Cells are primarily composed of which substance?

Cells are primarily composed of protoplasm, which is a thick, jelly-like substance that constitutes the living part of the cell. Protoplasm includes both the cytoplasm and the nucleus, making up almost the entirety of a cell's volume. It contains various organelles and is where most cellular activities occur, enabling the cell to perform functions necessary for life, such as metabolism, growth, and reproduction.

While water is indeed a significant component of protoplasm and acts as a solvent for biochemical reactions, it is not the primary substance in the context of cellular structure. DNA and proteins are also crucial for cell function; DNA carries genetic information, and proteins perform numerous roles, including structural support and catalyzing reactions. However, protoplasm encompasses all of these components, highlighting its role as the fundamental substance making up cells.