What is the basic structural and functional unit of all complex organisms?

The basic structural and functional unit of all complex organisms is the cell. Cells are often referred to as the building blocks of life because they are the smallest units that can carry out all essential life processes. Each cell performs specific functions necessary for the organism's survival and contributes to the overall function of tissues, organs, and systems.

Cells vary in type and specialize in different functions—for example, muscle cells are specialized for contraction, while nerve cells transmit signals. These specialized cells come together to form tissues, which then combine to form organs, creating a more complex organization within the body. Hence, the understanding of cells as the fundamental units of life is crucial in biology and nutrition science, as it provides insight into the metabolic and physiological processes that occur within living organisms.