cells and micro organisms

• All life forms have a number of distinguishing processes that identify them from nonliving things
• Cell theory


  All living organisms are made up of cells and the products of cells, and that cells come from pre-existing cells
• Cells


  • They are the unit of structure and function in all living organisms
  • They contain DNA which is the molecule of heredity
  • All organisms are either unicellular or multicellular
  • All cells have a cell membrane which defines them

  
• Characteristics of living things

  • Movement
  • Respiration
  • Sensitivity
  • Homeostasis
  • Growth
  • Reproduction
  • Excretion
  • Nutrition
• You can remember the characteristics of living things with the mnemonic MRS H GREN
• Unicellular organisms


  • Bacteria, archaea, unicellular fungi and unicellular protists
  • Can be prokaryotic or eukaryotic cells

  
• Multicellular organisms


  • More complex, made up of large numbers, sometimes trillions of cells
  • Animals and plants are multicellular
  • Cells within a multicellular organism are not all the same
  • Multicellular organisms are always made of eukaryotic cells

  
• Cell structure


  • The cell membrane encloses the cytoplasm that contains organelles
  • The cell membrane is explained with the fluid-mosaic model
  • The membrane is made of a phospholipid bilayer
  • The nucleus is the organelle that contains genetic material (DNA)
  • DNA is packaged in chromosomes

  
• Microscopy


  • Light microscopes use light to shine through thin layers of cells, can see specimens on the micrometre (µm) scale
  • Electron microscopes use electrons to scan specimens to generate an image, can see specimens on the nanometre (nm) scale