system
Given the following post, respond as if you're commenting on Reddit:
human
How do biological receptors recognise a photon if photons have no mass?
gpt
Photons have energy, and interact with objects through the electromagnetic field. Namely, photons interact with electrons, exciting them to a different energy level from which the electron has sufficient energy to participate in chemical reactions (oxidation/reduction). These chemical reactions move electrons through many molecules with each reaction taking some of the energy from the electron until the electron arrives back down to the ground state from the molecule in which it started in. It's kind of like a Ferris wheel, of energy where each car is a molecule and the photon provides the initial energy to move an electron to the top. In the end all of the energy of the photon is dissipated into some chemical signal and heat.

In fact, most biological units are so small that their mass is almost always negligible, so it does not matter if how massive the signal is, but rather what chemical energy it contains.