Unit 1 Target 1: Experimental Design

1. How many independent variables should there be in a controlled experiment?

In a controlled experiment, there should be only one independent variable. This is because the purpose of a controlled experiment is to isolate and manipulate a single factor to observe its effect on the dependent variable. By controlling all other variables, the researcher can confidently attribute any changes in the dependent variable to the manipulation of the independent variable. Having multiple independent variables would make it difficult to determine which variable is responsible for the observed changes in the dependent variable.

Explanation

In a controlled experiment, there should be only one independent variable. This is because the purpose of a controlled experiment is to isolate and manipulate a single factor to observe its effect on the dependent variable. By controlling all other variables, the researcher can confidently attribute any changes in the dependent variable to the manipulation of the independent variable. Having multiple independent variables would make it difficult to determine which variable is responsible for the observed changes in the dependent variable.

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2. Other than the independent variable, all other factors in the experiment should be kept ___ for both the experimental group and control group.

In order to accurately measure the effect of the independent variable, it is important to keep all other factors constant or the same in both the experimental group and control group. This ensures that any differences observed between the groups can be attributed solely to the independent variable and not to any other factors. Keeping all factors identical further ensures that there are no variations or discrepancies that could potentially affect the results of the experiment.

Explanation

In order to accurately measure the effect of the independent variable, it is important to keep all other factors constant or the same in both the experimental group and control group. This ensures that any differences observed between the groups can be attributed solely to the independent variable and not to any other factors. Keeping all factors identical further ensures that there are no variations or discrepancies that could potentially affect the results of the experiment.

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3. Mrs. Lewis set up a lab for her biology students using a culture of the small crustacean Daphnia, obtained from a pond that was 20°C. The students are to investigate the effect temperature has on Daphnia. The students will observe the crustacean's heartbeat under the microscope, at the following temperatures: 0°C, 10°C, 20°C, 30°C, and 40°C. They will count the number of heartbeats per sec.What is the independent variable in the experiment?

Number of heartbeats/sec

Temperature of the samples

Type of microscope used

Number of Daphnia in the cultures

The independent variable in the experiment is the temperature of the samples. This is because the students are investigating the effect temperature has on Daphnia's heartbeat. They are changing the temperature of the samples and observing how it affects the number of heartbeats per second. The other options, such as the number of heartbeats per second, type of microscope used, and number of Daphnia in the cultures, are not being manipulated by the students and are therefore not independent variables in this experiment.

Explanation

The independent variable in the experiment is the temperature of the samples. This is because the students are investigating the effect temperature has on Daphnia's heartbeat. They are changing the temperature of the samples and observing how it affects the number of heartbeats per second. The other options, such as the number of heartbeats per second, type of microscope used, and number of Daphnia in the cultures, are not being manipulated by the students and are therefore not independent variables in this experiment.

4. Morgan hypothesizes that the activity of amylase, an enzyme that catalyses the breakdown of starch, will be greater at 37°C than at 25°C. She prepares 2 tubes: Tube 1 and Tube 2. Morgan adds 2 g of starch and 1 mL of an enzyme suspension to Tube 1 and incubates it at 37°C for 20 min. To accurately test her hypothesis, Morgan should add 2 g of the starch and 1 mL of the enzyme suspension to Tube 2 and incubate it at ______ for ______.

25°C; 20 min

37°C; 20 min

25°C; 10 min

37°C 10 min

The correct answer is 25°C; 20 min. Morgan's hypothesis is that the activity of amylase will be greater at 37°C than at 25°C. To accurately test this hypothesis, Morgan needs to have a control group to compare the results to. Tube 1 serves as the experimental group, where the enzyme activity is being tested at 37°C. Tube 2 should be the control group, where the same conditions are applied except for the temperature. By incubating Tube 2 at 25°C for 20 min, Morgan can compare the activity of amylase at different temperatures and determine if her hypothesis is correct.

Explanation

The correct answer is 25°C; 20 min. Morgan's hypothesis is that the activity of amylase will be greater at 37°C than at 25°C. To accurately test this hypothesis, Morgan needs to have a control group to compare the results to. Tube 1 serves as the experimental group, where the enzyme activity is being tested at 37°C. Tube 2 should be the control group, where the same conditions are applied except for the temperature. By incubating Tube 2 at 25°C for 20 min, Morgan can compare the activity of amylase at different temperatures and determine if her hypothesis is correct.

