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Advanced Photosynthesis

Welcome to the Advanced Photosynthesis Unit!

Here, we will break down the simplified description of photosynthesis (as summarized below) into its many (many!) steps.





There are small holes in the bottom of leaves, where gases like CO2 and O2 enter and exit. Plants are made of cells. Within the cells of the leaves are little organs called chloroplasts.

The chloroplasts are represented by the little green circles (two of the many chloroplasts are labeled at the top right side in this image).





Carbon dioxide and water molecules diffuse by randomly moving around. Some move into the tiny chloroplasts in the cells.

A magnified chloroplast is shown to the right.






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This section describes the CO2 + RuBP reaction in more detail...


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The 6-carbon molecules quickly split into two 3-Carbon molecules, forming new molecules called "PGals".






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So, as you can see, the reaction for photosynthesis often given (shown again below) is an extremely simplified summary of what happens.




Summary

  1. Carbon dioxide (and other air) molecules enter plants' leaves in the little holes in the bottom of the leaves.
  2. Light hits chlorophyll molecules within thylakoid disks (which are inside chloroplasts, which are inside of plant cell leaves).
  3. Electrons in chlorophyll molecules get excited and escape from chlorophyll molecules. This leaves the chlorophyll molecules positively charged.
  4. So, chlorophyll molecules (through electric forces) pull electrons from nearby H2O molecules.
  5. This causes H2O molecules to split into two positively-charged hydrogen atoms and one oxygen atom.
  6. Oxygen atoms bond together to form O2, which exits from the little holes at the bottom of leaves.
  7. The leftover H+ atoms inside the thylakoid disks and water molecules outside the disks pull phosphate molecules off ATP molecules.
  8. The freed phosphate has a lot of energy of motion (kinetic energy).
  9. This energy and the energy from another molecule, called Rubisco, helps CO2 and RuBP combine to form PGal molecules.
  10. Finally, some of the PGal molecules combine to form a sugar molecule.