The Scientific MethodVariables

(Biology – Unit 1)

What is a variable?

What types of variables are there?

Variables

Controlled(Do not change)

Independent(Manipulated)

Dependent(Responding)

Independent Variable (Manipulated)

The variable that is manipulated or changed in an experiment.

• The one you are going to change.

• What you did. The treatment

• The Cause”

• Plotted on the x-axis on a graph.

Dependent Variable(Responding)

The variable that responds due to changes in manipulated variable.

• What you measure or observe

• What happened

• “The Effect”

• Plotted on the y-axis on a graph.

Controlled Variables

Things we keep the same in an experiment, since we are not testing or measuring a response in them.

• Things you keep constant, don’t change during an experiment.

• The constants during an experiment.

Example of Identifying Variables in an Experiment

• A student was investigating the things that affected how candy dissolved in water. They wished to determine how the size of the candy pieces affected the time it took them to dissolve.

IV - How big the pieces are (cause)DV - Time to dissolve (effect)CV - Amount of water

- Temp of water- Time of stirring- How hard stirred- Type of container

2nd Example

• Does an electric motor turn faster if you increase the voltage?

IV - Voltage of the electricity measured in volts

DV - Speed of rotation measured in revolutions per minute

CV - Same motor for every test Time motor is on Work

3rd Example

• How fast does a candle burn? ?

IV - Time measured in minutes DV - Height of candle measured in

centimeters at regular intervals of time (for example, every five minutes)

CV - Use same type of candle for every test Wind--make sure there is none Temperature

Experimental Design

How do you set up an experiment?

An experiment is designed to test if a hypothesis is correct or not.

An easy way to do this is make a comparison between two groups, the experimental and control groups.

Experimental Set-up (Group):

• The group which is experiencing the manipulation / treatment you are testing.

• The part of the experiment in which you change a factor (independent variable).

The experimental set-up is the experiment that contains the independent VARIABLE. This is the one you change.

If you set up an experiment where you give

one set of patients aspirin and another set of patients no aspirin, then the aspirin would be the variable.

Control Set-up (Group):

• is a standard against which any change can be compared and measured

• The group in which no changes are made. You compare this group against the experimental group.

The CONTROL is a duplicate experiment that does not contain the variable. The control tells you if the variable has any effect.

In the previous experiment where aspirin was given to two groups of patients, one group would get aspirin, but another group would get a “placebo” or a pill that does not contain any active ingredients.

Scientific Method:

• A formalized process of investigation designed to solve a problem, which incorporates the testing of a hypothesis.

Steps of the Scientific Method

• 1st Identify the problem - by asking questions

• 2nd Educate yourself about the problem, research the problem.

- library- reference books, magazines - ask the experts- internet, web sites, news groups

• 3rd Hypotheses, educated guess- always stated as an

“if-then” statement

• 4th Experiment- collect and record data

• 5th Analysis of data- stat’s

(average, mean, median, mode, range, etc.)

- graphs

• 6th Conclusions- Was your hypothesis correct or

not.- What does it mean?

• 7th Applications of findings

• 8th Communicate Findings

Example of an experiment to test if fertilizer affects the growth rate of bean plants.

Hypothesis:Hypothesis: Your best educated guess, answer to the problem you are trying to Your best educated guess, answer to the problem you are trying to solve.solve.

Stated as an Stated as an “if –then” “if –then” statement.statement. 

Example: If fertilizer is added to the bean plant then it will grow at a faster rate.Example: If fertilizer is added to the bean plant then it will grow at a faster rate.

Control or Control GroupControl or Control Group: : is a standard against which any change can be is a standard against which any change can be comparedcompared and measured and measured

For the above experiment it would be plants For the above experiment it would be plants not givennot given fertilizer. fertilizer. 

Experimental group:Experimental group: the group which is experiencing the treatment you are the group which is experiencing the treatment you are testing.testing.

For the above experiment it would be the plants For the above experiment it would be the plants givengiven fertilizer. fertilizer.

Independent Variable: Independent Variable: Amount of Fertilizer added to the plants.Amount of Fertilizer added to the plants.

Dependent Variable: Dependent Variable: How tall the bean plants grow.How tall the bean plants grow.

Controlled Variables: Controlled Variables: Type of plants, temperature, amount of light, how much Type of plants, temperature, amount of light, how much watered, type of soil.watered, type of soil.

Forming a TheoryA theory is a well-tested explanation that makes sense of a great variety of scientific observations.

•A theory may be formed after MANY related hypotheses have been tested and supported with experimental evidence

•It serves as a broad and comprehensive statement of what is thought to be true

•Must be supported by considerable evidence that ties together related hypotheses

A law

• A theory is different than a law.

• A law allows you to make predictions about a given situation.

• i.e, the theory of evolution vs.the law of natural selection.

• i.e., The law of universal gravitation vs. the theory of general relativity