The written book results from forty years of teaching and research experience. The book is written in easy language to understand by the users. Care has been taken to provide possible updated available information. Each topic has a colorful main head and subhead to mark the limit of the subtopic. The figures in the book are simplified, and some figures and metabolic cycles are drawn with colors when essential. At the end of each chapter are Key Takeaways and in-text questions for practice. A list of suggested readings is provided to help the readers better understand the topics. The book has been corrected grammatically to minimize grammatical mistakes. This book target audience /maker is all students engaged in UG, PG, and Postgraduate Research. The information on the topics related to the carbohydrate digestion in ruminants, bovine ketosis and pregnancy toxaemia have been added for the students of the Veterinary Science and Animal Husbandry Faculty. Various plant cycles like the C2 cycle, C3 cycle, and C4 cycle have been added to help the students of plant science. This book has been written keeping in mind the basic, master, and doctorate courses for beneficiaries of various streams, including Basic science, Nursing courses, Agriculture, Biotechnology, Microbiology, Botany, Zoological, Bioinformatics, Pharmacy, Veterinary Science and Animal Husbandry, and Medicine. moreover, it can also be very useful for various competitive examinations such as CSIR, ICMR, DMT, and ICAR JRF/NET.