what substances play an important role in communication between cells in a multicellular organism by acting as a chemical message

The correct answer is - ligands such as hormones and neurotransmitters.

Explanation:

Communications between the cells of the unicellular organisms take place by the chemical signaling and the substances that help in sending chemical signals between cells are called ligands.

A ligand is a chemical molecule that binds with a specific molecule or a specific signaling receptor, a protein in or on the target cell. Hormones and neurotransmitters are the ligands that help in cell signaling and send chemical messages to the target sites.

why do the isotopes of a particular element behave differently in nuclear reactions but the same in chemical reactions? chemical reactions involve changes to electrons in an atom; isotopes do not differ in electrons, and so they react the same way during chemical changes.

the answer is b. dilution