Laboratory 1: Introduction to Scientific Inquiry and Procedures
Science is a search for knowledge about the physical world, i.e. nature and the universe. The purpose of the search is to discover order, i.e. the facts or phenomena (on), in the universe and the natural laws that govern this order. The tool humans designed to search for knowledge about the physical world is the scientific method. The object of this part of the laboratory is to learn how the steps of the scientific method are used to gain knowledge about the phenomena of the universe.
A. Scientific Method of Inquiry
The scientific method of inquiry is a logical, practical, reliable way to approach and to solve problems and to
gain knowledge. This method of inquiry allows one to verify tentative answers to questions about the
physical world. Science concerns itself with observable phenomena or occurrences.
There are 5 steps to the Scientific Method.
1a. Making observations and stating a problem to be solved about the phenomena.
The scientist observes phenomena with a questioning attitude. The observations lead to recognition of a
problem, which requires a solution.
b. Asking questions related to the problem.
In this step, questions are asked about the observations. Questions such as how and what questions
science answers best, why questions are harder to answer in science.
2. Hypothesis and Prediction.
A hypothesis is a tentative reasonable answer to the question. It is a guess answer to the question that
tentatively explains the observations. The hypothesis also allows the scientist to make a prediction as to
the expected outcome of the problem. A hypothesis must be testable, i.e., allows for the collection of data
based on measurable, describable facts. This characteristic of the hypothesis is more important than if the
hypothesis is correct. No mysticism is involved.
Hypothesis and prediction are stated in an "if..., then..." format. Therefore before an experiment begins,
the scientist formulates a hypothesis and makes a prediction and then collects data.
3. Design and Conduction of an Experiment.
An experiment is designed and performed to test if the hypothesis is correct or not correct. What does an
experiment do? An experiment collects data by observations and measurements in a controlled manner.
The experimental procedure involves: a.
Controlled Design or Experiment - In a controlled experiment, except for the phenomenon being tested, two parallel set ups or groups are identical in all respects or conditions. The phenomenon being
tested is also considered as the independent variable, i.e., the condition under study. One group is the
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control. The other group, in which the independent variable is introduced, is the experimental group. In
the experiment, you are changing one independent variable at a time. Therefore any difference in the
result or dependent variable (the condition changed due to the independent variable) between the
experimental compared to the control groups is due to the difference in the single condition. Those
conditions that are kept the same in the control and experimental groups are called the controlled
variables. b.
Data Collection. – Accurate qualitative and quantitative unbiased observations and measurements are
made.
c. Data Analysis. - Review the data to see if cause and effect relationships exist or patterns of
observations exist to confirm or reject the prediction made in step 2. Tables, graphs and figures are
made to analyze the data. A tool of data analysis is statistics, which quantifies the probability the
hypothesis and prediction is correct or not correct.
d. Interpretation of the Data and Drawing Conclusions. – What does the data mean?
You determine by reasoning and logic that the data you observed during the experiment is probably true
or not. Further use of "if... then...” relationships allow you to correlate the data and ultimately arrive
at a general conclusion. Thus reasonably establishing if a possible cause and effect relationship exists
between the independent and dependent variables. Finally a concluding statement of the experiment
is made indicating whether the observations support or do not support the hypothesis and prediction
made in step 2.
If the observed results do not agree with what was predicted and there is no significant difference
between experimental and control, the original hypothesis is rejected or modified. A new hypothesis is
made and tested. If results are similar to what was predicted, the hypothesis is supported. If the
hypothesis is correct, the same results should be obtained on repeating the experiment leading to the
same conclusion. The general acceptance of the hypothesis as a valid explanation of the problem
elevates the hypothesis to a theory.
4. Theory.
