A alga cresce cada vez mais rápido.

In Portuguese, it is very common to use the definite article with nouns, even in cases where English might leave it out.

So a alga literally means the algae / the seaweed (singular), but it can also sound natural when talking about that organism as a subject in a general statement.

Portuguese often does this with subjects:

• O café faz mal para algumas pessoas. = Coffee is bad for some people.
• A alga cresce... = The algae / the seaweed grows...

Leaving out the article is sometimes possible in certain contexts, but a alga is the most natural form here.

Here, alga is singular.

• a alga = the algae / the seaweed (singular)
• as algas = the algae / the seaweeds (plural)

So:

• A alga cresce... = The algae grows...
• As algas crescem... = The algae grow...

Even though English algae often looks plural, Portuguese alga is a normal singular noun.

Cresce is the 3rd person singular of the verb crescer (to grow).

Conjugation in the present:

• eu cresço = I grow
• você / ele / ela cresce = you / he / she grows

Since the subject is a alga (singular), the verb must also be singular:

• A alga cresce.

If the subject were plural, the verb would change:

• As algas crescem.

Cada vez mais means more and more or increasingly.

Literally, it is something like each time more, but in natural English the idea is:

• more and more
• increasingly

Examples:

• Ela está cada vez mais feliz. = She is getting happier and happier.
• O problema fica cada vez mais difícil. = The problem gets more and more difficult.
• A alga cresce cada vez mais rápido. = The algae grows faster and faster.

This is a very common pattern in Portuguese.

Because the sentence is expressing a change in speed: it is growing faster and faster, not just fast.

• rápido = fast / quickly
• mais rápido = faster / more quickly
• cada vez mais rápido = faster and faster

So:

• A alga cresce rápido. = The algae grows fast / quickly.
• A alga cresce cada vez mais rápido. = The algae grows faster and faster.

This is a very common question.

In Portuguese, especially in everyday Brazilian Portuguese, adjectives are often used in an adverb-like way after verbs:

• falar baixo = to speak quietly / softly
• chegar cedo = to arrive early
• andar rápido = to walk fast
• crescer rápido = to grow fast

So rápido here works naturally, even though rapidamente is the formal adverb.

You could say:

• A alga cresce cada vez mais rapidamente.

That is grammatically correct and a bit more formal or more written-sounding.

But cada vez mais rápido is very natural and common in Brazilian Portuguese.

Because here rápido is not describing the noun alga directly. It is describing how it grows.

In other words, it behaves like an adverbial expression linked to the verb cresce.

So it stays in the default form:

• A alga cresce rápido.
• A menina corre rápido.
• O menino corre rápido.

Notice that rápido does not change to match the subject in these cases.

But if you were describing the noun itself, then it would agree:

• A alga é rápida. = The algae is fast.
• O animal é rápido. = The animal is fast.

So:

• cresce rápido = grows quickly
• é rápida = is fast

Yes, it is a very common pattern.

The structure is:

cada vez mais + adjective/adverb

It means more and more...

Examples:

• cada vez mais difícil = more and more difficult
• cada vez mais comum = more and more common
• cada vez mais cedo = earlier and earlier
• cada vez mais rápido = faster and faster

You can use this structure in many situations, so it is worth memorizing.

Yes. That is also correct, but it has a slightly different feel.

• A alga cresce cada vez mais rápido. = The algae grows / is growing faster and faster.
  This can sound more general, descriptive, or neutral.

• A alga está crescendo cada vez mais rápido. = The algae is growing faster and faster.
  This puts more focus on the action as something happening right now or in progress.

In Brazilian Portuguese, the estar + gerund form is very common for ongoing actions.

In Brazilian Portuguese, alga is pronounced approximately like AHL-gah.

A rough guide:

• al = like ahl
• ga = like gah

The stress falls on the first syllable:

• AL-ga

And cresce is roughly:

• KREH-see or KREH-si depending on accent

So the full sentence sounds approximately like:

• AHL-gah KREH-si KAH-dah VEHZ MAH-eez HAH-pee-do

That is only an approximation, but it can help you get started.

Yes, exactly.

To make it plural, you change:

• a → as
• alga → algas
• cresce → crescem

So:

• A alga cresce cada vez mais rápido. = The algae grows faster and faster.
• As algas crescem cada vez mais rápido. = The algae grow faster and faster.

Notice that rápido usually stays the same here because it is still functioning adverbially.