What ’ s a preceptor?

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 • Email Kevin at kbaker2@email.arizona.edu

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

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

Goals & Purpose • To test a common claim from textbooks • To build and understand tools you’re working with • recall: otherwise, it’s simplynotscience. It’s magical mumbo-jumbo • To generate meaningful data that allows drawing of conclusions. And to draw them

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 • 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...

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?

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?

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?

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)

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!)

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

Execution

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 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

Interpretation

All’s fair... if you make it that way • Does it matter if amount green(and other wavelengths) available light of the ‘greentube’ 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!

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

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. • How do you know your leaves are healthy? Control! • Description of what absorbance readings and graph represent, how was it used?

Homework • a lab report in my dropbox featuring... • Sound Logic & Presentation • Complete sentences • Correct spelling • Elements in correct places (methods, results, discussion)

What ’ s a preceptor?