How?
1
Why?
Putting photosynthesis
to the test
Applying tools to the question at hand
Goals & Purpose
•
To test a common claim from textbooks
•
To build and understand tools you’re working with
•
•
recall: otherwise, it’s simply not science. It’s magical
mumbo-jumbo
To generate meaningful data that allows drawing of conclusions.
And to draw them
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3
Theory
4
•
Looking at a leaf, what would you
hypothesize would be the most
effective wavelengths for
photosynthesis?
• WHAT IS YOUR MECHANISM?
5
Making it so...
•
How could we use last week’s tools
to address the question
Assertion: Photosynthesis in (green
plants) is more effective at the ends of the
spectrum than in the middle
Team efforts
•
Grounds 1 & 4: liquid permitting red light
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Groups 2 & 5: liquid permitting green light
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Groups 3 & 6: liquid permitting blue light
•
ALL: Make enough to share (yours + 2 others)
•
Final experiment in 20 ml, so...
6
Dance of the Buffers
•
Ca++ + PO4-- => precipitate
•
Thus, TWO 10x buffer components
•
Add either one LAST lest you lose CaPO4 as a solid
7
Consider
•
What is the mechanism by which we are ‘removing’ some
wavelengths of light
•
•
What are the implications for the volumes in your
beakers?
What will be the consequences if you fill the red beaker with
disks and it sits waiting while you fill blue, then green?
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9
Design
Designer helper
•
•
•
•
Plotulence: in Lab 11 Folder on desktops
‘New Table’
Enter data
Use sliders to set concentration/dilution
•
What calculation is the program performing?
10
Constraints
•
•
Let in as much light as possible* for your ‘region’ of
the spectrum
•
Red: include both 630 & 660
•
Blue: 350 & 430
Given the above, block as much as possible at other
wavelengths
11
12
All’s fair... if you make it
that way
•
Does it matter if amount green (and other wavelengths)
available light of the ‘green tube’ is similar to amount blue
(and other) available light of the ‘blue tube’
•
What should we do about it?
* Absorbance must be no greater than 0.2 at permitted wavelength
13
Execution
14
What’s the experiment look like?
•
What will you be comparing to what?
•
time, number, number per unit time?
•
If nothing floats, how will you know if your leaves were OK?
•
Will your comparison of tubes of different color be valid?
Make it so
•
Groups 1 & 3 & 5 will exchange so everyone has a redallowing, green-allowing & blue-allowing tube
•
2 & 4, & 6 will do the same
•
Each group shall write a lab report on their measurements &
findings
15
16
Interpretation
Measuring light...
17
•
What does the area beneath your absorbance curve represent?
•
...above the curve (and below our arbitrary ‘cap’ of 2)?
•
How could you approximate the total amount of light that your
disks ‘saw’?
Comparing curves
•
Generate smoothed curves based on your spec readings
•
Cut out ABOVE line; weigh for each*
•
What does the resulting number represent?
•
How should it be used?
*Drawing parameters:
Y-axis: set 4th major line from bottom as 2.00 absorbance units
X-axis: each major line is 100nm, plot 300->700 nm
18
Represent!
19
•
How should you take the differences in your graphs (the weights)
into account?
•
Suppose you had
•
•
red dye, graph-weight 3.0 g, and that floated in 5 minutes
•
blue dye, graph-weight 2.0 g, with flotation in 7’
How would you calculate the adjusted speed-of-flotation?
This is a critical part of your experiment. Failure to
explain & deliver this calculation = loss of points on
write up
Closing discussion
20
•
Did we find what we expected to find?
•
Are there stones left unturned (unexamined assumptions in our
experiment)?
Homework
a lab report in my dropbox featuring...
Sound Logic & Presentation
Complete sentences
Correct spelling
Elements in correct places (methods, results, discussion
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Biology, the Dynamic Science, Vol. I
Russell, Wolfe, Hertz, Starr