Name: _____________________________________
LS.1 Scientific Reasoning and Logic and the Nature of Science
The student will demonstrate an understanding of scientific reasoning, logic, and the
nature of science by planning and conducting investigations in which
a) data are organized into tables showing repeated trials and means;
b) a classification system is developed based on multiple attributes;
c) triple beam and electronic balances, thermometers, metric rulers, graduated cylinders,
and probeware are used to gather data;
d) models and simulations are constructed and used to illustrate and explain phenomena;
e) sources of experimental error are identified;
f) dependent variables, independent variables, and constants are identified;
g) variables are controlled to test hypotheses and trials are repeated;
h) data are organized, communicated through graphical representation, interpreted, and
used to make predictions;
i) patterns are identified in data and are interpreted and evaluated; and
j) current applications are used to reinforce life science concepts.
A
LS.1 Scientific Reasoning and Logic and the Nature of Science
At this point in your school career, you’ve probably studied the scientific method approximately
5-6 times. You’ve probably begun each year learning that scientists follow a specific set of steps that
makes up the scientific method: ask a question, do some research, write a hypothesis, follow some
procedures, gather some data, examine that data, draw a conclusion, and share your results. You may
have even conducted a science experiment or two of your own following those steps. You are
practically a full-fledged scientist now.
Wait! Aren’t scientists nerds? Don’t they look like this:
or
or
or
?
You may be thinking, “I don’t want to be a nerd!” Well, scientists can look like this but actually
everyone is a scientist. Science affects us all, every day of the year, from the moment we wake up,
all day long, and through the night. Your digital alarm clock, the weather report, the road you drive
on, the bus you ride in, your decision to eat a baked potato instead of fries, your cell phone, the
antibiotics that treat your sore throat, the clean water that comes from your faucet, and the light that
you turn off at the end of the day have all been brought to you courtesy of science. Furthermore,
when you watch the weather report to help you decide what to wear to the bus stop, you are being a
scientist. When a baby finds a new object and decides to put it in her mouth to see if it is something
to eat, she is being a scientist. In both examples, the scientist is learning something about the world
around him/her.
If you examine the word science, you will see the prefix “sci-” which means to know. Science is
actually defined as a way of learning about the natural world and the knowledge gained through that
process. Essentially being a scientist involves looking at the world and figuring out things about it.
Maybe we are not so nerdy after all.
B
LS.1 Scientific Reasoning and Logic and the Nature of Science
As a scientist you should understand certain characteristics about science. You need to know
that the natural world is understandable. That is the reason we do what we do: we want to
understand more about the natural world. As we seek to learn more about the natural world, we
cannot just make things up: science demands evidence. That’s where the experiments and
observations come in. As we work, we use logic AND imagination. How else do you think new
inventions are made? We know that scientific knowledge is durable. That means that we can build
upon the knowledge discovered by others. We understand that scientific ideas are subject to
change. As evidence is gathered, some ideas do grow and develop: in the past, we believed that
Earth was the center of the universe but with further study and observation, we have come to
understand that the sun is the center of our solar system. While working, we try to identify and
avoid bias. We want data to be as accurate and objective as possible so we try not to let our personal
opinions or background influence our work. Lastly, because we want and need to share our work
with others, science is a complex social activity. These characteristics help define science and the
work that we do as scientists.
Science does not always mean performing experiments. Often, there is more research and
observation involved than anything else. A good scientist needs great observation skills. Making an
observation means gathering information using ONLY your 5 senses: sight, hearing, smell, taste, and
touch. Although it is usually unwise to taste things involved in most scientific experiments, it can
still be an effective way to gather information about the world around you. Some observations are
quantitative which means they involve measurements. The plant is 5 cm tall and has 3 leaves are
examples. Some observations are qualitative; the leaves are yellow-green and drooping are good
examples. Qualitative observations involve descriptions of physical properties of matter like color,
odor, appearance, texture, etc. Scientists need to be very careful to make observations instead of
inferences. Inferences are interpretations of observations made. When you make an inference, you
pair observations with prior experiences and background knowledge to make a judgment about why
or how something happened. Making careful observations is one way to avoid bias or favoritism. By
reporting careful observations and avoiding inferences, a scientist minimizes his/her influence on the
outcome of an experiment or study.
C
LS.1 Scientific Reasoning and Logic and the Nature of Science
As part of his/her research, a scientist tries to find similarities and patterns amongst the objects
being studied. This is called classification. By observing an object’s attributes (characteristics), a
good scientist classifies or sorts those objects by their similarities, making them easier to study. Carl
Linnaeus, a famous Swedish scientist we’ll study later this year, developed a system of classification
for living things. Dmitri Mendeleev developed a system of classification for elements (now called the
Periodic Table). Galileo’s observation skills were so well developed; he was able to help convince
the world that the sun is at the center of our solar system when those around him believed otherwise.
