What's the difference between prefixes and suffixes?

What's the difference between prefixes and suffixes?
【正确答案】：Prefixes primarily change the meaning of the stem, while suffixes have only a small semantic role, their primary function being to change the grammatical function of stems. In other words, they mainly change the word class.
【题目解析】：从定义和作用两个方面分析它们的差别。