In the term trace element, the adjective trace means thata. the element is required in very small amounts.b. the element can be used as a label to trace atoms through an organism's metabolism.c. the element is very rare on Earth.d. the element enhances health but is not essential for the organism's long-term survival.

Trace elements are minerals that organisms require in very small amounts for various physiological functions. Despite their minimal presence, they play crucial roles in processes such as enzyme function, hormone production, and cellular metabolism. Examples include iron, zinc, and selenium, which are vital for health but needed only in minute quantities.

Nutritional requirements refer to the essential nutrients that organisms need to maintain health and support growth. These requirements can vary significantly among different species and can include macronutrients (like carbohydrates and proteins) and micronutrients (like vitamins and trace elements). Understanding these requirements helps in assessing dietary needs and deficiencies.

Metabolism encompasses all biochemical processes that occur within an organism to maintain life, including the conversion of food into energy and the synthesis of necessary compounds. Trace elements often act as cofactors in metabolic reactions, facilitating the activity of enzymes and ensuring efficient metabolic pathways. Their role is critical, even in small amounts, for overall metabolic health.