We grow up with both of them working together and never know the difference until we think about it or do some experiments. They are just working together like they were designed to do and we just roll with it. There is quite a bit of research that has been published on the subject. This writer recalls seeing some experiments where subjects swore that something tasted like a banana when it had no taste at all and only smelled like the longish yellow fruit we are so familiar with.
Smell and taste are two independent senses, but we are so used to using them simultaneously that it takes practice to "split" the two off and evaluate the smell of something in a separate activity to an act of tasting that thing. (There are people who work in labs whose job it is to evaluate things only by smell and then separately only by taste. Takes some skillz to do that kind of work. And lots and lots of practice.)