Biophotons (BPHs) are weak photons within or emitted from living organisms. BPH emission originates from a de-localized coherent electromagnetic field within living organisms and is regulated by the field. Based on experimental results concerning Poisson and sub-Poisson distributions of photocount statistics, the coherent properties of BPHs and their functions in cell communication are described in this paper. We discuss functions of BPH roles in some important processes, including DNA replication, transcription, protein synthesis, and cell signalling, and in the processes of oxidative phosphorylation and photosynthesis.