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Photosynthesis is a very crucial and vital process. It is a process in which sunlight is converted into chemical energy. This process occurs in almost all plants and also some algae. Plants use light energycarbon dioxide, and water to make sugar (glucose). Photosynthesis takes place in the mesophyll cells of the leaves, as these have chloroplasts which are organelles that contains a high concentration of the photosynthetic pigment chlorophyll

There are two stages of photosynthesis:

Light Dependent Reaction Light Independent Reaction

The Light Dependent Reaction occurs in the thylakoid membranes of the cholorplast and this provides a large surface area for the attachment of chlorophyll, electron carriers and enzymes. The function of this reaction is to produce reduced NADP, ATP and oxygen for the plant to be able to use in other processes. The Light Independent Reaction, also known as the Calvin cycle, occurs in the stroma of the chloroplast because it contains all the enzymes needed to carry out the reaction. This reaction reduces carbon dioxide to make sugars and other organic molecules [1].

The Light Dependant Reaction (LDR)

The LDR is initiated when light shines upon the leaves of the plant thereby providing additional energy to electrons in chlorophyll. These electrons are then released by chlorophyll and enter the electron transport chain within the thylakoid membrane, resulting in a series of redox reactions as the electrons are passed from one transport protein to the next. This series of redox reactions provides sufficient energy to form ATP from ADP and P. As electrons have been released by chlorophyll, it is now electron deficient; it obtains electrons through the photolysis of water during which electrons, oxygen and hydrogen are produced. The electrons produced are taken up by chlorophyll, the hydrogen produced is taken up by NADP and the oxygen produced is used during the light independant reaction. 


  1. Glen and Susan Toole (2008) A2 AQA Biology Textbook, Cheltenham, Nelson Thornes Ltd
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