AP Biology Photosynthesis Extension

PHOTOSYNTHESIS: Lab #4 EXTENSIONS

Flower Pigments
The Evolution of Photosynthesis
Chloroplasts as Indicators of Environmental Pollution
Fall Colors

The Pigments Found in Flowers

..... In visible light, flowers seem to be of infinite varieties of hues. ..Not only would be the exploration of the colors be a charming activity, but also it might shed understanding as to the origins of some or many of those colors. .. For example, do red flowers have the same red pigment in them as is found in the leaves? .. Or the yellows?

..... What to do? ..You are familiar with the paper chromatography done in the AP Biology lab manual. ..Merely apply this activity to various flowers. .. Roll the coin across petals and leaves from the same plant. .. See if any of the flower pigments line up with those in the leaves. ..If they do, the flower probably just used the same "color genes" as found in the remainder of the plant. .. If they do not match up, then the flower cells most likely turned on other special genes.

The Evolution of Photosynthesis

..... Following the steps in your AP Biology lab manual, you ran paper chromatography and demonstrated that you could separate the various pigments in leaves. ..Oh, oh! Here comes a quiz! .....

Most likely the leaves you used were from ... Choose the correct answer in each pair of words that follows:

  • an angiosperm or a gymnosperm
  • a vascular plant or a non-vascular plant
  • a "monocot" or a "dicot"

This ought to give you the big hint that there are not only many different kinds of plants, but also many different groupings of plants. ..(Just think about yourself: ..Homo sapiens is a member of the Anthropoids, which are members of mammals, which are members of creatures with backbones, which are members of the Animal Kingdom, which are Eukaryotes. ..All plants have also been arranged in a phylogenetic tree. ..Oh, by the way, who was Carl Linne (or Carolus Linneus)?)

..... What to do: The extension you can do on the paper chromatography exercise is to obtain photosynthetic members of a wide variety of plant groups such as algae (sea lettuce is good), mosses, liverworts, etc., etc., grass, and maple tree. .. It would be best to use a wide piece of chromatography paper and make your "coin-squashes" of each of the samples you have collected such that each squash is about one centimeter long right next to each other all on the same piece of paper. .. (Oh, and you have probably learned not to put any squashes within about a centimeter from the edges ("edge-effects" usually result in a "smile"). ..AND it might be wise for you to line your squashes such that the first one is your "simplest" organism (algae or cyanobacteria) upwards to more and more complex plants.

..... Results ..In which plant samples did you get the most number of bands? ..Did you find any samples that just gave you a single band of color? .. If you were to rearrange your squashes so that they would run from the fewest bands to the most, would that rearrangement correspond to what you would read in the taxonomic tree of plants?

..... Discussion:.. Why did you line up your plants from simplest to most complex? ..Was your subconscious working on the principle that the evolving earth saw the simplest things first and those begot more and more complex things? ..If your mind was thinking that way, give yourself a pat on the back because you were operating under a VERY fundamental principle: ..in phylogenetic evolutionary theory, simplicity begets both complexity and greater variety.

Where Do the Fall Colors Come From?

..... Your textbook most likely tells you that the tree leaves change into their fall colors because the chloro(green)phyll(stuff in leaves) is the most unstable and breaksdown. .. As it disappears, it unmasks other less dominant colors that were always there. ..Thus the reds and yellows appear. ..The reds (erythro- and rhodo-) then disappear and the long-lasting yellows (xantho- and carotino-) remain to eventually flutter to the ground. ..Can you demonstrate this?

..... What to do:

  1. Some lab writers suggest that you go out and collect a number of green and colored leaves from the same plant and chromatograph them next to each other. .. A few smart students however have really come up with something neat: .. pluck leaves that are only partially turned - green at their bases and colored at their tips. ..Usually there is a sharp demarcation between the two areas. ..Place the leaf on your chromatography paper such that the coin will roll from one area to the other in one continuous line. ..Any transitions between the two areas ought to become evident. ..Really neat idea!
  2. From a crafts shop obtain two bottles of water colors - green and red. ..The botanists are saying that green is so dominant that it can mask a good amount of red. ..With a brush, make two puddles of green paint on some white paper. One puddle is your comparison ("control"). .. Then add the smallest amount of red paint you can to the second puddle and mix it in. .. Keep adding red in small amounts until you see a change between the two puddles. ..Are the botanists correct?

..... Discussion: You must write the discussion for this extension. ..You will either agree or disagree with the botanists' explanation that green masks red. ..And either way your results come out, you will have to write an explanation as to how leaves change colors in the fall.

The Use of Chloroplasts as Indicators of Environmental Pollution

..... In your AP Biology lab manual, a portion of the chloroplast isolation and photoactivity exercise had you take some of the chloroplast suspension and boil it. ..Were the chloroplasts able to reduce the DPIP after boiling? ..No! ..What would you expect IF you had boiled the leaves first and then isolated the chloroplasts? .. Of course! .. No DPIP reduction then either. .. (This experiment is made easy by the fact that spinach chloroplasts are so easily and quickly isolated.)

..... Now let's consider treating the chloroplasts with some agent that "kills" them (i.e.: no DPIP reduction in light). ..Let's first treat the leaves with that agent, and then isolate the chloroplasts. ..Are the chloroplasts "dead"?

..... What kinds of agents might we use on the chloroplasts and on leaves prior to chloroplast isolation?

  • 10% ethanol or isopropanol (rubbing alcohol).
  • Dishwashing detergent (various concentrations)
  • Shampoos (various concentrations) Shampoos mostly consist of cationic detergents, while dishwashing and laundry detergents are anionic detergents.
  • Others: ..use your informed intelligence to try others.

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