Studying cells

• Name and explain the 3 conditions for cell fractionation

  Ice cold - lower kinetic energy prevents enzymes from digesting organelles

  Buffered - maintains a constant pH so proteins and enzymes are not denatured

  Isotonic - maintains a constant water potential so no osmotic damage to organelles occurs
• Describe the procedure of cell fractionation

  Homogenise - breaks open cell membranes to release organelles

  Filtration - removes any remaining whole cells and debris

  Centrifugation - respin supernatant at high speeds to remove less dense organelles
• Define magnification

  The number of times larger an image is compared with the actual size of the structure
• Define resolution

  The shortest distance at which two different structures can be seen as separate. It is dependent on wavelength of light/electrons
• Compare and contrast transmission electron microscopes (TEM) and scanning electron microscopes (SEM)

  -In TEM, electrons pass through the specimen but in SEM electrons bounce off surfaces

  -Both require specimens to be dead

  -SEM resolution is slightly lower than TEM

  -Both produce black and white images

  -TEM visualise internal structures but SEM visualise surfaces of structures

  -TEM produce a 2D image but SEM produce a 3D image
• What is the illumination source used by optical microscopes (OM)?

  Light
• What is the illumination source used by electron microscopes (EM)?

  Electrons
• Why do electron microscopes (EM) require thinner specimens than optical microscopes (OM)?

  Because electrons have a shorter wavelength than light, allowing for higher resolution
• Do optical microscopes (OM) require sample preparation?

  No
• Do electron microscopes (EM) require sample preparation?

  Yes, the sample must be in a vacuum
• What type of images do optical microscopes (OM) produce?

  2D images
• What type of images do electron microscopes (EM) produce?

  Both 2D and 3D images
• What structures can optical microscopes (OM) visualize?

  Only internal structures
• What structures can electron microscopes (EM) visualize?

  Both internal and surface structures
• What type of images do optical microscopes (OM) produce in terms of color?

  Images in color
• What type of images do electron microscopes (EM) produce in terms of color?

  Black and white images
• Which type of microscope has a lower resolution, optical microscopes (OM) or electron microscopes (EM)?

  Optical microscopes (OM)
• What is the maximum magnification of optical microscopes (OM)?

  x1000
• What is the maximum magnification of electron microscopes (EM)?

  x1500000
• How do electron microscopes (EM) achieve magnification?

  By using an electromagnet
• How do optical microscopes (OM) achieve magnification?

  By using different objective lenses with an eyepiece lens
• Describe the method to create a temporary mount

  -Add water to the microscope slide

  -Cut a thin section to allow light to pass through

  -Add a stain to increase contrast

  -Use a mounted needle to place the coverslip at an angle to avoid artefacts

  -Coverslip pressed firmly to create a single layer of cells, not rotated to prevent damage to the cell
• Describe the method to use an eyepiece graticule

  -Calibrate the graticule using a stage micrometre to calculate the value of one eyepiece unit

  -Measure the length of many cells using the graticule

  -Add the lengths together and divide by the number measured to get a mean length
• What are the 5 rules for biological drawings?

  -Use single, continuous lines and do not sketch

  -No shading

  -Add labels and annotations

  -Don't overlap label lines

  -Include magnification or a scale bar