The main building block of all living organisms is the cell. Cells are the fundamental units of life, consisting of various organelles that perform specific functions. They can be classified as prokaryotic or eukaryotic, with eukaryotes further categorized into plant, animal, fungi, and protist cells. Each cell type has unique characteristics but shares the common purpose of supporting life processes such as metabolism, growth, and reproduction. Cells also contain genetic material (DNA), which carries the instructions for development and functioning, making them crucial for the continuity of life.