These great scientists and many others have made major contributions to our world’s knowledge
using their observations skills.
A good scientist asks questions and lots of them. The questions he or she asks help him/her gain
an understanding of the world. This is probably a good time to point out that “the scientific method”
that you’ve had to memorize as a series of steps, in order, is not exactly “THE” scientific method.
Instead, the scientific method is the process by which scientists ask questions and form and test
hypotheses. That means there is not just one correct method. Sometimes, scientists make an
observation that leads them to ask a question, which requires research and/or an experiment. Other
times, it might be the results of an experiment that lead to more questions, which result in more
experiments. Maybe he/she records observations for a long period of time (like Jane Goodall, a
naturalist famous for spending 55 years studying family groups of chimpanzees) hoping to learn
about a particular part of the natural world. Inventing things is also “science”. The engineering
process of refining an invention involves finding a problem, proposing a solution, designing,
building, testing, re-designing, building, testing, and so on. What defines these processes/methods as
scientific is that they are organized and involve testing and/or data collection. Although scientists
may not record every step of their process, following a plan helps scientists think about and discover
things in an organized way. This is particularly important because a scientific discovery must be able
to be duplicated or repeated; otherwise it’s just an accident!
The scientific process might begin with a question or a problem, typically one that starts with
“how”. How does a plant grow? That question may produce more questions. What do plants need to
grow? Does pollution affect plant growth? Does acid rain really have an effect on plants? To be a
good “scientific” question, it needs to be specific and measurable. Does the pH of water affect the
growth rate of plants?
D
LS.1 Scientific Reasoning and Logic and the Nature of Science
Once you have your very specific question, it is important to do some research. Research involves
looking up information to help you with your experiment. You may read a book or a magazine
article, complete an Internet search, or even talk to an expert. Sometimes when you research, you
discover another scientist has completed your experiment already! In the case of the plants from the
previous paragraph, you might need to research what plants need to grow, what kinds of plants grow
best in Smithfield, or even what the pH of rainwater is before you could proceed with your next step.
You could go to the library, go on-line, or ask a gardener or chemist for help.
Armed with background knowledge, you are ready to make a hypothesis. A hypothesis is
possible explanation for your question. It is not just a guess because you have research that leads you
to believe you know what will happen. A good hypothesis should be stated in terms of a testable
relationship. A good way to write a hypothesis is using an IF/THEN statement: “IF a houseplant is
exposed to acid rain THEN it will not grow as tall as a houseplant that is not exposed to acid rain.”
When a hypothesis is written as an IF/THEN statement, it is easy to determine both the
independent and dependent variables. An independent variable (manipulated variable) is the factor
in a scientific experiment that the scientist changes; it is the part that is being tested. With our
houseplants, it is the exposure to acid rain. When a hypothesis is stated as an if/then statement, the
independent variable is the if part! A dependent variable (responding variable) is the outcome or
the result of changing the independent variable; it is the part being measured. In our plant
experiment, it is the growth of the plant, or the THEN part of our hypothesis statement. Stated this
way, your hypothesis sets up your controlled experiment. In a controlled experiment, the scientist
only tests one variable at a time. The plant not having the experimental acid rain applied to it is the
control to which all experimental plants will be compared. The plants receiving the acid rain are the
treatment group.
The most challenging part of designing an experiment is trying to control or account for all
possible factors except the one independent variable that is being analyzed. For instance, you may
inadvertently ignore the amount of sunlight a plant gets when placing your plants in the window.
Perhaps one is getting a bit more sunlight than the other. That might affect your outcome. The best
way to account for these sources of error is to brainstorm with your peers about all the factors that
could possibly affect your result. This brainstorm is best done before beginning the experiment so
that arrangements can be made to account for these variables before taking data.
E
LS.1 Scientific Reasoning and Logic and the Nature of Science
Now we begin testing! The scientist writes and/or follows a very detailed set of procedures
(instructions) to complete the experiment. Procedures that are not detailed and specific may result in
experimental errors. Procedures even need to explain how measurements are taken. Remember,
someone else may need to reproduce your experiment at a later time and you want him/her to get
similar results; it helps prove your hypothesis. The procedures usually include a list of materials
needed. In the case of our acid rain experiment, we are only going to change whether or not a plant is
exposed to acid rain. We will attempt to limit all other variables in the experiment by keeping
everything else the same – the type of plants, the soil, the amount of water the plants receive, the
amount of sunlight, etc. By keeping these constants (parts of an experiment that are kept the same),
we are trying to ensure that it is definitely the acid rain causing the difference in plant growth.
