Final answer:
Zinc is a trace mineral that supports immune function, antioxidant defense, and DNA and RNA synthesis. It serves as a co-enzyme, playing a role in various key processes including the synthesis of the heme portion of hemoglobin.
Step-by-step explanation:
Zinc is a trace mineral that has several essential functions within the human body. In particular, zinc functions as a co-enzyme, which is critical for various biological processes. These processes include the synthesis of the heme portion of hemoglobin, involvement in the body's immune function, its role in antioxidant defense mechanisms, and its necessity in DNA and RNA synthesis. Therefore, the correct answer to what zinc functions as a part of is D) Zinc is involved in all of these functions.