Learning about photosynthesis with simulations

Preparation

First, go to homepage for Photosynthesis activity (make sure you scroll down past the large square): https://sites.google.com/site/biologydarkow/photosynthesis-model

There’s also a student activity sheet:
https://docs.google.com/document/d/1vJtpMjq6KRkMUYSedeBSaH3ZK9kyutazsz8L25QEejg/edit

Print out a copy of the student activity sheet and have it handy when you do the simulation.

Some thinking questions before you start

1. Read through the information on the first link: https://sites.google.com/site/biologydarkow/photosynthesis-model (scroll down past the link to the simulation) and the background found on the actual simulation page: https://exchange.iseesystems.com/public/jon-darkow/photosynthesis-model/index.html#page2

They are a quick overview of photosynthesis and the reactions. Pull out your textbook and look at the pictures in the appropriate chapter and think about the following:

– – What are the major reactions happening here? When does the plant make glucose? What are the sources and the fates of the reactants and products in this reaction?
– – How does the structure of the chloroplasts and the leaf relate to the photosynthesis?
– – How do photosystems convert solar energy into chemical energy?
– – Think about how the electron flow in the light reactions results in the formation of ATP, NADH and O2.
– – How does the proton gradient formed in the light reactions is used to form ATP:
ADP + inorganic phosphate (from ATP synthase) —>>> ATP
– – How does the Calvin cycle use the energy molecules from the light reactions (ATP and NADPH) to produce carbohydrates (G3P) from CO2?

DO NOT worry if you can’t answer all of these! It is important to have an idea what you are trying to figure out before doing the simulation.

Open the simulation and play a little

2. Now, open the simulation: https://exchange.iseesystems.com/public/jon-darkow/photosynthesis-model/index.html#page3

And go back to the student activity sheet.
Under the “Variables Explained” section, play with the settings in the simulation so you know what they mean.

Note: the three graphs to the right show different things. The first one will only show results of last run, but includes all the products. The second and third one will only show one product, but will show multiple runs. If you want to clear those runs, use the blue rewind button to the left.

The Atrazine button:
Atrazine is a herbicide that stops the transfer of electrons from Photosystem II to Photosystem 1. Remember that transfer of electrons from Photosystem II to Photosystem I is essential for the production of photosynthetic energy. When the process of photosynthetic electron transfer is interrupted, the synthesis of ATP and NADPH in the chloroplast is compromised. This results in an inability to fix CO2 and produce the nutrients needed for the plant to survive.

Mr. Darkow also has a nice illustration of the light reactions and the dark reaction. You will want to perhaps have those handy as you work through the simulation, so set those aside.

Choose your experiment
Mr. Darkow has 8 suggested options for designing an experiment with the simulator, of which I have listed here with my comments. I highly recommend working through at least 2 of these simulations, along with the data analysis, it will help to make the light and dark reactions of photosynthesis come to life. If you have time, read through each simulation and think about how you would test the theory with the simulation at least. Even if you don’t do the runs or collect data, it is very worth your time.

Option A: Hydrolysis – How could you test the idea that solar energy is required for the hydrolysis of water during photosynthesis?

Think about what the products and reactants are for the hydrolysis of water in photosynthesis. I’m going to say that water breaks down into O2 and H2 gas when hydrolyzed, and yes, one of the graphs shows the moles of O2 produced per unit of time. How to vary the light, or the solar energy? Well, there is a “distance from light” button, so lets try that. Remember, you need to keep track of your data, but you can open the graph as an image and then copy it into a document. I generated this graph:

That blue line was with 0 distance, the orange line on the x-axis is 150 cm from the light source. The ones in between are 10, 20, 30, and 40 centimeters. See, you need to keep track! But the runs are so quick, it really doesn’t take much time to do these simulations.

And my independent variable (the one you set) is the distance of the light source, and the dependent variable (the one that changes according to the settings of the variables) is the moles of O2 produced.

Option B: Reduction of NADP+
Option C: Proton-Motive Force
Option D: Atrazine and the Electron Transport Chain
Option E: Chlorophyll and Photophosphorylation
Option F: Carbon Fixation in the Dark
Option G: Oxidation of ATP and NADPH
Option H: Optimal Temperature

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