Learn Hardcore Malay: Setiap penyelidik mengumpul data suhu dan warna air pada waktu yang berbeza. - Each researcher collected data on the water’s temperature and color at different times.

Setiap penyelidik = each researcher / every researcher (thinking of them one by one)
Semua penyelidik = all (the) researchers (thinking of the group as a whole)

So:

Setiap penyelidik mengumpul data …
= Each researcher collected data … (they all did it individually)

If you said:

Semua penyelidik mengumpul data …
= All the researchers collected data …
(grammatical, but the focus is less on the individual action of each person and more on the group doing it together).

Does penyelidik mean one researcher or many researchers? Do I need to mark the plural?

On its own, penyelidik is number‑neutral: it can mean researcher or researchers, depending on context.

In this sentence:

Setiap penyelidik clearly means each researcher (so we understand there are many of them).

You can mark plurals with:

para penyelidik = the researchers (as a group; formal)
penyelidik-penyelidik = researchers (reduplication; often sounds a bit “heavy” or emphatic in modern usage)

But here you don’t need any plural marker because setiap already implies there is more than one.

What is the structure and meaning of penyelidik? What is the root word?

Penyelidik comes from the root selidik, which means to investigate / to examine closely.

The morphology is:

peN- (prefix forming a person/agent noun)
selidik (root: investigate)

So:

selidik = to investigate
meny(elidik) → menyelidik = to investigate (verb, active)
peny(elidik) → penyelidik = investigator / researcher (person who investigates)

Thus penyelidik literally means an investigator, and in scientific contexts it’s usually translated as researcher.

Why is the verb mengumpul used, and what is the difference between kumpul, mengumpul, and mengumpulkan?

All three are related to the idea of gathering or collecting:

kumpul
- Base verb (often more casual) meaning gather / collect / assemble.
- E.g. Mereka kumpul di dewan. – They gather in the hall.
mengumpul
- meN- + kumpul
- Transitive verb, commonly used for collecting something.
- E.g. Mereka mengumpul data. – They collect data.
mengumpulkan
- meN- + kumpul + -kan
- Also to collect / to gather, but -kan can add a nuance of causing something to be brought together or of collecting something into one place.
- In many sentences, mengumpul and mengumpulkan are interchangeable, with mengumpulkan often sounding a bit more formal.

In Setiap penyelidik mengumpul data …, mengumpul is perfectly natural and common; mengumpulkan would also be correct but not necessary.

There is no word for “the” in this sentence. How is definiteness (the/a) expressed in Malay?

Malay generally does not use articles like English “a/an” or “the”.

Whether a noun is understood as definite or indefinite depends on context and sometimes on other words:

Setiap penyelidik – suggests a specific set of researchers, but we don’t mark it with “the”.
data suhu dan warna air – can be understood as “(the) temperature and water colour data” from context.

If you really need to be explicit, Malay can use:

itu (that) or ini (this) after the noun for definiteness.
- E.g. penyelidik itu = that/the researcher

But in most sentences like this, you don’t add anything; English translators add “the” or “a” as needed for natural English.

What exactly does data suhu dan warna air mean? Is suhu also “of the water” or only warna air?

Literally:

data suhu dan warna air
= temperature data and colour-of-water data

By default, warna air clearly means “colour of the water”.

Whether suhu is also interpreted as “temperature of the water” depends on context. Usually in a research context, readers will assume both refer to the same object (the water), so:

data suhu dan warna air is commonly understood as
“data on the temperature and colour of the water”.

If you want to make it completely explicit, you could say:

data suhu air dan warna air – data on the water’s temperature and the water’s colour
or slightly more compact: data suhu dan warna bagi air itu – data on the temperature and colour of that water (more formal).

Why is it warna air and not something like warna daripada air for “colour of the water”?

In Malay, possession or “of” relationships are often expressed simply by putting the two nouns together:

warna air = the colour of the water
suhu air = the temperature of the water
baju Ali = Ali’s shirt

You can use daripada to express “of/from”, but:

warna air is the normal, natural form.
warna daripada air would sound unusual or overly explicit here; it might be used only in some special emphasis or contrast and is not needed for ordinary “colour of water”.

So: for simple “X of Y”, Malay usually just uses Noun + Noun.

Why do we say pada waktu yang berbeza for “at different times”? What is the function of pada and yang here?

Breakdown:

pada = preposition “at / on / in” (for times, days, some locations)
waktu = time
yang berbeza = that is different / which is different

So:

pada waktu = at the time / at a time
waktu yang berbeza = a time that is different / different times

Yang turns berbeza (different) into a relative clause or descriptive phrase:

waktu berbeza – also understood as “different times”, but a bit more compact.
waktu yang berbeza – “times that are different”; slightly more explicit and often more natural in formal or careful writing.

pada is the normal preposition used with waktu when you mean “at (a) time”.

Could I drop yang and say pada waktu berbeza instead? Is there a difference?

Yes, you can say:

pada waktu berbeza

It is grammatical and still means “at different times”.

Nuance:

pada waktu yang berbeza – slightly more formal or careful; often used in written/scientific Malay.
pada waktu berbeza – a bit more compact and still natural.

In many contexts, they are interchangeable.

Is data singular or plural in Malay, and does the verb change depending on that?

In Malay, data is treated as a loanword that is effectively number‑neutral in everyday use:

data can mean data in general, a set of data, or data points.

Malay verbs like mengumpul do not change form for singular vs plural subjects or objects. So:

mengumpul data is correct whether you mean “collect data” or “collect a piece of data” (though normally “data” is uncountable anyway).

If you really want to mark countability, you might see:

sekeping data / satu set data / beberapa data etc.
(but in research contexts people usually just say data.)

Is the word order in data suhu dan warna air fixed? Could I say data warna air dan suhu instead?

You can change the order, but it slightly affects emphasis and clarity:

data suhu dan warna air
- Most natural and common.
- Lists “temperature” and “water colour” as two types of data.
data warna air dan suhu
- Grammatically OK, but feels a bit less tidy.
- It may briefly make the reader wonder: “colour of water and temperature of what?” before they infer it.

Malay generally keeps parallel items parallel:

data suhu air dan warna air
- both have air, so it’s clearly parallel.

For clarity and naturalness, data suhu dan warna air is the better choice in this sentence.