asita ha siken ga arimasu kara, sitizi ni watasi wo okosite kudasai.

は marks the topic of the sentence.

So 明日は means something like as for tomorrow or speaking of tomorrow. It sets the time frame for the whole sentence.

In this sentence, 明日は試験があります is not just tomorrow exists. It means as for tomorrow, there is an exam / the exam is tomorrow.

Using は here feels very natural because tomorrow is background information that the speaker is setting up first.

Because あります often takes が for the thing that exists or occurs.

So:

• 試験があります = there is an exam / an exam will take place
• 試験はあります would sound more like as for the exam, there is one or would contrast it with something else

In this sentence, 試験がある is the normal pattern.
The exam is the thing that is being stated as existing, so が is the natural choice.

That is a very common Japanese pattern.

ある / あります does not only mean to physically exist. It is also used for:

• events
• scheduled things
• meetings
• classes
• tests
• appointments

So 試験があります means:

• there is an exam
• I have an exam
• an exam is scheduled

All of these are natural English translations depending on context.

から means because or since.

So:

• 試験がありますから = because there is an exam / since I have an exam

In Japanese, the reason often comes before the main request or statement.

So the structure is:

• Reason + から
• Main request

That is exactly what happens here:

• 明日は試験がありますから = because tomorrow there is an exam
• 七時に私を起こしてください = please wake me up at seven

に marks a specific point in time.

So:

• 七時に = at seven o’clock

Japanese often uses に with exact times such as:

• 六時に = at six
• 月曜日に = on Monday
• 三月一日に = on March 1st

But に is usually not used with more general time words like:

• 明日
• 昨日
• 毎日

So in this sentence:

• 明日は = tomorrow
• 七時に = at seven o’clock

Both are time expressions, but they behave differently.

Because 起こす means to wake someone up, and it is a transitive verb.
A transitive verb takes a direct object, and that object is marked by を.

So:

• 私を起こす = wake me up
• 弟を起こす = wake my younger brother up

Here, 私 is the person being woken, so it takes を.

This is a very important difference.

• 起きる = to wake up / to get up
• 起こす = to wake someone up

So:

• 起きてください = please get up
• 起こしてください = please wake me up

In the sentence you gave, the speaker wants another person to do the waking, so 起こして is correct.

It is:

• 起こす → dictionary form
• 起こして → て-form
• 起こしてください → て-form + ください

The pattern て-form + ください is a standard polite way to say please do ...

So:

• 見てください = please look
• 待ってください = please wait
• 起こしてください = please wake me up

It is polite, but still a fairly direct request.

Very often, yes, it could be omitted.

Japanese frequently leaves out words that are clear from context. If you are asking someone to wake you up, it is often obvious that you are the person to be woken.

So a very natural version would be:

• 明日は試験がありますから、七時に起こしてください。

This still clearly means Please wake me up at seven, because I have an exam tomorrow.

Adding 私を is not wrong, but it can sound a little more explicit than necessary unless you want to emphasize me.

Japanese often omits the subject when it is understood from context.

In English, we need you for an imperative or request:

• Please wake me up

In Japanese, that you is usually left unstated. The listener is understood automatically.

So 起こしてください already implies:

• please (you) wake me up

This omission is very normal in Japanese.

Yes. It is politely phrased.

The clues are:

• あります instead of ある
• ください for the request

So it is more polite than a casual version like:

• 明日試験があるから、七時に起こして。

That said, even though it is polite, it is still a direct request. It would sound natural when speaking to someone you can reasonably ask for help, such as:

• a family member
• a roommate
• a friend
• possibly a coworker, depending on the situation

Yes, it is very natural.

Japanese often puts information in this kind of order:

• time/topic
• reason
• main request

So:

• 明日は = as for tomorrow
• 試験がありますから = because there is an exam
• 七時に私を起こしてください = please wake me up at seven

Also, the verb usually comes at or near the end of the clause, which is a basic feature of Japanese sentence structure.

No. In normal Japanese writing, spaces are usually not used between words.

A natural written version would be:

明日は試験がありますから、七時に私を起こしてください。

The spaced version is often used only in teaching materials to make the sentence easier for beginners to read.