1. Experimental Design
Practice Questions

2. A student wants to test the hypothesis that adding salt to water lowers the freezing point and raises the boiling point of the water. What would be the dependent variable, independent variable and controlled variables?

3. Answer: Dependent: The freezing and boiling temperatures.
Independent: Amount of salt
Controlled: The amount of water, amount of salt, and type of thermometer.

4. A student is investigating plant growth
A student is investigating plant growth.  The student can change the amount of light, heat, and water and the richness of the soil.  During the investigations, the amount of light, heat, and water remain the same.  Only the richness of the soil changes.  What is the independent variable in the experiment?
Light
Water
Heat
Soil

5. Answer:
Soil or soil richness

6. Phil wanted to find out which laundry soap was best for removing ketchup stains.  Each soap was mixed with warm water.  It was then used to scrub a piece of ketchup-stained cloth for 5 minute.  Then the size and deepness of the stain left on the cloth was measured.
What variable(s) should be controlled in this experiment?  Choose all correct answers.
Scrubbing Time
Water Temperature
Amount of Laundry Soap
Type of Laundry Soap

7. Answer: Scrubbing Time Water Temperature Amount of Soap
The type of soap is what we are testing, that is the independent variable.

8. Aphids are eating Rose's pea plants
Aphids are eating Rose's pea plants.  She wants to test some household chemicals to see if they will kill the aphids.  What is the best experimental question for Rose to ask?
What amount of soapsuds best kills aphids?
How are soapsuds best spread over a garden?
Are red or green aphids hardest to kill?
Will soapsuds, soapduds, weed-b-dead, or weed-bee-gone kill aphids the best?

9. Answer:
Will soapsuds, soapduds, weed-b-dead, or weed-bee-gone kill aphids the best?

10. Rose has a friend named Jill
Rose has a friend named Jill. Jill has some amazing flowers in her yard, unfortunately grasshoppers are eating Jill’s flowers.  She wants to test some household chemicals to see if they will kill the grasshoppers.  She used bleach, ammonia, and dishwashing liquid in equal amounts on different places on the same rose bush.  She will count the grasshopper population after one week to see which chemical killed the most grasshopper’s. Jill forgot to include a control group which of the following would be a good control group?
Spraying a section of the flowers with plain water.
Spraying a second the flowers with the same three chemicals.
Spraying a section of the flowers with a 4th chemical
Spraying the same three chemicals on a different type of plant.

11. Answer:
Spraying a section of flowers with plain water.

12. After a two-day fishing tournament at a local lake, it was observed that in one cove the bass caught were of an unusually small mass.  A large manufacturing plant was releasing hot water into the lake at this point.  A group of middle school ecology students wanted to know if there was a relationship between the water temperature, the mass of the fish, and the amount of dissolved oxygen present in the organisms' environment.  The students set up four aquaria and stocked each with three bass. Which of the following variables must be manipulated (independent variable)?
Food
Initial mass of the fish
Water temperature
Number of fish

13. Answer:
Water temperature

14. After a two-day fishing tournament at a local lake, it was observed that in one cove the bass caught were of an unusually small mass.  A large manufacturing plant was releasing hot water into the lake at this point.  A group of middle school ecology students wanted to know if there was a relationship between the water temperature, the mass of the fish, and the amount of dissolved oxygen present in the organisms' environment.  The students set up four aquaria and stocked each with three bass. Whenever scientists carefully measure an quantity many times, they expect that…
All of the measurements will be the same.
Two of the measurements will be the same.
All but one of the measurements will be the same.
Most of the measurements will be close but not exactly the same.

15. Answer:
Most of the measurements will be close but not exactly the same.
This is why we do repeated trials to make sure the data stays consistent.

16. Scenario
The Center for Disease Control (CDC) in Atlanta has discovered a new type of influenza, named the Carolina Flu.  The symptoms are severe stomach cramps, high fever, chills and headaches.  The CDC tested many different natural remedies to cure this fast spreading disease.  The test that yielded the best results had the following hypothesis; “Ten milligrams of Cilantro per day will weaken the symptoms within twenty-four hours.”

17. Which of the following would be the best independent (manipulated) variable in this scenario?
The Center for Disease Control (CDC) in Atlanta
The Symptoms were weakened.
The Carolina Flu.
Amount of Cilantro

18. Answer:
The amount of cilantro.

19. Which of the following would be the best dependent variable in this scenario?
The Center for Disease Control (CDC) in Atlanta
The Symptoms were weakened.
The Carolina Flu.
Amount of Cilantro

20. Answer: The symptoms were weakened.
How might you measure how the symptoms were weakened?