AP Biology is among the most frequently mis-prepared AP subjects, and the name is the reason. Biology suggests memorising terms; the exam largely measures reading data and reasoning from it.
The logic of the structure
The syllabus is organised not as a topic list but around a few big ideas: energy flow, transfer of information, interaction of systems, and evolution. Every topic attaches to one of these frames.
This means sections cannot be studied in isolation. Cellular respiration, enzymes and photosynthesis are parts of one energy story and the exam asks about them together.
The shape of the questions
A typical question presents the design of an experiment, shows a graph of the result, and asks for an inference. Or it presents a hypothesis and asks for the experiment that would test it.
Term knowledge is a precondition for these questions, not the answer to them. A student who knows the terms but has never read a graph understands the question and cannot answer it.
The free response section
Answers are read against a rubric, and the rubric looks for particular verbs: explain, justify, predict, design. Each verb calls for something different, and answering the wrong verb earns nothing.
Describing where explanation was asked for, or giving the result where a design was asked for, is the most common loss.
The mathematics load
Contrary to expectation there is calculation: standard deviation, chi square, population genetics and percentage change. Formulae are provided in a booklet.
These calculations are not difficult, but they slow down an unprepared student, because mathematics is not expected in a biology exam.
How to study
Settle the four frames first, then study topics by attaching them to those frames. After that, work only past exam questions and read every answer against the rubric.
Memorising term lists is the lowest yielding method on this exam; the terms appear inside the questions anyway.