The clear protein of an egg white becomes opaque and firm when cooked because the heat

The clear protein of an egg become opaque and firm when cooked because the heat CHANGES THE PROTEIN STRUCTURE BY DENATURING THE PROTEIN.
Each enzymes has its own range of temperature at which it remains active, when this temperature is exceeded the protein becomes denatured and loses its three dimensional structure which determines its functions.

There are  advantages  to being  multicellular  rather than unicellular. these include allowing: the  organism  to be larger.