Learn Hardcore Swahili: Daktari wa biolojia alituonyesha jinsi mapafu yanavyofanya kazi tunapopumua. - The biology doctor showed us how the lungs work when we breathe.

Putting it all together:
Daktari wa biolojia alituonyesha jinsi mapafu yanavyofanya kazi tunapopumua.
The biology doctor showed us how the lungs work when we breathe.

What exactly does wa mean in daktari wa biolojia, and why is it used?

Wa is the “of” connector between two nouns. It comes from the possessive/associative system in Swahili.

daktari wa biolojia – doctor of biology
mwalimu wa Kiingereza – teacher of English
kitabu cha Kiswahili – book of Swahili (different class, so cha instead of wa)

Which form you use (wa, cha, la, ya, vya, etc.) depends on the noun class of the first noun.

Here, daktari is in noun class 1 (people), which uses wa, so you get daktari wa biolojia.

You could also say mwanabiolojia (biologist as one word), but daktari wa biolojia is transparent and common.

How is alituonyesha built, and why is it one word instead of “ali tu onyesha”?

Swahili typically glues subject, tense, object, and verb into one word.

alituonyesha breaks down as:

a- – he/she (subject prefix, 3rd person singular)
-li- – past tense
-tu- – us (object prefix)
-onyesha – show

So alituonyesha literally means he/she-past-us-show → he/she showed us.

You don’t write these pieces separately; in normal Swahili spelling they form one verb word:

alitununulia – he bought us (something)
walimwambia – they told him/her
nitakuonyesha – I will show you

Same pattern: subject + tense + (object) + verb.

What is jinsi doing in this sentence? Can I leave it out?

Jinsi means how / the way that.

In the sentence:

jinsi mapafu yanavyofanya kazi – how the lungs work / the way the lungs work

It introduces a “how” clause. In English you often use how in the same way:

He showed us *how the lungs work.*

In Swahili you can sometimes drop jinsi when the relative form (-vyo-) already expresses the same idea, especially in more casual speech. For example:

Alituonyesha mapafu yanavyofanya kazi. – He showed us how the lungs work.

However, jinsi … -vyo- is a very natural, clear pattern:

jinsi anavyoongea – how he speaks
jinsi unavyoishi – how you live

What exactly is going on inside yanavyofanya? Why is there a vyo in the verb?

Yanavyofanya is a relative verb form meaning roughly “(they) do (in the way that …)” or “(they) work (how …)”.

Breakdown:

ya- – they (subject prefix agreeing with mapafu, noun class 6)
-na- – present tense marker
-vyo- – relative marker meaning how / the way that (linked to jinsi)
-fanya – do

So:

yanavyofanya – how they do / the way they do (it)
yanavyofanya kazi – how they work / how they function

Compare:

mapafu yanafanya kazi – the lungs work / the lungs function (plain statement)
jinsi mapafu yanavyofanya kazi – how the lungs work (relative “how” form)

Other examples:

jinsi anavyofanya kazi – how he works
jinsi unavyopika – how you cook
kitabu ninachovisoma – the book that I am reading (-cho- / -vyo- is part of this same relative system)

Why is it yanavyofanya and not wanafanya or yanafanya?

The choice of ya- vs wa- (or other prefixes) depends on noun class, not on “living vs non‑living”.

mapafu – lungs – class 6 (plural class; singular pafu is class 5)
→ class 6 subject prefix is ya- (for present tense: yana-)

So:

mapafu yanafanya kazi – the lungs work

Wan- is for class 2 (people, plural):

wanafunzi wanafanya kazi – the students work

In our sentence we use yanavyofanya, not just yanafanya, because we need the relative “how” form:

yanafanya kazi – they work
yanavyofanya kazi – how they work / the way they work

So both the noun class (hence ya- instead of wa-) and the relative use (hence -vyo-) are important.

What does tunapopumua mean exactly, and how is it different from tunapumua?

Both are related but not the same:

tunapumua – we breathe / we are breathing (simple present)
- tu- – we
- -na- – present
- -pumua – breathe
tunapopumua – when we breathe / as we breathe
- tu- – we
- -na- – present
- -po- – when / while (time marker)
- -pumua – breathe

The -po- adds a time/“when” meaning. It introduces a time clause:

tunapopumua – when we breathe
anapokuja – when he/she comes
watakapofika – when they arrive (future: -taka- + -po- → -kapo-)

So in the sentence:

jinsi mapafu yanavyofanya kazi tunapopumua
→ how the lungs work when we breathe

Why does Swahili say fanya kazi (“do work”) for lungs? Wouldn’t that normally mean “do a job”?

Fanya kazi literally means “do work”, but it is also the normal way to say “function / operate / work (properly)” in many contexts, including machines and body parts.

Examples:

Injini haifanyi kazi. – The engine is not working.
Kompyuta yangu inafanya kazi vizuri. – My computer works well.
Mapafu yanavyofanya kazi – how the lungs work / how the lungs function.

So in this sentence, fanya kazi naturally means “to function”, not “to have a job”.

What noun class is mapafu, and how does that affect yanavyofanya?

Mapafu is in noun class 6 (its singular, pafu, is class 5).

Class 5/6 examples:

tunda / matunda – fruit / fruits
gari / magari – car / cars
pafu / mapafu – lung / lungs

Class 6 uses ya- as the subject prefix in the present tense:

matunda yanaiva. – The fruits are ripening.
magari yanakuja. – The cars are coming.
mapafu yanafanya kazi. – The lungs are working.

In the relative “how” form, that ya- stays, and -vyo- is added:

matunda yanavyoiva – how the fruits ripen
magari yanavyokuja – how the cars come
mapafu yanavyofanya kazi – how the lungs work

So mapafu → ya- → yanavyofanya.

Is biolojia just the English word “biology” borrowed into Swahili?

Yes, biolojia is a loanword from a European language (ultimately from Greek via European languages), adapted to Swahili spelling and pronunciation:

biology (English)
biologie (French)
Swahili: biolojia (with -ia ending, common in academic terms)

Swahili uses many similar loanwords in scientific and academic fields:

kemia – chemistry
fizikia – physics
historia – history

So daktari wa biolojia is literally “doctor of biology”, i.e. a biology specialist / biologist.