Friday Sprog Blogging: photosynthesis.

Dr. Free-Ride: Any ideas for tomorrow’s sprog blog?
Younger offspring: I wanted to do how photosynthesis works.
Dr. Free-Ride: Did you do any research on that since last week?
Younger offspring: I don’t do research.

Dr. Free-Ride: You don’t do research?! How do you do science, then?
Younger offspring: I don’t research stuff.
Dr. Free-Ride: Well, then, how do you learn stuff?
Younger offspring: (after a pause) I didn’t do research about how photosynthesis works at night.
Dr. Free-Ride: Well, but does it work at night? ‘Cause, what is photosynthesis?
Younger offspring: The moon could make it work at night.
Dr. Free-Ride: Hmm.
Younger offspring: If it’s bright enough.
Dr. Free-Ride: You think moonshine — the light shining off the moon, not the backwoods liquor — you think that might be strong enough that plants could make some sugar during the night?
Younger offspring: Maybe.
Dr. Free-Ride: I guess we’d have to do research to find out. That actually sounds like kind of an interesting project to research, but we’d have to figure out some way to tell what was happening with the plants at the full moon — how to measure whether photosynthesis is actually happening. Any ideas about that, [elder offspring]?
Elder offspring: Well, you could have one plant that gets only sun, one plant that’s a control plant and gets both, and one plant that gets only moonlight.
Dr. Free-Ride: I see. And so, we could sort of take plant growth as at least an indirect measure of which plants are making sugar out of the available light. If we had fancy scientific equipment, are there other ways we could try to measure photosynthesis besides just comparing how the plants look?
Younger offspring: Stay up all night and watch the plant.
Elder offspring: A watched pot never boils.
Dr. Free-Ride: Well, I think you could watch the grass and it might still grow, although it would be kind of boring. (Also, a watched pot will boil, but the time it takes to come to a boil may seem longer while you’re watching it.)
Younger offspring: We could have entertainment outside.
Dr. Free-Ride: But then maybe we’d get distracted from what we’re supposed to be watching.
Younger offspring: We could listen to the radio, or music.
Elder offspring: But wouldn’t that disturb the neighbors?
Dr. Free-Ride: It might distract neighbors.
Younger offspring: Not too loud!
Dr. Free-Ride: What if we used earbuds? Because anyway, wouldn’t we have to worry about whether the music had some influence on the plant growth patterns, or on whatever reactions were happening inside the plant?
Elder offspring: Yeah.
Dr. Free-Ride: So, have you studied photosynthesis at all in school, or have you just read about it or heard about it?
Elder offspring: Haven’t studied it — we’re not to cells yet in science. In the spring, probably.
Dr. Free-Ride: Photosynthesis takes sunlight and uses the energy from that to make a chemical reaction go. But it’s also taking something out of the air to do that chemical reaction. Do you remember what plants take out of the air when they’re photosynthesizing?
Younger offspring: CO₂!
Dr. Free-Ride: CO₂, yes.
Elder offspring: They also use H₂O.
Dr. Free-Ride: Yes.
Elder offspring: And they make C₆H₁₂O —
Dr. Free-Ride: That’s glucose!
Elder offspring: — and O₂.
Dr. Free-Ride: So one thing we could do to measure how much photosynthesis is going on during a particular period of time, if we had fancy schmancy equipment, we could measure how much CO₂ gets used up. Maybe we’d have to put the plant we’re measuring in a container that keeps in the gasses but lets in the light, and measure how much CO₂ we start with, and then after however long in the sunlight or moonlight, measure how much CO₂ is in the container at the end. If the CO₂ decreases when the plant is in the moonlight, that might be a good clue that a plant can photosynthesize with moonlight. Or, we could measure how much O₂ (if any) is produced. Of course, there’s one complication.
Younger offspring: What?
Dr. Free-Ride: Photosynthesis isn’t the only thing plants do.
Elder offspring: They also respire.
Dr. Free-Ride: That’s right. Part of the point of making that glucose is being able to use it when the plant needs energy. And when they use the glucose —
Elder offspring: The plant takes in O₂ and gives off CO₂.
Dr. Free-Ride: So if we had a plant in a closed container and were set up to measure the different levels of gases, we could measure how the composition of the gas changes over a night with a new moon —
Younger offspring: And compare it to a night with a full moon!
Dr. Free-Ride: And that might tell us how much energy a plant uses at night when no photosynthesis is going on and let us figure out whether there could be any photosynthesis happening under a full moon.
Younger offspring: Cool.
Dr. Free-Ride: You didn’t do any research and somehow we still had a discussion about photosynthesis. You lucked out this time.