1. Characteristics & classification of living organisms (Cambridge IGCSE Biology 0610 2023,24 & 25)

Introduction to Biology

• Biology is the study of living things called organisms.

• Key topic covered: Characteristics and Classification of Living Organisms.

Characteristics of Living Organisms

• There are seven characteristics that define a living organism. Mnemonic: Mrs. Gren.

  • Movement: Change of position or place by an organism.

  • Respiration: Chemical reactions in cells to break down nutrients and release energy.

  • Sensitivity: Ability to detect and respond to changes in the environment.

  • Growth: Permanent increase in size and dry mass.

  • Reproduction: Process of producing more of the same kind of organism.

  • Excretion: Removal of waste products from metabolism.

  • Nutrition: Intake of materials for energy and growth.

Classification Systems

• Millions of species exist, classified into groups based on shared features.

  • Species: A group of organisms capable of reproducing to produce fertile offspring.

  • Binomial System: An international naming convention for species using two parts: genus and species.

    • Genus: Capitalized first letter.

    • Species: Lowercase letter.

    • Example: Homo sapiens.

Dichotomous Keys

• Dichotomous Keys: Tools used to identify organisms by answering a series of questions.

  • Each question presents two choices leading to further questions until the organism is identified.

Importance of Classification

• Classification makes it easier to study organisms, reflecting their evolutionary relationships.

• Traditional methods based on physical features are limited.

• Modern classification uses DNA sequencing to determine relationships:

  • More similar DNA sequences indicate closer relatedness and a recent common ancestor.

Five Kingdoms of Life

• Organisms are classified into five kingdoms:

  • Animalia: Multicellular, nucleus-containing cells, heterotrophic nutrition.

  • Plantae: Multicellular, nucleus-containing cells, autotrophic nutrition via photosynthesis (contain chloroplasts and cell walls made from cellulose).

  • Fungi: Mostly multicellular, non-cellulose cell walls, saprophytic or parasitic nutrition.

  • Protista: Mostly unicellular, nucleus-containing cells, variable modes of nutrition.

  • Prokaryotae: Unicellular, no nucleus or mitochondria (examples include bacteria).

Animal Kingdom Classification

• Divided into two major groups:

  • Vertebrates: Animals with a backbone.

    • Classes within vertebrates:

      • Mammals: Fur or hair, milk-feeding young, four-chambered heart.

      • Birds: Feathers, hard-shelled eggs, wings.

      • Reptiles: Scales, rubbery-shelled eggs.

      • Amphibians: Moist skin, eggs laid in water.

      • Fish: Gills, fins, most live in water.

  • Invertebrates: Animals without a backbone.

    • Characteristics based on limbs:

      • Arthropods: Jointed legs, divided into:

        • Myriapods: Many segments, multiple jointed legs (centipedes, millipedes).

        • Insects: Three-part bodies, six legs (grasshoppers, butterflies).

        • Arachnids: Four pairs of legs (spiders, scorpions).

        • Crustaceans: More than four pairs of legs (crabs, lobsters).

Plant Kingdom Classification

• Plant kingdom divided into:

  • Ferns: No flowers, reproduce by spores.

  • Flowering Plants: Reproduce with flowers and seeds, further divided into:

    • Monocotyledons (Monocots): Parallel leaf veins, branching root systems.

    • Dicotyledons (Dicots): Broad leaves with branching veins, taproot system.

Viruses

• Viruses are not classified within living organisms since they cannot perform life processes independently.

• Composed of genetic material and a protein coat, unable to reproduce without infecting a host cell.

Conclusion

• Overview of the six main topics covered in the chapter on characteristics and classification of living organisms.