Final answer:
Gap junction transmission is unique due to its ability to allow direct communication between adjacent cells through connexon channels, facilitating synchronized activities such as cardiac muscle contractions.
Step-by-step explanation:
What is unique about gap junction transmission is that gap junctions enable direct cellular communication through connexon channels composed of six connexin proteins. Adjacent animal cells can exchange ions and small molecules through these channels. This form of communication is essential for synchronized activities such as the simultaneous contraction of cardiac muscle cells for effective heart function. Unlike large molecules like proteins and DNA, which cannot pass through gap junctions, small molecules such as calcium ions can diffuse rapidly, ensuring efficient signaling between closely connected cells.