Pretty much all of the basics that are just skipped over, it's because we don't actually know in very much detail at all.
Smell / taste.
We have a vague model, we know what's going in and out, but the actual workings are a black box for the most part.
If we *knew* how they work, we'd have actual, proper, real, intelligent AI. We'd have buildings that would make their own food from the sun falling on their roofs. And we'd have robots that could tell you that the wine is off, and the recipe for Coca Cola was this, and industrial computers that are able to smell leaks in factories.
We have "some of" that kind of thing, via very limited mechanical means, but nothing anywhere approaching even a basic plant or insect's capabilities or senses.