Photosynthesis by: Evan messer

Light Reactions

First the light energy excites electrons in photosystem 2. The light energy also causes a water molecule to split, releasing an electron into the electron transport system, a hydrogen ion into the thylakoid space, and oxygen as a waste product. This breakdown of water is necessary for photosynthesis to happen.

The excited electrons move from photosystem 2 to an electron-acceptor molecule in the thylakoid membrane.

Next, the electron-acceptor molecule transfers the electrons along a series of electron-carriers to photosystem 1.

In the presence of light, photosystem 1 transfers electrons to a protein called ferrodoxin. The electrons lost by photosystem 1 are replaces by electrons moved from photosystem 2.

Finally ferrodoxin transfers the electrons to the electron carrier NADP+, forming the energy storage molecule NADPH.

Calvin cycle

In the first step of the Calvin Cycle called carbon fixation, six carbon dioxide molecules combine with six 5-carbon compounds to form twelve 3-carbon molecules called 3-phosphoglycerate. The joining of carbon with other organic molecules is called carbon fixation.

In the second step, the chemical energy stored in ATP and NADPH is transferred to the 3-PGA molecules to form high-energy molecules called glyceraldehyde 3-phosphates. ATP supplies the phosphate groups for forming G3P molecules while NADPH supplies hydrogen ions and electrons.

In the third step, two G3P molecules leave the cycle to be used for production of glucose and other organic compounds.

In the final step of the Calvin cycle, an enzyme called rubisco converts the remaining G3P molecules into 5-carbon molecules called ribulose 1, 5-biphosphates. These molecules combine with new carbon dioxide molecules to continue the cycle.


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