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Bio Honors Name

Part A: Science and the Scientific Method

There are many different and often valid ways to look at the world and to explain natural phenomena. For

example, history, religion, art, philosophy, literature, astronomy, and sociology all provide ways for people to

examine the world we live in, and they all contribute to today’s body of knowledge.

Science is one way of explaining the world, and the characteristics of science serve as a basis for establishing

what qualifies as science. Several characteristics generally define science.

1) Science is based on the results of observations and experiments

2) The results of these observations and experiments must be (a least in principle) repeatable and

verifiable by other scientists.

3) The findings of science must be refutable. In other words, if many scientists have accepted a hypothesis

(explanation to a natural phenomena), and later another explanation becomes better supported by evidence,

there must be a way to disprove the original hypothesis. This same principle holds true for theories: a

hypothesis that is supported by many experimental procedures.

4) Science is based on the assumption that the natural world can be investigated and explained in terms

we can understand.

Science is also committed to the idea that our explanations will change or become modified through

time as new knowledge is acquired. Methods of explaining natural phenomena that do not meet these standards

do not qualify as science.

The information and activities that follow in this packet deal with the process that is known as the

scientific method. This method is a way of studying the natural world, and developing a body of knowledge

called science. The five key elements of the scientific method include observations, questions, hypothesis,

predictions and tests. It should be noted that it is not possible to study all natural phenomena using all the

steps of the scientific method, but the method always acts as a general framework for scientific understanding.

General definitions you should be familiar with:

Observation-an observed or measured phenomena. Observations lead to problems or questions to be answered.

Hypothesis an idea used as the basis for experimentation. Sometimes called an educated guess to the problem,

it describes what is happening in a given situation. It is the “If” part of the “If…then,” statement.

Deduction or prediction-a statement that logically follows the hypothesis. It is the “then” part of the

“If…then,” statement. If the hypothesis is correct, then ‘such and such’ should happen. The ‘such and such’ is

the deduction. A deduction normally defines how an experiment will be designed.

Controlled experiment -the procedure designed to determine whether the hypothesis - is true. The experiment

tests only one variable or factor at a time.

Experimental group-the test group that is exposed to all factors including the experimental variable.

Control group- the test group that is exposed to all factors excluding the experimental variable. All

experimental groups are compared to the control group therefore it is considered the standard of comparison for

the experiment.

Experimental (independent) variable the single factor that the experiment tests. There may be additional

independent variables, such as time.

Dependent variable or Data - the facts collected in an experiment. The data is dependent on the independent

variable.

Qualitative and Quantitative data-Qualitative data cannot be measured and is subjective or based on the

opinion of the scientist. Quantitative data is objective, not based on opinion and can be measured.

Controlled variables-factors that are kept constant between the experimental and control groups so that you can

observe the effect of the experimental variable alone.

Analysis -the interpretation of the data. (What do the numbers or observations mean?)

Conclusion -whether the hypothesis has been supported by the data. A conclusion of a controlled experiment is

one of the following: The data supports the hypothesis, or the data do not support or rejects the hypothesis.

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Sequence of Steps in The Scientific Method

Observations- of natural phenomena and information from other sources such as

the Internet, library or other researchers.

may lead to

Questions-ask, “What is causing the observed phenomena?”

which lead to

Hypothesis-an educated guess that answers the question asked. The hypothesis

identifies a factor called an experimental variable, that may be

causing the outcome of observations.

which leads to

Prediction/deduction Statement-A statement in “If…,then… format. If (hypothesis), then (prediction).

The prediction statement identifies what the difference between the control and experimental group will be

if the hypothesis is true.

must be tested by

Controlled Experiment-A procedure designed to test the effect of the identified

variable. Only one variable is tested at a time.

Contains two parts:

a) Experimental/test/variable group- group(s) of test subjects that receive the experimental variable.

b) Control group-group of test subjects that do not receive the experimental variable or they receive a

standard level of the variable.

NOTE: Both the experimental and control groups are exposed to controlled variables.

what follows is

Data Collection-observations of the experiment are collected.

Data comes in two forms:

a) Quantitative data-data that is measured or counted. For example, the length of a butterfly wing,

Quantitative data is objective in that it is not based on emotion or personal opinion.

b) Qualitative data-data that is based on the opinion or judgment of the person observing the

experiment. For example, how many people like a new flavor of soft drink.

