1. Cell Communication

2. Forms of Signalling
Paracrine signals occur between cells that are close together.
Example:
Neurotransmitters (synaptic signals)

3. Endocrine Signals
Originate from endocrine cells (within the endocrine system) and send signals to distant cells. These signals are in the form of chemical messengers known as hormones.

4. Autocrine Signalling
Signalling and target cell are the same or similar.
Example: A cell that is infected with a virus can signal APOPTOSIS (cell death) in itself and neighboring cells.

5. Direct Signalling
Gap junctions between plant cells share small molecules via connectors:
Gap Junctions (animals) Plasmodesmata (plants)

6. Endocrine | Paracrine | Autocrine

7. Receptors Receptors on the surface of the cell receive signals.
Viruses can use these receptors to gain entry into the cell.