I. The Scientific Method
Figure 1: Tiger Salamander
Tiger Salamander Decline Data
Tiger salamanders are widespread across the United States. However, their numbers have been in sharp decline in
certain areas, especially in the ponds & lakes throughout the Rocky Mountains.
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Observation:
a) This observation begs the question: “What factor(s) may be contributing to the decline of tiger salamanders
throughout the Rockies?”
Researchers can attempt to answer such questions by employing a process known as the Scientific Method. As can be
seen in figure 2, this process involves a series of rigid steps that, if faithfully followed, allows a researcher to arrive at
an unbiased explanation for an observed phenomenon.
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Figure 2: Steps of the Scientific Method
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Hypothesis:
a) All scientific hypotheses allow researchers to make testable predictions.
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Prediction:
a) For example: “IF disease is responsible for tiger salamander decline, THEN a pathogen affecting salamanders or
their eggs will be found in salamander habitats” OR “IF water pollution is responsible for tiger salamander decline,
THEN a toxin affecting salamanders or their eggs will be found in salamander habitats”
b) Propose predictions for the remaining hypothesis:
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IF mutations are responsible for tiger salamander decline, THEN
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IF UV radiation is responsible for tiger salamander decline, THEN
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IF acid rain is responsible for tiger salamander decline, THEN
Upon further investigation, it was found that only acid rain was likely to have caused salamander decline, for the
lakes & ponds in the salamander habitats were found to be acidic (low pH).
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Question: other than the low pH of the salamander habitats, what else must be determined in order to validate the
hypothesis that acid rain is responsible for tiger salamander decline?
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In order to test if low pond water pH affects tiger salamanders or the development of their eggs, a Controlled
Experiment is performed.
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Figure 3: Controlled Experiment Setup
Test subjects are under “normal”
conditions in which no phenomena
are expected.
Conditions are IDENTICAL to the
control group except for a SINGLE
factor or variable.
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Identify factors that must be kept the SAME in both the control & experimental groups:
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The control & experimental groups will vary in terms of:
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The independent variable is:
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The dependent variable is:
* The factor that is varied between the two groups is called the Independent Variable, whereas the factor that is
being monitored or measured is called the Dependant Variable.
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Controlled Experiment:
When the experiment was performed & REPEATED, it was found that ALL of the salamander eggs in the control group
hatched & developed normally. In contrast, very few of the eggs in the experimental group hatched & developed
normally. This result suggests that the hypothesis proposing that acid rain is responsible for tiger salamander decline is
valid.
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Scientific Theory:
*Whereas laws describe WHAT happens, theories attempt to explain WHY things happen in the natural world.
III. Applying the Scientific Method
Studying the Reaction between Mentos & Diet Coke
Figure 4: Mentos & Diet Coke Reaction
It has been observed that when Mentos candies are placed in a bottle of Diet Coke, an intense fizzing reaction is
observed, whereby the cola is projected from the top of the bottle like a fountain. This is due to the carbon dioxide
bubbles in the Coke sticking to the rough surface of the candy, causing even more & larger bubbles to collect until the
pressure forces the liquid out of the bottle.
Consider ONE question that can be asked regarding the observed reaction between Mentos & Diet Coke.
1) State your initial question & propose a hypothesis.
2) State one prediction based on your hypothesis.
3) Design a controlled experiment to test your proposed hypothesis. Be sure to:
a) Describe the makeup of the control & experimental groups
b) Identify the independent & dependent variables.
c) Describe the data to be collected.
Designing Controlled Experiments: Practice Questions
1) A certain plant has white flower petals and it usually grows in soil that is slightly basic. Sometimes the plant
produces flowers with red petals. A company that sells the plant wants to know if soil pH affects the color of the petals
in this plant. Design a controlled experiment to determine if soil pH affects petal color. In your design be sure to:
• state the hypothesis to be tested in the experiment
• state one way the control group will be treated differently from the experimental group
• identify two factors that must be kept the same in both the control group & the experimental group
• identify the dependent variable in the experiment
• state one result of the experiment that would support the hypothesis
2) A scientist wants to determine the best conditions for hatching brine shrimp eggs. In a laboratory, brine shrimp
hatch at room temperature in glass containers of salt water. The concentration of salt in the water is known to affect
how many brine shrimp eggs will hatch. Design an experiment to determine which of three saltwater concentrations
(2%, 4%, or 6%) is best for hatching brine shrimp eggs. In your experimental design, be sure to:
• state how many containers to use in the experiment, and describe what would be added to each container in addition
to the eggs
• state two factors that must be kept constant in all the containers
• state what data must be collected during this experiment
• state one way to organize the data so that they will be easy to analyze
• describe a result that would indicate the best salt solution for hatching brine shrimp eggs
3) The amount of oxygen gas dissolved in water is important to the organisms that live in a river. The amount of
dissolved oxygen varies with changes in both physical factors and biological processes. The temperature of the water is
one physical factor affecting dissolved oxygen levels as shown in the data table below. The amount of dissolved oxygen
is expressed in parts per million (ppm).
Using the information given, construct a line graph on the grid on page 13, following the directions below. Mark an
appropriate scale on each labeled axis. Plot the data for dissolved oxygen on the grid. Surround each point with a small
circle and connect the points.
4) If the trend continues as shown in the data, what would the dissolved oxygen level most likely be if the temperature
of the water was 35°C? [1] _____________________ ppm
IV. Characteristics of Living Things
Life Processes
Although all organisms differ in many ways, they all perform the same activities. These activities common to all living
things are called Life Processes.
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Movement/Locomotion:
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Regulation (Irritability):
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Nutrition:
a) Heterotrophs: cannot make (synthesize) their own food. Must obtain food items in a preformed fashion from the
environment (via hunting, scavenging, foraging, etc). Examples: animals, fungi, some protists, & some bacteria.
b) Autotrophs: can synthesize their own food from inorganic raw materials (e.g. photosynthesis). Examples: plants,
algae, some protists, & some bacteria.
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Metabolism:
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Excretion:
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Reproduction:
a) Asexual Reproduction: involves ONE parent that divides to give rise to a single, genetically identical offspring.
Usually practiced by unicellular organisms & some multicellular organisms.
b) Sexual Reproduction: involves TWO parents that that produce cells (sperm & egg) which combine to give rise to
genetically unique offspring. Usually practiced by multicellular organisms.
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Growth:
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Homeostasis: