Experimental Science
Science is a word that we use to describe the method or means by which humans try to understand the world
around us. We do this by using a combination of two basic approaches
1. Discovery Science (Descriptive Research)
a. We observe some phenomenon
b. We record what we see, measuring when possible
c. We may make some type of hypothesis
d. We make sure that what we see happens over and over again
e. Ideas are developed to understand the observation (we “tailor” our idea to what we see)
f. In reality, our first experiment was descriptive research. We did not alter any variables, rather
we simply measured what “was”.
2. Hypothesis-driven Science (Experimental Research)
a. Discovery Science starts this type of science, BUT
b. We develop an idea (first) and predict what should happen
c. We use the scientific method (an organized, rational approach to problem-solving) to test a
hypothesis, which means altering a variable in the known system and seeing what happens – the
result will either support your hypothesis (We NEVER PROVE) or disprove your hypothesis.
d. We judge the “goodness’ of our prediction based on the designed experiment.
Experimental science can often be categorized as either pure science or applied science. Pure science, also
known as "basic science," tries to answer basic questions about reality, such as the nature of aspects of the
physical universe, the mechanisms of life, or the workings of the mind. Pure science isn’t conducting with an
application or product in mind. Examples include trying to understand the structure of a molecule, how a cell
works, or how groups of people become more cohesive or divisive are all questions of basic science.
Applied science tries to solve a specific problem or set of problems, or to create a product. Developing a better
solar panel to generate less expensive electrical power involves applied physics and chemistry. Creating a
treatment to prevent or cure a disease is applied biology. Applied science is used to make discoveries that
improve living conditions of humans (there is an application or product in mind).
Many major discoveries occurred “accidentally”. The idea for microwave ovens came about when Percy Spencer
(who worked at Raytheon) walked in front of a magnetron (which produced microwaves) and noticed that his
chocolate bars always melted. A Swiss engineer was hiking in the Alps and got burrs stuck to his pants. He
looked at the burrs and discovered “hooks” that would attach to anything that has a loop…thus Velcro was
created. Velcro didn’t become famous until NASA began using it to anchor things into place in microgravity.
Evidence for the Big Bang theory (Cosmic Background Radiation) came from Bell Labs engineers Penzias and
Wilson right here In New Jersey. Even Coca-Cola was an accidental discovery! In each case, the scientists saw
something “different” and asked “why”.
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What is the Scientific Method?
1. Make observations regarding some phenomenon (either directly, or using the knowledge of others).
2. Ask a question based on your observation
3. Create a statement that you believe explains the generalization (hypothesis)
a. Must be testable and measurable
4. Design an experiment to test the hypothesis. Your measurements and procedures should have
operational definitions if they might be interpreted differently by different people.
5. Conduct the experiment
6. Record results (observations and measurements)
7. Conclude, based on results. Conclusions are made by inferring from the data you have gathered and
your previous knowledge. Conclusions can support your hypothesis or lead to an new hypothesis.
8. If a hypothesis is tested in many ways, but is not disproved, it can become a theory
Over the next few days we will do several activities to ensure that you understand what
each of the vocabu
OBSERVATION
When you observe, you use one or more of your senses. Identify a specific “scientific” observation
that you could make with each of your five senses.
1.
4.
2.
5.
3.
Think about the observations you have written. Is your observation accurate and objective? Accurate
means that it is correctly measured and recorded. Objective means that it avoids a certain point of
view (we call this bias). Look at the next three statements. Which is not objective? Which is not
accurate? Which is accurate and objective?
a. The rain gauge showed that it rained two inches last night.
b. I used a ruler along the side of the street and determined it rained about 4 inches.
c. The weather was awful last night.
Additionally, your observation can be either qualitative (described by words and not numbers) or
quantitative (observations that include numbers). “Three centimeters of rain fell between 10am and
11 am today” is an example of a quantitative observation. In science, you often use tools (balances,
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microscopes, rulers, graduated cylinders) to make quantitative observations. Circle the quantitative
statements below.
a.
b.
c.
d.
The plant’s leaves are dark green
The plant has long , thin leaves
The plant grew 5 centimeters during the week.
Three grams of fertilizer were applied to the plant today
Finally, be sure you understand the difference between an observation and an inference (also called an
interpretation). An accurate observation is a correct, factual statement based on seeing, smelling,
tasting hearing, or touching. An inference is a judgment based on observation and past experience.
Inferences are not always correct. Be sure that what you write as an observation, is not an inference.
Identify the observation and the inferences.
a. This rock has a smooth surface
b. The school band will probably meet after school as usual
c. The band members must need extra practice after school to learn their new songs
DIFFERENTIATING OBSERVATION AND INFERENCE
Use the illustration to answer the questions
that follow.
1.
Make three qualitative observations
about the photograph
2.
Make two quantitative observations
about the photograph
What are two inferences that you could
make. What evidence do you have that
supports your inferences?
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MORE ACTIVITIES TO DIFFERENTIATE INFERENCE AND OBSERVATION
Why is it important to differentiate between observations and inference? An observation can be
interpreted many ways. In your conclusion you may believe that the data infers one thing, while your
classmate may believe it infers something else. It is important that others be able to identify what you
observed and separate it from your conclusions. Making an inference means choosing the most likely
explanation from the facts at hand. Inference is used when we make a conclusion or judgment
Because of this, written observations are included in the data section of formal lab report. Inferences
are reserved for the discussion/conclusion section of the same report. Scientists are not the only ones
to do this. Consider the following situation:
Suppose you are sitting in your car stopped at a red signal light. You hear screeching tires, then a
loud crash and breaking glass.
What did you observe?
What might you infer?
What would you tell a police officer if he asked you what happened?
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Newspaper Article
Read the article Stony Bacteria. Make a list of what the scientists actually observed. What
inferences were made based upon this data?
Observations:
Inferences
What conclusions can you make based upon the information in this article?
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LAB JOURNAL ENTRY
Summarize what you now know about observations and inferences. Write this in your
lab journal after experiment 1 (Human Proportions). Start on a new page (odd numbered) and
be sure to use appropriate vocabulary where needed.
1. Choose the best three explanations of observations vs. inferences you find on the
“class statements” sheet. Write these in your lab journal. If the best explanations are
not “good enough”, rewrite the statement changing as few words as possible to make
the explanation correct.
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Measuring
My grandmother was an excellent cook and I learned much about cooking from watching and helping
her. BUT, my grandmother’s method of measuring had to be “seen” to be understood. Her
measurements included “butter the size of an egg”, salt to taste, a dash of pepper, and 2-3 handfuls of
flour. Most of the time, she would just add things until it looked right or tasted right. She had similar
directions for “how to cook”. For example: cream butter and sugar, beat until frothy, and “beat till
soft peaks form”, add flour until dough is the right consistency and cook in an oven at medium heat.
My grandmother never had problems “repeating” her own recipes, but when others asked for a recipe,
their brownies or cake were never quite the same as Grandma’s.
So, why do you think that it was difficult for others to produce the same moist, chewy brownies that
my Grandma made? Think about her “measures”.
How many tablespoons are in a lump of butter which is the size of an egg?
What measure equals a “dash” of pepper?
How many cups are 2-3 handfuls?
In terms of procedures:
What does cream butter and sugar mean?
What does frothy mean?
And what is medium heat?
When we work in the lab, we are often using a procedure written by someone else. When that person
writes a procedure, they are, in reality, writing something that is similar to a recipe. If we are trying to
replicate an experiment, it is important that we have specific directions or procedures, so that we can
do the experiment in the same way. When we don’t replicate the amounts and the procedures, we
may obtain different results.
Cookbooks were written to provide standard recipes that had measures and instructions for how to
measure (level the flour by scraping off the excess flour with a knife) and how to combine ingredients.
Operational definitions (definitions of measures or procedures) are very important for consistency.
Let’s deal with measures (and calculations) first, and then work on operational definitions. When you
measure, is important to choose the RIGHT tool for whatever we are measuring. On the next page are
various tools and measures that we might use for liquids and solids. Additionally we will use a ruler
(generally cm or mm) or a balance (grams).
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Common laboratory equipment (including measurement tools)
We will most often measure liquid using a graduated cylinder. It is important to use the “right size”.
We have 10 ml, 100 ml, and 500 ml graduated cylinders
Beakers are utilized for reactions or to pour reagents from. They are NOT used to measure. Generally
flasks will be utilized for the same purpose. Again, use a size that is appropriate for the task. Finally,
we will use test tubes when the reactions (or amount of reagent) is small, and we want to be able to
examine the reactions “up close”.
Goggles MUST be used for all experiments using glass or reagents!
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When you make measures, consider the following:
1. Determine which unit is appropriate for the measurement you are making and “how large” the
container or measurement device needs to be.
2. Select the right tool for the measurement
a. If you a measuring 5 ml of fluid, you need a 10 ml graduated cylinder, NOT a beaker or a
100 ml graduated cylinder
b. If you are measuring your height, a meter stick will work better that a small ruler.
3. Be sure that you understand the units that are found on the measuring device. If you are using
a balance, make sure that you place your “dish” on the balance FIRST and tare it (zero it) so that
your measure actually represents the mass that is IN the container and not the mass + the
container.
4. Always measure as precisely as possible. If a graduated cylinder is marked in ml. You should be
able to estimate to the nearest 0.5 ml. If you are using a rulers that is marked in mm, you
should be able to estimate to the nearest 0.5 mm.
5. When calculating, make sure that the measures use the same units and that all calculations are
labeled with units.
PRACTICE
Identify the glassware and measuring tools found on your lab table. Each item has a letter. Put the
letters in alphabetical order, then identify the glassware or measuring tool associated with each letter.
Be sure to identify the size of the glassware (ie. 50 ml beaker), if it is available.
A.
E.
I.
B.
F.
J.
C.
G.
K.
D.
H.
L.
Complete the Skills Practice for Measuring: Length; Measuring: Liquid Volume; and Measuring
Temperature if needed. You will be responsible for understanding how to measure the mass, volume
and/or temperature of liquids and solids, and appropriate use (or non-use) of beakers, flasks,
graduated cylinders, balances and thermometers.
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Measuring Mass Using a Digital Scale.
Suppose that you needed to measure 5 grams of flour into a plastic weighing boat.
Using the digital scale provided, write a procedure that begins with unlocking the
balance and turning on the scale. Then explain how to zero the scale, zero the scale
with the empty container, and how you would go about placing 5 grams of flour in a
plastic weighing boat using a scoopula.
Explain cleanup (turn off scale and remove pan to clean it) and relocking the balance.
PROCEDURE:
What is the range of the electronic balance?
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CALCULATIONS AND GRAPHING
When completing labs, you will often be asked to utilize your measurements and make some type of
calculation or create a graph.
Calculations
One common kind of calculation in science and math is determining rates. One definition of rate is the
speed at which something happens. For example, you may need to know how often something occur
per minute, or determine the growth of a plant per day.
Rates are used by ecologists to determine birth and death rates. Rates are utilized by chemists or
biologists to determine how rapidly a reaction occurs. If you know the rate at which something
happens, you can use this information to determine how often something happens in any given time
period. For example, you check your pulse and determine that there are 20 pulses in a 15 second
period. You are now asked to determine your pulse rate per minute. To determine this, you need to
CONVERT the time unit you have into minutes.
Conversion is accomplished by multiplying by a term that is equivalent to 1, but contains both the unit
you start with and the unit you wish to end with. For example: 1 minute = 60 seconds.
20 pulses
15 seconds
We want to replace seconds with minutes. If we multiply this rate by 60 seconds
1 min
You can cross out “seconds” and are left with
1200 pulses
15 min
=
80 pulses
1 min
When asked to do calculations, show work, and each step of the calculation. Be sure you show units
and the conversion factor. Make sure your final answer is labeled with the correct units.
Complete the Skills Practice: Calculations
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Graphing
Graphs are utilized to help interpret data. Graphs are utilized so that patterns in the data can be seen.
Patterns help us to understand how the dependent and independent variable are related.
Data should be placed in a table (or in a spreadsheet) before attempting to draw a graph. It is
important to order the data in the table so that it best addresses the question you are trying to answer.
Example: Suppose that a scientist is measuring the speed that sound waves travel at different air
temperatures. An experiment was performed, and data were gathered on different days . All
temperatures are in oC.
Date
Temperature
Speed of sound (m/s
June 5
10
336
July 19
30
348
Aug 5
20
342
Oct 1
0
330
Oct 10
-10
324
Jan 20
-20
318
What question is the scientist trying to answer?
Which two columns of data are most important in answering the question
Which measure DEPENDS on the OTHER VARIABLE?
Rearrange the data in a table
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Graph Title
Title:
Variable on Y axis:
Variable on X axis:
Which variable, X or Y is dependent variable? (it DEPENDS on the setting of the other). Which variable
is the INDEPENDENT variable?
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Be sure to name the graph AND name the table and label the two axes (with the UNITS)
What number did you choose to start each axis? Why ? What type of graph did you choose? Why?
Graph the data. What can you conclude (or infer) from your graph?
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On Your Own
Number of Frog Croaks at Different
Temperatures
Croaks/Minute
30
25
20
15
10
20
22
24
26
28
30
32
34
Temperature C
Write a sentence that summarizes the data.
What is the difference between the greatest number of croaks measured in a minute and the least
number of croaks measured in a minute?
What was the greatest temperature at which information about frog croaks was collected?
What number of croaks would you expect to hear if the temperature were 21 C? Why?
Does the number of frog croaks increase the same amount for each degree of temperature increase?
Write a sentence that describes any trends you note in the data.
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OPERATIONAL DEFINITIONS
In science, exact definitions are important. An exact definition allows scientists to repeat their own
work and the work of others. An operational definition is a statement that describes how a particular
variable is to be measured, or how an object or condition is to be recognized. The word operational
means “to describe what to do”). Operational definitions are used whenever a term doesn’t have a
clear single meaning. In experiments, operational definitions are contained in “Materials and
Procedures”.
OPERATIONAL DEFINITIONS (PROCEDURES) IN EXPERIMENTS
Suppose you are conducting an experiment to determine how air temperature in a room affects the
growth rate of plants. If the lab report said “some of the plants were kept in a cold room, while others
were kept in a warm room”, you would not be able to repeat the conditions of the experiment. The
words cold and warm do not have a single clear meaning. An operational definition should be used in
your lab report. A statement such as “some of the plants were kept in a room with an air temperature
of 10 C and other plants were kept in a room with an air temperature of 30 C”, would have the
information that you needed to repeat the experiment’s conditions.
Operational definitions are also used to describe how variables are measured. In the
experiment described above, we are measuring the growth of a plant over time. So a lab report must
include how the rate of plant growth was determined.
EXAMPLE: The height of the plants was measured once every 24 hours using a centimeter ruler. The
height was measured to the nearest centimeter. The change in height was determined by subtracting
the previous day’s height from the current height. The rate of growth was reported based on change
in centimeters per day.
When you write an operational definition, make sure it describes what to do or what to observe. Be
sure that any terms in your lab report that do not have a single, clear meaning have an operational
definition. Here are some examples of operational definitions.
MORE EXAMPLES:
1. The maple tree population in an area of 100 square meters increased compared to last year.
OPERATIONAL DEFINITION: The maple tree population in an area was determined by counting
the number of maple trees in one tenth of the area and multiplying that number by 10.
2. Cut flowers stay fresh longer if they are kept in room temperature water (70F) than they do if
they are kept in cold water (45F).
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OPERATIONAL DEFINITION: Fresh: cut flowers are considered “fresh” if they were cut within 2
hours of being placed in water and have not lost any petals.
A good operational definition should also tell how frequently a particular measurement is made.
1. If an experiment requires the measurement of the temperature of a beaker of water as it heats
over a flame, the operational definition might be: the temperature of the water is measured in
o C at 5 min intervals, using a thermometer.
SUMMARY: Operational Definitions should be:
1.
2.
3.
4.
5.
Written as you plan your investigation or experiment
Written when a term does not have a single, clear meaning
Used to clarify methods used to measure variables
Used to allow someone to duplicate your work
Be checked by someone to ensure the directions are accurate.
Complete Worksheet: Forming Operational Definitions
For each phrase that is underlined on the next page, define what the phrase means (YOU assign
a definition to the phrase
Example: Look at the first example: smallest one is underlined. Does smallest mean: smallest
diameter or smallest mass? You define it more precisely.
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EXPERIMENTAL DESIGN.
1. Look over the material we have covered to date. Go back to page 2 and look at the terminology
that we have discussed and reviewed. A good check to determine whether or not you
understand the vocabulary is to write a “new story” using all of the words (in any order). Work
in your lab groups to write “sequential sentences” (to tell a story). Start the story (put a
sentence on an index card). If the statement correctly uses the vocabulary word or words, the
next person adds a second sentence. As the number of sentences increase, you may “insert”
sentences, rather than just “put them at the end.”
a.
b.
c.
d.
Observations
Hypothesis
Measure/Measurable
Measurement
e.
f.
g.
h.
Experiment
Procedures
Conclusion
Inference
i. Theory
j. Quantitative measure
k. Qualitative measure
2. In our first experiment the observations were quantitative. A. Explain what this statement
means and write an operational definition for one of the measures you did for lab 1.
3. Sometimes we cannot measure, we can only observe a color, an event (yes or no), or a
behavior. Suppose you are observing a small child (3-4 years old) making a puzzle. What
behaviors might you observe. What inferences might you make?
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Designed (Controlled) Experiments
So far, we have “asked a question”, restated that question as a hypothesis, developed a procedure with
measures to test the hypothesis, recorded observations, made inferences, and evaluated our process to
determine how we might make it “better”.
While the experiment we conducted tested a hypothesis, we really did not look at an experiment where a
“change in X” produced a change in “Y”.
A more formal experiment involves changing one variable to determine its effect on a second variable.
Designing an experiment involves putting all of the above steps together in steps that we call the experimental
method. When the scientific method is utilized to answer questions, experimentation has to be highly
organized and controlled to have any value.
Since many things (we call them variables) can affect the outcome of the experiment, it (the experiment) should
be designed so that there is potentially only a single explanation for the results. The variable that is being tested
(the variable you think affects the outcome of the experiment) is known as the independent variable (also called
the manipulated or experimental variable or the X variable). The variable that we believe will change in some
way when we change the level of the independent variable is called the dependent variable or Y variable.
Your hypothesis is always stated in terms of the effect of some level of the independent variable on the
dependent variable.
Look at the worksheet entitled “Analyzing Experiments”. Follow the directions for each of the three examples.
Review your results first with your group and then with Mrs. Landa. Once your group (all of you must have
completed the assignment) has “passed” the assignment, you should work on designing your “plant” experiment
(see next page).
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Designing a Plant Experiment
In your next experiment, you will design, conduct and analyze the experiment.
The question you are trying to answer: What are the requirements for germination of seeds. You will need to
research the three stages of germination so that you have benchmarks for your investigation. You should take
data on a daily basis (or as often as you are in the lab) and determine a) when the root emerges (the radicle),
when the hypocotyl emerges (what will become the stem and leaves), Development (growth) of roots and
leaves. You will need to observe your plants for 3-4 weeks (we will be doing other experiments “in between”).
During the study, you will need to hydrate the plant as needed so that a constant amount of water available to
the growing plant.
Think about what you plan to measure to show growth
Think about how you want to set up your independent variable to show the minimal requirements for
germination and the minimal requirements as plants grow and develop.
