Learn Hardcore Turkish: Psikoloji dersinde, yemekhane ortamının öğrenci davranışlarına etkisi tahlil edildi. - In psychology class, the effect of the cafeteria environment on student behavior was analyzed.

-nde is the locative case suffix, equivalent to English “in/at.”
Turkish case suffixes attach only after a possessive ending on nouns. Here ders (“class/lesson”) takes the 3rd-person possessive -i → dersi, then the locative -(n)de is added.
The extra n (buffer) appears because the suffix begins with a vowel and the base (dersi) ends in a vowel; the n prevents two vowels from clashing: dersi + nde → dersinde (“in the class”).

Why isn’t there a word for “the” or “a” before **Psikoloji dersinde}?

Turkish has no separate indefinite or definite articles. Nouns appear without a/the. Context or possessive suffixes (like -i in dersi) convey definiteness when needed.

How does yemekhane ortamının express “the environment of the dining hall”?

This is a possessive/genitive construction:

yemekhane = “dining hall” (noun)
ortamı = “its environment” (ortam + 3rd-person possessor -ı)
To show “of the dining hall,” yemekhane takes the genitive suffix -(n)ın to become yemekhanenin and ortamı is the head noun with possessor ending. In the full phrase we actually see only yemekhane ortamının, where ortamının uses the buffer n
- -ın (genitive) because ortamı ends in a vowel.
Together it literally reads “of the dining-hall environment.”

Why is there a double n in ortamının?

ortamı ends with the vowel ı (from the 3rd-person possessor).
Adding the genitive -ın requires a buffer n before a vowel-initial suffix.
So you get ortamı + n + ın → ortamının.

Why does öğrenci davranışlarına use -lara instead of an accusative ending?

davranışlar = “behaviors” (davranış + plural -lar)
-a/-e is the dative case suffix, here -lara, meaning “to/for” or in many contexts “on.”
English uses the preposition “on student behaviors,” but Turkish expresses “effect on X” with the dative: davranışlar → davranışlara (“to/onto behaviors”).
öğrenci simply modifies davranışlar (“student behaviors”).

What does etkisi mean, and why the ending -si?

etki = “effect”
The 3rd-person singular possessive suffix -si turns it into “its effect” or “the effect of (something).”
In the full phrase yemekhane ortamının öğrenci davranışlarına etkisi, etkisi is the head noun possessed by ortamının.

Why is tahlil edildi passive, and how is that passive formed?

tahlil = “analysis” (noun borrowed from Arabic/Persian)
etmek = “to do” → tahlil etmek = “to analyze”
To form the passive, Turkish often uses the suffix -il/-ıl/-ul/-ül after the verb stem, plus tense/person. Here:
1. Drop -mek from etmek → et
2. Add passive -il → edil
3. Add past tense -di → edildi (“was done”)
Combined with the noun: tahlil edildi = “it was analyzed.”

Could we rearrange the word order, and what is the typical Turkish order?

Typical Turkish is Subject-Object-Verb (SOV). Here the “subject” (passive subject) is the entire phrase “Psikoloji dersinde, yemekhane ortamının öğrenci davranışlarına etkisi”, and tahlil edildi is the verb.
Adverbials of place/time (Psikoloji dersinde) usually come first or just before the verb. The rest of the modifiers precede their heads.
You could shift elements for emphasis (word order is fairly flexible), but you cannot break apart the tightly bound suffix chains on each noun.

Is the comma after Psikoloji dersinde mandatory?

No. Turkish allows a comma to mark a fronted adverbial for clarity or pause, but it is optional. The sentence is perfectly grammatical without it.