What type of morpheme cannot stand alone and adds meaning to a word?

The answer identifies a bound morpheme as the correct choice because it is a type of morpheme that cannot stand alone and must be attached to a free morpheme to convey meaning. Bound morphemes include prefixes and suffixes, such as "un-" in "undo" or "-s" in "cats." These elements add specific aspects of meaning—such as negation or plurality—to the base word they modify.

For instance, the morpheme "ed" cannot exist independently; it needs to be attached to a verb, like "walk," to form "walked." This illustrates how bound morphemes enhance the meaning of a word by providing grammatical context or altering its meaning without functioning as standalone words.

In contrast, free morphemes can stand alone (e.g., "cat" or "run"). Base morphemes usually refer to the root form of a word, which can be free or bound, while inflectional affixes are specific types of bound morphemes that modify a word to express grammatical relationships but are still a subset of bound morphemes. Understanding the role of bound morphemes is crucial in literacy education, as they significantly contribute to students' understanding of word formation and meaning.