Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling?

(A) Cell signaling uses the highest molecularweight molecules found in living cells.

(B) Cell signaling has largely been replaced byother cell functions in higher mammals.

(C) Similar cell signaling pathways in diverseeukaryotes are evidence of conservedevolutionary processes.

(D) Cell signaling functions mainly during earlydevelopmental stages.

Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.

Explanation:

Cells communicate by signaling one another using chemical compounds. A signaling molecule binds to a receptor molecule on the cell surface or within the target cell to transduce the signal and to generate the desired cellular response. Cell signaling pathways are important for cell-cell communication in both unicellular and multicellular eukaryotes. Several signaling pathways are conserved and are exhibited by diverse groups of eukaryotes.

For example, cAMP serves as a second messenger in both unicellular and multicellular eukaryotes and serves to relay a signal from the plasma membrane to protein in the cytosol. The cAMP serves as the second messenger in amoeba-like cellular slime mold such as Dictyostelium under the conditions of food scarcity and directs the movement of several slime molds to form a multicellular slug-shaped colony.