Answer:
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.
