This book is a reference book for the students of biology subject. It is tailored as per the syllabus of Cambridge O level Biology but it can be used by other students as well. It is written in such a way so that students may find it fun while reading it. It is made easy so that students can not find words and concepts difficult to grasp. It is for basic biology concepts which can be used for students as well as professionals to clear basic concepts. The heading maybe copied from the syllabus to make as per syllabus requirement but the material is my own research. It is original and it is fun to read. It can be used a valuable tool to revise for the examination.