The ITT Dublin Library has an agreement with openstax college who have made available a number of free books covering many subjects.
The full list of books can be found here:
I have reviewed the Biology, Microbiology and Concepts in Biology books and think they are all well written and applicable to the course. If you need to read extra material to help you understand your notes I can wholeheartedly recommend them. If you’ve any queries just give me a shout.