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 electr...

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...he molecular bonds that are broken.

Glucose: C6H12O6

Respiration is the opposite of photosynthesis, and is described by the equation:

C6H12O6+6O2 ----------> 6CO2+6H2O+36ATP

Simply stated, this equation means that oxygen combines with sugars to break molecular bonds, releasing the energy (in the form of ATP) contained in those bonds. In addition to the energy released, the products of the reaction are carbon dioxide and water.

In eukaryotic cells, cellular respiration begins with the products of glycolysis being transported into the mitochondria. A series of metabolic pathways (the Krebs cycle and others) in the mitochondria result in the further breaking of chemical bonds and the liberation of ATP. CO2 and H2O are end products of these reactions. The theoretical maximum yield of cellular respiration is 36 ATP per molecule of glucose metabolized.