explanation

what is photosynthesis? photosynthesis is a food-making process the occurs in green plants. it is the the chief function of leaves. the word photosynthesis means putting together with light. green plants use energy from light to combine carbon dioxide and water to make sugar and other chemical compounds.

how is the light used in photosynthesis? is absorbed by a green pigment called chlorophyll. each food-making cell in a plant leaf contains chlorophyll in small bodies called chloroplasts, light energy causes water drawn from the soil to split into hydrogen and oxygen.

what are the steps of photosynthesis process?

Light Dependent Processes

The first stage of photosynthesis takes place in the thylakoid membrane and the thylakoid space. The various types of chlorophyll and carotenoid molecules are the pigments placed in the membrane. These pigments start the process by acting sort of like antennae that capture the solar energy. Light photons hit the chlorophyll or carotenoid molecules. This photon energy "knocks loose" an electron which provides the energy to other molecules to start the very complicated and fascinating photosynthesis process.

This is where the water comes in. There is a special enzyme molecule with the specific job of breaking apart water molecules. This procedure is called the photolysis of water. Water molecules are broken down into oxygen and hydrogen atoms. The hydrogen atoms are further broken down into a hydrogen ion and an electron.

the electrons go to the chlorophyll and other pigment molecules where they replace the missing electrons "knocked" loose by photons of light.

    the oxygen atoms go link up with another oxygen molecule to form O2, then they flow back out to the air from whence they came. That's where the oxygen made during photosynthesis comes from. It comes from the oxygen in water molecules (H2O) and is just an unwanted byproduct as far as photosynthesis is concerned. The electrons and hydrogen ions are used, and some of the oxygen may get used for respiration, but a lot of them just go back out to the atmosphere where you and I may breath them with our very own gas exchange systems.

     The hydrogen ions left behind stay for a very short while in the thylakoid space. This space is often referred to as the hydrogen reservoir because it is a reservoir for hydrogen ions - nice and straight forward

Light Reactions   

The hydrogen ions go zipping out of the thylakoid space, flowing through special channels in the membrane. It's the only way out. (Actually hydrogen ions are flowing both ways through the membrane during photosynthesis but we can't cover evrything - it would take pages and pages and pages.)

      The movement of these ions through the channels provides the energy to the ATP Synthetase enzymes where ATP molecules are made. ATP (adenosine triphosphate) and another molecule abbreviated NADPH (too big of a name to write) are the two energy carrying molecules that power the dark reactions (not to be confused with the dark side of the Force that powered Darth Vader) of photosynthesis part 2 occuring in the stroma.

      There is also a steady flow of electrons, from the water, through various steps through the membrane, and finally to NADPH. This electron flow is an electric current - electricity powered by solar energy. This electric current provides energy for the making of ATP and NADPH. 

     Basically, in step one, the light reactions, the energy of light is captured and transferred into ATP and NADPH, which are used to provide energy for the making of carbohydrates in stage two of photosynthesis, the carbon cycle.

Light Independent Reactions:

     Next we leave the thylakoids and head out into the stroma where the second stage of photosynthesis takes place. This stage is sometimes referred to as the carbon fixing process because during this stage carbon from carbon dioxide is "fixed" into the beginnings of simple sugar, or carbohydrate molecules. Other terms you may hear for this phase are the "dark reactions" or the "carbon cycle".

     Out here in the stroma, a bunch of different enzymes use the carbon dioxide molecules and hydrogen ions made during the light dependent phase to assemble sugar fragments which are half of a glucose molecule (just 3 carbon atoms, instead of the 6 required to make a complete glucose molecule).

The carbon cycle, like the light reactions, is extremely complex with many steps. It is powered by the NADPH and ATP molecules formed in the light phase.