Exam Boards assign different mark percentages to each of the skill domains and you should consult the particular syllabus you are following to see exactly how your Board assigns marks to each skill.
Typically, about 20% of the available marks in an exam are given for Knowledge and Understanding (although as much as 33% of the available marks may be assigned to these skills on some exam papers), whereas anything up to 80% of the available marks are given on the basis of your ability to do something with the things you know (that is, interpretation, application and evaluation).
This is significant because students who simply (not to put too fine a point on it) "regurgitate knowledge" and indulge in lengthy (and largely irrelevant) descriptions invariably fail to gain the marks and overall grade their ability deserves. This is because once you have achieved all the marks assigned to a particular skill you cannot be given any further marks in that particular area.
The key point to remember, therefore, is that you must use all of the required skills appropriately in your examination answers if you are to achieve a high grade...