1 What’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 Kevin at

2 Putting photosynthesis to the test Applying tools to the question at hand How?Why?

3 Biology, the Dynamic Science, Vol. I Russell, Wolfe, Hertz, Starr

4 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

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

6 Team 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...

7 Dance 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?

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

9 Design

10 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?

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 = Multiply each answer above by 10 to get final volume in 100mL solution (should be 10mL in TOTAL) 12

13 Measuring 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!)

14 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

15 Execution

16 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?

17 Make 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

18 Interpretation

19 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’ 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!

20 Represent! 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

21 Closing 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

23 Homework a 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)