Learn Hardcore Russian: В этом семестре мой любимый предмет — биология. - This semester my favorite subject is biology.

The meaning is still “This semester my favorite subject is biology.” The verb есть here would sound unnatural or overly formal; you normally see it only in special contexts (contrast, emphasis, older style, etc.).

Why is there a dash (—) between предмет and биология?

In Russian, a dash often replaces the missing present-tense “to be” between two nouns (or a noun and a noun phrase) when one is the subject and the other is what it equals or is defined as (the predicate nominative).

Here:

мой любимый предмет = “my favorite subject” (subject)
биология = “biology” (what the subject is)

So we write:
Мой любимый предмет — биология.

The dash is especially common when:

both parts are nouns/pronouns in the nominative case,
and neither part has a linking verb like является (“is, constitutes”).

Why is it в этом семестре and not на этом семестре?

Russian uses different prepositions than English in time expressions.

в этом семестре literally: “in this semester”
It’s the normal way to say “this semester” in Russian.

The preposition в is standard with many time-period nouns:

в этом году – this year
в этом месяце – this month
в эти выходные – this weekend

Using на with семестр would not be idiomatic in this meaning.

Why does этот change to этом in в этом семестре?

Этом is the prepositional case form of этот (“this”).

The pattern (masculine, singular) is:

Nominative: этот (this)
Prepositional: этом (in this / about this)

The preposition в with a location or time like в этом семестре requires the prepositional case, so:

семестр → семестре
этот → этом

Hence: в этом семестре.

Why is семестр written as семестре in в этом семестре?

That’s again the prepositional case.

Base form (dictionary form) is:

семестр – “semester” (nominative case, singular)

After the preposition в, when we’re talking about time or location (“in this semester”), we put the noun into the prepositional case:

семестр → семестре

So you get: в этом семестре = “in this semester / this semester”.

Why is мой любимый предмет in the nominative case, not some other case?

Мой любимый предмет is the subject of the sentence, so it’s in the nominative case.

мой (my) – masculine nominative singular
любимый (favorite) – masculine nominative singular, agreeing with предмет
предмет (subject) – masculine nominative singular

In sentences like “X is Y”:

X (the thing you’re talking about) is in the nominative,
Y (what X is) is also in the nominative.

So both мой любимый предмет and биология stay in the nominative.

Why is биология also in the nominative case, not биологией?

Here, биология is a predicate noun (what the subject “is”), so Russian normally uses the nominative case:

Мой брат — врач. (My brother is a doctor.)
Мой любимый предмет — биология. (My favorite subject is biology.)

The instrumental case (биологией) can also appear with linking verbs like являться:

Мой любимый предмет является биологией.

But that’s more formal/academic and not how people typically phrase this everyday sentence. The simple nominative-with-dash pattern is most natural here.

Can I change the word order, for example: Биология — мой любимый предмет в этом семестре?

Yes. Russian word order is fairly flexible.

All these are grammatically correct, with slightly different emphasis:

В этом семестре мой любимый предмет — биология.
Neutral; sets the time first, then identifies the subject.
Мой любимый предмет в этом семестре — биология.
Emphasizes “my favorite subject this semester” as a unit.
Биология — мой любимый предмет в этом семестре.
Puts биология first; can sound like you’re highlighting “As for biology, it is my favorite subject this semester.”

The meaning stays the same, but the focus shifts a bit.

What is the grammatical gender of предмет and биология, and how does it affect the sentence?

предмет – masculine noun
биология – feminine noun

Adjectives and pronouns agree in gender, number, and case with the noun they modify:

мой любимый предмет
- мой – my (masculine nominative singular)
- любимый – favorite (masculine nominative singular)
- both match предмет (masculine)

Биология stands alone here, so we don’t see the agreement, but if we added an adjective, it would be feminine:

интересная биология – interesting biology (feminine).

The gender difference does not prevent the “X is Y” structure; Russian allows different genders on each side of the dash.

Why is there no Russian word for “subject” like school subject урок here?

Russian has several school-related nouns, and they are not interchangeable:

предмет – a school subject, i.e., a discipline: math, biology, history.
урок – a lesson, class period, i.e., one session or class meeting.
занятие – a lesson/class/activity (more general or often used at university).

So:

Мой любимый предмет — биология.
= My favorite subject is biology.

If you said мой любимый урок, it would sound more like “my favorite class period” (e.g., “the first lesson on Monday”), not the school subject as a whole.

Could I say В этом семестре биология — мой любимый предмет? Does it change the meaning?

You can, and it’s correct.

В этом семестре биология — мой любимый предмет.

This version puts биология earlier for emphasis: “This semester, biology is my favorite subject.” It slightly highlights biology compared to other possible subjects.

The core meaning is the same; only the focus shifts.

Is семестр used the same way as “semester” in English? Can I always say в этом семестре?

Generally yes, but it depends on the educational system.

семестр – a term of study (often half of an academic year) in schools/universities that use semesters.

Typical phrases:

в прошлом семестре – last semester
в следующем семестре – next semester
в этом семестре – this semester

If the institution uses триместры (trimesters) or четверти (quarters), you’d use those words instead. But в этом семестре is the standard expression when the system is semester-based.