Andrew J. Penniman
1. Make and describe scientific observations.
2. State a hypothesis based on one's own observations and/or information from the literature.
3. Define and use the elements of a good experimental design: experimental variable,
controls or constant variables, quantification.
4. Design an experiment to test this hypothesis.
5. Collect, interpret, present, and discuss data in writing.
In this laboratory exercise, we will discuss and practice using the scientific method. This is, in fact, a process you have used all your life; it is simply a process of learning by trial and error (understanding that "error" is not necessarily a mistake). The scientific method formalizes one way people learn throughout their lives. Let's review the steps:
1. Observation: This is simply being aware of, and curious about, what goes on in the world around us. At one level, observation is a basic survival skill; we are taught from infancy to look both ways when we cross a street. Scientists are no different, but they have been trained (or train themselves) to pay attention to phenomena others might overlook or think unimportant and to carefully record their observations.
Thinking through what has been observed,
a scientist tries to relate what has been seen (or heard, felt, smelled)
to other observations, either his/her own or observations of others. A
scientist will often consult books and articles in scientific journals
(literature) in an effort to pull together all information that has a bearing
on his/her observations. Often, one tries to find cause-and-effect
relationships between observations.
2. Proposing a hypothesis: A hypothesis is a statement
that explains what has been observed within the context of current knowledge.
(Some textbooks characterize a hypothesis as an "educated guess."
It is NOT; a scientist doesn't guess.) A person practicing science reasons
that if the observations I know of are true, and connected as they seem
to be, then [state a hypothesis here] should be true. Most importantly,
the hypothesis must be testable; that is, further observations, often by
experiment, must be able to show the hypothesis to be true or false.
Scientists have no special claim to this step though they may formalize
it by writing down the facts and reasoning they've used to arrive at this
3. Test of the hypothesis: Here the scientist tries to find those observations that will prove his/her hypothesis wrong. This must seem paradoxical after expending so much mental energy making observations and coming up with a hypothesis. But the hypothesis is drawn up "within the context of current knowledge." Making more observations that confirm what we think we know may only reinforce our ignorance. Science makes progress, we learn something new, when we prove what we thought we knew was wrong; then some other idea is closer to real truth.
A hypothesis may be tested by simply continuing to observe, but with a sharpened idea of what to look for (astronomers can do little else). Most often though, a scientist realizes that many factors in nature other than the one stated in the hypothesis may have influenced the observations. Then, one designs an experiment to limit the test to the one experimental variable. In an experiment the experimental variable is allowed (or even caused) to vary and all other factors are held constant or controlled (controls). Then, any resulting effect can be attributed to the experimental variable.
A well-designed experiment specifies
the materials and quantities used to do the experiment and allows or demands
that results be quantified. Then the scientist can
state not only that an effect happened, but how much of an effect.
A small effect, or a minor difference between effects, may suggest the
experimental variable does influence the original observations, but some
other variable (one of the controlled variables) has a more significant
effect. In preparing to do an experiment, a scientist thinks carefully
about how the results will be measured or quantified.
4. Result of the test: Carrying out a test of the hypothesis and careful gathering of data* produces the results. Ideally, the results verify or confirm the hypothesis or show the hypothesis to be incorrect. In either case, the scientist is not done. If the hypothesis was verified, one tries again (and again and again …) to test and falsify the hypothesis. To do the same test again could only be expected to verify the hypothesis in the same way, so the scientist tries to devise a more rigorous test, or to find a way to measure the variables more precisely. If the hypothesis was falsified, the scientist must try to understand how and why the hypothesis failed to predict the result and then state a new hypothesis (and then test that one again and again …). Theoretically, one could get into an infinite loop with no logical exit. As a practical matter, how far a scientist goes in testing hypotheses depends on his/her time and energy.
* This word "data" is tricky. It is actually
a Latin plural. It is thus wrong to say, "This data is …"
Instead, it is correct to say, "These data are …" That sounds funny to most people, and most journalists
and even some scientists get it wrong. Now that you know, you will get it right.
During this lab exercise, you will use
observation, scientific curiosity, and investigational skills to learn
something about the ecology of ants. (Ecology refers to the branch
of biology dealing with the interactions of organisms [ants] with their
environment.) You will have at your disposal many species of ants,
several types of food (bait), meter sticks, and an outdoor laboratory (the
school campus or your yard). Using these materials and/or others
you provide, each student or group of students is to design and carry out
an experiment. This will then be written up as a lab report to be
turned in on the date assigned by your instructor.