Available to you are the following materials:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Plant soil
Miracle Grow soil
Water crystals (will absorb water, and form a gel that seeds can grow in (5 g crystals/ 1000 ml H2O
Water crystals with fertilizer (hydrate as above)
Liquid fertilizer
Three ounce plastic cups
Water
Lima bean seeds (soak overnight in water before planting)
Pea seeds (soak overnight in water before planting)
Lettuce seeds
Radish Seed
The cups can hold about 70 ml. of rehydrated gel. If you use dirt, fill cups to the same level (after watering)
as the gel). Plants will need enough water to germinate, but too much water could drown the seeds.
Plant 3 seeds per container.
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Three Stages of Germination
Plant with two fully opened leaves
The pictures above show potential “ benchmarks” for growth. Use the Layout for an Experimental Design
template on the next page to identify key factors and measurements in your experiment. Think about how you
will keep important factors constant.
General Layout for an Experimental Design Diagram
TITLE: The effect of ______________________________(Independent variable) on
__________________________ (Dependent variable.
HYPOTHESIS: Must state both dependent and independent variable and what general effect one will have on
the other.
PREDICTION:
POPULATION:
SAMPLE SIZE _______________________
INDEPENDENT VARIABLE: _________________________________________
LEVELS OF THE INDEPENDENT VARIABLE and REPLICATIONS (should have a control (if possible) and at least one
other level, or at least two levels.
Level 1 (Control)
Level 2
Level 3
Level 4
DEPENDENT VARIABLE(s): __________________________________
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What measures will you utilize? How often will you measure?
_____________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
WHICH VARIABLES SHOULD YOU KEEP CONSTANT (name those that you believe could
most affect the dependent variable besides the independent variable)?
1.
3.
2.
4.
In addition to just “stating the words”, it is often a good idea to draw a picture of the experiment you have just
designed. Draw a PICTURE of the experiment you have outlined in the previous exercise and label the
dependent variable and its levels, the independent variable, the constants and the control.
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So, if I asked you to design your own experiment right now, would you be able to come up with a specific topic
for an experiment? It is easier to come up with a general topic, but it is not as easy to translate this general area
into a focused topic for study.
You can use a four question strategy to explore possible variations of a general topic before attempting to state
a specific problem, hypothesis, variables, constants, and a control. When we teach students the process of
experimental design, we should model and practice this four-question strategy with students BEFORE asking
them to design an original experiment on his own. The teacher can lead the students in the class through one
example of the four-question strategy, all together, using the chalkboard. The students can then practice the
four-question strategy alone or in small groups, using a prompt provided by the teacher, before attempting to
work through the four questions for an experiment that they are interested in carrying out.
The four-question strategy involves the following four questions:
1.
2.
3.
4.
What materials are readily available for conducting the experiments on the general topic of interest
What action is observed when studying (the general topic of interest).
What are all the ways I can change the set of materials that would change the action
In what ways can I measure or describe the response or change.
A specific experiment follows from the answers to the four question strategy. One of the answers to question 3
will be the independent variable in the experiment. All the other answers to question 3 (other things that could
be changed to create an effect) need to be controlled (set at a constant value) when the experiment is
conducted. They will become the constants of the experiment. The answer to question 4 will become the
dependent (response) variable of the experiment.
The following example of the four question strategy might be answered using the general topic of plants.
1. What materials are readily available for conducting experiments on plants
a. (soil, plants, fertilizer, water, light/heat, containers)
2. How do plants act (plants grow)
3. How can I change the set of plant materials to affect the action (growth)a. Plants, spacing , kind, age , size,
b. Water: amount, scheduling, method of application, source, composition, pH
c. Containers: Location of holes, number of holes, shape , material, size color(possible changes in soil,
fertilizer, and light/heat would also be listed)
4. How can I measure or describe the response of plants to the change?
a. Count the number of leaves
b. Measure the length of the longest stem
c. Count the number of flowers
d. Determine the rate of growth
e. Weight the fruit produced
f. Measure the diameter of the stem
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