Bladlusen sitter på bladspissen.

Because -en is the definite ending on the noun.

• bladlus = an aphid
• bladlusen = the aphid

In Norwegian, the definite article is usually attached to the end of the noun instead of being a separate word like the in English.

So:

• en bladlus = an aphid
• bladlusen = the aphid

Yes. Norwegian very often makes compound nouns by joining words together.

Here:

• blad = leaf
• lus = louse
• bladlus = literally leaf louse, meaning aphid

Then the definite ending is added:

• bladlus
  • -en → bladlusen

This is very common in Norwegian, and English speakers often need time to get used to writing such compounds as a single word.

For the same reason: it is also a compound noun.

• blad = leaf
• spiss = tip / point
• bladspiss = leaf tip
• bladspissen = the leaf tip

Norwegian usually writes these as one word, not two.

So:

• en bladspiss = a leaf tip
• bladspissen = the leaf tip

Because the sentence is talking about a specific aphid and a specific leaf tip.

• bladlusen = the aphid
• bladspissen = the leaf tip

This is natural in Norwegian when both things are understood as particular, identifiable things in the situation.

A less specific version would be:

• En bladlus sitter på en bladspiss. = An aphid is sitting on a leaf tip.

So the definite forms make the sentence sound more like it is about a particular scene or a known object.

Yes, sitter is the present tense of sitte, and it often does mean sits / is sitting.

But in Norwegian, sitte is also commonly used more broadly for something that is positioned somewhere, especially in a resting or fixed way. So in a sentence like this, it can sound natural even if English might sometimes prefer something like is on.

• sitte = sit
• sitter = sits / is sitting

Norwegian often uses position verbs where English may be less specific. Other common ones are:

• stå = stand
• ligge = lie

Because Norwegian present tense usually expresses both the simple present and the present progressive without needing a separate verb like is.

So:

• sitter can mean sits
• sitter can also mean is sitting

English distinguishes:

• it sits
• it is sitting

Norwegian usually does not:

• den sitter

Context tells you which English translation fits best.

På often means on, and that is the natural choice here for something located on a surface or point.

So:

• på bladspissen = on the leaf tip

This is a very common Norwegian preposition, but like English prepositions, its usage does not always match perfectly word-for-word in every context. In this sentence, though, på corresponds neatly to on.

The basic word order is very similar to English:

subject + verb + prepositional phrase

So:

• Bladlusen = subject
• sitter = verb
• på bladspissen = prepositional phrase showing location

Literally:

• The aphid sits on the leaf tip.

This is a straightforward Norwegian main clause.

Yes, it matters because gender affects the indefinite article and the definite ending.

Both bladlus and bladspiss are typically common gender nouns, so they use:

• en in the indefinite singular
• -en in the definite singular

That gives:

• en bladlus → bladlusen
• en bladspiss → bladspissen

If a noun had a different gender, the forms could look different.

A rough pronunciation guide for an English speaker could be:

• bladlusen ≈ BLAH-dloo-sen
• sitter ≈ SIH-ter
• på ≈ paw (with a long vowel)
• bladspissen ≈ BLAH-dspis-sen

A few useful notes:

• å in på is a different vowel from English a; it sounds more like the vowel in law or more, depending on accent.
• The tt in sitter is pronounced as a clear t sound.
• Norwegian compounds are usually stressed early, often on the first part of the word.

Pronunciation varies by dialect, but this will get you close.

Yes, you could say:

• Bladlusen er på bladspissen.

That would mean The aphid is on the leaf tip.

The difference is that sitter gives a stronger sense of position or the way it is located, while er is more neutral and simply states location.

So:

• er = neutral location
• sitter = more specifically is sitting / is positioned there

In Norwegian, using a position verb like sitter is often very natural.