A particular species can be identified using the features (the phenotype) which are characteristic to only that species. Species with similar phenotypes are likely to be related to each other. A key of characteristics is used to identify the species. (see p10 – 11)

Organisms are classified into families according to similarity of features. The families start off large, but rapidly become smaller. This is the basis of a hierarchical classification system

Taxonomy: the science of classifying living things.

Biodiversity: the variety of life on our planet, measurable as the variety within species, between species, and the variety of ecosystems

If two organisms can interbreed to produce fertile offspring they are the same species. If not, they are different species



  • Microscopic prokaryotic cells (2 – 5m long rather than 10-100m)
  • Lack of a nucleus (DNA in cytoplasm) and possibly plasmids
  • Lack of membrane-bound organelles
  • Presence of 70s ribosomes
  • No cytoskeleton


  • Eukaryotic cell structure
  • Simple body form, either unicellular, filamentous (chains), colonial (ball) or macroscopic (large and visible)

The Proctoctist’s kingdom tends to be full of organisms that do not fit into any other Kingdom e.g. algae and yeast


  • Heterotrophic nutrition (get food from eating, unlike plants)
  • Made of a network of Hyphae, which form a 3D structure called a Mycelium. (look up Module 1 notes)
  • Call walls containing chitin


  • Multicellular with eukaryotic structure
  • Cell walls containing cellulose
  • Complex body form
  • Photoautotrophic nutrition (make food themselves through P/S)
  • Presence of photosynthetic cells with chloroplasts
  • 2 stages in the life cycle: a diploid spore-producing stage and a haploid gameteproducing stage.


  • Multicellular with eukaryotic cell structure
  • Cells without cell walls
  • Heterotrophic nutrition
  • Highly organised organs and tissues including nervous co-ordination
  • The only haploid cells they have are gametes