Cyclic phosphorylaton

• Cyclic photophosphorylation only uses photosystem one.
• 1. As light hits photosystem one, a pair of electrons in the chlorophyll molecule at the primary pigment reaction centre gains energy and become excited. They escape from and pass to an electron carrier system and passes back to photosystem one.
• 2. During the passage of electrons along the electron carriers, a small amount of ATP is produced. however no photolysis of water occurs so no protons or oxygen are produced. no reduced NADP is preduced
• Chloroplasts in guard cells contain only photosystem one. they produce only ATP which actively brings potassium ions into the cells. This will lower the water potential so that water moves into the cell via osmosis. So the guardcells will swell and the stomata will open