Learn Russian: Кто несёт ответственность за этот проект? - Who bears responsibility for this project?

Нести ответственность is a formal analytical predicate (a light verb construction). While отвечать simply means to be responsible or to answer in everyday speech, нести ответственность elevates the register. You will see it in legal, corporate, or official contexts, much like bearing responsibility versus being in charge in English.

Why do we use the verb нести (to carry) here instead of another verb?

In formal Russian, certain abstract nouns pair with specific light verbs to form a predicate. For responsibility (ответственность), the standard verb is нести (literally to carry). Just as English speakers bear responsibility, Russian speakers carry it.

Why is the phrase этот проект in the accusative case?

The preposition за takes the accusative case when it means for in the context of being responsible, fighting for, or paying for something. Both the simple verb отвечать за and the formal construction нести ответственность за require the accusative case for the object you are responsible for.

If we expect a group of people to be responsible, would we change несёт to the plural несут?

No, the question word кто grammatically acts as a third-person singular masculine pronoun, regardless of how many people the answer might involve. Therefore, the verb must always be in the singular form несёт.