Final answer:
Humans obtain glucose for cellular respiration from the food they eat. Digestion breaks down food, allowing glucose to be absorbed and later converted into ATP during cellular respiration.
Step-by-step explanation:
Humans get glucose for cellular respiration primarily from C. Food. Glucose, with the chemical formula C6H12O6, is an essential source of energy and is vital for the production of adenosine triphosphate (ATP), which cells use to carry out various functions. Through the process of digestion, the food we eat is broken down into glucose and other nutrients that are absorbed into the bloodstream and transported to cells for cellular respiration.
In plants, glucose is produced by photosynthesis using carbon dioxide and water. Humans, as well as other animals, consume plants or other organisms that have ingested plants to obtain glucose. Once inside an organism, glucose is available to enter the cellular respiration process, where in the presence of oxygen, it is converted into ATP and byproducts such as carbon dioxide and water.