1What’s a preceptor?• Learn by teaching

• Help your peers

• Make the labs better

• (maybe become an undergrad Lab Instructor one day)

• 184 Spring (lab and lecture combined), 181L Fall

• Email Kevin at kbaker2@email.arizona.edu

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Putting photosynthesis to

the test

Putting photosynthesis to

the testApplying tools to the question at handApplying tools to the question at hand

How? Why?

3

Biology, the Dynamic Science, Vol. IRussell, Wolfe, Hertz, Starr

4Goals & 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

5Making 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

6Team efforts• Grounds 1 & 4: liquid permitting red light

• Groups 2 & 5: liquid permitting green light

• Groups 3 & 6: liquid permitting blue light

• ALL: Make enough to share (yours + 2 others)

• Final experiment in 20 ml, so...

7Dance of the Buffers

• Ca++ + PO4-- => precipitate

• Thus, TWO 10x buffer components

• Add either one LAST lest you lose CaPO4 as a solid

• Want buffers at 1X concentration, how much of each in 100mL solution?

8Consider

• 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?

• Where should evacuated leaves be kept while you prepare all tubes?

99

DesignDesign

10Designer helper• Plotulence: in Lab 11 Folder on desktops• ‘New Table’• Enter data• Use sliders to set concentration/dilution

• What calculation is the program performing?

11

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

• Don’t use more than 3 colors! Gets murky

• * Absorbance must be no greater than 0.2 at permitted wavelength

Calculation in Plotulence

• We are using 10X dyes, want 1X final concentration, so how much TOTAL dye in 100mL of solution?

• Calculation example:

• Red slider at 2X, Yellow slider at 1.5X, Green slider at 0.5X

• Total concentration = 4X Divide EACH by 4X

• 2X/4X = 0.5, 1.5X/4X = 0.375, 0.5X/4X = 0.125

• Multiply each answer above by 10 to get final volume in 100mL solution (should be 10mL in TOTAL)

12

13Measuring light...• Get absorbance reading of your mixture at all specs, use

to generate a graph of wavelength vs. absorbance

• IMPORANT: Everyone’s graph MUST be labeled the same!

• Graph paper in the back of your manual

• 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’? (No calculus!)

14Comparing 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 unitsX-axis: each major line is 100nm, plot 300->700 nm

1515

ExecutionExecution

16What’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?

17Make it so• Groups 1 & 3 & 5 will exchange so everyone has a red-

allowing, green-allowing & blue-allowing tube

• 2 & 4, & 6 will do the same

• Don’t forget control with 1X buffer

• Each group shall write a lab report on their measurements & findings

1818

InterpretationInterpretation

19All’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’

• In others words, should the amount of light being allowed to reach the leaves in each colored tube be the same to make this a fair fight?

• What should we do about it?

• Standardization equation example coming up!

20Represent!• How should you take the differences in your graphs (the weights)

into account?

• Suppose you had

• red dye, graph-weight 3.0 g, with avg. floatation 5 minutes

• blue dye, graph-weight 2.0 g, with avg. flotation in 7’

• green dye, graph weight 1.5 g, with avg. floatation in 10’

• 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

21Closing discussion

• Did we find what we expected to find?

• Are there stones left unturned (unexamined assumptions in our experiment)?

• What errors could cause us to find results that are unexpected such as green disks floating first?

Don’t Forget to Include…• Calculations for dye mixture and standardization

• Description of contents of 100mL solution

• How did you determine what should be included in this final volume and why? Plotulence program!

• Where did you get your initial data table used in the Plotulence program?

• Avg. leaf float time, same leaves from each tube or different?

• Description of what absorbance readings and graph represent, how was it used?

22

2323HomeworkHomeworka lab report in my dropbox

featuring...Sound Logic & Presentation

Complete sentences

Correct spelling

Elements in correct places (methods, results,

discussion)

a lab report in my dropbox featuring...

Sound Logic & Presentation

Complete sentences

Correct spelling

Elements in correct places (methods, results,

discussion)