ZNOTES.ORG UPDATED TO 2023-2025 SYLLABUS CAIE IGCSE BIOLOGY SUMMARIZED NOTES ON THE THEORY SYLLABUS Prepared for Aree_ for personal use only. CAIE IGCSE BIOLOGY 1. Characteristics and Classification of Living Organisms 1.1. Characteristics of Living Organisms The Age-Old Acronym: MRS GREN Movement: an action by an organism or part of an organism causing a change of position or place Respiration: the chemical reactions in cells that break down nutrient molecules and release energy for metabolism Sensitivity: the ability to detect and respond to changes in the internal or external environment Growth: a permanent increase in size and dry mass Reproduction: Process which produces offspring genetically identical or different from the parent organism Excretion: the removal of the waste products of metabolism and substances in excess of requirements Nutrition: the taking in of materials for energy, growth, and development Organisms are classified into groups by the features they share. Species: a group of organisms that can reproduce to produce fertile offspring. Sequence of Classification: Kingdom → Phylum → Classes → Orders → Families → Genus → Species. Acronym: King Philip, Come Over For Good Soup The Binomial Nomenclature The Binomial System of Naming Species is an internationally agreed system in which an organism's scientific name is comprised of two parts, namely, the genus and species. The format is Genus species. The genus is capitalised, and the species are not. The binomial name is typed in italics or written with an ‘underline’ The classification of organisms helps show the evolutionary relationships between them. Scientists also use the DNA base sequence to help classify organisms. The similarity in DNA base sequence shows how closely the two organisms are related. Dichotomous Keys 1.2. Concept and Uses of Classification System Sequence of Classification WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Aree_ at undefined on 24/05/25. CAIE IGCSE BIOLOGY Dichotomous Keys use visible features to classify organisms. They give you a choice of two features, and you follow the one that applies: each option leads to another option until the organism is narrowed down to its genus and species. Animals: Multicellular ingestive heterotrophs (eat living organisms). Ex: cat, ladybird, newt, etc. Plants: Multicellular photosynthetic autotrophic (make their food) organism with a cellulose cell wall and chloroplasts. Ex: cactus, oak tree. Fungi: Single-celled or multicellular heterotrophic and saprotrophic (feeds on dead and decaying organic matter) organisms with cell walls not made of cellulose, spread by spreading spores in moist/dark/warm environments. Most have hyphae and mycelium in structure. Ex: yeast, mushrooms. Prokaryotes: Single-celled organisms with no true nucleus and mitochondria. Many also have plasmids (important for Genetic Engineering). Ex: E.coli, Salmonella. Protist or Protoctist: Single-celled organism with a nucleus. Some are multicellular. Ex: Amoeba, seaweed. Protoctists, fungi, plants, and animals are all eukaryotes (having a well-defined nucleus), whereas monera are prokaryotes. Animals are classified as vertebrates (have a backbone) and invertebrates (do not have a backbone). 1.3. Features of Organisms The Five Kingdoms 1.4. Vertebrates Types of Vertebrates Mammals Reptiles Fish Amphibians Birds Features Fur or hair on the skin, External ears (pinna), Internal fertilisation, Mammary Glands, give birth to live young Thick, dry, scaly skin, Usually four legs, Internal fertilisation, Soft Shelled Eggs Wet scales, Streamlined body shape, External fertilisation, and soft eggs Smooth, moist skin, External fertilisation, and soft eggs, Gills, & Lungs can live on land and water. Most have four legs. Feathers on the body and scales on legs, Constant internal body temperature, Hard eggs, Internal fertilisation, birth through eggs 1.5. Arthropods Arthropods are the largest group under invertebrates (Organisms that do not have a backbone). All arthropods have three standard features: WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Aree_ at undefined on 24/05/25. CAIE IGCSE BIOLOGY 1. Exoskeleton 2. Jointed legs 3. Segmented body Type of Arthropod Number of Legs Body parts Myriapods 5 pairs (1 modified as claws) Many Insects 3 pairs Arachnids 4 pairs Crustacean All body segments tucked under carapace Wings Antennae None 2 pairs Many None pairs (1 or both 3 (head, thorax, abdomen) 2may be vestigial) 2 (cephalothorax and None abdomen) 1 pair 1 pair None Viruses are not part of any classification system because they are not considered living things. They do not carry out the seven life processes for themselves; instead, they take over a host cell’s metabolic pathways to make multiple copies of themselves. Virus structure contains only a genetic material (RNA or DNA) inside a protein coat. Example of virus structure below (No mitochondria or ribosomes) 1.6. Classification of Plants In IGCSE Biology, the plant kingdom is classified into ferns and flowering plants. Ferns: Do not produce flowers/seeds They are plants with roots, stems, and feathery leaves (fronds) Reproduce by spores, produced on the undersides of their fronds Flowering plants: They are plants with roots, stems and leaves Reproduce sexually through flowers and seeds Seeds are produced inside the ovary in the flower Monocotyledons One cotyledon/One-seed leaf Parallel veins Long Narrow Leaf The Number of Petals is a Multiple of 3 Scattered Vascular Bundles Dicotyledons Two cotyledons/Two-seed leaf Branching veins Broad leaves The Number of Petals is a Multiple of 4 or 5 Ringed Vascular Bundles Tip: Differentiating monocotyledons and dicotyledons comes up frequently in Multiple Choice Questions 1.7. Viruses WWW.ZNOTES.ORG Copyright © 2025 ZNotes Education & Foundation. All Rights Reserved. This document is authorised for personal use only by Aree_ at undefined on 24/05/25. CAIE IGCSE Biology © ZNotes Education Ltd. & ZNotes Foundation 2025. All rights reserved. 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