Cells

• How are cells typically studied?

  Through the use of microscopes
• What are the two main types of microscopes?

  Light microscopes and electron microscopes
• What is the resolution limit of light microscopes?

  0.2um
• What type of lenses do light microscopes use?

  Convex glass lenses
• What limits the resolution of light microscopes to 0.2um?

  The wavelength of light
• What resolution can electron microscopes achieve?

  0.1nm
• What is the formula for calculating magnification?

  size of image/size of real object
• What is resolution defined as?

  Minimum distance to distinguish separate objects
• How does greater resolution affect an image?

  The image will be clearer
• Why are electron microscopes used for objects closer than 0.2um?

  Light microscopes cannot resolve that close
• What are the two main types of electron microscopes?

  TEM and SEM
• How do electron microscopes focus the electron beam?

  Using electromagnets
• Why do electron microscopes require a vacuum environment?

  To prevent electron deflection by air
• What does TEM stand for?

  Transmission Electron Microscope
• How does a TEM create an image?

  Electrons pass through a thin specimen
• How are areas that absorb electrons represented on a TEM micrograph?

  They appear darker
• How does a SEM create an image?

  Electrons scatter across the surface
• What does SEM stand for?

  Scanning Electron Microscope
• What type of image does a SEM produce?

  A 3D image
• What are the limitations of electron microscopes?

  • Vacuum needed, so living specimens can't be observed
  • Complex staining may introduce artefacts
  • Specimens must be very thin (especially for TEM)
  • SEM has lower resolving power than TEM
• What is cell fractionation?

  Separating cell parts for detailed study
• What is the most common method of cell fractionation?

  Differential centrifugation
• What is the fluid formed when cells are blended in an homogeniser called?

  Homogenate
• What happens to the homogenate in a centrifuge?

  It is spun at a slow speed
• Which organelles form the first pellet in differential centrifugation?

  Nuclei
• What is the fluid at the top of the tube after centrifugation called?

  Supernatant
• How does differential centrifugation separate organelles?

  By increasing speed each time

  
• Which organelles form the pellet after the supernatant is spun at a faster speed?

  Mitochondria
• What type of solution should the homogenate be placed in?

  Cold, buffered solution
• Why should the solution have the same water potential as the cells?

  To prevent organelles from bursting
• Why should the solution be buffered?

  So that the pH does not fluctuate
• Why should the solution be cold?

  To inactivate enzymes
• What are all living organisms made of?

  Cells
• What type of cells are humans made of?

  Eukaryotic cells
• What two things do all eukaryotic cells contain?

  A nucleus and membrane bound organelles
• What can be observed using a microscope to provide more cell structural detail?

  Ultrastructure
• What is the nucleus surrounded by?

  A double membrane called the envelope
• What do the nuclear pores in the nuclear envelope enable?

  Molecules to enter and leave
• What two things does the nucleus contain?

  Chromatin and a nucleolus
• What is the site of ribosome production?

  The nucleolus