“Research is what

I’m doing when I

don’t know what

I’m doing” – Werner von Braun (a German

aerospace engineer and one of

the leading figures in the

development of rocket

technology in Nazi Germany

during WWII and in the United

States after)

The

“Buzz” in

AP

Biology is

Inquiry

The Experimental Design

•

Step 1 - Define a Problem Based on

Observations and Background Research

Topic Statement – (briefly) captures the meaning of the research

Focused Research Question –this defines the whole process, guides your arguments and inquiry, and provokes the interests of the reviewer

Experimental Design –summarizes the method of research

Step 1 - Define a Problem Based on

Observations and Background Research

Hulley S, Cummings S, Browner W, et al. Designing clinical research. 3rd ed. Philadelphia (PA): Lippincott Williams and Wilkins; 2007.

Examples of a Focused

Research QuestionTopic: The distribution and growth of lichens on urban pavements

Research Question: How are the distribution and growth of lichens affected by sulfur dioxide and ozone levels in the atmosphere?

Experimental Design: Thalus diameter and population density data is collected from selected sites in different parts of the city. This data is then correlated with published data on the levels of sulfur dioxide and ozone.

Examples of a Focused

Research QuestionTopic: The effectiveness of commercial antibacterial cleaning agents

Research Question: Are commercially available antibacterial cleaning agents effective at controlling the growth of E. coli on nutrient agar under laboratory conditions?

Experimental Design : Pure strain E. coli are grown on nutrient agar plates under controlled conditions. Filter paper discssoaked in samples of the antibacterial agents are placed on the agar plates and the zone of inhibition (or exclusion) is measured and compared.

Step 2 - In order to formulate an answer to our problem we must design an experiment to test our hypothesis

Hypothesis - The tentative and testable explanation for an observation.

- should be explained.

- should be quantified

- should be written as an if/then/because statement

“If we knew what we were

doing, it wouldn’t be called

research, would it?”Albert Einstein

Critical Components of the Experimental Design

Critical Components of the Experimental Design•Independent Variable - The variable you

have control over, what you can choose

and manipulate;

What is varied in the experiment (for

example, time, pH, temperature,

concentration)

•Dependent Variable(s) - What you measure

in the experiment and what is affected

during the experiment (i.e. what the

investigator measures, counts, or records;

it is being affected in the experiment

•Controlled Variables - Variables that are

kept constant during the experiment

(variables not being manipulated)

Critical Components of the Experimental Design•Control Group or Control Treatment

- The treatment or set-up that

eliminates the independent

variable or sets it at a standard

value

-Positive controls : an experimental

treatment that will give the desired

result

-Negative controls: An

experimental treatment that will

yield a negative result

Other Critical Components of the Experimental Design

•Level of Treatment - The

appropriate values to use

for the independent

variable

•Replication - The number

of times the experiment

is repeated to verify the

results

Step 3 - Procedure/Protocol - The process

used to measure the dependent variable

(must be written so that it can be repeated

accurately)

Identify the variables in the following experiments. Underline the dependant

variable and circle the independent variable. Next, suggest a control treatment and list

at least 3 controlled variables

Height of bean plants growing at different

pH levels is recorded daily for 2 weeks.

CT

CV

CV

CV

Guinea pigs are kept at different temperatures for

6 weeks. Percent weight gain is recorded.

CT

CV

CV

CV

Percent absorption by the pigment chlorophyll is

measured for red, blue, green, and yellow

wavelengths of light.

CT

CV

CV

CV

Batches of seeds are soaked in salt solutions of different

concentrations, and germination is counted for each batch.

CT

CV

CV

CV

Scientific Method

Review Problem

Agricultural scientists were concerned about the

effect of air pollution, sulfur dioxide in particular,

on soybean production in fields adjacent to

coal-powered manufacturing plants. Based on

initial investigations, they proposed that sulfur

dioxide in high concentrations would reduce the

reproduction of soybeans. They designed an

experiment to test this hypothesis (see Figure

1). In this experiment, 48 soybean plants, just

beginning to produce flowers, were divided into

two groups, treatment and non-treatment. The

24 treated plants were divided into four groups

of 6.

One group of 6 treated plants was placed in a

fumigation chamber and exposed to 0.6 ppm

(parts per million) of sulfur dioxide for 4 hours to

stimulate sulfur dioxide emissions from a power

plant. The experiment was repeated on the

remaining three treated groups. The non-

treatment plants were placed similarly in groups

of 6 in a second fumigation chamber and

exposed to filtered air for 4 hours. Following

the experiment, all plants were returned to the

greenhouse. When the beans matured, the

number of bean pods, the number of seeds per

pod, and the mass of the pods were determined

for each plant.

a) For the soybeans, three dependent variables are measured, all of which provide information about reproduction. What are they? (3 points)

b) What is the independent variable in the experiment? (1 point)

c) Explain the importance of having only one independent variable. (1 point)

d) Why is it acceptable to have more than one dependent variable?

(1 point)

e) Name 7 controlled variables in this experiment. (7 points)

f) What is the level of treatment in this investigation? (1 point)

g) Describe how this investigation is replicated. (1 point)

Scientific Method

Review Solutions

a)For the soybeans, three dependent

variables are measured, all of which

provide information about reproduction.

What are they? (3 points)

-number of bean pods

-number of seeds per pod

-mass of pods

b)What is the independent variable in the

experiment? (1 point)

-sulfur dioxide

c)Discuss the importance of having only one

independent variable. (1 point)

-to determine the effect of that/one

particular variable only

-the need to know which factor is

affecting the dependent variable

d)Why is it acceptable to have more than

one dependent variable?

(1 point)

-each of the variables can be a way of

measuring the characteristic(s) being

affected

e)Name 6 controlled variables in this experiment.

(7 points)

-temperature -size of plants

-age of plants -variety of soybeans

-type of soil -pH of soil

-amount of fertilizer -amount of light

-water routine/amount

-day length -air flow

-humidity -etc.

f) What is the level of treatment in this

investigation? (1 point)

-0.6 ppm every 4 hours

g)Describe how this investigation is

replicated.

(1 point)

-the plants were divided into 4 groups

of 6 plants each and the entire

procedure was replicated 4 times.