Studying Cells

• What is magnification?


  A measure of how much larger the image of a specimen looks under the microscope.
• What is resolution?


  The ability to distinguish between two adjacent individual points as separate.
• What is a specimen?

  Something you want to study.
• Name the type of microscope which uses lights to visualise specimens.

  A light microscope.
• What is a light microscope used for?

  Observing living and dead specimens.
• What resolution are light microscopes limited to?

  0.2 micrometres.
• What are the pros of a light microscope?

  Can observe living specimens, can see in colour, easier to prepare specimen, no artefacts.
• What are the cons of using a light microscope?


  Limited magnification, poor resolution.
• Name the type of microscope which uses electrons to visualise specimens.

  Electron microscope.
• What type of electron microscope uses an electron gun to produce an electron beam which is focussed onto the specimen by a condenser electromagnet?

  Transmission electron microscope (TEM).
• In which type of electron microscope do electrons not penetrate the specimen?


  Scanning electron microscope (SEM).
• What is a transmission electron microscope used for?

  Observing the internal ultrastructure of cells under high magnification and resolution.
• What is a scanning electron microscope used for?

  Viewing the surface of objects under high magnification and resolution.
• What are transmission electron microscope artefacts?


  Things created during sample preparation.
• What can transmission electron microscope artefacts be mistaken for?

  Cellular components.
• What is the difference between a transmission and a scanning electron microscope?

  TEM sends a beam of electrons through the specimen, the SEM bounces electrons off the surface.
• What is the resolving power of a transmission electron microscope compared to a scanning electron microscope?

  -TEM = 0.1nm

  -SEM = 20nm
• What type of image is produce by a transmission electron microscope?

  2D image of the contents of the cell.
• What type of image is produced by a scanning electron microscope?

  3D image of the surface of an object.
• Why do electron microscopes give a clearer image than light microscopes?

  The wavelength of electrons allows a resolution of 0.1 nanometres.
• By which process are large quantities of cell organelles collected?

  Cell fractionation.
• What is the formula to calculate magnification?


  Magnification = Image Size / Actual Size
• How do we work out image size?

  Use a ruler and measure the image.
• What units do you always use when measuring image size?

  Millimetres.
• What is an eye piece graticule?


  A small ruler fitted to a light microscope's eyepiece.
• What is a stage micrometre?


  A millimetre long ruler etched onto a slide. It has 100 divisions, each of 0.1mm or 10 micrometres.
• What is cell fractionation?


  The process of breaking up cells to separate out the organelles.
• What are the two stages of cell fractionation?

  Homogenisation and ultracentrifugation.
• What is homogenisation?


  Breaking up of cells in a blender. This releases the organelles into the homogenate.
• What is homogenate?


  Fluid containing cell organelles, prior to ultracentrifugation.
• When the homogenate is being created why is it important to keep the solution cold?

  Reduces enzyme activity, to prevent breaking down organelles.
• When the homogenate is being created why is it important to keep the solution isotonic to the tissue?

  Equal water potential, prevents bursting or shrinking due to osmosis.
• When the homogenate is being created why is it important to add a buffer to the solution?


  Prevents pH fluctuations altering organelle and enzyme activity.
• Why is the homogenate filtered prior to ultracentrifugation?

  To remove whole cells and large debris.
• What is the fluid collected from the centrifuge called?

  Supernatant.
• What is the solid left in the centrifuge tube after the supernatant has been removed, called?


  Sediment.