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Photosynthesis is the process where light is converted by the plant into carbohydrates, namely glucose.  The reaction uses carbon dioxide from the air and water the roots have taken from the ground and shipped to the leaves.  Photosynthesis takes place at the cellular level.  The chloroplast is responsible for the photosynthetic process.  Actually a structure within the chloroplast is responsible for photosynthesis, it is called the Thylakoid.  The thylakoid is a disc shaped structure that occur in columns and are connected to other thylakoids.  The thylakoid hold the pigment chlorophyll.  Chlorophyll is called a pigment because it absorbs light, but only certain wavelengths.  Chlorophyll absorbs all the wavelengths of light except green.  This is why plants appear green, because the chlorophyll is reflecting the green wavelength of light. 

Photosynthesis occurs in main stages.  The Light Reactions and the Dark Reactions.  The light reactions occur only in the light and the dark reactions can occur in either light or dark as long as it has carbon dioxide, ATP and Hydrogen atoms.  All of these things are supplied by the light reactions.

Light Reactions

The light reactions occur inside the thylakoid in the presence of chlorophyll.  Chlorophyll accepts light energy and uses that energy to split a water molecule into 1 H atoms and an oxygen atom (  H2O   Light and chlorophyll   2 H + 1/2 O2  + ATP).  The hydrogen's are taken to the site of the dark reactions by a chemical called NADPH+.  When This chemical carries a Hydrogen it is called NADPH.  The ATP also is used in the dark reactions.  The main ideas to get from this part of photosynthesis is that:
 1.  Chlorophyll accepts light and makes ATP which is used to power the dark reactions.
 2.  The oxygen that is released is a waste (byproduct) of the hydrolysis reaction and is used by animals
 3.  Hydrogen is taken by the NADPH molecule to the dark reactions where is then placed in a cycle the result of which is glucose.

Dark Reactions

The dark reactions are a cycle because the 5 carbon chemical RuBP (ribulose bisphosphate) is recycled over and over in the reaction.  The following diagram describes the Dark reactions.

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