What is the primary function of hormones in cellular biology?

The primary function of hormones in cellular biology is to act as regulatory molecules that help control various cellular functions. Hormones are biochemical messengers, typically produced by endocrine glands, that are released into the bloodstream and travel throughout the body to target organs or tissues. Once they reach their targets, they bind to specific receptors, initiating signaling pathways that influence processes such as growth, metabolism, immune function, and homeostasis.

This regulatory role is crucial because hormones can modify how cells behave, ensuring that processes within the body are coordinated and respond appropriately to internal and external stimuli. For example, insulin regulates glucose metabolism, while adrenaline prepares the body for a 'fight or flight' response.

The other options do not accurately capture the role of hormones. While energy production through respiration is vital for cellular function, it does not pertain specifically to the role of hormones. Cellulose is a structural polysaccharide found in the cell walls of plants, which is unrelated to hormonal activity. Lastly, while some hormones can influence the synthesis of certain cellular molecules (like steroid hormones affecting gene expression), they do not direct the synthesis of all cellular molecules, which is a broader function carried out by various molecular processes including transcription and translation mechanisms.