Череп захищає мозок.

A natural pronunciation is roughly:

chE-rep za-khy-SHCHA-ye MO-zok

With stress marks:

• чере́п = CHER-ep
• захища́є = za-khy-SHCHA-ye
• мо́зок = MO-zok

A more careful breakdown:

• ч = like ch in chip
• х = a throaty sound, like German Bach or Scottish loch
• щ in modern Ukrainian is usually pronounced like shch
• є here sounds like ye

So the whole sentence sounds approximately like:

CHER-ep za-khy-SHCHA-ye MO-zok

Word by word:

• череп = skull
• захищає = protects / is protecting
• мозок = brain

So the sentence is literally:

Skull protects brain

In natural English: The skull protects the brain.

Ukrainian does not have articles like a / an / the.

So:

• череп can mean a skull or the skull
• мозок can mean a brain or the brain

You understand which one is meant from context. In this sentence, English naturally uses the:

The skull protects the brain.

Захищає is the 3rd person singular present tense form of захищати (to protect, imperfective).

That means it agrees with череп (skull), which is:

• singular
• third person
• the subject of the sentence

So:

• я захищаю = I protect
• ти захищаєш = you protect
• він/вона захищає = he/she/it protects
• череп захищає = the skull protects

It is present tense, but in Ukrainian, as in English, the present tense can also express a general fact.

So Череп захищає мозок usually means:

• The skull protects the brain
  or
• The skull is protecting the brain, depending on context

Here it most naturally sounds like a general biological fact.

Мозок is the direct object of the verb захищає, so it is in the accusative case.

However, for many masculine inanimate nouns in the singular, the accusative looks the same as the nominative.

So:

• nominative: мозок = brain
• accusative: мозок = brain

That is why the form does not visibly change here.

This is very common:

• Я бачу стіл = I see the table
• Він читає текст = He reads the text

Both стіл and текст are masculine inanimate nouns, and their accusative often matches the nominative.

There are two main clues:

1. Word order
   Ukrainian often uses subject + verb + object, just like English:

   • Череп захищає мозок

2. Meaning and grammar
   Череп is in the nominative form, which is the normal subject form.
   Мозок is functioning as the direct object.

Even though мозок looks the same as nominative, the sentence structure and meaning make it clear that:

• череп = subject
• мозок = object

Yes. Ukrainian word order is more flexible than English.

You may also see:

• Мозок захищає череп
  This would normally mean The brain protects the skull, because the first noun is now understood more naturally as the subject. So this changes the meaning.

But you could also get different orders such as:

• Череп мозок захищає
• Захищає череп мозок

These are much more marked and depend on emphasis, style, or context.

For learners, the safest neutral order is:

Череп захищає мозок.

The dictionary forms are:

• череп = skull
• захищати = to protect
• мозок = brain

The form захищає is not the dictionary form; it is a conjugated verb form from захищати.

The verb захищати is imperfective.

That matters because Ukrainian verbs usually come in aspectual pairs:

• захищати = imperfective, to protect, to be protecting, to protect regularly/in general
• захистити = perfective, to protect successfully / to defend / to finish protecting in a single completed sense

In a sentence like Череп захищає мозок, the imperfective is the natural choice because it describes:

• an ongoing function
• a general truth
• repeated or characteristic action

So it is similar to saying: The skull serves to protect the brain.

Yes, череп is a masculine noun.

One clue is that it ends in a consonant, which is very common for masculine nouns in Ukrainian.

Because it is singular masculine, the verb takes the matching 3rd person singular form:

• череп захищає

Usually череп means skull.

In everyday speech, it is the normal word for the bony structure of the head. Depending on context, it can overlap somewhat with cranium, but the most direct translation is skull.

So in this sentence, The skull protects the brain is the best translation.

Yes. Ukrainian normally does not write stress marks in ordinary text, but learners benefit from knowing them:

• чере́п
• захища́є
• мо́зок

Learning stress early is useful because incorrect stress can make a word harder to understand, even if your grammar is correct.