prerequsite vs requisite

Prerequisite = something that is required in advance, especially the subjects required as a prior condition or course of study (首要事物,必要條件,必须具有) If something is a prerequisite for another, it must happen or exist before other thing is possible or can be done.

A reasonable proficiency in English is prerequisite for this course.
A prerequisite to Calculus is Algebra. (Think admissions, getting into a class may mean you have to take other classes first.)

Prerequisite subject = 必修課目


Requisite: = something required by the nature of things, or by circumstances必需品,要素. You can use requisite to indicate that something is necessary for a particular purpose.

Breathing is requisite to human life. (If you don't breathe, you don't live; it is necessary.)
A university degree has become a requisite for entry into most professions.
He lacks the moral requisites for marriage.

Use of Requisite and Prerequisite together to illustrate the difference:
You must take the requisite number of courses in order to fulfill degree requirements for graduation. However, some of those requisite courses have prerequisite courses which you must take before you are allowed to take the requisite courses, i.e. Biology I and II before Biochemistry and Molecular Biology, however all courses are required to complete the degree.