What type of morpheme is represented by prefixes and suffixes?

Prefixes and suffixes are classified as bound morphemes because they cannot stand alone as independent words. Instead, they must attach to a base or root word to convey meaning. For example, the prefix "un-" in the word "unkown" requires the root word "known" to have a complete meaning. This characteristic distinguishes bound morphemes from free morphemes, which can function as standalone words (such as "book" or "run").

Bound morphemes play a critical role in the formation of words by altering the meaning or grammatical function of the root they accompany. In linguistic terms, they affix to other morphemes, thus expanding the vocabulary and enhancing the expressive capability of a language.

The other choices represent different concepts in morphology. Free morphemes can exist independently, allomorphs are variations of a morpheme that appear in different contexts, and graphemes are the smallest units of written language, not directly related to morpheme types.