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

Introduction to Biology

• Biology is the study of living organisms.

• Organisms exhibit seven essential characteristics which are remembered using the mnemonic “Mrs. Gren.”

Seven Characteristics of Living Organisms

• Movement: Change in position or location of an organism or its parts.

• Respiration: Chemical reactions in cells that break down nutrients to release energy for metabolism.

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

• Growth: Permanent increase in size and dry mass.

• Reproduction: Production of more individuals of the same kind.

• Excretion: Removal of metabolic waste products and excess substances from the body.

• Nutrition: Taking in materials for energy, growth, and development.

Classification of Living Organisms

• Classification involves grouping species based on shared features.

• Definition of a species: A group of organisms that can reproduce to produce fertile offspring.

• Features of Mammals: Hair, warm-blooded, give birth to live young.

Binomial Nomenclature

• The binomial naming system uses two parts for species names: genus and species.

• Genus: A group of related species; starts with a capital letter.

• Species: Follows the genus; starts with a lowercase letter.

• Example: Homo sapiens (italicized).

Dichotomous Keys

• Dichotomous keys: Tools for identifying organisms by answering a series of questions.

• Each question leads to further specific descriptions, ultimately identifying the organism.

Importance of Classification

• Classification systems simplify the study of organisms.

• They reflect evolutionary relationships, traditionally based on shared features and now increasingly using DNA analysis.

• The five kingdoms of life include Animals, Plants, Fungi, Protists, and Prokaryotes.

Kingdoms of Life

Animals

• Characteristics: Multicellular, cells with a nucleus, no cell walls or chloroplasts, nutrition by eating other organisms.

• Animal Cells: Contain a nucleus, cell membrane, mitochondria, ribosomes, and cytoplasm.

Plants

• Characteristics: Multicellular, cells with a nucleus, chloroplasts, and cellulose cell walls; nutrition through photosynthesis.

• Plant Cells: Include a cell wall and chloroplasts in addition to what an animal cell contains.

Fungi

• Characteristics: Mostly multicellular, nuclei containing cells, non-cellulosic cell walls; nutrition through saprophytic or parasitic methods.

• Fungal Cells: Have cell walls not made of cellulose.

Protists

• Characteristics: Mostly unicellular but some multicellular; all have a nucleus; may have cell walls and chloroplasts; varied nutritional methods.

Prokaryotes

• Examples: Bacteria.

• Characteristics: Mostly unicellular; no nucleus; cell walls not made of cellulose.; cytoplasm present.

Animal Kingdom Classification

• Divided into two primary categories: Vertebrates (with backbones) and Invertebrates (without backbones).

Vertebrates

• Main classes: Mammals, Birds, Reptiles, Amphibians, Fish.

  • Mammals: Hair or fur, young feed milk, hearts with four chambers.

  • Birds: Feathers, eggs with hard shells, beaks.

  • Reptiles: Scaly skin, eggs with rubbery shells.

  • Amphibians: Moist skin, can live on land and water, eggs in water.

  • Fish: Live in water, have scales and gills.

Invertebrates

• Characteristics: Animals without a backbone.

• Types of invertebrates include arthropods with jointed legs: Myriapods, Insects, Arachnids, Crustaceans.

  • Myriapods: Many segments, each with jointed legs (e.g., centipedes).

  • Insects: Three-body parts, three pairs of legs (e.g., grasshoppers).

  • Arachnids: Four pairs of legs, breathe through book lungs (e.g., spiders).

  • Crustaceans: More than four pairs of legs with gill breathing (e.g., crabs).

Plant Kingdom Classification

• Plants are green due to chlorophyll; can be classified into Ferns and Flowering Plants.

• Ferns: Reproduce by spores on fronds.

• Flowering Plants: Reproduce by flowers and seeds; can be further categorized into Monocotyledons and Dicotyledons based on leaf and flower structure.

Classification of Viruses

• Viruses do not fit into classification systems as they are not considered living organisms; they cannot perform life processes independently and require a host to replicate.

• Structure: Composed of genetic material surrounded by a protein coat.

Conclusion

• Summary of the key points from Chapter 1 on the characteristics and classification of living organisms.