Final answer:
Amino acids, sugars, glycerol, and fatty acids contain carbon, which is a crucial element that allows them to be burned for energy within the body.
Step-by-step explanation:
Amino acids, sugars, glycerol, fatty acids can be burned for energy because they contain the element carbon. For instance, carbohydrates such as sugars are composed of carbon, hydrogen, and oxygen. Amino acids, which make up proteins, also contain carbon, along with hydrogen, oxygen, nitrogen, and sometimes sulfur. Fats, another major energy source, consist primarily of carbon, hydrogen, and oxygen, and when they are completely burned, they release carbon dioxide and water, indicating that carbon is a key component. Moreover, when amino acids are not used to create proteins, they can be converted into other forms, such as acetyl CoA or glucose, again highlighting the importance of carbon in their structure and metabolic processes within the body.