For basic sciences;
-Showing the way to reach the conclusion/answer, explanations of the steps and assumptions to use them.
-The reasons for choosing specific equations
These are the characteristics of the answers. In the question, not a class-similar problem should be seen, in that way, the memorization of the answer will suffice to reach the correct conclusion.
In chemistry, for instance, you show three different reactions in lectures. Then in the exam, you gave two compounds which you demand the synthesis of the latter from former using any chemical necessary (and actually requires students to use the lectured reactions before the exam). Almost none of the students who did not understand the properties of the reactions can answer such questions.
In short, the question is much more important to understand the comprehension level of the students than to their answer structure.