A theory is a general statement that is considered a valid explanation of the problem and allows one to
make predictions as to occurrence of this phenomenon in the future. A hypothesis is elevated to a theory,
when there are no significant observed exceptions.
5. Law.
When a theory has universal validity, i.e. no exceptions to the observations, then the theory becomes a Law
of Nature. There are many laws in physical sciences but only a few laws in biology. In biology there are
many theories.
Inductive vs. Deductive Reasoning
Inductive Reasoning -uses information from many facts or situations to arrive at a general statement.
Deductive Reasoning - the general statement is used to predict what will happen in a particular situation.
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Science and the Scientific Method
Science
Science is a human activity, which makes observations about phenomena (occurrences) in the universe, asks questions concerning these phenomena, make generalizations about these phenomena and seek explanations about these phenomena.
Scientific Method – is a logical, practical, reliable way of approaching and solving a problem to gain knowledge. The tool used by Science to carry out these activities is the scientific method. Scientists as well as others use it in every day decision-making. The method provides a framework of reference to understand new information, make logical analysis, draw conclusions and make intelligent decisions. It is in essence a method of critical thinking.
The scientific method has several steps.
1. Identify a problem by making observations about the phenomenon.
2. Asking questions about the observations.
3. Formulating a hypothesis or guess answer to the question, i.e. tentatively explains the observations. From
the hypothesis you can make prediction by if ... then format.
The hypothesis must be testable in that data (or additional observations) can be collected in a designed
controlled experiment to prove or disprove the hypothesis based on measurable, describable facts. This
characteristic is more important than the hypothesis being correct. No mysticism is involved.
4. Experiment – devised to test if the hypothesis is true or not true.
a. Methods are devised for observation and data collection.
b. Collection of unbiased qualitative and quantitative observations and data. c. Analysis of the data by tables, graphs and statistics to establish if cause and effect relationships exist
between the observation and the methods used.
d. Interpretation of the data. What does the data mean?
e. Drawing conclusions, with the help of prior knowledge.
If the interpretation of the data and conclusions drawn do not support the original hypothesis, then the
hypothesis is modified or discarded and a new hypothesis is formulated and the experiment redesigned.
5. Theory
If the observations and data obtained are consistent on repeated experimentation and the same conclusions
are reached that this hypothesis is the most probable explanation of the observed phenomena, then the
hypothesis is elevated to a theory. A theory is a hypothesis, which has been sufficiently tested that there is
confidence in the probability that it is true. A theory is not absolute, as it is still open to possible exception
and thus modification or disproof.
6. Law (of Nature)
When there is no exceptions to the observations, that is this is the only explanation to the observed
phenomenon, then the theory becomes a Law.
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Experimental Design
The design of the experiment is to make the observed data as valid as possible. The experiment is a test by which nature is manipulated to explain the initial observations. This consists of designing of a controlled experiment involving a large sample size so the observations obtained (the results) would not be due to chance alone.
In a controlled experiment, one group of "normal" subjects or control group is compared to a group undergoing the manipulation where the variable factor is introduced, called the independent variable. This group of subjects is the experimental group. The results obtained in the experimental group are the dependent variable. The control group is used to evaluate any possible side effects of the manipulation caused by the introduction of the independent variable. Ideally the control group is identical to the experimental group in all respects except for the variable introduced. Only one variable at a time is introduced between the control group and experimental group, while all other conditions are exactly the same. This insures that the single independent variable introduced truly caused the observed effect or the dependent variable (the result).
Summary of the Steps of the Scientific Method
Identify a problem by making observations

