Methods of studying cells

Cells (AQA AS Biology) PART 3 of 6 TOPICS



TOPICS: Structure of eukaryotic cells  Structure of prokaryotic cells and viruses  Methods of studying cells  All cells arise from other cells  Transport across cell membs  Cell recognition and the immune system

Methods of studying cells:

Optical microscopes


  • Cheaper than electron microscopes


  • Magnification and resolution is not as electron microscopes


Transmission electron microscopes


  • Smaller wavelength of electron beam allows organelles smaller than mitochondria to be seen



  • Specimen has to be dead


Scanning electron microscopes


  • Gives 3D structure of organelles


  • It is very expensive



Cell fractionation has three processes:

  1. Homogenisation is where the cell membrane is broken to release the organelles into an ice cold (preventing enzyme activity), isotonic (preventing shrivelling and bursting of organelles) buffer (to keep the pH constant to prevent the enzymes and organelles from denaturing).
  2. Filtration is where the cell membrane is separated from the organelles as well as large debris using a gauze.
  3. Ultracentrifugation is where the organelles are separated from each other. All the organelles are poured into a tube and centrifuged where it is spun at high speed at an angle. Heaviest organelles such as nuclei form a pellet at the bottom with all the lighter organelles at the top called the supernatant. The supernatant is drained off into another tube where it is spun at a higher speed at an angle to get the next heaviest organelles (mitochondria) and the process is repeated until all the organelles are separated.