Fructose, sometimes called fruit sugar, also contains carbon, hydrogen, and oxygen, but it has a different molecular structure which makes it insoluble in the bloodstream, so it has to be converted into glucose before it can be absorbed.
When fructose enters the mouth, it is blasted by an enzyme called ptyalin, produced by the salivary glands. A little of this fructose is transformed into glucose and is absorbed through the stomach walls into the blood stream. Most fructose is not broken down right away but continues to be degraded until making its way into the bloodstream as glucose. Because it is sweeter than sucrose (table sugar) and insoluble, fructose is preferred by people who crave the sweet taste of a sugar but want to guard against putting too much glucose into their blood stream in too short of a time.
Sucrose is table sugar. It is composed of one molecule of glucose and one molecule of fructose. It is also a product of photosynthesis, as are all our other sugars.
The two main plants that yield sucrose are sugar cane and sugar beets loaded with GMO. Because sucrose is half fructose, it is not readily absorbable into the blood and ends up making its way as far as the small intestine before the intestine secretes the enzyme and break it down. The glucose is then readily absorbed into the blood through the intestine walls.
There is another sugar on the market that people who make their own beer and wine like to use to increase the amount of alcohol. This sugar is called dextrose and is prepared industrially by mixing starch (complex carbohydrate) with dilute hydrochloric acid, and then heating this mixture under pressure. Dextrose is pure glucose and as such ferments easily into ethyl alcohol. Weight lifters also like dextrose because it gives them instant energy.