IV Detective
A scientist wants to know whether the amount of sunlight affects plant growth.
The scientist changes the amount of sunlight.
What is the independent variable?
Amount of sunlight
A scientist changes the amount of sunlight given to plants and measures plant height.
What is the dependent variable?
Plant height/growth
What is the main purpose of a control group?
A. To receive every treatment
B. To provide a comparison
C. To change the IV
D. To collect no data
B — To provide a comparison.
A student changes only the amount of water given to identical plants and measures their growth.
Is this generally a fair experiment?
Yes.
A student wants to test whether water temperature affects how quickly sugar dissolves.
They use different amounts of sugar in each cup.
What should they change to make the experiment fair?
Use the same amount of sugar in each cup.
A student investigates whether drinking different amounts of water affects how often a person needs to use the restroom.
What is the independent variable?
Amount of water consumed
A student investigates whether music affects reaction time.
What is the dependent variable?
Reaction time
A student tests whether fertilizer affects plant growth.
Both groups receive the same:
What do these factors represent?
Constants
A student tests whether music affects memory.
Fair or invalid? Explain.
Fair. The main factor being changed is the presence of music, while important factors are kept the same.
A student wants to test whether exercise affects pulse rate.
They measure one student's pulse before exercise but measure another student's pulse after exercise.
What should they change?
Measure the same participant under both conditions, or use equivalent groups with consistent measurement conditions.
A scientist investigates whether exercise intensity affects heart rate.
Group A walks for 5 minutes.
Group B jogs for 5 minutes.
What is the independent variable?
Exercise intensity/type
A scientist investigates whether physical activity affects breathing rate.
What should the scientist measure for the dependent variable?
Breathing rate, such as breaths per minute.
A student tests whether a medicine lowers body temperature.
Group A receives the medicine.
Group B does not.
Which group is the control/comparison group, and why?
Group B, because it provides a comparison to the group receiving the medicine.
A student tests whether exercise affects heart rate.
What makes this experiment unfair?
Multiple important factors are different between the groups, including exercise duration and when heart rate is measured.
A student writes this procedure:
"Exercise and check your pulse."
What is wrong with this procedure, and how could it be improved?
It is too vague. It should specify the type and duration of exercise, how pulse will be measured, how long it will be measured, when it will be measured, and how the data will be recorded.
A student wants to know whether water temperature affects how quickly sugar dissolves.
The student uses:
What is the independent variable, and why?
Water temperature because it is the factor the student intentionally changes.
A student asks:
"How does water temperature affect the amount of sugar that dissolves?"
The student measures how many grams of sugar dissolve.
What is the DV?
Amount of sugar dissolved.
A student tests whether exercise affects pulse rate.
Which should be kept constant?
A. Exercise amount
B. Pulse rate
C. Measurement method
D. The results
C — Measurement method.
A student investigates whether sunlight affects plant growth.
Plant A receives 4 hours of sunlight and 100 mL of water.
Plant B receives 8 hours of sunlight and 200 mL of water.
Both plants are measured after two weeks.
Is this a fair experiment? Explain.
No. Both sunlight and water amount are changed, so the student cannot determine whether sunlight, water, or both caused the difference in growth.
A student wants to determine whether physical activity affects breathing rate.
Their procedure says:
Identify TWO problems and explain how you would fix them.
Possible problems:
A student wants to determine whether physical activity affects pulse rate.
Their plan is:
What is the independent variable? Explain why this experiment may make it difficult to determine exactly what caused changes in pulse rate.
The amount/type of physical activity is the IV. The activity and duration are changing between trials, making it difficult to determine which difference caused the change in pulse rate.
A student is testing whether exercise affects heart rate.
They record:
Which measurement should be the dependent variable if the research question is "How does exercise affect heart rate?" Explain why.
Heart rate, because it is the outcome being measured to determine how it changes in response to exercise.
A student says:
"My experiment is fair because I have a control group."
Is the student correct?
Explain why or why not.
Not completely. A control group helps provide a comparison, but a fair experiment also requires important factors to remain constant and a clear IV and DV.
A student tests whether a new medicine lowers body temperature.
The student records the patient's temperature before and after taking the medicine.
The temperature decreases.
The student concludes:
"The medicine definitely caused the temperature to decrease."
Is this conclusion fully supported by the experiment? Explain what is missing.
No. There is no control/comparison condition. Other factors could have caused the temperature to change. A comparison group or condition would provide stronger evidence.
A student says:
"If my results are different from what I predicted, my experiment failed."
Do you agree or disagree?
Scientists don't change the data to match their prediction. They use the data to determine what the evidence shows.