They are all part of this beautiful subject called science.
They all study the natural world and the physical world.
Biology needs chemistry to be understandable with its chemical reactions (e.g. digestion).
Chemistry needs physics to be understandable such as particle movements.
Vice-versa, physics needs chemistry to be understandable such as the structure of atoms and molecules.
There is a lot more to this but here are some examples I can think of.