Qualitative data is subjective because it is based on personal opinion, prejudices or emotion.

Conditions: data can be placed in tables or graphed to make interpretation of the results easier.

data undergoes

Analysis- interpretation of the data. An attempt is made to determine if the data supports the hypothesis or

rejects it.

experimenter makes a

Conclusion-a statement that restates the hypothesis as supported or rejected by the data.

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There are two possible outcomes to a conclusion:

a) The hypothesis…. is supported by the data. In other words, the data collected is the same as expected by

the prediction statement. If the hypothesis is supported, the experiment should be repeated many times to

further confirm the results. The findings of science must be refutable. A hypothesis can never be

proven! Example: The hypothesis, water is essential for life, is supported by the data.

b) The hypothesis… is rejected, refuted or not supported by the data. In other words, the data collected is

not the same as expected by the prediction statement. If the hypothesis is rejected by the data, the

experimenter will need to rethink the hypothesis and formulate a different hypothesis to explain the

observations. Example: The hypothesis, alcohol has no effect on the nervous system, is rejected by the

data.

There is usually more than one way to test a given hypothesis. If you want to know if a cancer medication

will kill cancer cells, you could test it on cancer cells in a petri-dish. If that works, you may test it in rats, or

monkeys. If the data supports your hypothesis, your final test will be on humans.

If a hypothesis is tested and supported many times over, it can lead to the development of a theory.

Theory- The best explanation that science can offer in order to explain a natural phenomenon. A theory is a

explanatory hypothesis that is based on many observations and data from experiments.

The development of a theory depends upon the input of many researchers in many different fields of science.

For example, the most accepted theory of evolution, proposed originally by Charles Darwin in 1859, has been

supported by evidence from such fields of science as zoology, botany, anthology, archeology, geology, ecology,

etc. The theory of evolution by natural selection, as proposed by Charles Darwin, is still the most accepted

explanation for how evolution occurs, but recent evidence suggests that there might be other possible

mechanisms. As stated earlier, even theories have to be able to be changed in light of new evidence. Today

there is a worldwide network of communication between scientists in many countries where information can be

shared so that everyone can remain up to date and contribute to ongoing research.

Technological advances, developed using The Scientific Method, allow us to apply scientific discoveries to

benefit our lives. Examples include advances such as the microscope, DNA fingerprinting, agricultural

advances, genetic engineering, and medical advances such as organ transplants, new medications, artificial

hearts and pacemakers.

Review Questions:

1) List the five key elements of the scientific method:

2) List the 8 steps to the scientific method (go to pages 2-3 in the packet for the answers):

_1_______________________________________5______________________________________________

_2_______________________________________6______________________________________________

_3_______________________________________7______________________________________________

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_4_______________________________________8______________________________________________

3) What is a hypothesis?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

4) True or False (circle one). Once a scientist collects data to support his hypothesis, it can never be disproven.

5) What are the names of the two, test groups in a controlled experiment?

_1_____________________________________________________________________________________

_2______________________________________________________________________________________

6) What is the name of the most important factor tested for in a controlled experiment?

______________________________variable.

7) What is the difference between a controlled variable and a control group?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

8) Explain the relationship between the experimental variable and the experimental group?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

9) What is the difference between a controlled variable and an experimental variable?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

10) What is the difference between a hypothesis and prediction statement?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

11) Are scientific explanations expected to remain constant and never change? Explain your answer.

12) What are the two types of data called? ________________________and __________________________

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13) Which type of data can be measured? __________________Which is based on opinion? _______________

_____14) Which of the following is an example of quantitative data?

a) the breed of mouse most likely to develop tumors c) the odor of a dead animal

b) the color of a paperclip d) water temperature of 850C

15) Which groups in an experiment are exposed to controlled variables – control group(s), experimental group(s)

or both? ______________________ _____

__________________________________________________________________________________________

16) This statement is false – rewrite it so that it is correct.:

A conclusion to an experiment can prove the hypothesis is true.

________________________________________________________________________________________

17) What should be the next step if a scientist determines that the hypothesis was not supported in their

experiment?

18) What is the difference between a hypothesis and a theory?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

19) What is the difference between a theory that states that “All cells come from preexisting cells,” and the

‘theory’ that “Little green men live in outer space?”