METHODS & MATERIALS
The class and the instructor should discuss
what you (as a group) already know about ants. Unless you have lived
all your life in Antarctica or on the Arctic tundra, you must have seen
ants. Think about where and when you've seen some and what they were
doing. Some questions the class might discuss are:
1. What are ants? What other animals are like ants? In what way are they alike?
2. Ants live in groups called colonies or nests. Who are the members of a colony and what
are their social/biological roles? How does a colony grow? How are new colonies
3. How do ants forage for food? What have you and classmates seen ants eating?
What foods are nutritious for ants?
4. How do ant colonies interact with other colonies of the same or other species?
Notes: Observations or background material.
Based on these observations and/or background material from the instructor, each lab group should discuss and develop a hypothesis. Remember that the hypothesis must be testable and you should discuss how you will test it. Some questions that may lead you to a hypothesis are:
Do ants have food preferences or do they forage on any food available? Do ants choose the most nutritious food or the tastiest?
Do different ants live in different habitats? How many different kinds can be found in a habitat? (Closely related species of ants may be similar in size and color, but if they look different they should be different species.)
How long does it take for a "scout" to recruit other members of the nest? Does the time depend on distance to the nest, temperature, nature of the bait, or some other factors?
What species interactions can be observed? If two or more species compete for food, what happens?
How far from the nest do workers forage? Does the
maximum distance depend on size of ant, temperature, or some other factors?
meter sticks, 15 cm rulers, index cards, wooden splints, top loading balance,
Carbohydrates Fats Proteins Complex foods
sucrose (table sugar) cooking oil
molasses lard canned chicken cheese
cane syrup shortening egg white mayonnaise
aspartame (artificial sweetener)
saccharine (artificial sweetener)
Now it is time to use your ingenuity to develop a test for your hypothesis. Remember, the most effective experiments are well controlled, in other words they are designed so that all factors are the same (constants), except for the one experimental variable. For example, you may alter the food choice(s) available, or the distance that food is from the nest, but you would not want to alter both those variables in the same trial. Plan your experiment and write out your procedure below. This should be the exact procedure that you will use. In good science, experiments are replicated (repeated) several times to confirm that the results were not simply a coincidence. You should plan to repeat your experiment in at least two places, or with at least two species of ants, or on at least two dates.
What is your experimental variable?
What factors or variables will be kept constant? (It is hard to
think of everything, but consider how you will present baits to the ants.
For example, if you place baits on index cards, the index card becomes
a variable--you should offer the ants an empty [control] card to see if
it is the card itself that attracts ants.)
How will you gather data? How often? (Will you watch the ants
continuously, or will you check at regular intervals to see what they're
doing? What will the intervals be?) How long will each experimental
How many times will you repeat this experiment?
Run your experiment and collect your data. Do not discard, change, or "fudge" on any of your observations. Use measurable quantifiable factors that can be presented in graph or table form.
Depending on time available and the nature of your hypothesis you may or may not be able to test your hypothesis today. You might also try testing your hypothesis and find a need to change the hypothesis or the test methods.
Different lab groups do different things.
Some groups meet on campus and carry out their test together. Other
groups are unable to meet together, so they agree on a procedure which
each member carries out at home (or wherever), and they share data later.
This requires that all understand the details of the procedure. Other
groups find themselves unable to work together, so each individual decides
on a hypothesis and tests it by him-/herself. Any of these alternatives
is OK as long as every student participates and can write his/her own paper.
Analyze your results and form some conclusions. Do your data support your hypothesis?
Were there any variations (inconsistencies) in the observed behaviors?
Were there any surprises?
If you were to do this experiment again, what new hypothesis might you
make? Where there any factors that might have inadvertently affected
the outcome of your experiment? What are the implications of your
results? How might this information prove useful? When writing
up this lab, follow the scientific paper format
in the format preferred by your instructor.
Some Useful References:
Goetsch, Wilhelm. 1957. The Ants. University of Michigan Press, Ann Arbor.
Holldobler, Bert, and E.O. Wilson. 1990. The Ants.
Belknap Press of Harvard University Press,
Holldobler, Bert, and E.O. Wilson. 1994. Journey to the
Ants. A story of scientific exploration.
Belknap Press of Harvard University Press, Cambridge, MA.