the Island of Daphne Major for 30 years. They have identified, marked, and measured every finch on the island. They recorded the parents and offspring for generations of finch species. The medium ground finches, Geospiza fortis, are medium-sized, seed-eating birds. The Grants determined the relationship between seed size and hardness with beak depth (Figure 6). Which finches are able to crack the hardest seeds? State the trend,

In 1977, the Galapagos Islands experienced a severe drought that resulted in the death of many plants, severe competition for seeds among the finches, and death of many birds. Beak size for the medium ground finch offspring born in 1976 before the drought and those born in 1978, the year following the drought, are shown in Figure 7 (Grant and Grant, 2003). Compare the average beak depth for the offspring from 1976 and 1978.

Approximately how many birds in the population each year had beaks larger than 9.3 mm?

During the drought of 1977, which group of medium ground finches were more successful in finding food and reproducing, those with large beaks or those with small beaks? Explain.

Based on Figures 6 and 7, what kind of seeds were available in 1977, soft or hard?

Using guidelines for graphs presented earlier, how could you improve the axes labels on this figure?

3. Review the guidelines for graphs and critique Figure 8. This figure illustrates the changes in risk factors that are important in chronic diseases such as coronary heart disease, lung cancer, diabetes and stroke.

Scientific Investigation _

 

  

 

Figure 8.

 

RISK-FACTOR PREVALENCE IN U.S.

 

 

 

1960 1970 1980

Year

Data from the Centers for Disease Control and Prevention. Graph by Rodger Doyle, “Lifestyle Blues,” Scientific American, vol. 284, p. 30. Copyright © 2001. Rodger Doyle. Used with permission.

Practicing Experimental Design

1. Beginning in 2006, scientists have been alarmed by the decline in bat populations in the northeastern U.S. Bat populations in some caves have declined by 50% or more. Bats (dead and living) are found with a white fungus on their faces, ears, and wings, and thus the name “white-nose syndrome.” Many bats have come out of hibernation early and during daylight; without insects to eat they are emaciated or starve to death. White-nose syndrome is spreading into caves in Virginia and West Virginia. The main question is whether the white fungus, Geomyces sp., is the primary cause of death. Scientists are investigating other explanations. For example, other pathogens (viruses or bacteria) may be the primary infective agents, and the white fungus may be secondary. Scientists also have found that the digestive systems of affected bats have fewer bacteria necessary for the digestion of insects. Therefore, less energy is available to them during hibernation. This could result in starvation and increased susceptibility to the fungus (Zimmerman, 2009). Using the criteria in Lab Study B, Developing Hypotheses, select the hypothesis you would pursue as a scientist and justify your choice.

2. “Grains of paradise” plants grow in the swampy region inhabited by the western lowland gorilla, makeup 80-90% of their diet, and are even utilized in constructing their nests each night. Captive lowland gorillas in zoos are not fed grains of paradise, but rather have a complex diet of processed vitamin-rich food plus fruits and vegetables available in the marketplace. Recently scientists identified potent anti-inflammatory and antimicrobial compounds in grains of paradise that may hold the key to a puzzling question: “Why do western lowland gorillas in zoos have an alarmingly high rate of cardiomyopathy (a type of heart disease)?” Hypothesize about the effect of diet (grains of paradise) on rates of heart disease. Describe a simple preliminary experiment to test your hypothesis, and state a prediction.

Hypothesis:

Experiment:

Prediction:

3.Red-cockaded woodpecker. A federally endangered species that lives in old growth longleaf pine forests of the southeastern U.S.

Barry Mansell/Nature Picture Library

The red-cockaded woodpecker (Picoides borealis), listed as a federally endangered species, lives in old growth longleaf pine forests of southern Georgia and other southeastern states (Figure 9), Populations of these birds are declining because of loss of suitable habitat. Red-cockaded woodpeckers excavate nesting holes primarily in living longleaf pines with red heart disease, a fungus that affects the tree's heartwood. The ideal forest has short, sparse undergrowth, usually maintained by fire. Establishing new populations of these woodpeckers is limited by their preference to colonize sites with existing nesting holes, rarely moving into new territories, perhaps because of the high energy demands of excavating new cavities, which can take from 10 months to several years. Hoping to find management techniques to help increase populations of these birds, four researchers from North Carolina State University questioned if artificially constructed nesting cavities could be used to increase family groups of birds. They hypothesized that artificially constructed cavities in unoccupied habitats or those abandoned because of unsuitable cavities would increase groups of birds (Walters et al., 1992).

To test this hypothesis they identified 20 suitable sites that had not been previously occupied and contained trees suitable for cavities. In 10 of these sites, they constructed clusters of new cavities. In the remaining 10, they constructed no cavities. In addition to the new sites, they chose 20 abandoned sites with trees suitable for cavities. In 10 of the sites, they constructed new cavities, but in the remaining 10 they constructed no cavities.

What prediction might the researchers make based on their hypothesis and experiment?

The results of the experiment show, of the 20 sites with constructed artificial cavities, 18 were subsequently occupied (Table 6).

In this experiment, what is the independent variable?

What is the dependent variable?

Identify the controls.

How many replicates were used?

What controlled variables might need to be considered in designing this experiment?

 

Artificial Cavities

No Artificial Cavities

 

Unoccupied

Abandoned

Unoccupied

Abandoned

Total Number of Sites

10

10

10

10

Groups Nesting

9

9

0

0

 

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