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Entire Process of Photosynthesis

Uploaded by biblegirl22 on Aug 02, 2005

The Entire Process of Photosynthesis

Photosynthesis is the process by which organisms that contain the pigment chlorophyll convert light energy into chemical energy which can be stored in the molecular bonds of organic molecules. Photosynthesis powers almost all trophic chains and food webs on the Earth.

The net process of photosynthesis is described by the following equation:

6CO2 + 6H2O + Light Energy = C6H12O6 + 6O2

This equation simply means that carbon dioxide from the air and water combine in the presence of sunlight to form sugars; oxygen is released as a by-product of this reaction.

Photosynthesis begins when light strikes Photosystem I pigments and excites their electrons. The energy passes rapidly from molecule to molecule until it reaches a special chlorophyll molecule called P700, so named because it absorbs light in the red region of the spectrum at wavelengths of 700 nanometers.

Until this point, only energy has moved from molecule to molecule; now electrons themselves transfer between molecules. P700 uses the energy of the excited electrons to boost its own electrons to an energy level that enables an adjoining electron acceptor molecule to capture them. The electrons are then passed down a chain of carrier molecules, called an electron transport chain. The electrons are passed from one carrier molecule to another in a downhill direction, like individuals in a bucket brigade passing water from the top of a hill to the bottom. Each electron carrier is at a lower energy level than the one before it, and the result is that electrons release energy as they move down the chain. At the end of the electron transport chain lies the molecule nicotine adenine dinucleotide (NADP+). Using the energy released by the flow of electrons, two electrons from the electron transport chain combine with a hydrogen ion and NADP+ to form NADPH.

When P700 transfers its electrons to the electron acceptor, it becomes deficient in electrons. Before it can function again, it must be replenished with new electrons. Photosystem II accomplishes this task. As in Photosystem I, light energy activates electrons of the Photosystem II pigments. These pigments transfer the energy of their excited electrons to a special Photosystem II chlorophyll molecule, P680, that absorbs light best in the red region at 680 nanometers. Just as in Photosystem I, energy is transferred among pigment molecules and is then directed to the P680 chlorophyll, where the energy is used to...

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Uploaded by:   biblegirl22

Date:   08/02/2005

Category:   Biology

Length:   6 pages (1,360 words)

Views:   15025

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