Also before our experiment starts, it is important to think about the kind of data we will observe
and how we are going to record it. Gathering data in a chart or table may help keep it organized for
analysis later. Since plant growth is the dependent variable in our example that is the observation we
need to record. Data is recorded for this experiment using centimeters to measure plant growth. It
may also be helpful to make qualitative observations about our plants: the leaves are turning yellow,
for example. Your qualitative observations may be recorded in your chart as well.
Control
Growth in cm
Treatment
Observations
Growth in cm
Observations
Day 1
Day 2
After gathering data for a specific amount of time, the data must be examined for patterns that
may help determine if there is a relationship between the independent and dependent variables. In
this example, it makes the most sense to organize the data collected into a line graph because we are
examining growth over a period of time. Presenting data in a graph also makes it easier for the
scientist to share the results with others. Photographs may also help tell your story.
Now it is time to draw a conclusion. A conclusion examines the results of the experiment and
states whether or not the hypothesis was correct. Based on the results of this experiment, and this
experiment only, the scientist states that acid rain does have an effect on plant growth. “When
exposed to acid rain, this plant grows slower than it would grow without acid rain.”
F
LS.1 Scientific Reasoning and Logic and the Nature of Science
This could be an accurate conclusion. Of course, the scientist could also have made a mistake
somewhere in the experiment and the result could be totally wrong! Before the scientist shares the
results of the experiment with anyone else, he/she should perform several trials (repeated attempts at
an experiment). If the results consistently support his/her original conclusion, it is probably accurate.
A good experiment should be repeated at least three times but more is better for accuracy.
Sometimes, despite a scientist’s very best efforts, mistakes happen. As mentioned previously, this
is particularly true if the written procedures are not detailed or clear. Another source of experimental
error can be the measurement instruments. They must be calibrated or adjusted correctly. Even if
calibrated correctly, if the observer is not familiar with how to use the instruments, errors may result.
Remember how we said that scientists try to avoid bias? This is an excellent example: though the
result of the experiment may have seemed obvious to you from the start, a good scientist does not
allow his/her judgment to interfere with the process. He/She records the data exactly as it is
observed. It would have been simple to make an inference in this particular case. You have learned
that acid can be dangerous. You may even remember from 6th grade that aquatic organisms need
water to have a pH between 6.5 and 7.5 (remember water quality testing day?). You could infer that
acid rain would be bad for the plant (another living organism) as well. A good scientist will record
the data as it is observed and report his/her findings based on the data collected.
The acid rain experiment results could now be published and shared with other scientists all over
the world who are also researching the effects of acid rain on living organisms. Several scientists
may choose to duplicate our experiment. If we’ve done our research and experimentation carefully,
they should get the same results. It is the sharing of information within the scientific community that
helps advance scientific discovery.
To keep it easier for everyone, the worldwide scientific community records results using the
metric system. Scientists use the metric system because it is used throughout the world (only 3
countries do not – Liberia, Myanmar, and the United States) and it is a simple system to use. Units of
measurement are related to each other by factors of 10; for instance 10 mm = 1 cm.
G
LS.1 Scientific Reasoning and Logic and the Nature of Science
The metric system uses meters as its unit to measure distance/length.
Distance/length is measured with a meter stick. For short lengths, like the length of
a pencil, we use millimeters (1/1000 of a meter) or centimeters (1/100 of a meter).
For long distances, like the Hog Jog race, we use kilometers (1000 meters).
The liter is used to measure volume. It is measured with a graduated cylinder,
even if it is a solid object. As odd as that sounds, to measure the volume of a solid,
we use a method called water displacement. You do this by filling a graduated
cylinder with enough water to cover the object. The amount of water in the
graduated cylinder is recorded. The solid object is then placed into the graduated
cylinder. The new water level measurement is recorded. To find the volume of the
object, you subtract the first measurement from the second measurement. In the
illustration, the Minion has a volume of 28 mL because 47 – 19 = 28 mL.
The gram is used to measure mass (measured with a triple beam balance
or a digital balance). Just like small lengths can be measured in millimeters,
small masses can be measured in milligrams. Likewise, larger masses can be
measured in kilograms. Mass is different from weight: mass is the amount of
matter in an object. Your weight depends on gravity. Weight is measured
with a scale. The scale uses the force of gravity acting on your body to measure your weight. If an
experiment were performed on the moon, mass would be accurate, weight would not because the
moon has different gravity than Earth!
Metric temperature is measured in Celsius by a thermometer. We know that water
boils at 100°C (212° F) and freezes at 0°C (32° F). Other temperatures that we should
be familiar with are room temperature 21°C (70° F) and our body temperature 37° C
(about 98° F).
Scientists use many other tools to gather data. If you remember Water Quality Testing Day from
th
6 grade, you may remember the probeware that was used to measure dissolved oxygen
and pH. This kind of equipment can be used to measure lots of different parameters.
There are different probes for just about every test you can imagine. In fact,
many detective programs on television show crime scene investigators using
probeware to gather evidence at a crime scene.
H