Which statement best represents a key concept of cell theory?

The statement that "cells reproduce to create more cells" encapsulates one of the foundational principles of cell theory. Cell theory posits that all living organisms are composed of cells, and one of the key components of this theory is that cells arise from pre-existing cells through the process of cell division. This process is essential for growth, development, repair, and reproduction in living organisms.

Understanding cell reproduction is crucial because it highlights the continuity of life and the mechanism by which genetic information is passed on from one generation of cells to the next. This concept is fundamental to both biology and the understanding of how organisms function and evolve.

While the other statements may relate to biological concepts, they do not directly reflect the core principles of cell theory. For example, the presence of a nucleus pertains specifically to eukaryotic cells and is not universally applicable, while processes like photosynthesis and the formation of embryos, though important, focus on specific biological functions rather than the nature of cells themselves.