Presentation on theme: "Lab 5 Substitute – Algae Photosynthesis It’s easy being green. And photosynthesizing. Side note: Our last lab, Lab 5, is a stand-in for Lab 6 in our lab."— Presentation transcript:
Lab 5 Substitute – Algae Photosynthesis It’s easy being green. And photosynthesizing. Side note: Our last lab, Lab 5, is a stand-in for Lab 6 in our lab manual. This is a stand-in for Lab 5 in your lab manual.
The Background If you’re a heterotroph, metabolism is fairly simple. – Oxygen and sugar in, carbon dioxide and water out. If you’re an autotroph, metabolism has two competing reactions. – In this corner, photosynthesis is producing O 2. – In this corner, respiration is producing CO 2. The two reactions do not usually run at the same rate.
The Background In order to study which reaction is occurring at a greater rate, we’re going to need an organism whose products can be measured. – So redwood trees are out. Meh. Let’s go with something a bit smaller. – Algae!
Okay. Algae. Great. Now what? Algae, of course, undergo both respiration and photosynthesis. We just need to be able to determine the dominating reactions. Which one is happening faster? To do that we need to rely on one other principle that’ll make this whole study fantastically elegant: – When CO 2 dissolves, carbonic acid (H 2 CO 3 ) forms, lowering the pH of the solution. – Therefore, we just need a pH indicator. Today, we’re using hydrogen carbonate indicator. How appropriate.
About the indicator… There’s one little bit of prep we need to do for the indicator. Suppose you prepare a hydrogen carbonate indicator for CO 2 concentration but you seal it off and never expose it to normal CO 2 concentration. When you start the experiment, just the exposure of the indicator to the air will make the indicator change color and will skew your results.
About the indicator… To “tune” the indicator before you seal it off in a container, use a straw and exhale gently and deeply into the solution. – You want the solution to be “bright red.” If it is already, this step is unnecessary. – DO NOT inhale the solution. No, really. I’m serial. Straws are disposable, FYI.
The Test Subjects Remember our yeast lab? Spheres of yeast encased in sodium alginate? This time, it’s spheres of algae encased in sodium alginate. – Sodium alginate being an extract of an algal product. Weird. They’re a little greener and far more autotrophic, but otherwise they’re prepared the same way. – Drop the algae/alginate mix into a 0.15 M CaCl 2 solution to gel it all up.
The Procedure Your control group is as follows: – Put about 20 algal spheres inside a bijou bottle. Yes, they’re called bijou bottles. I have no idea why. – Do the same for a second bottle. You need a replicate. – After 30 minutes (OR A TIME DETERMINED BY ME) sitting in some “normal” region of the classroom, observe the shade of the indicator solution and record the approximate pH.
The Procedure Your variable group is as follows: – Put about 20 algal spheres inside a bijou bottle. Yes, they’re still called bijou bottles. I still have no idea why. – Do the same for a second bottle. You need a replicate. – Time it for 30 minutes again (OR A TIME DETERMINED BY ME), but make sure the algae spheres are in some kind of experimental condition. Let me know what you’d like to do. Think things like light intensity… – Very bright or completely dark. …light color… – Red or green light is available. …or possibly temperature. – Chilled algae.
The Lab Report This is an informal lab report. Follow the rubric and construct a quality report, but make sure you include the specific points mentioned at the bottom of your lab direction sheet.
Clean Up When you’re done, dump the indicator solution down the sink with some running water. Algae balls can be disposed of in the trash. Dry your bijou bottles as best you can. Hmm…what else…? Oh! Two things: – Work on your Photosynthesis POGIL during the lab downtime. Skip 23, 28, and 32. – How do you tell what color is what pH?