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

20) Review the definition of “control group” on page 2 of this packet. Suppose you were breeding rabbits and

wanted to design an experiment to see if a new type of food would help your rabbits have fluffier fur. How would

you treat the rabbits in the experimental group differently from those in the control group?

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Biology Honors Homework: Science and the Scientific Method

Directions: Read the introduction completely before starting this activity. Write in full sentences for credit. Please

re-read your sentences out loud. Do they make sense to you? Would someone who was not in class

with you know what your answers mean?

Introduction: Science is more than a lot of information. Science is a way of knowing - it is constantly growing and

changing. Scientists carry on an unending search for new information. With that new information, they

reevaluate old information to find out if it is still accurate.

The scientific method offers a means of testing ideas and solving problems. Experimentation is the

foundation upon which all science rests.

Procedure

The following fictional experiment demonstrates the use of the scientific method.

Many people in the small Midwestern town of Hootville are stricken with the disease "Buggo." Most of

those who get sick recover in seven to nine days.

Buggo has been shown to be caused by a bacterium (single for bacteria) called "Gotcha." Antibiotic "X"

is a new drug that has been shown to kill Gotcha bacteria in a test tube. Antibiotic X was also found to cure

dogs that were sick with Buggo.

Researchers decided to test the new drug on some of the people in Hootville. They hypothesized that

the drug would effectively cure Buggo in humans. They decided that if they gave patients Antibiotic X, the

patients would recover more quickly than those who did not take the antibiotic.

The researchers prepared tablets containing Antibiotic X. They also prepared a second batch that

contained all the same ingredients (inactive ingredients) as Antibiotic X without any antibiotic. A table like this

that is similar but without medication is called a placebo.

The researchers selected two groups of people who had just contracted the disease. Twenty-five people

in group A were given tablets containing the drug antibiotic X. Twenty-five people in group B were given the

placebos.

Twenty of the twenty-five people given the drug recovered within one day. The other five people took

seven to nine days to recover - the normal recovery time for people sick with Buggo.

One of the people given the placebo recovered in one day. The rest of the people in group B took from

seven to nine days to recover.

1). List three facts or observations known before the start of the experiment.

____________________________________________________________________________________________

____________________________________________________________________________________________

____________________________________________________________________________________________

2) State the researchers' hypothesis.

____________________________________________________________________________________________

3) Form a prediction statement for the experiment. Use the “If…, then…” format. ______

______

4) What is the independent experimental variable in this study?

5). Describe a dependent variable for this experiment. Will the data be quantitative or qualitative?

_______________________________________________________________________________________

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6) What analysis do you think the researchers made of the data?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

7) What conclusion do you think they reached?

_______________________________________________________________________________________

_______________________________________________________________________________________

_______________________________________________________________________________________

Use the following information to answer the questions.

The enzyme catalase speeds the breakdown of hydrogen

peroxide in cells. In an investigation, 2 grams of liver

pieces (which contain catalase) were added to separate

dishes. Each dish contained the same amount of a 3%

solution of hydrogen peroxide. However, each of the

seven dishes was kept in an area with a different

temperature, ranging from 20 to 50 degrees. The relative

activity of the catalase was determined and the data was

recorded in the table to the right.

8) What is the independent (experimental) variable being tested in this experiment?

9) Is the above data qualitative or quantitative? (choose one)

10) Suppose the scientist’s hypothesis was “Temperature has no effect on the relative rate of catalase activity”.

Write a short conclusion explaining whether the data supports or does not support the hypothesis.

11) The scientist tested her hypothesis using dishes in seven different temperatures (increasing by 5 degrees

each time as shown in the data table above). Suppose she tested an eighth sample at a temperature of 55

degrees. Based on the pattern of data shown above, predict whether you would expect to see the activity

increase or decrease. Be sure to explain your reasoning.

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12) Given the following hypotheses, underline the experimental (independent) variable.

a) Plant growth is dependent on light.

b) Water is necessary for life.

c) Bacterial infections of the human ear can be cured by antibiotics.

d) The survival rate of baby pigs is increased by warm-water baths.

e) High levels of pesticides in drinking water can reduce egg laying in hens.

f) The number of colds experienced by school children can be reduced if they take vitamins.

g) For maximum growth, orchids require a 25-30% nitrogen concentration in the soil.

