Since the internal structure of many protists is much more complex than that of cells of multicellular organisms, does this mean that protists are engaged in more complex activities than multicellular organism? If not, why should the protistan cell be much more complicated?
Protistan cells are much more complex (complicated) because these protist unicellular organisms carry on all life functions at the cellular level. Compare this to the multicellular organism that uses division of labor to specialize various life functions to various cell or cell groups. Thus while protistan cells are engaged in complex activities, they are not engaged more complex activities than multicellular organism and are more complicated in structure because each protistan cell performs all the functions of all the various special cells in a multicellular organism.