Glucose

Glucose is an essential molecule for many organism on earth including humans. Glucose is a carbohydrate made naturally through human metabolism. Glucose is a simple and important sugar for the body because it helps fuels cellular respiration. In plants it is the main product of photosynthesis to also help power respiration. Glucose can come in many different forms and types such as cyclic or open form.Glucose can be found in the blood to aid in supplying energy to the body. Glucose is a very important molecule that drives many metabolism in life. 

http://www.webmd.com/diabetes/blood-glucose

http://www.elmhurst.edu/~chm/vchembook/543glucose.html