O percurso tem uma subida e uma descida?

Because the subject is O percurso, which is singular.

In Portuguese, the verb agrees with the subject, not with the things that come after it.

• O percurso tem... = singular subject → tem
• Os percursos têm... = plural subject → têm

So uma subida e uma descida are the things the route has, but they do not control the verb.

That is very normal in Portuguese.

Yes/no questions in Brazilian Portuguese are often formed with the same word order as a statement. The main difference is:

• intonation in speech
• the question mark in writing

So:

• O percurso tem uma subida e uma descida. = statement
• O percurso tem uma subida e uma descida? = question

Unlike English, Portuguese usually does not need does, inversion, or a special question structure here.

Percurso means something like route, course, path, or itinerary, depending on context.

It is a fairly common word, but it can sound a little more neutral or slightly more formal than caminho in some situations.

Possible comparisons:

• percurso = the route/course as a whole
• caminho = path/way
• trajeto = route/journey from one point to another
• trilha = trail, especially in nature/hiking contexts

So if this is about hiking, people might also say trilha or trajeto, depending on the situation.

In Brazilian Portuguese, ter is very commonly used in everyday speech to mean that something has, contains, or includes something.

So O percurso tem uma subida e uma descida? sounds natural.

You could sometimes hear more formal or less direct alternatives, but they are not the most natural choice here:

• Há uma subida e uma descida no percurso?
• Existe uma subida e uma descida no percurso?

These are grammatically possible, but they shift the focus more toward existence. In normal conversation, tem is usually the most natural option.

Here, subida and descida are nouns.

They refer to:

• subida = an uphill stretch, climb, ascent
• descida = a downhill stretch, descent

So they are not just the abstract actions of going up and going down. In this context, they mean parts of the route.

This is very common in Portuguese: verbs can become nouns like this.

• subir → subida
• descer → descida

Yes, the articles can sometimes be omitted, but the meaning changes slightly.

With articles:

• uma subida e uma descida = one ascent and one descent, more clearly counted as separate sections

Without articles:

• subida e descida = uphill and downhill in a more general sense

So both are possible:

• O percurso tem uma subida e uma descida?
• O percurso tem subida e descida?

The version with uma ... e uma ... sounds a bit more specific, as if you are asking whether there is one of each.

Because they are feminine nouns in Portuguese, so they take uma, not um.

• uma subida
• uma descida

A useful pattern is that many nouns ending in -a are feminine, though that is not a perfect rule for every word in Portuguese.

In this case, you simply need to learn their gender as part of the noun.

Yes, it is natural.

That said, Brazilians might also say it in slightly different ways depending on context:

• O percurso tem subida e descida?
• O trajeto tem subida e descida?
• A trilha tem subida e descida?
• Tem subida e descida no percurso?

A few nuance notes:

• percurso is perfectly good, but a little neutral/general
• trajeto is also very common
• trilha is especially natural for hiking or nature trails

So your original sentence is correct and natural, but not the only way to say it.

A simple approximate pronunciation is:

• O percurso → oh pehr-KUR-soo
• tem → tehng / tehm, depending on accent
• uma subida → OO-ma soo-BEE-da
• e uma descida → ee OO-ma deh-SEE-da

Stress:

• perCURso
• suBIda
• desCIda

A couple of useful pronunciation notes:

• The r in percurso is not an English r
• Final o in Brazilian Portuguese often sounds like oo
• Unstressed vowels may sound weaker than an English speaker expects

Yes.

That would mean the route has multiple uphill and downhill sections:

• O percurso tem subidas e descidas?

This suggests repeated elevation changes, not just one climb and one descent.

So the difference is:

• uma subida e uma descida = one of each
• subidas e descidas = several ups and downs

Both are natural; it depends on what you want to ask.