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Steps of Photosynthesis

How Plants Make Food


This is a generalized diagram of the process of photosynthsis.

This is a generalized diagram of the process of photosynthsis through which plants convert solar energy into chemical energy.

Daniel Mayer, Free Documentation License

Here is a summary of the steps used by plants and other organisms to use solar energy to make chemical energy:

  1. In plants, photosynthesis usually occurs in the leaves. This is where plants can get the raw materials for photosynthesis all in one convenient location. Carbon dioxide and oxygen enter/exit the leaves through pores called stomata. Water is delivered to the leaves from the roots through a vascular system. The chlorophyll in the chloroplasts inside leaf cells absorbs sunlight.


  2. The process of photosynthesis is divided into two main parts: light dependent reactions and light independent or dark reactions. The light dependent reaction happens when solar energy is captured to make a molecule called ATP (adenosine triphosphate). The dark reaction happens when the ATP is used to make glucose (the Calvin Cycle).


  3. Chlorophyll and other carotenoids form what are called antenna complexes. Antenna complexes transfer light energy to one of two types of photochemical reaction centers: P700, which is part of Photosystem I, or P680, which is part of Photosystem II. The photochemical reaction centers are located on the thylakoid membrane of the chloroplast. Excited electrons are transferred to electron acceptors, leaving the reaction center in an oxidized state.


  4. The light-independent reactions produce carbohydrates by using ATP and NADPH that was formed from the light-dependent reactions.
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