Light dependent reactions and energy storage

These are more things covered by the photosynthesis tutorial.

• Chlorophyll (the green stuff) is the major photosynthetic pigment. Other pigments, though, absorb light it misses and "hand it over" to chlorophyll. These are called "accessory pigments". Together, they make it so all colors of light can be used.

• Reaction centers are places where the captured light energy is transduced ... changed in form to electrical energy.
  Here, the energy causes electrons to leave the chlorophyll molecules and be transferred to other a series of other compounds (electron transport chain).
  The delivery of electrons to a final product (NADPH*) is an important energy storage step. Here, electrical energy is transduced to chemical energy

Once electrons are used, they have to be replaced.

• In plants, replacement electrons to continue the process come from water.
  In this case, chemical energy is transduced to electrical energy.
  This is a very difficult reaction and evolution of water splitting capacity was a BIG evolutionary event.

• Besides electrons, oxygen and protons are released when water splits. ATP production (*) is another energy storing step. It uses energy temporarily stored with the protons.

More help with the terminology!

Energy -

Though light, electrical and mechanical energy are all part of biology, when we talk about your body needing energy, or a plant storing energy, we mean chemical energy, the stuff that fuels life. Chemical energy can be "extracted" from almost any compound in a living organism. But in pretty much all cases, it ends up being stored for some period of time in easily used, rapidly recycled compounds. Two of these are called ATP and NADPH.

Photon -

Light is weird stuff. Even though it has no mass, it comes in small packets. These are called "photons".

Pigment -

Any chemical which absorbs light. In plants, the one we see most absorbs red and blue light, but not green... chlorophyll. Paints have their color due to pigments, also.

Reaction center -

The place in a chloroplast (actually, in the thylakoid membrane) where proteins and chlorophyll molecules are in just the right places so that, when light energy gets there, it is transduced (changed) into electrical and chemical form.

Transduction -

The conversion of one form of energy into another. If, for example, you pedal a bicycle to run a generator to light a light bulb, chemical energy in your muscle cells is "transduced" into the mechanical energy of your moving muscles (pedalling). The mechanical energy is "transduced" by the generator into electrical energy. The electrical energy is "transduced" into light and heat in the bulb. Of course, the light energy could be "transduced" by a plant into chemical energy which you could then eat and recycle into the pedalling of the bicycle.