Glucose is a simple sugar that can be stored in a variety of forms. It is a vital component for most types of life on earth. Plants have the ability to create glucose instead of absorbing it from other sources. Photosynthesis is the process in which they take the energy of the sunlight and the molecules from carbon dioxide and create nutrients for themselves.
During photosynthesis, plants use specific cells called chloroplasts, which house layers and layers of chlorophyll, a pigment that holds energy from light photons that pass through it. This energy is then converted into a chemical that is easier for plants to use. Some of the light energy is converted directly into ATP, the same type of molecule that helps human muscles move, while the rest of it is made into nicotinamide adenine dinucleotide phosphate (NADPH). The ATP energy goes directly into running the other "factory" parts of the plant, while the NADPH is combined with carbon dioxide to create glucose. NADPH provides hydrogen atoms that are bonded to other molecules to create the simple sugar. This process differs in some plants, and is usually based on how many single molecules are needed to form one molecule of glucose.
Glucose is a carbohydrate, a molecule that living organisms use to gain energy. Plants draw up the nutrients and minerals they require from their roots, the building blocks for their cells, and breaking apart the glucose, they make the energy needed to combine the building blocks into leaves, flowers, seeds and other important parts, including cellulose, the vital material that plants use to make their cell walls. Essentially, when the chemical bonds that hold the glucose molecule together are broken, they release electrons that, now free, need to join with other atoms, thus giving the molecules inside cells more energy.
Some plant organisms that use photosynthesis produce all of the energy they need and store very little, such as green algae. But most plants create more glucose than they need. This extra glucose is used during cold or dry months when the plant has a difficult time manufacturing new glucose for its needs. Since it needs to be stored until then, the plant changes it into a lost-lasting starch. This starch is stored deep within the plant, inside roots and stems and, at certain times, seeds. Some plants, especially those in the cacti family, required this starch to survive.