11

Putting photosynthesis to

the test

Putting photosynthesis to

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

How? Why?

2Goals & 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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TheoryTheory

Looking at a leaf, what would you hypothesize

would be the most effective wavelengths for photosynthesis?

(what is your mechanism? Your

WHY?)

4

5Making it so...

• How could we use last week’s tools to address the question

Hypothesis: Photosynthesis in (green plants) is more effective at the ends of the spectrum than in the middle BECAUSE…

6

Photosynthesis: Review

7Team efforts

• Grounds 1 & 4: liquid permitting red light (low absorbance @ 630 and 660 nm)

• Groups 2 & 5: liquid permitting green light (low absorbance @ 590)

• Groups 3 & 6: liquid permitting blue light (low absorbance @ 350 and 430

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

• Final experiment in 20 ml, so...

8

9

10Dance of the Buffers

• Ca++ +____--=> precipitate

• Thus, TWO 10x buffer components

• Add either one LAST lest you lose a solid

• Add CaCl2 FIRST

• Add NaHCO3(without CaCl2) AFTER the dyes

• THEN add enough water to get to 80mL

11What’s the experiment look like?

• Need to place disks in at same time?

• What do you time?

• Does volume in the beaker matter?

• Does concentration matter?

• How can you make comparisons valid?

1212

DesignDesign

13Designer helper

• Plotulence: in Lab 11 Folder on desktops

• ‘New Table’

• Enter data

• Use sliders to set concentration/dilution

• What calculation is the program performing?

• The ‘slider’ numbers on the side correspond to end concentration of that dye color in your final solution

• Check with other group of same color

It’s a “Helper”• ‘Start Table’• Enter your data• Use sliders

Red = 630 and 660Blue = 350 and 430Green = 500 and 590

Absorbance no more than 0.2 at your wavelength!!!!

Your data are based on a “1X”Solution. Dyes in back are 10X

Dilute your dyes with distilled water

Mix It• Remember there are TWO ‘buffers’• Compare your plan to other group’s• Mix your color• Trade ‘colors’ with your friends; collect all

three!!!!• Get your disks• Float ‘em

16All’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?

17Comparing 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

1818

ExecutionExecution

19Make 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

2020

InterpretationInterpretation

21Closing discussion

• Did we find what we expected to find?

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

22Represent!• 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’

• Green dye, graph-weight 3.5 g, with flotation in 11 min

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

GIVE BACK QUIZ 9

• Tonight’s quiz (Quiz 10) is a take home quiz

• If you received less than an ‘A’, I want you to write me a paragraph explaining where you went wrong in studying for Quiz 9 and how you plan to improve this for the future

• If you received a 90 or higher, explain how you prepared effectively for this quiz

23

2424HomeworkHomeworka 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

25

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