Observer, MVC, Singleton and Flyweight - similarities?

This is not really homework, but it is something I've been wondering about since I did not get an answer for these questions in school:

Observer Design Patterns is a pattern of its own, of course, but it can also be a part of MVC pattern/architecture. It's the "view" part of MVC - but I do not understand how exactly that is?

Also, Singleton and Flyweight are also two different patters - but do they share some similarities? On an exercise file I got, it indicates that these two patterns share something?

If someone could explain it for me, I'd be very grateful.