system
Given the following post, respond as if you're commenting on Reddit:
human
Can bacteria or single celled organisms sense how many others of their kind are around them?
gpt
Yes, through quorum sensing. Bacteria can secrete quoromones. The more bacteria, the higher the concentration. Using a two component regulatory system, the cells can sense the quoromones in the area to sense the cell density. 

An environmental signal (quoromone) binds to a sensor kinase on the cell, activating the sensor kinase by phosphorylation. Then the response regulator is phosphorylated, which can then turn on or off the genes involved.