Controlled Experiment Lesson

Experimental Design
Scientist conduct controlled experiments to answer questions and provide
evidence to support hypotheses.

Important concept: In a controlled experiment
we can only test one variable at a time. All other
variables that may affect the outcome must be
held constant.

Key terms:

●Controlled experiment

●Variable

●Independent variable

●Dependent variable

●Controlled variables aka: constants

●Experimental group

●Control group

A controlled experiment is an experiment where
you change one thing (independent variable) and
measure how this change affects something else
(dependent variable). In doing so, you must control
(hold constant) all other variables that may affect the
outcome of the experiment.

Multiple Choice

In a controlled experiment how many variables are purposely changed by the experimenter?

• five

• one

• zero

• 67

Multiple Choice

Before conducting an experiment you must have a

• theory

• testable hypothesis

• conclusion

• observation

In a controlled experiment, you’ll need to focus on 3 types
of variables

Independent variable: The variable the experimenter purposely changes to see if
it will affect the dependent variable.

Example: amount of sunlight plants receive

Dependent variable: The variable that is observed or measured to see if it
changes response to the independent variable.

Example: The height of the plants

Controlled variables: variables that are held constant throughout the experiment

Example: Type of plant, amount of water, type of soil, temperature

Multiple Choice

The variable in an experiment that is allowed to change and observed or measured to see if it changes is called the __________________.

• control group

• dependent variable

• controlled variables

• independent variable

Multiple Choice

The variable in an experiment that is purposely changed by the experimenter is called the ____________________.

• dependent variable

• experimental group

• independent variable

• controlled variables

Multiple Choice

A controlled variable is best described by which of the following?

• the variable in an experiment that is purposely changed by the experimenter

• a variable that is allowed to change

• a variable that is intentionally kept the same throughout the experiment

• a variable that is observed or measured and changes are recorded

When doing experiments involving living subjects you will need to
establish 2 groups

Control group: the group that does not receive the IV. It serves as a baseline to
compare the results of the experimental group

Example: The group of plants that receive no extra light (natural light only)

Experimental group: This group receives the IV. If multiple levels of the IV are
being tested, there will be more than one experimental group.

Example: Plants that receive extra light.

Key point: The control group is essential because it helps you see the difference
caused by the IV

Multiple Choice

The group of organisms or objects that does not receive the treatment (independent variable) is called the:

• control group

• experimental group

• controlled variable

• hypothetical group

Multiple Choice

In an experiment, the experimental group is the:

• group of organisms or objects that does receive the treatment (independent variable)

• group of organisms or objects that does NOT receive the treatment (independent variable)

• group of scientists who like doing experiments

• a rock band that performs songs about science

Now it’s time to plan and conduct your experiment

●Plan and write a procedure for your experiment with the following
considerations

○How will you measure/ observe the possible changes to the DV?

○How will you manipulate the IV?

○How will you hold controlled variables constant?

○How will you set up the experimental group and control group?

○Logical sequence of steps to carry out the experiment

●Do the experiment

●Collect and record data in a data table

●Organize the data by creating an appropriate graph

●Make a conclusion - Use the CER framework

Reorder

Reorder the following in the sequence of events to conduct a controlled experiment.

• Testable hypothesis

• Identify variables

• Plan and write procedure

• Collect data from your experiment

• Use CER to make a conc

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Match

Match the following

• variable changed by the experimenter

• variables not allowed to change

• group that serves as a basis of comparison

• group where the IV is changed

• variable that is allowed to change and measured

Independent variable

controlled variables

control group

experimental group

dependent variable

• Independent variable

• controlled variables

• control group

• experimental group

• dependent variable

Multiple Choice

A group of scientists want to determine if increases in temperature affects the amount of dissolved carbon dioxide gas in water. To find out they use 10 equal sized samples of water from a local lake. The temperature of each sample was changed so that there were 10 different temperatures to analyze. The amount of dissolved carbon dioxide was measured and recorded for each sample. 

For this experiment, what was the independent variable?

• amount of dissolved carbon dioxide

• amount of water

• water source

• temperature of the water

Multiple Choice

An advertisement claims that a certain brand of fertilizer designed to be applied to a plant's leaves will lead to more plant growth than ordinary fertilizer that is absorbed through the roots. A student doing a science fair project decides to test this claim. Her experimental design is as follows.

3 groups of 10 Roma tomato plants (Group A had no fertilizer applied, Group B had fertilizer applied to the leaves, and Group C had the fertilizer applied to the roots.

All the plants of similar size were transplanted into standard 12 inch terra cotta pots using 1 kg of the same brand of potting soil.

Each plant was watered 250 ml of water each day at the same time of day.

The plants were allowed to grow for 3 weeks in a standard green house that was maintained at a temperature of 25 degrees Celsius.

The mass of the plants was measured at the beginning and end of the study.

What was the dependent variable for this experiment?

• height of the plants

• type of fertilizer used

• mass of the plants

• amount of water given to the plants