An Affix is a morpheme (a linguistic unit that cannot be divided into smaller meaningful parts) that attaches to the stem (root) of a word to form either a new word of a new form of the same word.
Affixes can be Derivational (the process of forming a new word from an existing word) and Inflectional (the modification of a word to express different grammatical categories such as tense, voice or person) There are also Prefixes (affixes placed before the stem of a word) and Suffixes (affixes placed after the stem of the word).
These are the roots and affixes of these words:
Alternate:
Root Word: Altern.
Suffix: –Ate which makes the word a verb.
Alternate: To perform by turns or in succession.
Biannual:
Root Word: Annual.
Prefix: Bi- which means two (in this case two times).
Biannual : Occurring twice a year.
Autobiography:
Root Word: Biography,
Prefix: Auto- which means self
Autobiography: The biography of a person narrated by him/herself.
Recognize:
Root Word: Cognize or Cognise. which means to perceive, become aware of or know.
Prefix: Re- which means again or back
Recognize: To perceive something or someone previously known.
Affixes can be class-changing and class-maintaining.
Class-maintaining affixes do not change the word class but change only the meaning of the word.
Class-changing affixes, when added to stems, immediately change the class of the word, making them as verbs, nouns, adverbs or adjectives.
So in the previous examples class-maintaining affixes and class-changing affixes were also used.