13) In the following examples, you will read a description of an experiment and identify the experimental and

control groups. Underline the control group and circle the experimental group.

a) An experimenter wants to know the effect of a particular pesticide (poison) on the growth of tobacco

caterpillars. One group of caterpillars will is sprayed with 2% pesticide in water and another

group will be sprayed only with water.

b) A hypothesis stating that added vitamins will improve longevity of housecats is being tested. An experiment

is run in which cats are fed a normal diet with added minerals and a second experiment will be run with

cats fed a normal diet without added minerals.

c) A doctor predicts that walking two miles per day will improve the health of his cardiac patients. He

compares the health of patients that walk two miles per day to the health of patients who don’t.

d) A horse trainer wants to know if an extra 3 laps around the racetrack will improve the performance of his

racing horses. He runs a group of 5 horses for the usual 2 laps around the track and runs a different

group for 5 laps around the track.

14) A farmer wants to know if a pesticide application will increase the yield of her crop of tomatoes. She

chooses a large field and applies two different pesticides. Each pesticide is applied to one half of the field.

At harvest time, she determines the yield (bushels per acre) of tomatoes on each half of the field. Field A

yields 35 bushels per acre and Field B yields the same. Her conclusion is that since both halves of the field

had the same yield of tomatoes, a pesticide application of some type was necessary.

A) Explain what is wrong with this experiment.

____________________________________________________________________________________

B) What is the independent experimental variable? _____________________________________________

C) What is an additional independent variable? _________________________________________________

D) What is the dependent variable? ___________________________________________________________

E) List 3 good controlled variables.___________________________________________________________

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15) The following statements are in an “If…,then…” format. Underline the hypothesis and circle the

prediction.

a) If there is life in outer space, then we should be able to pick up radio signals from extraterrestrials.

b) If calcium is necessary for healthy bones, then mice fed a diet rich in calcium should have healthier bones

than mice fed a regular diet.

c) If 20 acres of grassland is necessary to raise one cow, then cows raised on at least 20 acres will be healthier

than cows raised on fewer acres.

16) Label each of the following as Qualitative or Quantitative data:

_____________________ a) Customers in a pet store are asked to pick their favorite pet.

_____________________ b) The altitude (feet above sea level).of several mountains is determined.

_____________________ c) Data from taste tests is collected to determine how sour a new candy is.

_____________________ d) Length of the index fingers of 8 year old boys is collected.

_____________________ e) Color of hair in humans is observed.

_____________________ f) The number of scorpions entering an underground den is counted.

_____________________ g) A group of students is asked to rate their teacher’s intelligence.

17) Review the format for an appropriate conclusion statement on page 3. Write a conclusion statement for

the following experimental results.

a) An experimenter predicts that the size of the heart in

mammals is dependent on the weight or mass of the organism.

The data is graphed to the right.

Conclusion statement:

____________________________________________

____________________________________________

____________________________________________

____________________________________________

b) Frogs have the ability to take in oxygen through their skin

and through their lungs. An experiment is conducted to

determine if oxygen uptake is the same between the two organs.

The following results are graphed.

Conclusion statement:

_______________________________________

_______________________________________

_______________________________________

_______________________________________

c) If either of the hypotheses in the heart mass or

frog experiment were rejected, rewrite the

hypothesis so that it is supported by the data.

__________________________________________________________________________________________

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Biology Honors Part B. Scientific Method: Controlled Variables

There are many different types of experimental procedures that can present the experimenter with problems that

must be solved before reliable data can be collected. One such problem presents itself when many variables

affect the dependent variable. For example, you want to determine the best method for studying for a test. You

have taken many tests and have an idea that making note cards before a test will help you get a good grade.

You pose a question, “Will using note cards help me get a good grade on tests?” You set up a test in which you

use note cards for one test (experimental group) and plan to take the next test without note cards (control

group). Your independent and experimental variable will be the note cards, the dependent variable will be the

grade you get on the test.

Immediately, you see the problems. What if one test is a math test (hard) and the other is a health test (no-

brainer)? What if you have time to study for one test and don’t have the time to study for the other test? What

if you are feeling great the day you take one test and feel lousy the day you take the next test? All of these

differences are variables that can affect the dependent variable (your grade). You need a way to control these

variables so that you can be sure that any differences between the data in the control group and the experimental

group is caused by the experimental variable alone.

