Noun clauses that begin with if or weather

Noun clauses that begin with if or weather

Let's show you how a Yes/No Question turns into a Noun Clause that starts with IF:

Do horses sleep standing up?

I don't know if horses sleep standing up.

You can add Or Not if you want:

I don't know if horses sleep standing up or not.

Or use Whether, it means the same thing as IF:

I don't know whether horses sleep standing up.

Here is another Yes/No Question that turns into a Noun Clause:

Do fish close their eyes to sleep?

I've often wondered if fish close their eyes to sleep.