1. Aim: How are controlled experiments designed?
DO NOW
1. Define what a controlled experiment is.
2. How would you set up an experiment where you would like to see which level of salt works best to hatch brine shrimp eggs?

2. Controlled Experiment
Made up of 2 groups: control & experimental
Control group is a comparison group
Experimental group is exposed to the independent variable (manipulated variable)
A dependent variable is a responding variable
This type of experiment tests one variable at a time

3. Example Experiment
Problem: My fig plant is dying despite being watered every day.
Observation: The fig plant’s leaves are brown and falling off & the soil is very wet.
Inference: I am watering my plant too much.
Hypothesis: Fig plants do best if you only water them once a week.

4. Setting Up the Experiment
4 pots with healthy fig plants (same species)
Same pot size, same soil, same amount of sunlight (limiting variation in the experiment)
Pots are labeled A, B, C & D
Pot A: no water
Pot B: watered every day
Pot C: watered 3 times a week
Pot D: watered once a week

5. Questions Q1: Which pot is part of the control group?
Q2: Is the control group exposed to the variable?
Q3: Which pot (s) is/are part of the experimental group?
Q4: Which pot(s) is/are exposed to the independent variable?
Q5: Which pot is a standard for comparison?

6. Data Collection After a month’s time Plant A doesn’t look good
Plant B doesn’t look good either
Plant C looks a little better
Plant D is doing alright

7. Make a Conclusion
Conclusion: Of the four watering schedules we tested, fig plants seem to grow best when they’re watered once a week.
Q1: Does the conclusion support the initial hypothesis?
Q2: How can we measure growth of the fig plants?

8. Summary Questions Q1: Can a hypothesis be revised?
Q2: Should a small or large sample size be used when designing a controlled experiment?
Q3: Should an experiment be conducted only once?

10. Brainpop Video

11. Homework
Please complete the handout on identifying controls and variables (Simpsons)