Learn Turkish: Öğrenciler araştırma yapıyor. - The students are doing research.

In Turkish, when the subject is a plural human (like öğrenciler), making the verb plural is optional. Both yapıyor and yapıyorlar are grammatically correct, but leaving the verb singular is very common and natural. Keep in mind that if the plural subject is not human (like animals or things), the verb usually must be singular.

Why is the noun araştırma used without any suffixes or articles?

Because it represents a general, non-specific category here rather than a specific thing. When you talk about doing a general activity, you leave the direct object bare. The combination araştırma yapmak functions as a single idea: doing research. If you added bir (bir araştırma), it would mean they are doing one specific research project.

The word araştırma ends in -ma. Does that mean it is a negative verb?

Not in this sentence! The -ma / -me suffix has two completely different jobs in Turkish. While it is used for negative commands (like yapma meaning don't do), it is also used to turn a verb into a noun (often called a verbal noun). Here, it transforms the verb araştırmak (to research) into the noun araştırma (research).