Aim How are controlled experiments designed DO NOW

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?

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

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.

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

Questions • Q 1: Which pot is part of the control group? • Q 2: Is the control group exposed to the variable? • Q 3: Which pot (s) is/are part of the experimental group? • Q 4: Which pot(s) is/are exposed to the independent variable? • Q 5: Which pot is a standard for comparison?

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

Make a Conclusion • Conclusion: Of the four watering schedules we tested, fig plants seem to grow best when they’re watered once a week. • Q 1: Does the conclusion support the initial hypothesis? • Q 2: How can we measure growth of the fig plants?

Summary Questions • Q 1: Can a hypothesis be revised? • Q 2: Should a small or large sample size be used when designing a controlled experiment? • Q 3: Should an experiment be conducted only once?

Brainpop Video • https: //www. brainpop. com/science/scientifici nquiry/scienceprojects/

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