READING – SCIENTIFIC METHOD (SECTIONS 1.8 AND 1.9)
What is a hypothesis?
A proposed explanation for a set of observations (can you say this in your own words)
How is a theory different from a hypothesis?
A theory is much broader in its scope than a hypothesis. It also has a large amount of data
supporting it.
According to the reading, a scientific hypothesis must lead to __predictions____________
that are ___ testable_______
Can a hypothesis be proved to be correct? (Explain why or why not).
No. It is impossible to exhaust all alternative hypotheses to explain the phenomenon. There
may be some other explanation consistent with all the data and observations to date that has
not yet been considered.
One of the QUESTIONS posed in the reading was "Why doesn't the flashlight work?"
What are the two HYPOTHESES suggested by the authors?
1. the battery is dead
2. the bulb is burned out
PREDICTIONS often have the format: if (hypothesis is true), then (expected result of an
EXPERIMENT or test). For example, if the flashlight isn’t working because its battery is
dead, then replacing the batteries should fix the flashlight.
Using the “if…then” format, write out a prediction for the experiment suggested in the
reading to test the “burned out bulb” hypothesis:
If the flashlight isn’t working because the bulb is burned out, then replacing the bulb should fix
the problem.
What test result would support the “burned out bulb” hypothesis?
The flashlight works when the bulb Is replaced with a new bulb.
What test would falsify the burned out “bulb hypothesis?”
The flashlight DOESN’T work when the bulb Is replaced.
The authors suggest that even if changing the bulb makes the flashlight work we don't
know for certain that the problem wasn’t something else like a loose bulb that was also
corrected when we changed the bulb.
Complete the following predictions for a follow up experiment.
If the flashlight wasn’t working because of a loose bulb, then when I put the old
bulb back in, then the flashlight should work fine as long as the bulb is in tightly.
If the flashlight wasn’t working because of a dead bulb, then when I put the old
bulb back in, then the flashlight should not work even when the bulb is tight.
PRACTICING YOUR UNDERSTANDING:
Suppose you go out to your car and you OBSERVE that it won't start. You ask yourself the
QUESTION, "Why isn't my car working?"
Name three possible HYPOTHESES for why your car isn’t working.
1. dead battery
2. out of gas
3. you’re in the wrong car
(There are MANY other possibilities ... loose battery cables, wrong key, dead alternator, dead starter, etc.)
Choose one of your hypotheses and PREDICT the outcome of two tests you could perform
to test your hypothesis. Be sure to use the "if .... then" format.
(Examples only …
If my car isn't working because its battery is dead, then the headlights shouldn’t turn on.
If my car isn't working because its battery is dead, then it should start if I jump it.
Suppose the results falsify this first hypothesis; choose a second of your hypotheses and
predict the outcome of yet another test you could perform to test this hypothesis.
If my car isn't working because I am out of gas, then the gas gauge should be on E.
In laboratory experiments and field studies there should be at least two groups of
experimental subjects: a control group and an experimental group. In the experiment
described in section 1.9, in sandy habitat the control group was _the light colored “mice”__ and
the experimental group was _the dark colored “mice”__. The experiment was designed such
that these two groups differed only in one variable, which was __their coloration __. This
variable would be considered the _____independent______variable. The # of attacks on the
model mice would be considered the ___dependent_____variable. All other conditions
should be kept constant. For example, the kind of plastic the white and brown model mice
were made of should have been __the same__ , and the # of light colored and dark colored
“mice” placed in each area should have been ___ the same __ for the experiment to be “fair.”
These conditions that are the same for all are controlled variables.
CHECKING FOR UNDERSTANDING:
Cricket chirping experiment:
When you tested the effect of humidity, the # chirps per minute was __ dependent ___
variable and the atmospheric pressure was ____ controlled _____ variable. The control
group(s) was/were ___ the crickets kept in a terrarium with 15% humidity (which was the humidity
in their habitat in the White Tanks) _____ and the experimental group(s) was/were _____ the
crickets kept in terrariums with humidities higher and lower than 15% __
An example of a controlled variable from this experiment was _____ wind speed (or air
temperature or pressure or # of nearby crickets but NOT # chirps) __. It would be considered a
controlled variable because ______ it was KEPT the same in all terrariums ___
Elements of scientific investigation:
Identify each of the following as either a hypothesis, observation, prediction, question, results, or
theory
1. Why do cacti have spines? ________________ question ______________.
2. There aren’t many animals that graze on cacti.________ observation ___________.
3. If spines are protective and I remove the spines from a cactus (without harming it), then it
should be eaten more often than the same species of cacti with spines. prediction____.
4. Spines protect cacti from predation. ______ hypothesis ____________________.
5. When both spiny and spineless cacti were put into a tortoise enclosure, more pads of the
genetically spineless cactus variety were eaten than those of the spiny kind.
______ experimental results ____________________.