Designing Controlled Experiments
Important Terms:
Experimental Question: What is this experiment about?
Hypothesis: If I change (independent variable), then the (dependent
variable) will change… because
Independent Variable: the variable that is deliberately changed
Dependent Variable: the response that changes because of the
independent variable; it is usually measured
Control: Comparison, the one that you do not add the independent
variable to
Constant: Everything must be kept the same
Conclusion: A wrap up of the experiment.
Lab Report Format
In general lab reports will be written in the following format:
I. Introduction: this section explains the purpose of doing the lab. It
is here that you give background information on the general topic
this lab is studying.
II. Experimental Question: Clearly written experimental question,
which accurately states what is being investigated.
III. Hypothesis: Your hypothesis for this lab, written in proper
If…Then…Because format.
IV. Procedures: You explain in list/numbered form the steps you
took during the experiment.
V. Results/Data: Observations, sketches, diagrams, tables, charts,
&/or graphs.
VI. Discussion: Explain your results (put your observations, diagrams
etc. into paragraph form) why you obtained the results that you did,
were they expected, why or why not.
Includes the question to be answered, your hypothesis, date & time
experiments were performed, procedures, observations, essential
results gathered during the lab, any errors that may have occurred
that had an effect on the experimental results and essential data,
including graphs & diagrams gathered during the lab used to answer
the initial question. Also how correct were you with your hypothesis?
*Lab reports will include the headings for each section (underlined
above)
*Results and discussions are generally worth more points
*Individual labs will have specific instructions
Experiment 1:
Nick & Brandon wanted to know if light influenced how fast a seed would germinate
(sprout). They took 30 bean seeds and divided them into 5 groups. Each group of 6 seeds
was planted in the same sized container, and given the same amount of water. The five
containers of seeds were then placed in different locations in the lab (see below) and
observed every 3 days for a period of one month.
Container 1 (in closed cabinet)
Container 2 (in front of window)
Container 3 (on front demo table)
Container 4 (under gro-lights for 8 hrs/day)
Container 5 (under gro-lights for 24 hrs/day)
1. What is the experimental question?
2. What is the independent variable in this experiment?
3. What is the dependent variable?
4. What is the control?
5. What things are kept constant?
6. What other things should be kept constant?
7. What do you predict will happen in this experiment?
Experiment 2:
After studying recycling, members of Jamie’s biology class investigated the effect of various
recycled products on plant growth. Jamie’s lab group compared the effect of different aged
grass compost on bean plants. Because decomposition is necessary for the release of
nutrients, the group hypothesized that older grass compost would produce taller bean plants.
Three flats of bean plants (25 plants/flat) were grown for 5 days. The plants were fertilized
as follows:
1.
2.
3.
Flat A: 450g of 3-month-old compost
Flat B: 450g of 6-month-old compost
Flat C: 0g of compost
1. What is the experimental question?
2. Write the hypothesis (If (IV), then (DV), because.
3. Why was Flat C included in this study?
4. What factors need to be kept the same for all three plants?
5. What do you predict will happen in this experiment to all 3 flats?
Experiment 3:
Caleb wondered if the height of a hole punched in the side of a quart-sized milk
carton would affect how far from the container a liquid would spurt when the carton was
full of liquid.
He used 4 identical cartons & punched the same size hole in each. A hole was placed
at a different height on one side of each of the containers. The height of the holes varied in
increments of 5 cm, ranging from 5cm to 20 cm from the base of the carton.
He put his finger over the holes and filled the cartons to the height of 25 cm with a
liquid. When each carton was filled to the proper level, he placed the carton in the sink and
removed his finger.
Caleb measured how far away from the carton’s base the liquid had spurted when it
hit the bottom of the sink.
1. What is the experimental question?
2. Write the hypothesis (If (IV), then (DV), because.
3. What is the independent variable in this experiment?
4. What is the dependent variable in this experiment?
5. What is the control in this experiment?
6. What was kept constant?
Experiment 4:
In chemistry class, John determined the effectiveness of various metals in releasing
Hydrogen gas from Hydrochloric acid. Metals that are very active release a lot of Hydrogen
gas from Hydrochloric acid.
Several weeks later, John read that a utilities company was burying lead next to iron
pipes to prevent rusting. John hypothesized that less rusting of the iron pipe would occur
with more active metals.
He set up the following experiment to test his hypothesis:
He placed the following into separate beakers of water…
a) an unwrapped iron nail
b) one iron nail wrapped in an aluminum strip
c) one iron nail wrapped in a magnesium strip
d) one iron nail wrapped in a lead strip
John used the same amount of water in each beaker, equal amounts of each metal, and the
same type of iron nails.
At the end of 5 days, he rated the amount of rusting as small, moderate, or large. He also
recorded the color of the water.
1. What was the experimental question?
2. Write the hypothesis (If (IV), then (DV), because.
3. What is the independent variable?
4. What is the dependent variable?
5. What is the control?
6. What things did John keep constant?
7. How could this experiment be improved? List all of the specific improvements.