Definition of species (basic unit of classification):

Members of a species are similar (phenotype) to each other but different from other species
- Similarity of organisms in same species can be
  - physical (branching pattern of trees)
  - biochemical (haemoglobin structure)
  - immunological (antibody against an antigen equally effective)
  - development (similar growth of embryos)
  - ecological (occupy identical ecological niche)
(Group of) organisms able to interbreed/reproduce giving fertile offspring
- Each species is reproductively isolated from every other species

The five-kingdom classification of organisms

Nomenclature: Naming of organisms
Binomial: Biological name of an organism → Genus species
Taxon: Set of organisms within a category / Taxonomy / Study of biological classification
Different levels of taxons: SPECIES, GENUS, FAMILY, ORDER, CLASS, PHYLUM, KINGDOM
- Most number of species on right
- Most similar organisms on left
Unicellular: Single cell; Colonial: Groups of cells; Multicellular: Many cells
Autotrophs produce energy from inorganic sources
- Phototrophs from photosynthesis/sunlight
- Chemotrophs from simple inorganic (oxidative) processes
Heterotrophs digest and absorb organic molecules

Cell structure:
- Prokaryotes, unicellular
- Prokaryotes lack cytoplasmic organelles found in eukaryotes
Cell wall: murein
Nutrition: autotrophic (photosynthesis, chemosynthesis), aerobic heterotrophs
Divide by binary fission, not by mitosis
≈10μm in size (bacterial cell, filaments of blue-green bacteria)
Mutualistic nitrogen-fixing bacteria live in nodules on the root of legumes / symbiotic

Cell structure: eukaryotes, unicellular and multicellular
Cell wall: (sometimes) polysaccharide
Nutrition: autotrophic, heterotrophic
Placed in this category by exclusion / cannot be placed in any other kingdom
- Slime moulds / fungi characteristics
- Protozoa / heterotrophic and ingest food
- Algae / photosynthesis
≈10μm (amoeba) - 1m (Laminaria / large brown alga)

Cell structure: eukaryotes, multicellular and unicellular (yeast)
Cell wall: chitin
Nutrition: heterotrophic / saprotrophic decomposers or parasitic
Genus Penicillium
- Body of a fungus is composed of thin filaments called hyphae / form a mycelium
- Secret enzymes / external digestion / absorbs resulting nutrients
- Erect hyphae that grow upwards from the mycelium carry their reproductive spores
- Chains of spores on the erect hyphae / coloured mould visible on stored food
Break down organic matter

Cell structure: only multicellular, eukaryotic; large vacuoles
Cell wall: cellulose
Nutrition: autotrophic (photosynthetic)
Growth is restricted to meristems (layers/patches of dividing cells)
Non-motile; adapted to land / strong tissues, leave gas exchange system, waterproofed
Eg mosses, ferns, conifers, angiosperms (flowering plants)

Gametophytes, hidden in plant / sexual reproduction forms multicellular zygotes
Sporophytes, what we call plant / asexual reproduction to form spores that germinate into gametophytes
Gametophyte (n) → gamete (n) → fertilisation → zygote (2n) → mitosis → sporophyte (2n) → meiosis → spore (n) → mitosis → gametophyte (n)

Cell structure: eukaryotic, multicellular, no cell wall
- Develop form a blastocyst / embryo
- Have nervous and hormonal control systems
No cell wall!
Nutrition: heterotrophic, involving a digestive system
Are motile and grow throughout tissues (no mersitems)
Viruses → acellular → not included in classification system → pathogenic