This is a good question. Are we obliged to answer it?
Good question? Yes.
The question is clearly formatted and clearly presents the attempts for finding an answer. So, this is a perfectly valid question for the SO in general and SO.Biology in particular.
Obliged? No. Nobody is obliged to answer any questions. If you feel you can answer it -- just go ahead. But SO is a community project and everything is purely volunatarily.
Restrictions on homework questions Referencing to the comment by Mad Scientist I see the following options possible:
Answer proposal: Every "homework" question is expected to have a suggested answer from the asker, which can be right or wrong, but it should be comprehensive enough to show the presence of some basic knowledge on the topic.
Staging: The answer is given 3-7 days after the question was asked. Given this rule it becomes useful to ask questions for the classes that take place in shorter than a week.