Which of the following compounds is categorized as a steroid?

The compound categorized as a steroid is testosterone. Steroids are a type of lipid characterized by a specific structure composed of four fused carbon rings. This structure is distinct from other types of macromolecules in biology, such as proteins and carbohydrates.

Testosterone is a well-known steroid hormone produced primarily in the testes in males and ovaries in females, as well as in smaller amounts by the adrenal glands in both sexes. It plays critical roles in development and maintenance of male characteristics, but it also has functions in females, such as influencing libido and bone density.

In contrast, insulin is a peptide hormone made up of amino acids, glucose is a simple carbohydrate (a monosaccharide), and hemoglobin is a protein composed of amino acids that facilitate oxygen transport in the blood. These compounds have entirely different structures and functions compared to steroids.