Controlled variable – variables that can affect the dependent variable. Controlled variables are ‘controlled’ by

the experimenter. They are held constant (the same) between both the control group and the experimental

group so that the only variable that is different between the two groups is the independent experimental

variable.

Once you recognize what variables you need to control, you can set up your experiment. Suppose you use note

cards for two different history tests. You plan to study 2 hours for each test. You eat breakfast before each test

and only use the data from a test if you feel good. You are reducing (‘controlling’) the variables that may

interfere with the reliability of your results. The only variable remaining is the use of note cards during one test.

That is your experimental variable.

Independent and Dependent Variables

The graphs you just looked at are drawn using specific methods. For example, in the body mass vs. heart mass

graph, the body mass is on the X, or horizontal axis and the heart mass is on the Y or vertical axis. Why did the

experimenter do this? Couldn’t the body mass have be graphed on the vertical axis and the heart mass on the

horizontal axis? The answer lies in the identification of two different variables:

Independent Variable- Independent variables may affect the data or the outcome of the experiment. In all

experiments, the experimental variable is an independent variable. It is the factor in the experiment that the

experimenter is most interested in. If there is only one independent variable (the experimental variable), it is

graphed on the X-axis. If an experiment has an experimental variable and an additional independent variable,

such as time, time would be graphed on the X axis, and the experimental variable is drawn as different lines on

the graph. Keep in mind that in some experiments, time will be the experimental variable.

Dependent Variable- The ‘d’ in dependent stands for ‘data.’ It is what was ‘discovered’ during the

experiment. Don’t be confused by the name ‘variable.’ The dependent variable is simply the data collected

during the experiment. The dependent variable is always graphed on the Y axis.

Knowing this, you can understand why the experimenter graphed the body/heart data the way he did. The

prediction statement indicated that the size of the heart was dependent on the size of the organism, not that the

size of the body was dependent on the size of the heart! The heart mass is therefore the dependent variable and

the body mass is the independent variable.

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The second graph with the oxygen uptake by lungs and skin of the frog includes TWO independent variables.

The dependent variable was the oxygen uptake measured in mL of O2. What 2 things did the O2 uptake depend

on? One was the month of the year and the other was whether the measurement was taken in the skin or the

lungs. Both are independent variables. But which one of those two is the independent experimental variable?

When an experiment has more than one independent variable, the experimental variable is the one the

experimenter is MOST interested in, and it’s what the experimenter was actually testing, in other words what

he/she changed in the way the groups were setup. Although time is also considered an independent variable, in

many experiments, it is not the experimental variable because BOTH groups are tested over the same period of

time. In the frog experiment, the experimenter wanted to determine if the oxygen uptake was the same between

the frog lungs and the frog skin. The respiratory organs (lungs and skin) are the experimental variable. The

additional independent variable, the ‘month of the year,’ adds information to the experiment. If the

experimenter had only looked at the data at the end of February, he might have concluded that his hypothesis

was supported. By looking at the data over several months, he was able to determine much more!

Questions:

7) In each of the following statements, circle the dependent variable, and underline the independent variable(s).

Put a * next to the independent experimental variable. Some will have more than one independent variable.

a) Guinea pigs are raised at different temperatures. Percent weight gain is recorded each week.

b) Height of bean plants treated with two different fertilizers is recorded daily for 2 weeks.

c) Number of minutes required for a two different species of snake to kill and consume a prey animal based

on the age of the snake.

d) Batches of seeds are soaked in salt solutions of different concentrations (1%, 10%, 20%) and the number of

seeds germinating is counted for each batch.

e) The number of correct answers on a memory test is recorded for students who ate breakfast compared to

students who didn’t eat breakfast.

f) Yield of cotton plants (bales of cotton per acre) is determined for two different varieties or types of cotton

plants grown in both Texas and Georgia.

g) Customers from New York City and Omaha Nebraska rated the level of violence in three different police

shows.

h) Label the X and Y axis on the following graphs (be sure to include the units of measurement):

Graph A. A test in which the amount of food (in grams) Graph B. A test in which the weight of a water balloon (grams)

given to fish affects the weight of the guppies (grams). affects the diameter of the splash it makes (centimeters).

