The answer is:
INTRACELLULAR: situated or happening within a cell.
Root: cell
Affixes:
intra-: prefix meaning inside or within.
-ular: suffix forming adjectives from nouns ending in -ule. It usually posseses a diminutive impact.
A definition is the exact meaning of a word. The root of a word is the word alone without any affixes. Affixes are morphemes attached to words that modify their meaning, such as prefixes and suffixes.