Have we become a caste society? Why or why not?keeping in mind what Marx meant by (1) class (2) superstructure (3) ideology
Are you asking if we have become a caste society instead of the sort of class-based society that Marx talks about? If so, I would say that the answer depends largely on the degree to which you think that inequality is inherited and immutable in the US today. The general distinction between a society based on class and one based on caste is that there is at least some social and economic mobility possible in a class society but none in a caste society.
You mention superstructure and ideology here. I suppose that you could argue that we feel that we are a class society when that is, in truth, simply an ideology put forth by the elites as a means of cultural hegemony. In other words, it may be that the dominant class gets the rest of us to believe that we have class mobility so as to keep us happy. If we believe that we actually have the ability to achieve the American Dream, we will be less likely to rebel against the system as it is.
My own view is that we are not a caste society. It is certainly difficult to move up significantly in class from that of your parents. However, it is not impossible to do so. In addition, we do not enforce the sorts of social distance between the upper and the lower classes that are expected in true caste societies.