For Biology, "Biology" by Neil Campbell is the recommended source.
To start off, you can start studying from the link provided: https://www.ck12.org/student/. You will need to create an account but the content itself is free. It is great for elementary resources and starting readings.
The link below has all the free resources for all the subjects such as virtual labs and chapter by chapter quizzes.
What Was Covered in Class and Assigned Homework
Based off of Material Covered in "Biology" by Neil Campbell