A quarentena protege a espécie.

Because a is the feminine singular definite article in Portuguese, meaning the.

• a quarentena = the quarantine
• a espécie = the species

Both nouns are feminine singular, so they take a.

Also, Portuguese often uses the definite article in places where English might sound more flexible. In a sentence like this, a espécie can refer to the species in a general sense.

Yes. Quarentena is feminine, so it takes feminine words with it:

• a quarentena
• longa quarentena
• esta quarentena

A good habit in Portuguese is to learn nouns together with their article, so think of it as a quarentena, not just quarentena.

Protege is the third-person singular present indicative form of the verb proteger.

So it can mean:

• he protects
• she protects
• it protects
• you protect (formal você)

In this sentence, it matches a quarentena, which is singular:

• A quarentena protege... = The quarantine protects...

The infinitive is proteger, meaning to protect.

A few present-tense forms are:

• eu protejo = I protect
• você/ele/ela protege = you/he/she protects
• nós protegemos = we protect
• eles/elas protegem = they protect

A learner may notice that eu is irregular-looking: protejo, not proge. That is normal for this verb.

Because proteger is usually a direct transitive verb in Portuguese. That means it can take a direct object without a preposition.

• proteger a espécie
• proteger a criança
• proteger o meio ambiente

So a espécie is the direct object of protege.

Portuguese commonly uses the definite article to talk about a whole class or category in a general way.

So:

• A espécie can mean the species in a generic sense
• Compare English, where we might also say the species, but English sometimes allows article patterns that Portuguese does not

This is similar to other generic statements in Portuguese:

• O cachorro é um animal fiel. = The dog is a loyal animal.
• A baleia é um mamífero. = The whale is a mammal.

The accent in espécie shows the stressed syllable and helps mark pronunciation.

It is pronounced roughly ES-pe-ci-e, with the stress on the first syllable.

Without getting too technical, the accent tells you that the stress does not fall where you might otherwise expect it to. In Portuguese, written accents are very important because they often show exactly how a word should be stressed.

A natural Brazilian Portuguese pronunciation is approximately:

a kwa-ren-TE-na pro-TE-ji a es-PE-si-e

A few notes:

• qu in quarentena sounds like kw
• te in protege is often pronounced something like chi/ji depending on accent, so protege may sound close to pro-TE-ji
• espécie has four syllables: es-pé-ci-e

The stress falls like this:

• qua-ren-TE-na
• pro-TE-ge
• ES-pé-ci-e? Actually, in standard pronunciation the stress is on PÉ: es-PÉ-ci-e

So a better rhythm guide is:

a kwa-ren-TE-na pro-TE-ji a es-PE-ci-e

The normal order here is subject + verb + object:

• A quarentena = subject
• protege = verb
• a espécie = object

This is the most neutral and natural order.

You could rearrange parts in special contexts for emphasis, but for a learner, the standard pattern is best:

A quarentena protege a espécie.

Usually, yes, in modern everyday use it refers to quarantine. Historically, the word is related to the idea of forty days, but in normal modern Brazilian Portuguese, learners should understand it mainly as quarantine.

So in this sentence, it simply means the isolation measure, not necessarily a literal period of forty days.

It is singular.

• singular: a espécie
• plural: as espécies

So this sentence talks about the species as one category or collective idea, not multiple separate species.

That would sound unnatural in standard Portuguese.

Portuguese generally prefers the articles here:

• A quarentena protege a espécie.

Leaving them out can sound incomplete, overly telegraphic, or non-native in normal writing and speech.

So for a natural sentence, keep both a articles.