Why is it best to have six or less life-cycle phases in an epm system?

How did the research presented in the article affect scientists' understanding of the evolution of eukaryotes

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

The tubes transporting minerals and water upward are called ?