Kto opiekuje się żółwiem, kiedy wyjeżdżacie na dwa dni?

Because the full verb is opiekować się, which means to take care of or to look after.

In Polish, się is part of many verbs and does not always translate directly into English. Here, you should learn opiekować się as one whole unit.

So:

• opiekować się kimś/czymś = to take care of someone/something

You cannot normally drop się here.

Because opiekować się requires the instrumental case.

The dictionary form is żółw = turtle / tortoise, but after opiekować się it changes to instrumental:

• żółw → żółwiem

So:

• opiekuje się żółwiem = is taking care of the turtle

This is a very common kind of Polish pattern: certain verbs require a specific case.

It is the instrumental singular.

You often see the instrumental after verbs like:

• interesować się = to be interested in
• zajmować się = to զբաղy oneself with / deal with
• opiekować się = to take care of

So in this sentence:

• żółwiem = instrumental singular of żółw

Because Polish very often uses the present tense of an imperfective verb to talk about a future event, especially when the future is understood from context.

Here:

• wyjeżdżacie literally looks like you are leaving / you leave
• but with kiedy and the whole context, it means when you leave / when you are going away

This is normal Polish usage.

It comes from wyjeżdżać, which means to leave, to go away, or to depart, especially by going somewhere away from your current place.

The prefix wy- often suggests movement out or away.

So:

• wyjeżdżacie = you are leaving / you leave / you are going away

In this sentence it means something like when you go away for two days.

Because Polish usually leaves out subject pronouns when they are clear from the verb ending.

The ending -cie in wyjeżdżacie already tells you the subject is you plural.

So Polish does not need wy here.

Compare:

• wy wyjeżdżacie = you are leaving
• wyjeżdżacie = also you are leaving

The second version is more natural unless you want extra emphasis.

It can mean either, as long as the subject is more than one person.

So wyjeżdżacie can be used for:

• you two
• you three
• you all
• a group such as a family, couple, or friends

It is simply the second person plural form.

Because kto means who, and in Polish it normally takes a third person singular verb.

So even though in English we may think of who as open-ended, Polish grammar treats it as singular in this kind of sentence:

• Kto opiekuje się żółwiem? = Who is taking care of the turtle?

That is why it is opiekuje, not opiekują.

With verbs of going or leaving, na + length of time often means for a certain period.

So:

• na dwa dni = for two days

In this sentence, it means the people are going away and will be gone for that amount of time.

This is very natural with verbs like wyjechać / wyjeżdżać.

Not with exactly the same feel.

• na dwa dni means for two days in the sense of going away for that period
• przez dwa dni focuses more on something lasting throughout two days

With wyjeżdżać, na dwa dni is the more natural choice when talking about the planned length of the trip.

Yes, in this sentence kiedy and gdy can both mean when.

• kiedy is very common and neutral
• gdy is also common, but can sound a bit more formal or literary in some contexts

So:

• Kto opiekuje się żółwiem, kiedy wyjeżdżacie na dwa dni?
• Kto opiekuje się żółwiem, gdy wyjeżdżacie na dwa dni?

Both are correct.

Yes. Polish word order is more flexible than English word order.

For example, you could also say:

• Kiedy wyjeżdżacie na dwa dni, kto opiekuje się żółwiem?

The meaning stays basically the same, but the emphasis changes slightly.

The original version starts with the main thing being asked:

• Who takes care of the turtle...?

So it sounds very natural as a direct question.

Yes, opiekować się is imperfective.

That fits well here because the sentence is about ongoing care during the time the people are away.

Polish often uses imperfective verbs for actions seen as:

• ongoing
• repeated
• habitual
• not focused on completion

That is exactly the idea in Who takes care of the turtle when you go away for two days?