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

Biology is the study of living organisms.
Organisms exhibit seven essential characteristics which are remembered using the mnemonic “Mrs. Gren.”

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 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.

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: Tools for identifying organisms by answering a series of questions.
Each question leads to further specific descriptions, ultimately identifying the organism.

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.

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.

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.

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.

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

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

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

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).

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.

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.

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