I took bio 1A03 last semester, and now I need to get rid of the textbook.
Is it possible to sell the used access code too? I heard that the code is valid for 1 year, so if I used it for semester 1, someone else could use it for semester 2?
Is this true?

Would probably be the login (username/password) that is useable. Codes typically become useless once actually typed into the site.

Of course if you mean you didn't use the code, then of course you can use it. When I took 1a03 I belive 1m03 was part of the same book package, but is not the case now? (or at least the second book covered evolution/ecology)