Final answer:
The fundamental difference between cell types is their unique genetic expression and specialization, which is the result of different gene expression patterns dictated by transcription factors.
Step-by-step explanation:
The fundamental difference between two different cell types within the same organism is their unique genetic expression which leads to specialization. This process, known as differentiation, involves cells undergoing major changes in size, shape, metabolic activity, and overall function to fulfill specific roles. The process is similar to actors reading only their parts from a movie script, with all cells containing the same DNA but only 'reading' the parts relevant to their functions. Cells specialize by expressing different sets of genes and producing different proteins, a result of the action of different transcription factor proteins.
This specialization allows cells to perform diverse functions. For example, muscle cells, liver cells, and skin cells each express different genes that enable them to carry out their unique functions. Additionally, cells can activate or suppress genes in response to environmental changes or during development stages. The actin cytoskeleton and cell adhesion are also vital components that contribute to the structural differences between cell types.