Which complex chemicals are essential for normal body function in humans and animals?

Vitamins are complex organic compounds essential for various bodily functions in both humans and animals. They play a critical role in metabolic processes, including energy production, immune function, and cellular repair and maintenance. Each vitamin has specific functions and is necessary in minute amounts, often functioning as coenzymes or precursors for enzyme activity, which is vital for the body's biochemical reactions.

For instance, Vitamin C is crucial for collagen synthesis, Vitamin A is important for vision and immune function, and the B-vitamins are integral to energy metabolism. A deficiency in any of these vitamins can lead to various health issues, highlighting their importance in maintaining health and facilitating normal physiological processes.