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Physiology: Carbon Pathway
Looking at the same slides used to follow the water path through plants, we will now look at the path of carbon from carbon dioxide in the air to sugar. Sugar can be used by growing regions of the plant or stored as starch in a parenchyma cell in the stem or root. The diagrams that you made for the water pathway will mostly serve for this lab as well, although there is an extra slide and you may need to record some extra features. You will end up producing another "cartoon" to represent the carbon path.
Syringa leaf
Where does CO2 enter the leaf and how does it get to the cells where most photosyntheses occurs (and which cells are these?)?
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How are the sugars from these cells going to get out of the leaf and what kinds of cells will they pass through? _____________________________________________________________
Cucurbita stem, longitudinal section
Why do you think that Cucurbita (pumpkin, squash, melon) is chosen to look at cells involved in sugar transport and why choose a longitudinal section? _____________________________________________________________
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Ranunculus root, transverse section
In which cells of the root will the sugars end up and what cells would they pass through to get there?
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Now you are ready to draw your cartoon. Here is your cast of characters:
Fit
these cells together to illustrate the path of carbon
translocation. When you are done indicate the path in a different
color, preferably red. Sometimes there is more than one possible
path.
Now look at the carbon path and the water path. Where do you see the possibility of conflict between water and carbon requirements? In which cells is this regulated?
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Do you think water can move between the two paths? If so in what direction and what is the effect?
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In the past two labs you have looked at leaf sections of lilac which is a "mesic" plant because it has a normal water requirement. A few weeks ago we looked at pine trees which are "xeric" plants, adapted to grow where water availability is low.
Pine leaf T.S., prepared slide
What three xeric features does the leaf have? (compare with lilac leaf if necessary)
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(The strange red structures are outgrowths of the mesophyll cell walls and the two conspicuous channels are resin ducts.)