system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does "weed and feed" know the difference between the grass it should feed and the weeds it should kill?
gpt
Different organisms have different physiologies. Same way chocolate is fine for human consumption, but will kill dogs. Monocots like grasses have different cellular components than dicots like dandelions and other types of weeds and herbicides can be designed to differentiate them.