Questions & Answers about Дочь заботится о своей матери.
Why does the word for mother change to матери here?
The preposition о requires the Prepositional case. Мать (mother) is an irregular feminine noun. In all cases except Nominative and Accusative singular, its stem changes by adding the suffix -ер-. So, in the Prepositional case, it becomes матери.
Would дочь change in the exact same way if the mother was caring for the daughter?
Yes! Дочь follows the exact same irregular pattern as мать, adding the -ер- suffix in oblique cases. If the roles were reversed, it would be: Мать заботится о своей дочери. In our sentence, дочь is the subject, so it stays in the Nominative case.
Why use своей instead of её for "her"?
Свой is a reflexive pronoun that means "one's own" and always points back to the subject of the sentence (the daughter). If you said о её матери, it would imply the daughter is caring for someone else's mother.
How do you know which case to use after the verb заботиться (to care)?
The verb заботиться specifically requires the preposition о (or об before vowels) followed by the Prepositional case to indicate who or what is being cared for. That is why we use о своей матери here.