Review previous class (what structures were we looking for–in the leaf, in the photosynthetic plant cell? why?)
Anticipate Summative project on supporting the claim of photosynthesis. To be described on Wed. Due the following Tuesday by the end of class.
- FYI–Benson’s story:
Today’s activity provides an experience with a crucial technique in the understanding of photosynthesis. The technique uses the varying solubility of different molecules (the plant pigments) in a solvent. The solvent moves up a strip of paper by capillary action. See reference: < https://water.usgs.gov/edu/capillaryaction.html >.The different molecules move at different rates. Separation is one part of discovering the reaction pathways in complex processes. How did Benson and Calvin separate the molecules involved in the numerous photosynthesis reactions? After separation, analysis is carried out to describe the properties, create models, name, and identify the products of the separation. What do you think are the techniques used for such analysis?
In science it is important always to ask–How do we know? The next task is to describe the evidence and to explain how the evidence is linked to claims. Connecting claims with evidence is what is meant by the phrase scientific argument. Your summative assessment on photosynthesis will involve organizing the evidence both from historical experiments and from your own first hand activities, experiences, and experiments and linking the evidence to the (over)simplified claim of photosynthesis. Data that have been analyzed and interpreted in light of an hypothesis, theory, claim become evidence.
Follow instructions for the extraction and separation of plant pigments through paper chromatography. See board. Listen closely to verbal instructions. Watch demonstrations of techniques. Follow all safety guidelines. Record all procedures (verbal descriptions, diagrams-sketches, photos). Record all observations.
BIG QUESTIONS FOR TODAY:
- What do Chlorophyll and other pigments have to do with the claim of photosynthesis?
- What does the technique of paper chromatography have to do with the claim of photosynthesis?
- (In other words, why would we conduct this activity at this time in our study of photosynthesis? What do you learn?)
This image provides an idea of the proper set-up:
See the image from someone’s experiment: http://socrates.acadiau.ca/COURSES/BIOL/REEKIE/1113/photo/cpaper.gif
There are a number of articles on the history of chromatography. Here is one: history chromatography
More on procedures for chromatography–also interpretation of results:
- Plant pigments:
- How plants make pigments:
See–Why aren’t all plants black? by Physics Girl–excellent youtube science channel:
- Prior knowledge assessment prompt: http://rfrazier.msblogs.aes.ac.in/files/2016/01/chlorophyllprompt.pdf
- Examine the pages on the following website about Pigments, Plants, Chlorophyll http://www.webexhibits.org/causesofcolor/7H.html
- Examine the pages on the following website. See how three images are given for each pigment: 1) Picture of plant part, 2) graph of absorption spectrum of light, 3) diagram of pigment molecule. Why do you think these 3 images are presented?http://harvardforest.fas.harvard.edu/leaves/pigmen
- Examine the following short video on photosynthesis–what is the role of chlorophyll? What questions do you have? https://www.youtube.com/watch?v=D6tbOBhbOZU
- Next class we will carry out chromatography on extracts of pigments from plants. See this video in preparation. Be sure to write down your questions.
- Basics of Chromatography https://www.youtube.com/watch?v=SnbXQTTHGs4
- A review of the simplified claim of photosynthesis: http://photosynthesiseducation.com/
- See this very cool animation/model of the chlorophyll molecule: http://www.biotopics.co.uk/jsmol/chlorophyll.html
- An animation of chromatography: http://www.austincc.edu/biocr/1406/laba/chromatography/