Studying cells

• What is resolution 


  Ability to distinguish between two objects that are next to each other
• what is magnification 


  tells you how many times bigger the image produced by microscopes is than real life object
• optical light microscope fact sheet

  uses light to form image

  low resolution as light wavelength is long

  maximum resolution of 0.2 micrometers

  can see eukaryotic cells but not smaller organelles like ribosomes , endoplasmic reticulum or lysomes

  maximum magnification 1500x
• electron microscopes fact sheet

  uses electrons to form image

  higher resolution as electrons have shorter wavelength

  maximum resolution of 0.0002 micrometers

  can see smaller organelles like ribosome , ER and lysosomes

  maximum magnification 1500000

  two typeas transmission and scanning
• TEM microscope fact sheet

  uses electromagnets to focus beam of electrons and specimen . denser part absorb electrons and appear darker

  advantages highest resolution and can see internal structures

  disadvantages : specimen has to be very thin . specimen is dead so can not observe live cells as done in a vacuum. artefacts can be introduced due to long treatment to prepare specimen , can interfere . do not produce colour image
• scanning electron microscope fact sheet

  scan a beam of electrons across specimen which bounce off surface and form a image

  advantage: can be used on thick or 3-D samples . allows external structures to be observed .

  disadvantages : give lower resolution images. can not be used to observe live samples . do not produce colour. Lower resolution that TEM
• what is a graticule 


  small disk that has a engraved scale and placed on eyepiece of microscope to take measurements of sample
• how to detect starch grains

  iodine in potassium iodid solution is added to sample and this stains starch grains making them darker
• magnification equation 


  image = actual size of image X magnification
• Unit converter 


  Units

  
• process of homogenisation 


  sample of tissue placed in solution that is

  Cold : it reduce enzyme activity that can break cell

  isotonic : so has same water potential to prevent water moving via osmosis that can damage cell organelles

  buffered to have same ph to stop proteins denaturing

  tissue then homogenised(blended) to break up plasma membrane to release organelles .

  homogenate then filtered to separate large debris or unbroken tissue leaving filtrate solution
• process of ultracentrifugation 


  filtrate placed in centrifuge and spun at low speed causing largest organelle to sink to bottom . solution filtered and pellet of large organelles removed . supernatant then returned to centrifuge and spun at higher speed to separate next heavier organelle . process repeated increasing speeds each time
• order of organelles heaviest to lightest

  nuclei

  chloroplast

  mitochondria

  lysomes

  endoplasmic reticulum

  ribosomes
• what are artefacts 


  dust , air bubbles ,fingerprints . can occur when preparing slides common in electron micrographs