A B

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Review Questions:

8) In your own words, why is it important to test only one experimental variable at a time?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

9) Describe three controlled variables in each of the following experiments:

a) A medication is used to reduce swelling after insect bites.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

b) Three different concentrations of air freshener are tested on public bathrooms.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

c) Plants are grown red, blue and green light.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

d) A taste-test is used to compare a new flavor of cherry Jell-o to the regular cherry flavor.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

A Special Case: The Placebo Effect

A difficulty arises when performing experiments on human subjects that can affect or invalidate the results of

an experiment. When patients are given a substance that is supposed to help their condition, a psychological

phenomenon known as the “placebo effect” may occur. The placebo effect causes patients to experience an

improvement in their condition even if the substance that they took did not contain any therapeutic ingredient.

For example, you might give someone a pill that contains harmless sugar and flour and tell them it will cure

their headache. A patient experiencing the placebo effect will describe a lessening or outright end to their

headache even though the pill did not contain a headache remedy. The patient may think that just because you

gave them a pill, their headache has been cured. This psychological placebo effect can actually end the

patient’s headache!

The placebo effect can be considered a variable that must be controlled. If one group of participants receives a

pill for a headache, and the other does not receive a pill, the first group will experience the placebo effect while

the second group will not. The experimenter won’t know if the difference between the two groups is due to the

placebo effect or the medication! Both the control group and the experimental group must experience the

placebo effect equally otherwise the data will not accurately reflect the effectiveness of the drug. The use of a

placebo in the control group will help to control the placebo effect.

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Placebo- Control treatment given to the subjects in the control group. It is a substance without the ingredient

under study. A placebo is identical to the experimental substance in every way except it will not contain the

active ingredient.

Example: A cough syrup contains the medicine (active ingredient) as well as water, sugar syrup, flavoring,

coloring, etc. The placebo will have water, sugar syrup, flavoring, coloring, etc.—that is, everything except the

active ingredient.

It is pretty obvious that an experimenter must not tell the participant if they are receiving the placebo or the

active ingredient. Humans are biased (prejudiced) and will come to their own conclusion if told, “Take this but

it’s just sugar syrup and flavoring.” To minimize any bias, researchers use blind and double-blind studies.

Blind Study- This is an experimental study in which the patient does not know if he/she has received the

experimental treatment or the placebo (control treatment).

Blind studies are great but researchers are human and biased themselves. If a patient tells the researcher that

they experienced a lessening of their headaches, the researcher, who knows the patient received only a placebo,

may be biased and record that the patient still had headaches. The researcher may form opinions or conclusions

about the effectiveness of the experimental drug before the end of the trial. A double-blind study will eliminate

bias on the part of the researcher and the patient.

Double-blind Study- This is an experimental study in which neither the patient not the Dr./researcher knows if

the patient has received the experimental substance or the placebo (control). Treatments/placebo have no labels

and look exactly alike.

How do you analyze the results of data from a double-blind study? Doesn’t someone need to know which

patients received the active ingredient and which received the placebo? A technician will set up the treatments

so that although the researcher/doctor administering the drug doesn’t know what the patient is receiving, a

record of the treatment is available. When it is time to analyze the data, the researcher will be given the

information as to which patients received the placebo or the active ingredient.

Blind and double-blind trials also help researchers understand the nature and appearance of side effects

associated with medications. For example, a new drug for indigestion is being tested with a double blind trial.

The side effects recorded for the experimental group were that 3% experienced stomach cramping. This may

seem significant (important) but when compared to the control group in which 3% also experienced stomach

cramping, it was not. The stomach cramping may have been a function of the indigestion for which the

patients had entered the study and not a function of the medicine being tested at all.

Questions:

10) Describe an appropriate control treatment for the following experiments. For human studies, identify

when a placebo is used:

a) A doctor tests the effectiveness of a sunburn ointment with the active ingredient NOBURN.®

__________________________________________________________________________________________

b) A researcher injects humans with a medication to reduce the size of cancer tumors.

__________________________________________________________________________________________

c) Jellyfish, normally reared in 20% salt water, are reared in 3 higher concentrations of salt water.

__________________________________________________________________________________________

d) Children are given a liquid medication to reduce cavities in their teeth.

