Help!! Photosynthesis anyone???

Question

Describe the production of NADPH and ATP in photosynthesis.

Include in your answer:

1. the action of light on light-harvesting complexes and the influence of light on the photochemical change of pigment molecules such as chlorophyll,

Answer 1

Photosynthesis in higher plants is basically divided into two major processes; the light and dark reactions.  The dark reactions are catalyzed by a combination of enzymes that use NADPH and ATP to fix CO2 and convert it into carbohydrate.  The purpose of the light reactions is to produce the NADPH and ATP.  The light reactions start in a complex called photosystem II that uses light energy to extract electrons from water.  The energy level of these electrons is raised during this process.  Some of this energy is "given back" to transport H+ ions from the outer to the inner side of the chloroplast thylakoid membrane.  As the H+ ions flow back down the gradient the energy is used to make ATP from ADP + orthophosphate.  The electrons originally produced in photosystem II are given a second boost from light quanta in a second complex called photosystem I.  Electrons leaving photosystem I are used to reduce NADP to NADPH.  Both photosystem I and II act somewhat like  satellite dishes and are designed to intercept sunlight and collect it then direct this trapped energy to reaction centers where the electrons actually are energized.  Thus, a major structural feature of such a photochemical complex is the existence of light-harvesting pigment/proteins that simply intercept light and trap it in the excited pigment molecules.  These pigment/protein complexes contain chlorophyll and carotenoid molecules attached to proteins (practically no free pigment exists in the system).  Interestingly, the reaction centers of both photosystems contain chlorophyll molecules that go oxidized and then get re-reduced.