Storage Forms of Glucose in Organisms

When carbohydrates from the foods you consume are digested, glucose is the smallest molecule into which a carbohydrate is broken down. Glucose molecules are absorbed from intestinal cells into the bloodstream. The bloodstream then carries the glucose molecules throughout the body. Glucose enters each cell of the body and is used by the cell’s mitochondrion as fuel.

Carbohydrates are in nearly every food, not just bread and pasta, which are known for “carbo loading.” Fruits, vegetables, and meats also contain carbohydrates. Any food that contains sugar has carbohydrates. And, most foods are converted to sugars when they are digested.

Once an organism has taken in food, the food is digested, and needed nutrients are sent through the bloodstream. When the organism has used all the nutrients it needs to maintain proper functioning, the remaining nutrients are excreted or stored.

You store it: Glycogen

Animals (including humans) store some glucose in the cells so that it is available for quick shots of energy. Excess glucose is stored in the liver as the large compound called glycogen. Glycogen is a polysaccharide of glucose, but its structure allows it to pack compactly, so more of it can be stored in cells for later use. If you consume so many extra carbohydrates that your body stores more and more glucose, all your glycogen may be compactly structured, but you no longer will be.

Starch it, please: Storing glucose in plants

The storage form of glucose in plants is starch. Starch is a polysaccharide. The leaves of a plant make sugar during the process of photosynthesis. Photosynthesis occurs in light (photo = light), such as when the sun is shining. The energy from the sunlight is used to make energy for the plant. So, when plants are making sugar (for fuel, energy) on a sunny day, they store some of it as starch. When the simple sugars need to be retrieved for use, the starch is broken down into its smaller components. They literally save some energy for a rainy day!