Азотный цикл снова работает.

Because азотный цикл is the subject of the sentence — it is the thing that works.

• цикл is a masculine singular noun in the nominative
• азотный is an adjective describing it, so it also appears in the masculine singular nominative

So the structure is basically:

• Азотный цикл = the subject
• снова работает = what the subject is doing

Азот is the noun nitrogen, while азотный is the adjective nitrogen-related / nitrogen.

Russian often turns nouns into adjectives when English uses a noun-noun combination. Compare:

• азот = nitrogen
• азотный цикл = nitrogen cycle

This is very normal in Russian. English often says nitrogen cycle, but Russian prefers an adjective here.

The adjective азотный matches цикл in gender, number, and case.

Since цикл is:

• masculine
• singular
• nominative

the adjective must also be:

• masculine
• singular
• nominative

That is why you get азотный цикл.

If the noun changed, the adjective would change too.

Работает is the 3rd person singular present tense form of работать.

So:

• я работаю = I work / am working
• ты работаешь = you work / are working
• он / она / оно работает = he / she / it works / is working

Here the subject is цикл, which is singular, so the verb is also singular: работает.

It can mean either, depending on context.

Russian present tense often covers both:

• works
• is working

So Азотный цикл снова работает could mean:

• the nitrogen cycle works again
• the nitrogen cycle is working again

English chooses between simple present and present progressive more strictly than Russian does.

Yes. In Russian, работать is used very naturally not only for people, but also for:

• machines
• systems
• mechanisms
• devices
• processes

So with something like цикл, работает means something like:

• is functioning
• is operating
• is working

It sounds normal in scientific or technical language.

Снова means again.

It shows that the situation has returned: the cycle was not working before, and now it is working once more.

In this sentence, снова modifies the verb работает:

• снова работает = works again / is working again

Often yes: Азотный цикл опять работает is possible.

Both снова and опять can mean again, but there is often a nuance:

• снова = again, anew; often more neutral
• опять = again; sometimes can sound more emotional, like again...

In a neutral scientific-style sentence, снова is often the safer choice.

Yes, Russian word order is flexible.

The sentence given is a natural neutral order:

• Азотный цикл — topic/subject
• снова — adverb
• работает — verb

Other orders are possible, for example:

• Снова работает азотный цикл.
• Азотный цикл работает снова.

These can sound more marked or place emphasis differently. The original version is a very standard, neutral way to say it.

A helpful pronunciation guide is:

• азо́тный цикл сно́ва рабо́тает

Approximate pronunciation:

• азо́тный = ah-ZOT-ny
• цикл = TSI-kl
• сно́ва = SNO-va
• рабо́тает = ra-BO-ta-yet

A few notes:

• The stress in азотный is on -зо́т-
• The stress in снова is on сно́-
• The stress in работает is on бо́
• цикл has no written stress mark because it is only one syllable

Russian has no articles.

So Азотный цикл can mean:

• the nitrogen cycle
• a nitrogen cycle

The exact meaning depends on context. In many scientific contexts, it will naturally be understood as the nitrogen cycle.

Yes, but it would change the meaning.

• Азотный цикл снова работает = the nitrogen cycle is working again / works again
• Азотный цикл снова заработал = the nitrogen cycle started working again

So:

• работает focuses on the current state: it is functioning
• заработал focuses on the moment it began functioning again

Both are possible, but they are not identical.

Yes, цикл is masculine.

A common clue is that many Russian nouns ending in a consonant are masculine. Since цикл ends in -л, it is typically masculine.

That is why you get:

• азотный (masculine adjective form)
• работает (singular verb form matching a singular subject)

Yes, it is a complete sentence.

It has:

• a subject: Азотный цикл
• a verb: работает
• an adverb: снова

So grammatically it is fully complete and natural on its own.