Introduction

Light independent reaction

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Light dependent reaction

 

Light-dependent reaction

In this part light energy is converted into chemical energy. The light energy is absorbed by chlorophyll molecules. ATP and reduced NADP is produced. It takes place on the thylakoid membrane (see work on chloroplast structure).

Water is split at a manganese protein to produce oxygen, hydrogen ions and electrons. The electrons are taken up by photosystem II (PSII) which absorbs light at 700nm wavelength.

The electrons are 'excited' by the light energy and then passed on to a series of electron carriers. The energy is used to pump hydrogen ions from the stroma into the intra-thylakoid space.

The hydrogen ions diffuse out through special protein channels. In doing so this drives the synthesis of ATP by the enzyme ATP synthetase.

The electrons are passed on to PS I, which absorbs light at 680nm. The electrons are excited and the energy used to reduce NADP to NADPH.

THIS PROCESS IS KNOWN AS NON-CYCLIC PHOTOPHOSPHORYLATION.

Try the following web sites;

The American hypertext site;

http://esg-www.mit.edu:8001/esgbio/ps/light.html

For a more detailed treatment try;

http://www.tayloru.edu/upland/departments/biology/authorware/photosynthesis/photosynthesis.html

OR

http://www.sciencenet.org.uk/database/Biology/Lists/photosynthtable.html