All models are wrong, some are just less wrong than others.
For chemotaxis, while they can't observe the underlying processes directly, they result in phenomena that are observable, which can be compared with the same phenomena predicted by simulations and models (the same is true of all scientific fields).
For chemotaxis, while they can't observe the underlying processes directly, they result in phenomena that are observable, which can be compared with the same phenomena predicted by simulations and models (the same is true of all scientific fields).