The diagram illustrates how a biofuel named ethanol is produced. Overall, there are four steps before processing and four stage after processing which results in formation of ethanol.
Initially, Energy in the form of sunlight and carbon dioxide is consumed by plants and trees which helps them to grow. These trees later on are harvested with the help of machines such as a tractor. Additionally, after harvesting these plants, they are placed into a machine that reduces them to cellulose. Later this cellulose is sent for processing.
After processing, the cellulose is converted into sugars, which is later fed to microbes. After the microbes digest the sugars, they release ethanol. Futhermore, this ethanol is used to fuel cars, trucks and aeroplanes, and the by-product of these automobiles is carbon dioxide. Carbon dioxide along with sunlight serves as a energy source for plants, which is our main resource for producing ethanol.