This is a revision guide prepared for Human Biology Units 3 and 4. It consists of Revision Questions and Answers, Trial Tests and Answers, and a Glossary. The chapters of Revision Questions follow the order of the Unit Content as described by the current syllabus for the WACE ATAR course. They include material from the original course and new material from the area of molecular biology, as well as topics related to our modern lifestyle. Each chapter begins with a Syllabus Checklist. This is followed by a list of terms that are used in that section of work and then questions. Detailed answers are provided, often with more information than is required. With each set of Review Questions there is a practise test except in Chapter 8 where there are two tests. This is because the content lent itself more easily to two. Again, detailed answers are provided. The tests have multiple choice questions, short answer questions and an extended answer question. They are designed to reflect the structure of the external examination. You should attempt to complete each test in the recommended time. Check your answers carefully. The extra information is to assist your understanding.