"Maria is also a student."
Is there a reason Maria can't be a "seito"?
学生 (gakusei) by itself means a university student and can be listed as one's "profession".
生徒 (seito) is used to refer to students in compulsory education and high school.
高校せい (koukousei) - high school student
中学生 (chuugakusei) - junior high school student
小学生 (shougakusei) - elementary school student
This is a very good question. I also think 生徒 (せいと) should be accepted.
Although there may be a technical distinction between 学生 and 生徒 as you described, from my experience working in a Japanese junior high school, the students were referred to by either word. It's hard to pin down the difference in usage, not least because I never really paid it much attention, but they seemed interchangeable in many cases.
My understanding is that "san" (Mr. Mrs, Ms.) is one of the honorific titles that should always follow someone's name (but never the speaker's). There are other honorifics, depending on the circumstances (chan for a child, sama for a customer). I read an article some years ago where two men in Japan had fisticuffs because one refused to use "san" with the other.
Because さん does NOT mean "Ms." It's an honorific suffix used to show respectful deference to someone of similar social stature. "Ms." can sometimes be used for that purpose, but for one thing, it's gendered while さん (typically) isn't, and another, the use of "Ms." varies a lot by country/region and culture so it doesn't always line up with the usage of さん.
Yes, it's optional, but unless you know your way around Japanese honorifics, I'd suggest using さん for everyone except yourself.
Also, the general honorific is さん san, not ちん chin as you have written. ちん is kind of a weird, sort of creepy to some, honorific otaku tend to use for nicknames.
"desu" indicates the state of being. As Jake says, you can think of it as to the verb "to be". In polite speech, you have to put it whenever is needed. In informal informal conversation it can be omitted.
Is a perfectly legit informal conversation which, in a context where a person is directly talking to another, would basically translate to:
-(are you a) student? -(Yes, I'm a) student.
That said, it's safe enough to put "desu" whenever you would use the verb "to be" I guess.
The も modifies the word it attaches to, so because it's マリアも学生です, it's saying Maria is also a student among other students..
If we wanted to say that Maria is also a student, among the many things that Maria is, we actually have to use a different grammatical structure. In that case we would say マリアは学生でもあります (maria wa gakusei demo arimasu).
か is used to indicate a question and can be used with any subject pronoun, though a question with no stated subject pronoun is usually being asked directly to the person you're speaking to (implying "you").
がくせいですか？ (gakusei desu ka?)
Are you a student?
But it could also be "is she a student?", "are they students?", etc. in the context of a conversation.