Glucose

Glucose is a six-carbon monosaccharide sugar (formula C₆H₁₂O₆) that serves as a primary energy source for cells. It is a key product of photosynthesis and the main fuel metabolized during cellular respiration to produce ATP.

• Glucose is an aldohexose - a hexose sugar with an aldehyde group. It shares the formula C₆H₁₂O₆ with fructose and galactose, but they differ in structure (they are isomers).
• In humans, glucose is the "blood sugar." The normal blood glucose concentration is tightly regulated (about 70-100 mg/dL fasting). Excess glucose is stored as glycogen (in liver and muscle), and plants store glucose as starch.
• Glucose is central to metabolism: glycolysis breaks glucose into pyruvate in the cytoplasm, yielding energy. In the presence of oxygen, the breakdown continues in mitochondria (Krebs cycle and oxidative phosphorylation) to generate a large amount of ATP.

• If a question asks "What monosaccharide is the main energy source for the brain and body-" the answer is glucose. Clues might include "blood sugar" or a scenario involving insulin, diabetes, etc., which revolve around glucose.
• Be prepared for comparisons among sugars. For example, an exam might mention that glucose and fructose are both C₆H₁₂O₆ but one is an aldose and one a ketose - identifying glucose as the aldose (and fructose as the ketose) is key.
• Photosynthesis and respiration questions often highlight glucose. E.g., "What molecule is produced by photosynthesis and broken down in cellular respiration-" Answer: glucose (produced by plants, consumed by organisms for energy).