Læreren studerer cellen.

Because both nouns are in the definite singular form.

• lærer = teacher / a teacher
• læreren = the teacher
• celle = cell / a cell
• cellen = the cell

In Norwegian, definiteness is usually added to the end of the noun instead of using a separate word like the in English.

Læreren by itself already means the teacher, so den is not needed.

Use den læreren only when you mean something more like:

• that teacher
• that particular teacher

So in a simple sentence like Læreren studerer cellen, the normal form is just læreren.

This is the normal Norwegian main clause word order:

subject + verb + object

So:

• Læreren = subject
• studerer = verb
• cellen = object

This is very similar to English:

• The teacher studies the cell

Yes. Studerer is the present tense of å studere.

Examples:

• å studere = to study
• læreren studerer = the teacher studies / is studying

In Norwegian, the present tense often ends in -er for many verbs.

It can mean both, depending on context.

Norwegian present tense often covers both:

• The teacher studies the cell
• The teacher is studying the cell

Usually the surrounding context tells you which sense is meant.

Celle is usually a feminine noun, but in Bokmål many feminine nouns can also be treated as masculine.

That means you may see:

• ei celle / cella
• or en celle / cellen

In your sentence, cellen uses the masculine-style definite ending -en, which is completely normal in Bokmål.

Lærer is a common gender noun in Bokmål, usually treated as masculine in traditional descriptions:

• en lærer = a teacher
• læreren = the teacher

Unlike English, grammatical gender in Norwegian does not necessarily tell you anything about the real-life sex of the person. So læreren can mean the male teacher or the female teacher, unless something else makes it clear.

A careful approximation is:

LÆ-re-ren

A few useful points:

• æ sounds somewhat like the vowel in English bad, though not exactly the same.
• The r is pronounced in Norwegian, though its exact sound depends on dialect.
• The stress is on the first syllable: LÆreren.

If you are learning standard Eastern Norwegian pronunciation, the word is roughly /ˈlæːrərən/.

A simple approximation is:

SEL-len

Points to notice:

• The c in celle is pronounced like s here.
• The stress is on the first syllable: SELlen.
• The double ll does not mean you hold the sound extra long in English style; it mainly affects the preceding vowel.

A rough pronunciation is /ˈselːən/ or similar, depending on dialect.

Because Norwegian usually marks the by adding an ending to the noun:

• læreren = the teacher
• cellen = the cell

This is one of the big differences from English. Instead of writing the teacher, Norwegian often uses one word: læreren.

Yes. Then it would be:

En lærer studerer en celle.

That means:

• A teacher studies a cell

So the definite forms in your original sentence tell us that it is the teacher and the cell, not just any teacher or any cell.

Yes, grammatically it is completely natural.

Whether it feels common depends on context. In everyday life, studere can sound a bit formal or academic, so the sentence suggests a scientific, educational, or analytical setting. For example, it could fit well in a biology classroom or lab context.

Sometimes, but Norwegian word order is fairly strict in main clauses.

The basic sentence is:

• Læreren studerer cellen.

You can also put another element first, but then the verb must still come second:

• I dag studerer læreren cellen. = Today the teacher is studying the cell.

What you generally cannot do in a normal statement is use English-style freer rearrangement like:

• Læreren cellen studerer ❌

So the original order is the standard and safest one.

The dictionary forms are:

• lærer = teacher
• å studere = to study
• celle = cell

The sentence uses:

• læreren = definite singular of lærer
• studerer = present tense of å studere
• cellen = definite singular of celle