The aim of this book is to provide an A-level text which can be followed easily and understood by the average student at this level. The language, while inevitably embracing the complex terminology found at A-level, has been made as accessible as possible. The chapters have been divided up into sections and sub-sections for easy reference. Frequent cross-references are made in the text to help to integrate the various topics. Extensive use has been made of diagrams and photographs throughout the book in order to make points clearer and improve understanding. As part of the attempt to make the information in the book accessible, tables have been used at every opportunity. Through use of these tables it has been possible to include a comparative approach to much of the work. Each chapter is followed by a sample of recent A-level questions relevant to the subject matter it contains. These have been selected to include examples from all the A-level examining boards and to reflect the various styles of questions used by each. it is hoped that this will assist the reader in preparing for A-level examinations. To further this aim there are two additional chapters at the end of the book. The first is designed to give the student guidance on acquiring the various essential A-level skills such as in reading, essay writing, revising, etc. The second gives detailed advice on preparing for examinations in biology. With a few exceptions, laboratory work has not been included. However, an extensive number of references to such work and the practical evidence for much of the factual information is included. The book has been written after an analysis of every current A-level biology syllabus and therefore includes all the important topics contained within them. It is hoped, therefore, that it will prvide a sound basis for the A-level work of all students, regardless of which board's syllabus they are studying.