Photosynthesis: a process that converts light energy into chemical energy

The first phase of photosynthesis occurs in the thylakoid, inside the chloroplast. This is a light-dependent reaction. In this phase, light energy will be absorbed and then converted into chemical energy in the form of ATP and NADPH.

Chlorophyll is the major light-absorbing pigment in plants. They are more abundant than other pigments in most leaves.

This is the electron transport chain. First, light energy excites electrons in photosystem II. The light energy causes water molecules to split, releasing an electron into the system, a hydrogen proton into the thylakoid space, and oxygen as a waste product. This breakdown of water is essential for the process to occur.

Then the excited electrons move from photosystem II to an electron-acceptor molecule in the thylakoid membrane which transfers the electrons along a serious of electron carriers to photosystem I. In the presence of light, photosystem I transfers electrons to a protein called ferrodoxin. Electrons lost in photosystem I are replaced by electrons from photosystem II. Ferrodoxin then transfers electrons to the electron carrier (NADP+), forming an energy molecule (NADPH). NADPH goes out to the stroma for the Calvin Cycle and hydrogen protons go through an enzyme called ATP synthase.

The hydrogen protons make ATP in the stroma for the Calvin Cycle. The Calvin Cycle is a process that produces sugars and can also be called carbon fixation. The first step is where 12 3-carbon molecules(PGA) are produced. The chemical energy stored in NADPH and ATP transfers to the 3-PGA molecules to form G3P. Two G3P molecules then leave the Calvin Cycle for the production of glucose. Ten more G3P molecules moves on to be converted to RuBP by an enzyme called rubisco. The RuBP will combine with carbon and start the cycle over again.

Sugars produced are used as energy and as building blocks for complex carbohydrates that provide structural support for the plant.

This is the process of photosynthesis. All plants use it. It's what keeps all people alive and healthy in the world today. Without photosynthesis, there would be no life on the plant.


Created with images by Freeimages9 - "leaf background lines" • Freeimages9 - "banana beautiful botany" • diego_torres - "sunset field poppy sun" • NASA Goddard Photo and Video - "Eclipses Yield First Images of Elusive Iron Line in Solar Corona" • niknak09 - "autumn leaves essex"

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