Study Island: Experimental Design

Zoe is performing an experiment on plants. During her investigation, she forms the following hypothesis. If a leaf has a smaller surface area, then it has a better chance of surviving when there is little water available. What is the independent variable in Zoe's experiment?

the surface area of the leaf

Dr. Torres discovers a new drug that he hypothesizes will decrease fat storage in mice. He designs an experiment to test his hypothesis. Dr. Torres separates twelve mice into two equal groups and measures their body fat individually. He gives one group of mice the drug but does not give the drug to the other group. He keeps everything else about the mice's living environment the same, including the amount of water and food provided. After a month, he measures the body fat of the mice in both groups. The group of mice that is not given the drug is known as the control. Why do scientists use controls when designing experiments?

At the end of an experiment, the control group is compared to the experimental group in order to determine if the factor had the hypothesized effect.

Why are multiple trials necessary in scientific investigations?

Multiple trials reduce the impact of random measurement errors on the overall results.

An excerpt from the procedure of an experiment is shown below. "In order to determine the effectiveness of various enzymes on the rate of a reaction, we prepared six samples, adding a different enzyme to each sample. Each sample was kept at 70°C for the duration of the reaction..." Based on the information in the excerpt, which of the following is true?

One sample should have had no enzyme and acted as a control.

A biologist is conducting an experiment to determine how light affects the reproduction of Bacteria X. The biologist is trying to decide the best way to conduct his experiment in order to collect meaningful data. Which of the following experiments would help him collect the best data?

Place a Petri dish with Bacteria X in a lighted area and a Petri dish with the Bacteria X in a darkened area, and then observe the rate of reproduction over time.

Prior to starting their science fair investigations, the students in Mrs. Hensley's biology class are required to submit a summary of their experimental designs. One student submitted the following: Hypothesis: Fertilizer X increases fruit production in tomato plants. Procedure: Two tomato seeds will be germinated at the same time. Each germinated seed will be placed in a separate 500 mL container. Exactly 500 g of soil will be added to each container, and the germinated seeds will be placed 1 cm below the surface. 20 g of Fertilizer X will be added to one plant. 0 g of Fertilizer X will be added to the second plant. Each plant will receive the same amount of water and light each day. After 60 days, the total number of tomatoes produced by each plant will be counted The teacher identified a problem with the procedure and asked the student to revise the method. Which of the following is a problem with the student's procedure?

The procedure is lacking multiple trials.

Examine the table below. It shows the results of an experiment done to test the hypothesis that a certain brand of pesticide would eliminate scorpion egg production. Which variable was manipulated in the experiment?

amount of pesticide

the factor in an experiment that serves as a comparison in order to determine the magnitude of the experiment's results

control

the factor in an experiment that responds to changes in the manipulated variable

dependent variable

Each time a scientist repeats an experiment, he or she is performing a trial. Which of the following would add support to a scientific explanation based on the results of several different trials?

getting the same results for each trial of the experiment

the factor in an experiment that is purposely changed by the researcher

independent variable

A scientist forms a hypothesis and conducts an experiment to test it. The experimental results support the hypothesis. What could the scientist do next to improve the reliability of his results?

repeat an experiment

A scientist performs an experiment. The results of his experiment contradict a theory that is well-known in the scientific community. The scientist should

repeat his experiment to see if he was correct.

Marissa has observed that bread spoils faster in her pantry during the summer months than during the winter months. Based on this observation, she hypothesizes that cooler temperatures slow the growth of mold on bread. She decides to test the following prediction: "If bread is placed in the refrigerator at 2°C, then mold will not appear as quickly as it does on bread that is stored in the pantry at 20°C." What data should Marissa collect during her experiment?

temperature at which the bread is stored number of days before mold appears

Dr. Grey discovers a new drug that she hypothesizes will increase fat storage in rabbits. She designs an experiment to test her hypothesis. Dr. Grey separates twelve rabbits into two equal groups and measures their body fat individually. She gives one group of rabbits the drug but does not give the drug to the other group. She keeps everything else about the rabbits' living environment the same, including the amount of water and food provided. After a month, she measures the body fat of the rabbits in both groups. What is the control in Dr. Grey's experiment?

the group of rabbits that are not given the drug

When organisms perform normal metabolic processes, hydrogen peroxide is often created as a byproduct. Hydrogen peroxide can be harmful to cells, however, so organelles known as peroxisomes release an enzyme known as catalase to break down hydrogen peroxide into water and oxygen. 2 H2O2 + catalase → O2 + 2 H2O Emily wanted to perform an experiment to test how temperature affects the action of catalase. To do this, she obtained four identical test tubes and poured 5 mL of hydrogen peroxide into each tube. Then, she placed the tubes into separate incubators set at 5°C, 25°C, 35°C, and 45°C. She allowed the tubes to equilibrate at their respective temperatures for 20 minutes and then added exactly 1 mL of cold catalase to each tube. After three minutes, she added 6 mL of sulfuric acid to each tube to stop the reaction. Finally, she titrated each solution to determine the amount of hydrogen peroxide remaining in each tube. Which of the following factors was allowed to change during Emily's experiment?

the temperature of each incubator the amount of hydrogen peroxide remaining in each tube

Protists are microscopic organisms that are found in aquatic ecosystems. A student wonders if protists are more common at certain depths than others. After considering factors such as photosynthesis, the student hypothesizes that the surface waters of his neighborhood pond contain the greatest number of different protist species. To test his hypothesis, the student collects several water samples from different depths in the same region of his neighborhood pond. Which data must be collected from the samples in order to address the hypothesis?

the total number of protist species in each sample