Asking questions about the observations

Formulate a hypothesis and make predications

Design a controlled experiment

Collect observations and data

Analyze data

Interpret data

Draw a conclusion(s)

Repeat experiment, if results and conclusions reached are the same on repetition

Accept the hypothesis as the probable explanation, this is known as the Theory

If no exceptions to the theory, then the theory becomes a Law of Nature
If results are not repeatable propose alternate hypothesis and redesign the experiment.
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Introduction to Scientific Procedures
B. Scientific Measurement and Equipment
The ability of the scientific method to gain knowledge and to make valid predictions depends on the
accuracy of the observations. The accuracy of observations depends on use of specific laboratory equipment
to quantify (measure) phenomena accurately (ability to obtain the true value) and precisely (ability to obtain
the same value on repeated measurements).
Accurate laboratory equipment is essential for standardization of equipment and once standardized this
equipment can be used to quantify the observable phenomena.
To simplify mathematical calculations and to standardize measurements throughout the world a single
interrelated system of measurement, the metric system, is used. The metric system is a decimal system of
measure.
The metric system is based on the standard unit of length, the meter. The meter is one ten-millionth of the
distance from the equator to the pole. If 0.01 of a meter, the centimeter, is cubed, a measure of volume, the
cubic centimeter (cc or cm
3
) is obtained. Since the cc is equal to the milliliter (mL) a measure of capacity,
the milliliter is derived. The standard unit of weight (mass), the kilogram, is the weight of 1000 cc or mL of
water at 4 o
C. Temperature in the Celsius (centigrade) scale uses water as its basic substance, at 0 o
C water
freezes, at 100 o
C water boils.
Standard Units of Measurements
Directly measured:
Measurement Unit
Length meter
Weight (mass)
Temperature kilogram centigrade
Time second
Calculated value:
Volume-space occupied liter
by an object
This is a calculated unit
derived from the mL.
Measurement in the metric system is easy since larger or smaller units than the standard units of measurement are created by multiplying or dividing by 10 or multiples of 10. Moving the decimal point performs conversions within the metric system. From the basic unit 1.0 to multiply, move the decimal point to the right; to divide, move the decimal point to the left.
To multiply 1.0
To divide 1.0
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Laboratory measurements in biology laboratories are usually 1.0 or less than 1.0.
Linear measurement - measurement in one dimension, i.e. measuring the length of an object along a straight line.
Linear measurement along two dimensions is square area measurement.
Area = length x width (A = l x w)
Area of a square = edge
2
(A = e
2
)
Total surface area of a cube = 6 x edge
2
(SA= 6e
2
)
Linear measurements in three dimensions result in volume.
Volume = length x width x height (V = l x w x h)
Volume of a cube = edge
3
(V = e
3
)
Volumetric measurement
Use of the Pipette
A pipette is a narrow glass or plastic graduated tube used to measure and dispense fluids. The most commonly used pipettes are 1.0 mL and 10.0 mL capacity. The 10 mL pipette is graduated to 0.1 mL, 1 mL are graduated to 0.1 or 0.01 mL.
Technique
1.
Place solution you want to dispense in a clean, dry beaker. Never put the pipette directly into the reagent
bottle. Pipette must be dry inside and out.
2.
Use pipette filler. Never pipette by mouth. The pipette fillers are attached to the top of the pipette and by screw-type mechanism creates a vacuum to regulate fluid uptake and delivery.
a. Insert the zero end of the pipette into the chuck of the pipette filler as far as it will go.
b. Place tip of pipette into solution to be transferred.
c. To aspirate or suck up fluid, rotate suction screw until fluid reaches the desired level, at the meniscus
of the column of fluid. This will be accomplished by raising the vertical screw with the thumb.
d. To deliver the solution, move the screw in the opposite direction until the meniscus of the desired
volume has been released. As the pipette is emptied, keep the tip above the fluid level and against the
wall of the vessel.
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Significant Figures
Digits that arise as a result of a measurement are termed significant. There are two categories of numbers, exact and inexact. An exact number is obtained as the result of a count. An inexact number is obtained when a measuring device is used. Design limitations of instruments, restricts the number of digits obtained from a particular measurement. In general, when reading an instrument, determine how it is calibrated and estimate the value to one more place.
Significant Figures in Results of Calculations
Addition or Subtraction
The result should be rounded off so that it has as many decimal places as the measurement with the fewest decimal places.
Multiplication or Division
The calculated result should be rounded off to the same number of significant figures as the measurement with the fewest number of significant figures.
Rounding Off Numbers
When we drop figures that are not significant, we have rounded off the number.
1. If the digit being dropped is less than 5, the last remaining digit remains the same.
2. If the digit being dropped is 5 or greater than 5, the last remaining digit is increased by 1.
Temperature Measurement
Temperature measures the amount of energy in the form of heat generated by molecular motion. Celsius ( o
C) is the basic metric unit of temperature. The decimal scale from 0-100 o
is of biological significance, as it defines the limits of pure water’s freezing and boiling points, the centigrade scale.
0
F=9/5(
0
C) +32
=1.8(
0
C) +32
0 C=5/9( 0 F-32)
=0.56(
0
F-32)
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Metric System Supplement
1. 1 m = _________cm 16. 98.6
o
F = __________ o
C
2. 1 mL= __________L 17. 0.222 m = 22.2 __________ (unit)
3. 1 g = __________ mg 18. 3 kg = __________ g
4. 1 x 10
-3
=__________ (decimal) 19. 35 cm = __________ m
5. 1 x 10
-2
=__________(decimal) 20. 3.7 x 10
-2
= __________ (decimal)
6. 350 mL = __________ L
7. 1 mm =___________ cm
21. 0.00172 = __________ (exponential)
22. 182 = __________ (exponential)
8. 14 cm = __________ mm 23. 0. 2 = __________ (exponential)
9. 750 microns (

