Ideas for Students
Meg Deppe
I stumbled upon your endeavor while looking for real-world projects in which to involve my middle school and high school students out here in California. Our elementary teachers work hard to provide exciting, relevant, hands-on science for students. They still make volcanoes; build circuits, and plants seeds. By middle and high school, with the demands of large classes often much of the teaching is out of the book, with few real world, data-rich investigations that develop lasting science skills and curiosity.
I believe the tool you are designing would allow students to make a great many observations that could peak their curiosity and lead them along the path toward investigation and perhaps allow them take "data," discuss and develop scientific arguments and finally to see themselves as scientists.
I’m not completely clear as to the capabilities of Photosynq, however I’m hoping we could tackle some of the following:
Possible avenues of observation / research:
Comparison of native desert vs. non-desert plants
o How much do the drought resistant properties of the leaves reduce the photosynthetic rates - or do they?
Comparison between native desert plants
o Which plants have higher photosynthetic rates - Larrea tridentata (Creosote Bush) or Atriplex canescens (Saltbush)?
o Comparison of C3 and C4 plants (The students “read” about this, but to “discover” this on their own prior to reading could be meaningful.)
o Under which conditions are C3 plants more efficient?
o Under which conditions are C4 plants more efficient?
o Comparison of one plant under different conditions
o Ocotillo during a dry spell and right after a rain
o Mulberry Tree - spring (new leaves) summer (established leaves) fall (leaves about to drop)
o Tomato plants in the garden - stressed for water and after irrigation
o Comparison of monocots vs. dicots
o Comparison of a local native plant vs. an invasive plant that is replacing the native.
o Determining the yearlong photosynthetic rate for a pine tree (evergreen) vs. a cottonwood tree (deciduous).
o Determining the advantage given the Palo Verde tree (Parkinsonia florida) with its ability to use its green (chlorophyll) trunk for photosynthesis as compared to the Mesquite (Prosopis alba) which has a normal brown trunk.
o Comparison of photosynthetic rates in the lab under different lighting conditions.
o Comparison of photosynthetic rates in the lab of Wisconsin Fast Plants during their 28-day life cycle.
o Then on a national / international level - teaming with Journey North - http://www.learner.org/jnorth/ and using your Photosynq tool to add to their studies of seasonal change.
Those are a few of my wild ideas…. Meg Deppe - Teacher - California
eliezer...@gmail.com
This is going to be a bit technical, but bear with me:
To start with, what the photosynq primarily does is measure a parameter called Phi PSII, which is the quantum efficiency of photosystem II, or just "quantum efficiency". while this parameter is related to the overall rate of photosynthesis, it is not the same thing. To measure what you might call the bottom line "rate of photosynthesis" you normally need to measure the rate of CO2 assimilation by the leaf, which requires a bulky and expensive infrared gas analyzer. The final version of the photosyqn will incorporate a technology that should allow for a simplified version of this kind of measurement.
What the quantum efficiency measurement tells you is how much, or specifically what percentage, of the light that is being absorbed by a leaf is successfully being used for photosynthesis. so the parameter tells you something about photosynthesis, but it is in a sense normalized to the individual leaf - it depends on how much light is being absorbed to begin with. so very young leaves, for instance, are still yellowish because they are still building their photocenters and they do relatively little total photosynthesis....but they have high quantum efficiency because they use all of the light that they do absorb for photosynthesis. that is, they don't absorb as much light, but they use it very efficiently. conversely a very dark green leaf can have very low quantum efficiency because it wastes most of the light that it absorbs, but it has a high overall photosynthetic rate.
this doesn't mean that this measurement on its own isn't useful, or isn't indicative of photosynthetic rates, it just means the comparisons you can make are more limited and you have to be careful not to over interpret the data. if you are comparing two mature leaves, for example, it can tell you which is more adapted to a given light intensity - a full sun leaf will have peak efficiencies at much higher intensities than a shade adapted leaf, and so forth. different leaves at different levels of a canopy will be adapted to different intensities. c4 plants should have higher efficiencies than c3 plants under certain conditions because their photosynthetic rates are not as limited by co2 or water stress. etc. additionally, taking a phiPSII measurement in a dark adapted leaf gives you another parameter (called Fv/Fm, or max efficiency) which is an indicator of leaf health - damaged or unhealthy leaves have reduced maximum efficiencies.
hope this helps
regards
Dr. Eliezer Schwarz
Kramer Lab
MSU DOE-PRL
Greg Austic
Personally I really like the comparison of the Palo Verde tree - that would be really interesting to get a general (if not exact) sense of how much energy is coming from it's trunk versus it's leaves.
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