Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because:
a. they are species specific. b. they always lead to the same cellular response. c. they amplify the original signal manyfold. d. they counter the harmful effects of phosphatases. e. the number of molecules used is small and fixed.

The correct answer is option C. they amplify the original signal manyfold.

Explanation:

A phosphorylation cascade is a chain or sequence of the reactions that are categorized by the events where one enzyme phosphorylation another up-to phosphorylation of thousands of proteins.

The phosphorylation cascade can be experienced in involving the protein kinases as they the signal transduction of different cellular hormone messages due to their ability to amplify the original signal multiple time and make it more effective.

Thus, the correct answer is option C.