IGCSE Biology Study Notes

IGCSE Biology Study Notes

1. Characteristics of Living Organisms

• Learning Outcomes:

  • List and describe the characteristics of living organisms.

  • Define the following terms:

  • Nutrition

  • Excretion

  • Respiration

  • Sensitivity

  • Reproduction

  • Growth

  • Movement

1.1 Life Processes

• Definition of Life Processes:

  • If an entity is considered alive, it will carry out all seven life processes:

  • Movement

  • Respiration

  • Sensitivity

  • Growth

  • Reproduction

  • Excretion

  • Nutrition

1.2 Detailed Explanations of Life Processes

• Movement:

  • An action taken by an organism or part of an organism which results in a change of position or place.

• Respiration:

  • Refers to the chemical reactions occurring in cells that break down nutrient molecules and release energy for metabolism.

• Sensitivity:

  • The capability to detect or sense stimuli from both the internal and external environment and to respond appropriately.

• Growth:

  • A permanent increase in size and dry mass attributed to a rise in cell numbers, cell size, or both.

• Excretion:

  • The process of removing waste products from the body at the cellular level, including waste from metabolic processes (e.g., respiration) and any toxic materials.

• Nutrition:

  • The act of taking in materials necessary for energy, growth, and development.

  • Plants require: light, carbon dioxide, water, and ions.

  • Animals require: organic compounds, ions, and typically water.

• Reproduction:

  • The biological process through which organisms produce more individuals of the same species.

2. Classification of Organisms

• Learning Outcomes:

  • Define and describe the binomial system of naming species.

  • Classify the five main classes of vertebrates.

  • List main features used in classification of flowering plants, arthropods, annelids, nematodes, and molluscs.

  • List the main features used for classification of viruses, bacteria, fungi, and their adaptations to the environment.

2.1 The Importance of Classification

• Purpose of Classification:

  • Simplifies the identification of living organisms by organizing them into groups based on shared characteristics.

• Hierarchy of Classification:

  • Largest group is the Kingdom, while the most basic unit of classification is the Species.

  • Species Definition:

  • A species is defined as a group of organisms that can mate and produce fertile offspring.

2.2 Naming Species

• Binomial Nomenclature System:

  • Each organism is identified by two names: Genus and Species.

  • The Genus name is always capitalized.

  • Examples:

  • Canis lupus - the wolf

  • Panthera leo - the lion

2.3 Classification Hierarchy

• Classification Levels:

  1. Kingdom (e.g., Animalia)

  2. Phylum (e.g., Chordata - organisms with a spinal cord)

  3. Class (e.g., Mammals - animals that suckle their young)

  4. Order (e.g., Primates - related to apes)

  5. Family (e.g., Hominidae - the great apes)

  6. Genus (e.g., Homo)

  7. Species (e.g., Sapiens - thinking humans)

• Mnemonic for Classification Levels:

  • Keep Pots Clean Or Family Gets Sick.

3. The Five Kingdoms of Life

3.1 Overview of Kingdoms

• Organisms are primarily divided into five kingdoms:

  • Animalia

  • Multicellular

  • Heterotrophic (cannot produce their own food)

  • Cells lack cell walls and have complex structures with nuclei.

  • Plantae

  • Multicellular

  • Autotrophic (produce their own food by photosynthesis)

  • Cells have cell walls made of cellulose and contain chloroplasts with chlorophyll

  • Fungi

    • Mostly multicellular (except yeasts which are unicellular)

    • Heterotrophic (absorb nutrients from decaying matter or other organisms)

    • Cells have cell walls made of chitin

    Protista

    • Mostly unicellular, some simple multicellular forms

    • Can be autotrophic or heterotrophic (varies by species)

    • Cells have nuclei; some have cell walls, others do not

    Monera (Prokaryotae)

    • Unicellular

    • Can be autotrophic or heterotrophic

    • Cells lack a true nucleus (prokaryotic); some have cell walls (not made of cellulose or chitin)

3.2 Animal Kingdom Classification

• Types of Animals:

  • Split into two main categories:

  • Vertebrates: Animals with backbones.

  • Invertebrates: Animals without backbones.

3.2.1 Vertebrates

• Categories of Vertebrates:

  1. Mammals

  2. Birds

  3. Reptiles

  4. Amphibians

  5. Fish

• Characteristics of Vertebrates:

  • Mammals: Give birth to live young, have hair or fur, possess mammary glands.

  • Fish: Live in water, breathe through gills, lay eggs.

  • Amphibians: Go through metamorphosis from water-breathing larvae to land-adult.

  • Reptiles: Cold-blooded, lay eggs with soft shells.

  • Birds: Warm-blooded, lay eggs with hard shells.

3.2.2 Invertebrates

• Main groups of invertebrates include:

  • Cnidarians: Jellyfish, sponges, corals; have stinging cells.

  • Flatworms

  • True Worms

  • Molluscs

  • Echinoderms

  • Arthropods (e.g., insects, arachnids, crustaceans)

4. Classification of Plants

4.1 Key Features of Plant Groups

• Plant Characteristics:

  • Multicellular organisms with cellulose cell walls and sap vacuoles.

  • Roots, stems, leaves, some possess chloroplasts.

4.2 Flowering Plants Classification

• Two groups of flowering plants:

  1. Monocotyledons:

  2. Dicotyledons:

4.3 Types of Non-flowering Plants

• Gymnosperms: Seed-producing non-flowering plants like conifers which reproduce through seeds in cones.

• Non-Vascular Plants:

  • Includes mosses and liverworts, which reproduce using spores and do not have a proper vascular system.

4.4 Vascular Plants

• Ferns: Have proper roots and stems, reproduce via spores.

  • Vascular tissues (xylem and phloem) are present.Gymnosperms: Seed-producing plants that bear their seeds directly on their surfaces, such as pine cones, and possess a vascular system.

5. Classification of Fungi, Bacteria and Viruses

5.1 Fungi

• Do not make their own food.

• Typically reproduce via spores.

• Cell walls composed of chitin.

5.2 Bacteria

• Unicellular organisms found in various habitats.

• Lack a nucleus and exhibit a range of sizes.

5.3 Viruses

• Extremely small and not classified as living organisms.

• Composed of a DNA or RNA strand encapsulated in a protein coat (capsid).

• Exhibits the life process of reproduction only inside host cells.