What is the basic unit of structure and function for all living organisms?

The correct choice, which is the cell, is recognized as the basic unit of structure and function for all living organisms. Cells serve as the fundamental building blocks of life, where various biological processes essential for survival occur. Each cell has specific structures known as organelles that perform distinct functions necessary for maintaining the life of that cell.

In multicellular organisms, cells can specialize and group together to form tissues and organs, but the cell itself remains the smallest entity that can carry out all life processes independently. This includes metabolism, growth, response to stimuli, and reproduction. Understanding this foundational concept emphasizes the importance of cellular biology and clarifies that even complex life forms are ultimately composed of these basic units.

Other options, such as tissue, organism, and organelle, represent higher levels of biological organization or specific components within a cell rather than a standalone unit of life. Therefore, identifying the cell as the basic unit highlights its critical role in life science and biology as a whole.