5. Dr. Hansen performs an experiment testing the effectiveness of different cough syrups. Identify the dependent variable in the experiment.

Type of cough syrup

Effectiveness of the cough syrup

Number of people taking each cough syrup

Number of days people take each cough syrup

The dependent variable in the experiment is the effectiveness of the cough syrup. This is because the effectiveness of the cough syrup is being measured and is expected to change based on the different types of cough syrup being tested. The other options, such as the type of cough syrup, number of people taking each cough syrup, and number of days people take each cough syrup, are not being measured or expected to change in response to the different cough syrups being tested.

Explanation

The dependent variable in the experiment is the effectiveness of the cough syrup. This is because the effectiveness of the cough syrup is being measured and is expected to change based on the different types of cough syrup being tested. The other options, such as the type of cough syrup, number of people taking each cough syrup, and number of days people take each cough syrup, are not being measured or expected to change in response to the different cough syrups being tested.

6. Lydia works in a flower shop after school. She notices that the hydrangeas inContainer 1 have pink blossoms, while the hydrangeas in Container 2 have blueblossoms. She makes sure they all receive the same amount of light and water. Her boss tells her that the flowers were all grown from the same seed variety. Lydia discovers, after testing the soil, that although the same type of soil was used, the soil in Container 1 has a pH of 6.0, and the soil in Container 2 has a pH of 5.0.Lydia most likely conducted her investigation to answer what question about hydrangeas?

How does the chemistry of the soil affect the color of hydrangea blossoms?

What role do genetic factors play in hydrangea color?

Do varying degrees of light affect hydrangea color?

What type of soil will produce a hydrangea with both pink and blue blossoms?

Lydia conducted her investigation to answer the question of how the chemistry of the soil affects the color of hydrangea blossoms. She noticed that the hydrangeas in Container 1 had pink blossoms while the ones in Container 2 had blue blossoms. Despite receiving the same amount of light and water and being grown from the same seed variety, the only difference was the pH of the soil in each container. This suggests that the pH of the soil plays a role in determining the color of the hydrangea blossoms.

Explanation

Lydia conducted her investigation to answer the question of how the chemistry of the soil affects the color of hydrangea blossoms. She noticed that the hydrangeas in Container 1 had pink blossoms while the ones in Container 2 had blue blossoms. Despite receiving the same amount of light and water and being grown from the same seed variety, the only difference was the pH of the soil in each container. This suggests that the pH of the soil plays a role in determining the color of the hydrangea blossoms.

7. Mrs. Lewis set up a lab for her biology students using a culture of the small crustacean Daphnia, obtained from a pond that was 20°C. The students are to investigate the effect temperature has on Daphnia. The students will observe the crustacean's heartbeat under the microscope, at the following temperatures: 0°C, 10°C, 20°C, 30°C, and 40°C. They will count the number of heartbeats per sec.If the experiment is designed correctly, what will the students choose for the experimental treatment?

Placing 5 identical cultures of Daphnia at 20°C

Placing each of 5 identical cultures of Daphnia at a different temperature

Placing 5 cultures, each with a different type of crustacean, at 20°C

Placing 5 cultures, each with a different type of crustacean, at a different temperature

The students will choose to place each of 5 identical cultures of Daphnia at a different temperature for the experimental treatment. This is because the students want to investigate the effect of temperature on Daphnia's heartbeat. By exposing each culture to a different temperature, they can compare the number of heartbeats per second at each temperature and determine how temperature affects the crustacean's heartbeat. Placing identical cultures ensures that any differences observed in the heartbeats can be attributed to the temperature variation rather than any other factors.

Explanation

The students will choose to place each of 5 identical cultures of Daphnia at a different temperature for the experimental treatment. This is because the students want to investigate the effect of temperature on Daphnia's heartbeat. By exposing each culture to a different temperature, they can compare the number of heartbeats per second at each temperature and determine how temperature affects the crustacean's heartbeat. Placing identical cultures ensures that any differences observed in the heartbeats can be attributed to the temperature variation rather than any other factors.

