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Sit with last week’s group
Turn in…
• Dilutions worksheet
Goals
• Consider implications of plants being ‘green’
• Use O2 creation as a measurement of photosynthesis
• Test a common claim from textbooks
Here’s an assertion…
Can we test this?
Photosynthesis in (green plants) is more effective at the ends of the spectrum than in the middle
HOW can we test it
• What did we do with leaves last week?– Leaf assay– Graph of absorption spectrum
• How did that happen?
• How can you make your data meaningful?
• How might we subject leaves ONLY to certain wavelengths?
• Groups 1 & 2: liquid permitting red light
• Groups 3 & 4: liquid permitting green light
• Groups 5 & 6: liquid permitting blue light
• All: make enough to share (yours + 2 others)
• Final exp. 20 mLs, so how much to make?
Getting Started
What will it look like?• Need to place disks in at same time?
• What do you time?
• Does concentration matter?
• How can you make comparisons valid?
Consider…
• What is the mechanism by which we are ‘removing’ some wavelengths of light?
• Implications for volumes of beakers?
• Consequences if red sits waiting while you work with blue and green
• Again, when should we start extracting O2?
Buffers• Ca++ and PO4-- precipitate
• So, TWO different 10X buffer components
• Add ONE of the them last or get a solid
A tool for making dyes:Plotulence
Plotulence
Plotulence
Absorbance values
Plotulence
Concentration (_X)Absorbance values
Plotulence
Concentration (_X)Absorbance values
Resulting mixture
Your Goal• Let in as much light as possible for your
‘region’ of the spectrum– Red: include both 630 & 660– Blue: 350 & 430– Green: 500 & 590
• Given the above, block as much as possible at other wavelengths
• Absorbance no more than .2 at your wavelengths and no greater than 2 at other waves
Plotulence
• Use ‘Plotulence’ to develop your dye cocktail
• Again, sliders indicate how much more concentrated than last week
• Check with other group of same color
• We’re not making artificial hearts or sending a probe to Mars
Open Plotulence
• On desktop
Plotulence• ‘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 and no greater than 2 at other wavelengths!!!!
Plotulence
Concentration ( e.g., 1.35X )Absorbance values
Resulting mixture absorbances
mixture
What do we have?• Starting concentration of dyes/buffers?
What do we have?• Starting concentration of dyes/buffers?
– 10X
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?– Yes, we have that, too! – slider values
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?– Yes, we have that, too! – slider values
• What are we missing?
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?– Yes, we have that, too! – slider values
• What are we missing?– Indv. dye volumes
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?– Yes, we have that, too! – slider values
• What are we missing?– Indv. dye volumes
• What makes up the rest?
What do we have?• Starting concentration of dyes/buffers?
– 10X
• Final volume?– 100 mLs (how much of it is buffer?)
• Desired dye concentrations?– Yes, we have that, too! – slider values
• What are we missing?– Indv. dye volumes
• What makes up the rest?– Distilled water
Mix It• Remember there are TWO ‘buffers’
– Do not place at same time – ONE goes last
• Compare your plan to other group’s• Mix your color• Trade ‘colors’ with your friends; collect all
three!!!!• Get your disks• Float ‘em• Controls?
What if one ‘color’ is darker?• What can we do to account for differences in
the AMOUNT of light allowed through the solution? HOW?
What if one ‘color’ is darker?• Test your color using specs• Graph (from lab manual) your data using
smoothed curves• Cut out the graph ABOVE line• Weigh it; record it; compare it• What does that number represent?• Y-axis:4th major line from bottom as 2.0 abs• X-axis: each major line is 100nm; plot 300-700
nm• Give your graph weight to ‘sharing’ groups!
What Now?
• Did you find what you expected?
• Stones left unturned?
• Differences in graph weights?– Red, graph 3g, floated in 5 min– Blue, graph 2g, floated in 7 min
• Adjusted time?
This is a critical part of your experiment. Failure to explain and deliver this calculation = loss of points on write up
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