Who gets corresponding authorship in the biological sciences and what does it mean? Let's imagine several levels.

(1) Graduate student.
(2) Post-doctoral student.
(3) Assistant professor.

[Cultural context]
(I don't know if this has any impact on the question, providing the information just in case)
In Japan, assistant professor(s) don't usually have their own independent lab. They work in the same lab "under" an associate or full professor. Their level of independency highly depends on the professor above them. Some of them may have a small team within the big team. Lab management and teaching grad students how to do experiments usually rely heavily on the assistant professor(s). In big labs, there may be several assistant professors.


In which cases can (1) and (2) expect to take corresponding authorship?
Should (2) or (3) be granted corresponding authorship if they made the research with grant money they managed to get in their name?
What is/are the benefit(s) of having corresponding authorship? Is it a requirement to be considered for some higher level grants?
Should the corresponding author always be the last author? Or is it OK for any other author to be corresponding author?
The corresponding author serves as the point of access for readers to inquire about a paper. This does not imply it should be any particular author, though particularly common choices seem to be first or last author.

The corresponding author should be the author that is least likely to change institutions. Changing institutions generally implies losing your contact details where you left (including email). The corresponding author should be the one that is most likely to remain a consistent point of communication.

This is often the last author because that is the common spot for the supervising PI (typically tenured). This is not always true, for example some domains like maths and theoretical computer science organise authors alphabetically.