Download Unit 2 and 3 Scientific Method and Spectrophotometry

Scientific Method
• Unit 2
• We will set up the scientific method experiment
today and will work on it for the next 2 weeks.
• Mealworm or Tenebrio molitor
– Weigh mealworm this week
– Place in one of 2 substrates
• Oat bran or peat moss
– Reweigh next week
– Do statistical analysis of data (weight gain or loss) to
determine which substrate best supported growth of
the mealworm
• Independent variable
– What the investigator varies
– Type of substrate
• Dependent variable
– What is measured or counted
– Change in mass of mealworm
• Control variables
– Amount of water, amount of substrate, light
conditions, others
Review Scientific Method
Terminology
• Hypothesis
• Steps on scientific method
• Discuss with your lab group a valid
hypothesis for your mealwork experiment.
Scientific Research Articles
• Scientists must publish their research in a peerreviewed journal for the information to be a part
of scientific knowledge.
• Your lab reports will be similar to these research
articles and will contain the following 5 sections.
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–
–
–
–
Abstract
Introduction
Materials and Methods
Results
Discussion
• Research articles
Scientific Method (Mealworm)
• Measure and record Day 7 mass
• Dispose of mealworm and substrate in trash.
Place vial and stopper in labeled container
• Add your data into instructor’s computer (Excel
spreadsheet) so that all students can record all
of the class’s data
• Run statistical program in Excel.
• Review the meaning of the statistical analyses.
Comparison of 2 independent sample means
Refer to p. 23 for definitions
• Mean
– average
• Deviation
– How the measurements vary from the mean (+ or -)
• Variance
– Sum of the squared deviations
• Standard deviation
– Square root of the variance
• Minimum value
• Maximum value
• Sample size
•
 x  x 
2

n 1

 89.17
Formula for standard79
deviation


79  89.17 
2
 , 85  89.17  , 92
2
2
 85  89.17   92
2
Hypothesis Testing
• Null hypothesis Mean A= Mean B
• Alternate hypothesis Mean A = Mean B
• p value is the most important value in this
section
• If p is less than or equal to 0.05 then you can
REJECT the null hypothesis
• If p is greater than 0.05 then you FAIL TO
REJECT the null hypothesis
What does the p value mean?
• The p (probability) value is determined by
a statistical test called a t-test.
• Level of significance is set at 0.05
• This means that 5% of the time, the
differences observed between the weights
of the 2 groups would be due to chance.
• Lab report over Scientific Method will be
due soon.
• Include the statistical analysis information
– P values
– Means
– Statement of REJECT or FAIL TO REJECT
Null Hypothesis and why you did so.
• Use outside references for background on
mealworm nutrition.
Spectrophotometry Unit 3
• Electromagnetic spectrum
–
–
–
–
All the available energy in the universe
Travels through space as a wave
Shorter wavelength-higher energy
Longer wavelength-lower energy
• Visible spectrum
– Portion of the spectrum that humans perceive as
color
– Wavelengths range from 380(violet) to 720 (red) nm
http://www.abrisa.com/images/visible.spectrum.gif
• Substances possess color because of
their ability to absorb and transmit certain
wavelengths.
• Chlorophyll absorbs wavelengths of red
and blue light, green light is transmitted.
• The colors we see are the colors that are
transmitted or reflected to our eyes.
Spectrophotometer
• Instrument used to determine absorption
of different wavelengths of light
• View the parts of spectrophotometer
http://www.hamline.edu/depts/biology/courses/biocon2/specuse.html
Exercise 3.1
• Relationship between wavelength and
color.
• View what colors are seen at different
wavelengths.
Determining % transmittance and
absorbance
Blank and Unknown (ex 3.2)
• Blank
– 1 ml distilled water + 5 ml indicator solution
• Unknown (experimental)
– 1 ml unknown protein solution + 5 ml indicator
solution
• Record readings on p37 for unknown on p 37.
• Readings for blank are not recorded here.
Why?
Procedure for measuring absorbance
1. Turn on the Spec-20. Let instrument warm up for 5 minutes.
2. Set the wavelength with the wavelength control knob.
3. With the Mode Select button set the Mode to Transmittance.
4. With no tube in the sample chamber, set the transmittance to 0%
with the zero control knob.
5. Wipe smudges of tube with KimWipe, then insert the blank and set
the transmittance to 100% with the 100% transmittance control.
6. Change the mode to Absorbance. The absorbance should be
0.000.
7. Insert a sample and read the absorbance (OD).
Ex. 3.3 Standard Curve
• A standard curve will be developed using protein
solutions of known concentrations.
• By comparing the unknown to the standard
curve, you can determine the protein
concentration of the unknown.
• Perform serial dilutions of known protein
solution.
• Plot on graph on p 38.
• Also, plot on Excel program using instructions
from p.212