Seli hii ni ndogo.

In Swahili, demonstratives like this usually come after the noun.

So:

• seli hii = this cell

This is different from English, where we say this cell.

A very common Swahili pattern is:

• noun + demonstrative
• mtoto huyu = this child
• kitabu hiki = this book
• seli hii = this cell

Ni is the basic word for is / are in simple identification or description sentences.

So in:

• Seli hii ni ndogo

ni connects seli hii and ndogo, like is in English:

• This cell is small.

It is one of the most common words in Swahili.

Because the sentence is making a full statement: This cell is small.

The structure is:

• seli hii = this cell
• ni = is
• ndogo = small

So the pattern is:

• noun phrase + ni + adjective

Compare:

• Seli hii ni ndogo = This cell is small.

If you want small cell as a noun phrase rather than a full sentence, the structure is different:

• seli ndogo = a small cell / small cell

So:

• seli ndogo = small cell
• seli hii ni ndogo = this cell is small

Swahili demonstratives change according to the noun class of the noun.

Seli belongs to the noun class that takes:

• hii for this
• hizi for these

So:

• seli hii = this cell
• seli hizi = these cells

You cannot just use one single word for this with every noun in Swahili. The form must match the noun class.

Yes. In Swahili, adjectives often agree with the noun class too.

Here, ndogo is the correct agreeing form with seli.

So the sentence is internally matched:

• seli ... hii ... ndogo

This agreement is an important part of Swahili grammar, even though sometimes the adjective form may not look very different from a dictionary form.

Seli is a loanword. Depending on context, it can mean things like:

• a biological cell
• a prison cell
• a small organizational cell

Like many borrowed nouns in Swahili, it fits into an existing noun class pattern for agreement.

That is why you get:

• seli hii
• seli hizi

Swahili normally does not use articles like English a, an, or the.

So seli can mean:

• a cell
• the cell
• cell

The exact meaning depends on context.

In this sentence, hii already makes it specific:

• seli hii = this cell

So no separate word for the is needed.

In many descriptive sentences with ni, especially for beginners, it is safest to keep it.

So:

• Seli hii ni ndogo = correct and clear

In some kinds of Swahili sentences, especially with pronouns or in more natural speech, structures can vary. But for a learner, ni here is the normal form to learn first.

You would change the demonstrative from hii to hizi:

• Seli hizi ni ndogo = These cells are small.

In many cases, a borrowed noun like seli may stay the same in both singular and plural, so the main clue is the agreement word:

• seli hii = this cell
• seli hizi = these cells

A simple pronunciation guide is:

• se-li hi-i ni ndo-go

Some helpful points:

• Swahili vowels are usually pronounced clearly.
• hii is pronounced with both vowels sounded: hi-i
• nd in ndogo is pronounced together, not separated.

Very roughly, an English speaker might say:

• SEH-lee HEE-ee nee NDOH-goh

Also, Swahili words usually have stress on the second-to-last syllable of each word.

Standard Swahili strongly prefers:

• Seli hii ni ndogo

Putting the demonstrative after the noun is the normal pattern.

So although an English speaker may want to say this cell in English order, Swahili usually uses:

• noun + this/that

That is one of the first word-order differences learners need to get used to.

They are related, but they do different jobs.

• seli ndogo = small cell
  This is just a noun phrase.

• seli hii ni ndogo = this cell is small
  This is a complete sentence.

So:

• seli ndogo could be part of a bigger sentence.
• seli hii ni ndogo already expresses a full idea.

That distinction is very useful in Swahili:

• noun + adjective = a thing described
• noun + ni + adjective = a full statement about it