This document is a study guide on the characteristics and classification of living organisms for CAIE IGCSE Biology. It introduces the acronym MRS GREN (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition) as the seven life processes that define living things. The resource explains classification systems, including the hierarchy of Kingdom → Phylum → Class → Order → Family → Genus → Species, and the use of binomial nomenclature for naming species. It covers the five kingdoms—Animals, Plants, Fungi, Prokaryotes, and Protists—outlining their features and differences. Detailed notes describe vertebrates (mammals, reptiles, fish, amphibians, and birds) and arthropods (crustaceans, myriapods, insects, and arachnids), focusing on structural traits like body segmentation, exoskeletons, and reproductive methods. The classification of plants into ferns and flowering plants (monocotyledons vs dicotyledons) is also explained with distinguishing features such as leaf structure, vein patterns, and vascular bundle arrangements. Finally, the guide highlights that viruses are not classified as living organisms since they cannot carry out life processes independently. With clear explanations, examples, and key distinctions, this resource equips students with the foundational knowledge needed to understand biological diversity and classification for exams.