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ACT Science: Scientific Investigation

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By the end of this lesson, you will be able to: • Recognize the steps of scientific methods and experiments • Distinguish between dependent and independent variables • Use approximations and inferences to obtain unspecified values • Combine results from multiple experiments to make conclusions

Scientific Investigation Learning Objectives

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Essential Steps of Experimentation The Scientific Method

The purpose of an experiment is the main idea. The method is how the researchers set up the experiment. The results are what the researchers have found out.

What phenomenon do the researchers want to understand? What question or problem is the researcher trying to solve?

What have the researchers kept constant or changed? What apparatus or procedure was used?

What is shown in any charts, graphs, or tables? Are there any clear trends or obvious outliers in the data?

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The Scientific Method Passage I Enzymes serve as catalysts (compounds that increase the rate of a chemical reaction but are themselves not used up) during digestion. The enzyme trypsin is involved in the breakdown of proteins into smaller subunits during digestion. A student investigated the effects of temperature, incubation time, and pH on enzyme activity.

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The Scientific Method

Experiment 1 To each of 11 test tubes, 6 milliliters (mL) of a casein (a protein) solution was added. One mL of a trypsin solution was added to each of Tubes 1–10. Tube 11 received 1 mL of water without trypsin. The tubes were then stirred in water baths at various temperatures, and incubated (heated) from 0 to 15 minutes (min). After incubation, 0.1 mL of CaCl2 solution was added to each tube. CaCl2 stops the reaction and forms a precipitate (solid) with the protein that is not broken down by the trypsin. The precipitates were removed from the tubes and dried. The masses of the precipitates, in milligrams (mg), were measured to determine the relative amount of protein that remained in each tube. The results are in Table 1.

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The Scientific Method Experiment 2 To each of 6 test tubes, 6 mL of casein solution and 1 mL of trypsin solution were added. Tubes were adjusted to various pHs. Each tube was stirred and incubated at 25°C for 10 min. The relative amount of protein present in each tube was determined as in Experiment 1. The results are in Table 2.

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Independent and Dependent Variables Experimental Design

A variable is something that can be changed. The independent variables of an experiment are the factors changed by the experimenter. The dependent variable are the factors that are changing because of the independent variables. The controlled variables (or constants) are parts of the study that the researchers keep constant.

Scientists do experiments to understand the relationship between variables. What specific data are they trying to find out? What is on the x-axis of any graphs? The first column(s) of a table?

What occurred when the scientists changed the independent variable? What is on the y-axis of any graphs? The last column of a table?

What stays the same during the experiment? Between multiple experiments?

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Experimental Design

1. In which of the following ways are the designs of Experiments 1 and 2 different?

A. B. C. D.

A larger volume of trypsin solution per test tube was used in Experiment 1 than in Experiment 2. Temperature was varied in Experiment 1 but held constant in Experiment 2. Incubation time remained constant in Experiment 1 but was varied in Experiment 2. The pH of the solutions in the tubes varied in Experiment 1 but not in Experiment 2.

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Predicting Results Using Given Information Hypothetical Data Points

Some science questions ask you to make predictions about information not given. Some predictions are between two given values. Some predictions are below the lowest value or above the highest value.

Generalize the information in the charts, tables, and graphs. Identify any trends and assume the trends continue for future values.

Identify the given values directly above and below the value given. Estimate a reasonable value using the given data and current trends.

Draw a line of best fit for the data given and extend it to the new value. Assume any trends shown continue to occur for the new range of data.

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Hypothetical Data Points

2. According to the results of both experiments, one would predict that the LEAST amount of precipitate would be formed if tubes were incubated for 12 min under which of the following conditions?

F. G. H. J.

25°C at pH of 4 25°C at pH of 8 30°C at pH of 4 30°C at pH of 8

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Common Question Types Scientific Investigation

One question type asks you to locate information in a chart or graph. Another question type asks you to understand the purpose and method of an experiment. Another question type asks you to use trends to predict unknown data.

What general concept are the researchers testing? What specific data are they trying to find out?

What have the researchers kept constant or changed? What apparatus or process was used?

Was there a difference between expected and actual outcome? Are there any clear trends or obvious outliers?

