Photosynthesis

What is Photosynthesis? 

  • Photosynthesis is the process by which plants convert the products of Cellular Respiration (Water and Glucose) into sugar and oxygen
Step 1: Light Dependent Reactions --> Take place in Thylakoid Membranes
  • First the chlorophyll in the plants absorb sunlight which excites electrons and moves them to a higher energy state.
  • Once the electrons have been excited, they start the ETC (Electron Transport Chain) which generates energy
  • Since the electrons are transferred in the ETC, chlorophyll must recoup the electrons that it has lost, so the water molecules are broken down into oxygen, H+ ions, and electrons (oxygen is a byproduct and it exits the cycle)
  • The energy released from the ETC is used to pump the H+ ions across the membrane, creating a difference in the number of H+ ions on both sides of the membrane (proton gradient)
  • Due to the creation of the proton gradient, protons try to get back to the other side of the membrane in an effort to  (this is done through ATP synthase) and in the process, they create ATP from ADP
  • As the electrons move through the ETC, they reduce NADP+ into NADPH, which is a energy storer just like ATP

Step 2: Calvin Cycle --> Takes place in the Stroma of the chloroplast 

  • Carbon fixation: The enzyme Rubisco catalyzes a reaction between CO2 and ribulose - bisphosphate (RuBP) to produce 2 molecules of 3-phosphoglycerate (3 PGA)
  • The molecules of 3 PGA are converted to glyceraldehyde-3-phosphate (G3P) using NADH and the ATP made in step 1 
  • A few molecules of G3P are used to produce glucose and the rest are used to make RuBP so that the cycle can continue 
*Note: There are a lot of reactions taking place but you will most likely not have to learn how they are happening. If you don't want the chapter getting too complicated for a Freshman Biology class just know what happens and don't go too much into detail of or research on your own of why it happens. 




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