__________________________________________________________________________________________

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Numbers of Test Subjects

A new vaccine has just been discovered. It will keep you from contracting Lyme disease. It is hailed as a

miracle drug and the first 100 people to receive the drug will get it for free. Sounds pretty good until you find

out it has been tested successfully only one time, on one individual. Perhaps that individual is healthier or

genetically superior to you. Will the vaccine work on you too? To be sure of the validity of a hypothesis,

researchers must test it on many individuals. By having many test subjects, any individual or genetic

differences that may affect the results are minimized. When designing the experiment, it is also important to

randomly select test subjects to the test groups. Then each test group has the same chance of having an unusual

participant.

Randomization-When individual subjects are randomly assigned to either the control or experimental groups.

Randomization ensures that both the control and experimental subjects are representative samples of the

original population. When any test group is not representative of the original population, sampling error is

introduced into the experiment. Then one can argue that any experimental results were due to difference in the

composition of the different test groups, instead of a result of the independent variable.

The number of test subjects within an experiment depends on many factors. How many test subjects are

available? What is the cost of administering the treatment? How long will the experiment last? The researcher

must use enough test subjects such that he/she is certain of the validity of the data. In addition, the numbers of

subjects in control and test groups should be the same.

Example: A medication is tested to determine its efficacy (usefulness) in reducing heart disease. The

medication is tested on a male, age 40 who is overweight and suffers from diabetes. The results conclude that

the medication did not help this individual. The experimenter decides to try again. This time, he sets up a

controlled experiment with 100 individuals. All the participants are male, age 40, overweight and suffer from

diabetes. Fifty individuals are randomly assigned to the test group and 50 to the control group (receiving a

placebo). This time the medication works.

11) What could be a reason why the medication didn’t work on the first individual?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

12) Testing a medication on 50 people sounds great but the test subjects were strictly controlled (male, age 40,

overweight, etc.). What about the effect of the medication on other groups of people? What additional types of

tests would you consider to determine the efficacy of the medication?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

Replication, or repeating an experiment, further validates a hypothesis.

Replication- The process of repeating an experiment to validate the results. If several different research firms

test a vaccine on several hundred people, and find it effective in preventing Lyme disease, the general public

will be more likely to take the vaccine.

15

Levels of the Experimental/Independent Variable

Many times an experimenter is interested in determining the correct level of the experimental variable. For

example, how much herbicide (weed killer) is necessary to control dandelions in lawns? If the researcher is

interested in trying three different levels of the herbicide, instead of conducting three different experiments at

different times, it would be better to conduct all three experiments at the same time. In that way, differences in

rainfall, temperature and season (controlled variables) won’t affect the results.

Example: The control group is a 1 acre lawn that does not get any herbicide. The researcher then sets up three

experimental subgroups. Each experimental subgroup is composed of a 1 acre lawn. The three subgroups

receive 2%, 4% and 8% concentrations of herbicide, respectively. The number of dandelions per acre in the

control and each experimental subgroup is counted. The results of each experimental subgroup can be directly

compared to the control group.

Questions:

13) Given the following information, describe the control and experimental subgroups. Be sure to include the

number of test subjects in the control and experimental subgroups and describe the different levels of the

experimental variable. Identify if a placebo is used.

If you are not sure how to describe the subgroup levels, you can use words like, “high, medium, low” or

you can make up any percent or metric measurement (grams, centimeters, liters) you wish. You won’t be

expected to know exactly which levels to use.

a) A researcher wants to test different levels of a medication to control warts.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

b) Test to determine the level of fluoride in toothpaste that produces the fewest cavities in children.

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

c) Nesting boxes for bluebirds are usually placed 10 feet above ground. Determine the preferred height of

nesting boxes for bluebirds. How will you determine if a nesting box is preferred by the birds?

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

__________________________________________________________________________________________

d) In the last experiment, how many total nesting boxes did you use in the experiment? _____________

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In Summary:

The example below illustrates a classic experimental design in biology. This experiment is designed to test the

hypothesis that DDT ingested with food will not have harmful effects on laboratory rats over a period of time.

Rats similar in genetic background were randomly assigned to one of two different test groups. The control

group did not receive the independent variable (DDT) while the experimental group received DDT with food.

Subgroups were not used in this experiment. Additional independent variables like time or age of rat could be

measured for both test groups. Controlled variables were held constant such that test results should refute or

support the hypothesis. Note that more than one dependent variable was measured during this experiment.