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Scientific Investigation

3. In which of the following tubes was the greatest amount of protein broken down by trypsin?

A. B. C. D.

Tube 1 Tube 3 Tube 8 Tube 10

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Identifying Similarities and Differences Multiple Experiments

Identify the independent variable, dependent variable, and controls of each experiment. Identify the purpose of the study, the methods of each experiment, and the results. Analyze each chart or graph for the variables, trends, and units of measurement.

What are the scientists trying to understand? What changes between experiments? What stays the same?

What is the point of that paragraph? How might this get tested as a question?

The independent variable is usually located on the x-axis. The dependent variable is usually on the y-axis.

Identify the trend in the data. Is it direct, indirect, or another type of pattern?

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Multiple Experiments

4. Suppose that CaCl2 had been added immediately to Tube 16 with no incubation time allowed. Based on the results of Experiment 1, one would predict that the amount of precipitate formed would have been approximately:

F. G. H. J.

2.0 mg. 2.3 mg. 2.6 mg. 3.0 mg

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Mixed Practice Passage II The seeds of some plants attract ants with a nutritious structure called an elaiosome. The ants carry the seeds to their nests, eat the elaiosomes, and then leave the seeds in a waste pile, where some seeds germinate (begin to grow). Three studies were conducted to examine this process. Study 1 For 2 plant species (A and B), seed mass per seed in milligrams (mg), elaiosome mass per seed (mg), and percentage of seed mass composed of elaiosome were recorded (see Table 1).

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Mixed Practice Study 2 Three study sites were established in order to determine the rate of seed collection by a single species of ant for the plants used in Study 1. In Site 1, Species A plants were absent; in Site 2, Species B plants were absent. Both plants were absent in Site 3. Two seed dishes were placed in each site: 1 containing 20 Species A seeds and 1 containing 20 Species B seeds. The dishes were left out for 48 hours and the number of seeds taken from each dish was recorded. The results appear in Table 2.

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Mixed Practice Study 3 The researchers planted 2,550 seeds from a third species, Species C. They also observed 2,550 Species C seeds that were planted by ants in similar environments. All seeds were observed for 2 years. Table 3 presents the results.

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Mixed Practice

5. Based on the results of Study 3, one could generalize that compared to hand-planting of seeds, ant-planting of seeds results in:

A. B. C. D.

increased seed germination. increased seed production per plant. decreased plant survival after 1 year. decreased plant survival after 2 years.

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Mixed Practice

6. Which of the following variables was controlled in the design of Study 2?

F. G. H. J.

The number of ants in each site The number of seed dishes placed in each site The mass of the elaiosome of each seed The type of seeds taken by the ants in each site

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Mixed Practice

7. According to the results of the studies, Species A and Species B are most similar in that their:

A. B. C. D.

seed masses are the same. germination rates on ant waste piles are the same. percentages of elaiosome mass per seed are the same. rates of production of seeds after 1 year are the same.

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Mixed Practice

8. In Study 2, Site 3 was used to study the:

F. G. H. J.

preference of a different ant species for the seeds of both plant species. seed preference of ants in an area in which both plant species were absent. growth and survival of both plant species in an area where ants were not present. effects of elaiosome mass on the seed preference of ants.

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Mixed Practice

9. Which of the following is a weakness of the design of Study 2 ?

A. B. C. D.

Some plants were not present at each site. Some seeds were not present at each site. The seeds may have been removed from the dishes by animals other than ants. The plants may have been eaten by animals other than ants.

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Mixed Practice

10. The results of Study 2 suggest that which of the following factors most affects the seed preference of ants?

F. G. H. J.

Seed mass Elaiosome mass Percentage of seed mass composed of elaiosome Abundance of a plant in a given area

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Now that you have completed this lesson, you should be able to: • Recognize the steps of scientific methods and experiments • Distinguish between dependent and independent variables • Use approximations and inferences to obtain unspecified values • Combine results from multiple experiments to make conclusions

Scientific Investigation Learning Objectives

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Scientific Investigation Homework

Effort and practice are the keys to Test Day Success. Now that you have completed this lesson, do the following for homework: • Click on the Practice Tab from your Online Prep Live homepage • Choose Scientific Investigation under Science • Answer 40 Questions • Don’t forget to review the explanations!