I assume you are asking about carbon dioxide.
Nicholas de Saussure
First of all it's not photosynthesis II, its photosystem II. well basically, the hydrogen atom within the water molecule loses its electrons and the electrons basically travels through all the photosytems via electron transport chains, towards the NADP Reductase where NADP+ is attached with the electrons from the hydrogen atoms of the water molecule to form NADPH
Chlorophyll molecule
Glycolisis is common to both.It is the first step.
During the first step of photosynthesis, the chloroplasts (which give plants their green color) capture the energy from the sunlight. In the second step, the cell uses the captured energy (ATP) to produce sugars in the form of glucose.
Water 
Nicholas de Saussure
No, "begun" is not a present tense verb. It is the past participle form of the verb "begin" and is used to create past perfect or present perfect tense. The present tense of "begin" is "begins" (third person singular) or "begin" (first/second person singular and all plural forms).
The first tRNA molecule is the anticodon. It contains the sequence UAC and drops off the amino acid methionine to begin the polypeptide chain.
Began is past tense. Begin is present tense.Sample text:"Let's begin at the beginning. It was early last year that I first began to realise that my memory was not good as I had thought. But I can't remember what it was that made me realise this."
It is unsure were the first oxygen molecule came from came from, but my bet was that it was from the process "Outgassing" in which Water, Carbon Dioxide, and other fluids, were spewed out of volcanoes. The Carbon Dioxide was used by Cyanobacteria, or Stromatolites(sp?),in photosynthesis, thus producing oxygen.
RuB binds carbon dioxide (CO2) and it is the first step of carbon fixation - incorporating inorganic carbon into a organic molecule.
The Roman Empire(present-day Italy) was the first to establish Christianity as an official religion.
Glucose and oxygen begin the process of respiration.
CO2 is a molecule of carbon dioxide. The first 6 tells how many molecules.
It is the first step. First step of the photosynthesis.
Water is required for the 'photolysis of water' which is the first stage of photosynthesis. Light enters the cell and strikes the water molecule splitting it into Hydrogen and Oxygen (from H2O).