Russian preposition за

Do you know that the Russian preposition за has several meanings?

1. it expresses an aim after verbs of movement: Я иду за хлебом. I am on my way to buy bread.
2. it expresses responsibility or gratitude (after the words спасибо, извините, платить, отвечать): Извините за беспокойство! Sorry for bothering you!
3. it is used to express expathy after verbs беспокоиться, волноваться, бояться, радоваться: Я беспокоюсь за тебя! I am worried about you!
4. it shows the amount of time that is necessary to finish the action: Я сделаю это за три часа. It will be done in three hours.