IGCSE Biology Study Notes: Characteristics and Classification of Living Organisms

Introduction to Biology

Biology: Study of living things (organisms)
MRS GREN: Mnemonic for characteristics of living organisms
- M: Movement
- R: Respiration
- S: Sensitivity
- G: Growth
- R: Reproduction
- E: Excretion
- N: Nutrition

Movement: Change of position/place by organism or parts
Respiration: Chemical reactions in cells breaking down nutrients to release energy
Sensitivity: Detection and response to changes in environment
Growth: Permanent increase in size and dry mass
Reproduction: Processes to create more organisms of the same kind
Excretion: Removal of metabolic waste and excess substances
Nutrition: Intake of materials for energy, growth, and development

Species: Group of organisms that can reproduce to produce fertile offspring
Binomial System:
- Scientific naming system (Genus + Species)
- Genus: Starts with a capital letter
- Species: Starts with a lowercase letter
- Names written in italics (e.g., Homo sapiens)

Dichotomous Keys: Identification tool using a series of questions about features
- Branching into two options at each step
- Example: Identify an organism through descriptive choices

Classification: Grouping organisms to simplify study
Aim: Reflect evolutionary relationships
Traditional classification based on physical features; recent methods use DNA sequencing for accuracy
Five Kingdoms of Life:
- Animals
- Plants
- Fungi
- Protists
- Prokaryotes

Characteristics: Multicellular, nucleus present, no cell walls/chloroplasts, heterotrophic
Classes of Vertebrates:
- Mammals: Hair, four-chambered heart, feed milk to young (e.g., cats, elephants)
- Birds: Feathers, lay hard-shelled eggs, beaks (e.g., toucans, parrots)
- Reptiles: Scaly skin, rubbery-shelled eggs (e.g., snakes, turtles)
- Amphibians: Moist skin, dual life (e.g., frogs, toads)
- Fish: Live in water, gills, fins

Invertebrates: Animals without a backbone
Arthropods: Invertebrates with jointed legs
- Groups of Arthropods:
  - Myriapods: Many segments, jointed legs (e.g., centipedes)
  - Insects: Three body parts, six legs (e.g., grasshoppers)
  - Arachnids: Four pairs of legs (e.g., spiders)
  - Crustaceans: More than four pairs of legs (e.g., crabs)

Characteristics: Multicellular, cell walls (cellulose), autotrophic via photosynthesis
Groups:
- Ferns: Non-flowering, reproduce by spores
- Flowering Plants: Reproduce via flowers and seeds
  - Monocotyledons: Parallel veins, branching roots
  - Dicotyledons: Broad leaves, taproot system

Viruses: Not classified in any kingdom
- Not considered living; require host cells for replication
- Structure: Genetic material surrounded by a protein coat

Summary of key points from chapter on characteristics and classifications of living organisms.