The USA Biology Olympiad (USABO) is a prestigious biology competition for high school students in the United States. It motivates students to pursue a career in science. There are two rounds of the competition: the open exam which is held in February every year and the semifinal exam which is a 120-minute exam for the top 10% students of the Open Exam. The Worked Solutions book serves as a guide to help students understand the questions and how to answer them.