Photosynthesis

I made this SketchFu on Photosynthesis to show everything we have learned so far. However, I am also going to write about Photosynthesis to help further explain it. Photosynthesis has two main steps the Light Reaction and the Calvin Cycle. First we have the Light Reaction which takes place in the thylakoid membrane. Its purpose is to convert visible light into chemical energy, which in turn powers the production of sugars in the Calvin Cycle. Chlorophyll and other pigments inside the thylakoid absorb most light but reflect green light, which is why most leaves appear to be green. Those pigments form two clusters, photosystem I and II. As you will see in this presentation the PSII actually comes before PSI. This is because PSI was discovered first. Photons from the suns rays give the electron, located in PSII, extra energy causing it to jolt to other molecules. These molecules are known as electron carriers, and they are embedded along the thylakoid membrane. They are located in such a way that allows the electrons to move easily. Once the electrons reach PSI they are given an energy boost allowing them to reduce NADP+ into NADPH. However, these electrons need to constantly be replaced. To do this, water molecules are broken down into 2H+, 2e-, and O2. This leaves H+ ions, situated in the lumen, which are then pumped across the ATP Synthase to create ATP. 

Next there is the Calvin Cycle. Using the ATP and NADPH created by the Light Reaction as well as three CO2, the Calvin Cycle creates a networth of 1 G3P or PGAL which as you may recall is half of a glucose. However there are steps that need to occur before this happens. First a molecule of CO2 bonds with a 5-carbon sugar, thus creating an unstable 6-carbon molecule that immediately separates into two 3-carbon molecules. Now keep in mind that with three molecules of carbon dioxide there would now be 6, 3-carbon molecules. Each one of those needs one ATP and one NADPH to re-shape and lose a phosphate. Other reactions cause this to rearrange to form the PGAL, which then produces a 5-carbon sugar-phosphate.  Another molecule of ATP is then used to add another phosphate to this, producing RuBP.  So with 3 carbon dioxide molecules six PGALS would be created, five of which would be used to regenerate RuBP. Leaving the plant with one PGAL to use for growth.  

P.S. I think weather and the amount of water will affect the rate of photosynthesis.



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