Differentiated cells are needed because they allow an organism to have specialized cells that perform specific functions essential for survival, growth, and development. Differentiation is the biological process by which unspecialized cells become specialized in form and function, enabling the complex organization of tissues and organs in multicellular organisms. Specialized, differentiated cells have unique structures and compositions of subcellular components tailored to perform particular tasks, such as nerve cells for signal transmission or red blood cells for oxygen transport. This specialization makes biological processes efficient and allows organisms to develop diverse tissues and organs with distinct roles. Moreover, differentiation is critical during development, as it transforms a single fertilized egg cell into a fully formed organism composed of many cell types. Differentiated cells also play roles in tissue repair and normal cell turnover, maintaining organismal health. In summary, differentiated cells are essential because they give multicellular organisms the ability to develop specialized tissues and organs, carry out varied biological functions, and maintain homeostasis through ongoing cell replacement and repair.