Quiz• Which lab did you like? Why?

(25pts)

• Which lab did you learn the most from? (25pts)

• Which lab did you not like? Why? (25pts)

• How do you think the labs could be improved? (25pts)

Photosynthesis &e- transport

Photosynthesis &e- transport

Pathway thinkingPathway thinking

How? Why?

What is DCPIP?

• What are its uses

• What does it ‘indicate’

X1

X2

Following the Scientific Approach: Predicting

The experiment’s afoot!

• Hypothesis I: The herbicide (‘X ’) acts before DCPIP has a chance to nab the electron

• Hypothesis II: The herbicide (‘X ’) acts after DCPIP has a chance to nab the electron

X1

• NO reduction of DCPIP (stays blue)

If we get this result, are we ready to publish a conclusion?

If we get this result, are we ready to publish a conclusion?

• Rampant reduction of DCPIP (turns clear)

X2

Technical Aspects 1• What do you want?

– Round 1 – KEEP the LIQUID– Round 2 – KEEP the CHUNK

• Part B– Step 9 – three minutes– Step 11 – five minutes– **DON’T change the speed on the

centrifuge

• MAKE THE CHANGE*– Page 13-10, STEP 6: target

absorbance should be 0.1 instead of 0.2 specified in the manual

Corrections Continued

• PART C, STEP 6

• Adjust the concentration of your chloroplast solution so that it would have an absorbance of 0.1, not 0.2

• Ask me if you still have questions about how to do this after reading the lab manual carefully

• How long do you let it go?• At what point in time will the chloroplast-

induced reduction have taken place, but the random reduction not yet have occurred at significant levels?– How often do you need to measure the

absorbance?

– When will you start measuring the absorbance?

– How will you know you can stop making measurements?

Technical Aspects 2

• What does herbicide ‘need’ to ‘do its thing’?• What’s happening to DCPIP sitting in the

tube prior to the experiment starting?• What happens to results if tubes are not

thoroughly mixed?• Is there a difference between 600 & 660 nm?

Should you pay attention to which the protocol calls for when?

• If you have a tube that’s supposed to be ‘dark’, where should it be most/all of the time?

Technical Aspects 3

LASTLYYour chloroplast

preparationDiluteinto

ACETONE

1

Read at 660

Compare reading to 0.1

Dilute the original material by the ratio (actual reading/0.1)

2

Apply your calculated dilution to

the preparation

(dilute using

BUFFER, not

acetone!!!)

3 Your experimental

material!

4

DO NOT DO YOUR EXPERIMENT IN

ACETONE!!! (that is only for the

dilution calculation)

More reminders…• DO NOT DO YOUR EXPERIMENT IN

ACETONE!!! (that is only for the dilution calculation)

• Measure the absorbance of the acetone + chloroplast solution at 660 nm (only use the spec that are marked with a post-it for that)

• Measure the absorbance for the rest of your experiment at 600 nm (any spec. in the room will work for that)

Thinking thoughts

• Why is acetone used?

• Why do you think the stock chloroplast solution must be diluted?

• Why is the chlorophyll concentration an important factor?

More thoughts• Where should your tubes be relative to the lights?

• Should you allow your contents to settle to the bottom of the tube?

• Is it advantageous to have the tubes vertical this week?

HomeworkHomeworkWhence the herbicide conclusions?

Description of tube contents, purposes, model for events therein (per the

rubric)

Whence the herbicide conclusions?Description of tube contents, purposes,

model for events therein (per the rubric)