Understand Changes in Photosynthesis Graph

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Discussion Overview

The discussion revolves around understanding a graph that depicts changes in the concentrations of ribulose 1,5-bisphosphate (RuBP) and phosphoglyceric acid (PGA) in leaf mesophyll cells during a six-minute interval of sunlight, particularly focusing on the effects of a sudden decrease in carbon dioxide concentration.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that PGA concentrations decrease, suggesting this is related to carbon fixation and the loss of carbon dioxide as a source.
  • Another participant questions the role of RuBP, implying it may be consumed in the process that generates PGA, referencing the Calvin cycle.
  • A third participant provides a link to additional reading material, indicating that further context may be necessary for understanding the graph.
  • It is mentioned that carbon dioxide acts as a limiting factor, which could affect the rate of photosynthesis.

Areas of Agreement / Disagreement

Participants have raised various points regarding the relationships between RuBP, PGA, and carbon dioxide, but there is no consensus on the interpretation of the graph or the underlying processes at play.

Contextual Notes

The discussion does not clarify specific assumptions regarding the graph's data or the mechanisms of photosynthesis, leaving some aspects unresolved.

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This graph shows changes that occur in the amounts of ribulose 1,5 - bisphosphate (RuBP) and phosphoglyceric acid (PGA) in leaf mesophyll cells during a six minute interval of sunlight with the concentration of carbon dioxide being suddenly diminished at the middle of the interval.

Can anyone help me understand what's going on this graph?
 
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Well, to start with PGA concentrations go down. Can you see why? ie., where does PGA come from? It must have something to do with carbon fixation, right? Why? because you just lost your fixable carbon source when the CO2 levels go to almost zero.

RuBP is used for what? Does it seem like RuBP must be used up in the process that creates PGA? Or not? Hint: Calvin's cycle
 
Here is what you need to read if none of the above makes sense.
http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/dark.htm
 
Carbon Dioxide is a limiting factor, so the rate of photosynthesis will vary.