) = __________ mm 24. 0.371g = __________ mg
10. 750

= __________ cm 25. 4 mm = __________ microns (

)
11. 4L = __________ mL 26. 1 mL H
2
O = __________ cc= __________ g
12. 300 mg = _________ g 27. 6.6 lb = __________ kg
13. 45 mL = __________L 28. 2 in = __________ cm
14. 100 o
C = __________ o
F 29. 100 mL = __________ dL
15. 32 o
F =___________ o
C 30. 10 qt = ___________ L
31. 8 oz = __________ g
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Solutions and Serial Dilutions
Solutions consist of substances dissolved in the fluid medium. The substance dissolved is the solute; the dissolving fluid is the solvent. In living things the solvent is water.
When a solution is diluted it is mixed with a diluting solvent. The original solution (“stock") is combined with the diluting solvent ("diluent") in a definite proportion. The new concentration is the ratio of the volume of the stock solution to the total volume of the new dilute solution (stock plus diluent).
If a 10-fold dilution were required, the ratio of stock volume to total volume would be 1:10.
1 mL stock
------------------------------- = 1/10
1 mL stock + 9 mL diluent
Technique: Preparing a 10-fold Serial Dilution
1. Use a 10 mL pipette; pipette 9 mL distilled water (diluent) into 6 test tubes. Number each tube.
2. Use a 1 mL pipette; add 1 mL of the stock methylene blue (MB) solution to the first tube, mix. This tube is
now diluted 1:10, that is, the solute concentration is 0.1 that of the original.
3. With the 1 mL pipette, pipette 1 mL of solution from tube #1 into tube #2, mix. Since a 1:10 solution (tube
#1) is in turn diluted 1:10; the concentration in tube #2 is 1:100.
4. Continue the serial transfer of solution to diluent for all remaining tubes.
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Measurement of Dilution Concentration
Colorimetry
Colorimetry allows us to make qualitative and quantitative determinations on "unknown" solutions. Since solutes in solution have the capacity to absorb light (radiant energy) waves, we can make distinctions among solutes based upon their absorbance characteristics. Light waves of the visible spectrum have wavelengths ranging from 400 millimicrons
(m

), violet to 700 m

, red.
A spectrophotometer (colorimeter) is an instrument that measures kind and amount of light energy a sample of solution absorbs.
The solution's absorbance of light determines the kind and amount of solute present in the solution. The specific wavelengths of light being absorbed determine the kind of solute in solution. The amount of the light energy or wavelength absorbed determines the concentration of the solute in solution. The spectrophotometer performs two type of analysis:
1. Qualify (identify) a substance by its absorption spectrum, i.e., its absorbance pattern at different wavelengths.
The absorbance pattern at specific wavelengths is the key to its identity.
2. Quantify a substance, i.e., indicate how much of the substance is present depends on the amount of a
specific wavelength of light is being absorbed. The absorbance of the unknown is compared to that of a
"standard", a solution of known concentration. The color intensity of a solution is directly proportional to its
concentration of the solute in solution. The spectrophotometer compares the unknown's color with a standard
color.
To determine concentration:
1. Turn spectrophotometer on. Set wavelength control knob to 570-575 m

for MB.
2. Rotate zero control knob until needle on the meter reads 0% (%T) on the transmittance scale.
3. Place "blank" solution into the sample holder, adjust light control knob to position the needle at 100%
transmittance. A "blank" contain everything in the solution except the solute, the amount you want to
determine. This subtracts out all other solutes that may absorb at the wavelength of the substance you want
to measure.
4. Replace the "blank" with the unknown and read %T as an indication of the concentration of the dilutions.
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