8. Ebola virus is a potentially deadly virus in the blood which causes Ebola fever. Ebola virus is often spread by monkeys. Scientists used 2 groups of monkey kidney cells in an experiment to confirm the first human case of Ebola fever. The scientists inoculated cells in Group 1 with samples of the Ebola virus taken from a human with Ebola fever. They did not inoculate the cells in Group 2. What was the control group in the experiment?

The Ebola virus

All of the monkey kidney cells

Monkey kidney cells in Group 1

Monkey kidney cells in Group 2

The control group in the experiment was the monkey kidney cells in Group 2. This group did not receive any inoculation of the Ebola virus, serving as a baseline comparison for the experimental group (Group 1) that did receive the virus. By comparing the results of the two groups, the scientists can determine the effects of the Ebola virus on the monkey kidney cells.

Explanation

The control group in the experiment was the monkey kidney cells in Group 2. This group did not receive any inoculation of the Ebola virus, serving as a baseline comparison for the experimental group (Group 1) that did receive the virus. By comparing the results of the two groups, the scientists can determine the effects of the Ebola virus on the monkey kidney cells.

9. Aisha wants to conduct an experiment to determine whether sun and shade varieties of the same plant species prefer the same wavelengths of light. She plans to measure rates of photosynthesis. Which design would be best for her experiment.

1 plant of the sun variety tested under blue light only, and 1 plant of the shade variety tested under blue light only

4 plants of the sun variety: 1 tested under blue light, 1 under green, 1 under red, and 1 under yellow light with 4 plants of the shade variety: 1 tested under blue light, 1 under green, 1 under red, and 1 under yellow light

10 plants of the sun variety tested under blue light only; and 10 plants of the shade variety tested under blue light only

40 plants of the sun variety: 10 tested under blue light, 10 under green, 10 under red, and 10 under yellow light with 40 plants of the shade variety: 10 tested under blue light, 10 under green, 10 under red, and 10 under yellow light

The best design for Aisha's experiment is to have 10 plants of the sun variety tested under blue light only, and 10 plants of the shade variety tested under blue light only. This design allows for a direct comparison between the sun and shade varieties under the same conditions, specifically focusing on the effect of blue light on photosynthesis. By controlling for other variables such as the type of light, Aisha can determine whether the sun and shade varieties prefer the same wavelengths of light. This design also provides a large enough sample size to ensure reliable results.

Explanation

The best design for Aisha's experiment is to have 10 plants of the sun variety tested under blue light only, and 10 plants of the shade variety tested under blue light only. This design allows for a direct comparison between the sun and shade varieties under the same conditions, specifically focusing on the effect of blue light on photosynthesis. By controlling for other variables such as the type of light, Aisha can determine whether the sun and shade varieties prefer the same wavelengths of light. This design also provides a large enough sample size to ensure reliable results.

10. Scientific experimentation can most likely answer which question regarding a bird population?

How does a baby bird learn to recognize the type of food it can eat?

How does the type of food a bird eats affect the number of offspring it produces?

What is the relationship between beak size and the number of offspring a bird produces?

Why does a bird with a very short beak produce more offspring than a bird with a very long beak?

Scientific experimentation can most likely answer the question "What is the relationship between beak size and the number of offspring a bird produces?" because through controlled experiments, researchers can measure and compare the beak sizes of different bird populations and observe the number of offspring they produce. By analyzing the data collected, scientists can determine if there is a correlation or relationship between beak size and the number of offspring. This type of experimentation allows for a systematic investigation of the variables involved and can provide insights into the impact of beak size on reproductive success in birds.

Explanation

Scientific experimentation can most likely answer the question "What is the relationship between beak size and the number of offspring a bird produces?" because through controlled experiments, researchers can measure and compare the beak sizes of different bird populations and observe the number of offspring they produce. By analyzing the data collected, scientists can determine if there is a correlation or relationship between beak size and the number of offspring. This type of experimentation allows for a systematic investigation of the variables involved and can provide insights into the impact of beak size on reproductive success in birds.