In cellular respiration the main source of energy is glucose. Here it is used to create ATP for a cell allow the processes of life to take place. While these sugars can be obtained from many organism they mostly originate from photosynthetic organisms such as plants and algae. In cellular respiration glucose is used in a process called glycolysis.
Most of and organisms carbohydrate supply is used to create energy in the form of ATP. However in plants excess carbohydrates are made into starch while animals create glycogen. Organisms also use carbohydrates for structural purposes such as the cell walls in plants as well as the shell of a crab. While most mammals cannot break these structural carbohydrates down they still are an essential part of the diet in the form of fiber.
Sugar tags may also be added to proteins to act as a protein identifier for a cell. This helps keep a cells processes organized and allows the cell to properly control it resources. Carbohydrates are an important molecule in life and due to this they are found in many forms within life on the planet. Due to this they are redily obtainable and can be used by almost every lifeform in existence.