1. The nature and variety of living organisms

• Which characteristics do all living organisms share?

  • movement
  • respiration
  • sensitivity
  • control of internal conditions / homeostatsis
  • growth
  • reproduction
  • excretion
  • nutrition
• Common features shown by plants:

  • multicellular
  • cells contain chloroplasts so they can carry out photosynthesis
  • cells have cellulose cell walls
  • store carbohydrates as starch or sucrose
  • Examples:
  • cereals (eg maize)
  • herbaceous legume (eg peas)
• Common features that animals share:

  • multicellular
  • no chloroplasts so can't carry out photosynthesis
  • no cell walls
  • (usually) have nervous coordination and can move around
  • Usually store carbohydrates as glycogen
  • Examples:
  • mammals (eg humans)
  • insects (eg mosquito)
• Common features that fungi share:

  • can't photosynthesise
  • body is usually organised into thread-like structures called hyphae which contain many nuclei
  • some are single-celled
  • cell walls made of chitin
  • feed by extracellular secretion of digestive enzymes onto food material (saptrophic nutrition)
  • may store carbohydrates as glycogen
  • Examples:
  • mucor (typical fungal hyphal structure)
  • yeast (single celled structure)
• Common features protoctists share:

  • microscopic single-celled organisms
  • some have features like an animal cell (eg Amoeba)
  • some have chloroplasts and are more like plants (eg Chlorella)
  • some are pathogenic (eg Plasmodium)
• Common features shown by bacteria

  • microscopic and single-celled
  • have a cell wall, cell membrane, cytoplasm and plasmids
  • don't have a nucleus, instead have circular chromosome of DNA
  • some carry out photosynthesis but others feed off of other organisms
  • Example:
  • Lactobacillus (used to make yogurt)
• What is a pathogen?


  A microorganism that causes disease
• What microorganisms can be pathogens?

  fungi, bacteria, protoctists, viruses
• Common features of viruses:

  • they are not living
  • smaller than bacteria
  • they are parasitic
  • can only reproduce inside living cells
  • they have a protein coat and one type of nucleic acid (DNA or RNA)
  • example:
  • influenza (causes flu)