Concept:Mature red blood cells in humans are enucleated, meaning they lack a nucleus.
Explanation:In the human body, most cells contain a nucleus, but mature red blood cells (erythrocytes) do not.
This absence of nucleus and other organelles provides more space for hemoglobin, increasing oxygen-carrying capacity.
Red blood cells have a biconcave shape that aids in gas exchange and flexibility to pass through capillaries.
Muscle cells contain one or more nuclei.
Phagocytic cells (e.g., macrophages) have a nucleus and are involved in immune defense.
Ciliated cells, found in respiratory tract, also contain a nucleus to support their function of moving mucus.
Thus, only red blood cells among the listed options are nucleus-free in their mature form.
Answer:Red blood cells (Option C)