Photosynthesis Model



Background
The purpose of this simulation is to allow you to experiment with some of the main factors affecting photosynthesis. Photosynthesis in plants takes place within chloroplasts. The inner membranes of the chloroplasts (the thylakoid membrane) contain a series of proteins with light-sensitive pigments, like chlorophyll. As light strikes chlorophyll on chloroplasts, that energy from the light is transferred to move electrons on chlorophyll to a more energetic state. The series of proteins along the thylakoid membrane, and throughout the chloroplast, use these more energetic electrons to transfer energy to create glucose.  The first phase of photosynthesis converts solar energy into chemical energy and is called the Light Reaction. The second phase, called the Calvin Cycle is where carbon fixation takes place.                                                                                From www.sivabio.50webs.com/plastids.htm


The Photosynthesis Model allows you to stimulate the chloroplasts ability to excite electrons. For example, you can increase light intensity and the wavelength of light. Additionally, the Photosynthesis Model allows you to observe the major products from this Light Reaction


Specifically, the simulation tracks the amounts of glucose, oxygen, ATP, and NADPH concentrations over time. Glucose is a major product of photosynthesis. Additionally, the Photosynthesis Model allows you to manipulate the pH (H+ concentration) in the stroma, NADPH amount, and the concentration of atrazine (an herbicide that affects a protein in the light reaction.)




During photosynthesis, after the the energy from the energy has been transferred to synthesize NADPH and ATP, those molecules are used in the second phase of photosynthesis called the Calvin Cycle (also known as the dark reaction because it can take place at night.) During the Calvin Cycle energy is transferred from ATP and NADPH molecules in the chloroplast to chemically react carbon dioxide with organic molecules. The energy transferred from ATP and NADPH to carbon dioxide and some organic
molecules allow glucose to be made. This
carbon fixation (chemically reacting inorganic carbon dioxide with organic molecules) is the purpose of photosynthesis. Light energy is used to make inorganic carbon dioxide into organic fuel to power cell processes.

The Photosynthesis Model allows you to track the amount of glucose produced, NADPH consumed, and ATP consumed during the Calvin Cycle. 








Assumptions

  • Each RUN of the simulation is with a new plant sample that is continuously being monitored for glucose, oxygen, ATP, and NADPH production.
  • Each new plant sample has been incubated with the new conditions set by adjusting the sliders and buttons prior to each RUN of the simulation. 



INDEPENDENT VARIABLES:
  • Light exposed to the virtual plant which can be manipulated in the following ways:
    • Complete darkness (binary)
    • Distance from light (cm)
    • White light (all wavelengths)
    • Specific wavelengths (nm)
  • Initial pH of stroma =  based on the pH scale (0-14)
  • Atrazine = Relative percentage of the herbicide atrazine.
  • Added NADPH = Adding relative concentrations of NADPH to the start of the experiment.
  • Temperature = degrees Celsius of the experiment.


Student Activity Sheet


DEPENDENT VARIABLES:
  • Glucose produced (grams/mol) during the experiment.
  • Oxygen produced (grams/mol) during the experiment.
  • ATP produced (grams/mol) during the experiment.
  • NADPH produced (grams/mol) during the experiment.








What can the model do?
  • Track the reduction of NADP+ (to NADPH) in response to the light reaction.
  • Phosophorylation of ADP (to ATP) in response to the light reaction and a decrease in pH in the thylakoid space.
  • Increase in oxygen production as a result of photosynthesis.
  • Glucose production as a result of photosynthesis.
  • Destruction of photosystem II as a result of increase in atrazine.
  • Glucose production without light by adding NADPH and increasing the pH in stroma. (Increasing pH in the stroma creates the proton-motive force for ATP synthase.)