TEST POPULATION

100 genetically identical rats

EXPERIMENTAL GROUP

50 rats

CONTROL GROUP

50 rats

EXPERIMENTAL (INDEPENDENT)

VARIABLE

Some specified amount of DDT in food

Fed rat food with DDT Fed rat food only

ADDITIONAL INDEPENDENT VARIABLE

time

CONTROLLED VARIABLES

Temperature, water, living space, age of rats,

and all other conditions kept the same for both

groups for several months.

Outcome ?

DEPENDENT VARIABLES

Outcome ?

1. body weight

2. disease, deaths

3. births

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Part C: Building Tables and Line Graphs From the Data

Data Table- a convenient way to organize data in a visual manner. Although not as visual as a graph, tables

can hold a large amount of data in a minimum amount of space. Placing data in a table is far better than putting

it in paragraph format.

Graph- a visual representation of data. Graphs are more useful than a data table because they can enable the

researcher to make predictions of the dependent variable between the data points.

Here are some rules to follow when building a line graph to illustrate your data:

Dependent variable measurements go on the Y-axis,

Independent variable measurements go on the X-axis.

If you have an additional independent variable, for example, “time” or “date,” it is graphed on the X axis.

The experimental independent variable will be charted as two or more different lines on the graph.

Be sure to correctly and fully label the axes, remembering to include the measurement unit that was

used For example, “Number of eggs per leaf,” or "Height of Flowers, cm."

Scales are the measurement charts along the X and Y axes. Make sure that whatever scale you use is

properly spaced and is in regular intervals. The purpose of making a graph is to see the pattern that

the data illustrates. Without appropriate scales, you do not see the true picture of the data.

Generally it's a good idea to make your graph nice and large. When you're looking at a picture of

data (which is really what a graph is), it's better if the picture is LARGE. Use the whole paper.

Space out your scales, skipping lines if necessary, while maintaining proper scaling patterns.

Titles should include a description of all independent and dependent variables.

You can use the following plan: “Effect of (independent variable) on (dependent variable) given

(additional independent variable like time or age, if present).”

Consider the following scientific hypothesis and experimentation:

A biologist in the tropical rain forest observes small vines that grow up the trunks of trees. The trees seem

to be in good health and undisturbed by the presence of the vine. The biologist makes a hypothesis: The

vines in this forest depend upon the trees for physical support only. The biologist then makes a prediction

based upon her hypothesis: If the vine depends on the tree only for physical support, then a vine

transplanted onto an artificial tree should grow as rapidly as a vine transplanted onto a real tree.

Testing this prediction and hypothesis, the biologist constructs an experiment. This experiment consists of

two groups, Group A and Group B. Each group consists of three vines and three trees. Group A consists of

three vines transplanted onto three live trees, similar to natural conditions in the forest. Group B consists of

three vines transplanted onto artificial trees. Each group would contain the same type of soil, same

temperature , same amount of sunlight and water.

Questions:

1) On what basis did the biologist develop her hypothesis? ______________________________________

____________________________________________________________________________________

2) Why were factors such as soil, temperature, sunlight and water kept constant between the two groups?

__________________________________________________________________________________

__________________________________________________________________________________

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Data Collected:

Data table of vine length measurements(cm) of plants grown on live and artificial trees over four days.

*You must calculate the Averages

Test Group Date: 10/01 10/02 10/03 10/04 10/05

Group A

(Live Trees)

Vine 1 5 8 12 20 25

Vine 2 5 9 15 24 29

Vine 3 5 7 13 20 22

Average

Group B

(Artificial Trees)

Vine 1 5 8 10 12 15

Vine 2 5 8 9 11 13

Vine 3 5 8 12 13 17

Average

Questions:

3) Fill in the following for the above experiment:

a) experimental variable/independent variable _______________________________________________

b) dependent variable _____________________________________ Why? _______________________

__________________________________________________________________________________

c) additional independent variable __________________________________________

d) type of data (quantitative/qualitative) _____________________________________

e) control group _____________________________________________________________________

f) experimental group _________________________________________________________________

19

4) Graph the data from the previous experiment on the graph below. Include appropriate labels for each

axis. You will be graphing the averaged data.

Title: Effect of ___________________________ on average _________________________________

over ____________________________________________

5) Draw an inference or conclusion to the data. Does it support or refute the biologist’s hypothesis?

_______________________________________________________________________________________

_______________________________________________________________________________________