Reining in the hordes

Don’t let the students go too far without clear guidance on next task/goals. Suggested stops are in the slides

Interested in Being a Preceptor?

• Reinforce your own understanding of topics

• Help peers navigate 182L

• Help make the course better

• Learn teaching techniques while earning 3 credits

Interested in Being a Preceptor?

• Work with TAs to teach and develop labs

• Travel to exotic locations (okay, not that)

• Contact Kevin Baker (kbaker2@email.arizona.edu) for more info (link on Bio181L homepage)

44

Putting photosynthesis to

the test

Putting photosynthesis to

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

How? Why?

5

Dilution re-visited• Dye standards are at 10x last week’s concentrations

• There is also a 10x bottle o’ (bicarb + PO4) and one of CaCl2

• why?

• If you wanted to make a 5-ml solution of green dye that matched last week’s absorbance, & had bicarb, what would you do?

6Making 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

7Team 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...

8Dance of the Buffers

• Ca++ + PO4-- => precipitate

• Thus, TWO 10x buffer components

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

9Consider

• 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?

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?

11Constraints

• 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

* Absorbance must be no greater than 0.2 at permitted wavelength

12

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?

13All’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?

14

Comparing curves

• Generate smoothed curves based on your spec readings

• Cut them out; weigh them*

• What does the resulting number represent?

• How should it be used?

*Curve parameters:Y-axis, set 4th major line from bottom as 2.00 absorbance unitsX-axis, each major line is 100nm, plot 300->700 nm

15Make it so

• Groups 1, 3, 5 will exchange so everyone has a red-allowing, green-allowing & blue-allowing tube

• 2, 4, and 6 will do the same

• Each group shall write a lab report on their data

16

Putting a cork in it

• These tests prepare you for NEXT WEEK

• One more thing: confirming an herbicide is a photosynthecide

• 0.15ml herbicide/ml final

• Blue one (DCPIP): 0.2 ml/ml

17

Closing discussion

• Did we find what we expected to find?

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

18Represent!

• How should you take the differences in your graphs (the weights) into account?

• Suppose you had

• a red dye whose graph-weight was 1.5g, and that floated in 10 minutes

• a blue dye whose graph-weight was 1.0g, with flotation in 5’

• How would you calculate the adjusted speed-of-flotation?

19

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

2020HomeworkHomework

Assessor: Photosynthetic pathwayAssessor: Logic of Disproof

And a lab report featuring...

Sound Logic & Presentation

Complete sentences

Correct spelling

Elements in correct places (methods, results,

discussion)

Assign/cover the 16 questions from NEXT

WEEK’s lab?

Assessor: Photosynthetic pathwayAssessor: Logic of Disproof

And a lab report featuring...

Sound Logic & Presentation

Complete sentences

Correct spelling

Elements in correct places (methods, results,

discussion)

Assign/cover the 16 questions from NEXT

WEEK’s lab?