Final answer:
Cells in multicellular organisms are specialized; cells express different sets of genes, leading to variations in their structure and function.
Step-by-step explanation:
Cells in multicellular organisms are specialized; cells in different tissues look very different and perform different functions. This differentiation occurs because cells express different sets of genes. All cells contain the same DNA, but each type of cell only 'reads' the portions of DNA that are relevant to its own function. This is referred to as the unique genetic expression of each cell.