Cell Structure and Transport Notes

Microscopy Techniques

  • Light microscopes were developed in the mid-17th century and are still widely used.
  • Electron microscopes were invented in the 1930s, allowing for greater understanding of subcellular structures.

Microscope Types

  • Light Microscopes:
    • Use a beam of light to form an image.
    • Magnify up to approximately 2000x.
    • Relatively cheap and can be used almost anywhere.
    • Can magnify live specimens.
  • Electron Microscopes:
    • Use a beam of electrons to form an image.
    • Magnify objects up to around 2,000,000x.
    • Large and very expensive, requiring controlled environments.
    • Transmission Electron Microscopes (TEM): Provide high magnification 2D images.
    • Scanning Electron Microscopes (SEM): Provide 3D images but at lower magnifications.

Magnification and Resolution

  • Magnification: Makes objects appear larger.
  • Resolution: The ability to distinguish between two separate points. Affects the amount of detail.
  • Light microscope resolving power: approximately 200 nm.
  • Scanning electron microscope resolving power: approximately 10 nm.
  • Transmission electron microscope resolving power: approximately 0.2 nm.

Magnification Calculations

  • Overall magnification = Eyepiece lens magnification × Objective lens magnification
    • Example: Eyepiece (x4) × Objective (x10) = Overall (x40)

Object Size Calculation

  • Formula: magnification = \frac{size \space of \space image}{size \space of \space real \space object}
  • Rearranged: size \space of \space real \space object = \frac{size \space of \space image}{magnification}
  • Example: Image size = 1 mm, Magnification = x40, then Real object size = \frac{1}{40} mm = 0.025 mm = 25 μm

Units of Measurement

  • 1 kilometre (km) = 1000 metres (m)
  • 1 m = 100 centimetres (cm)
  • 1 cm = 10 millimetres (mm)
  • 1 mm = 1000 micrometres (μm)
  • 1 μm = 1000 nanometres (nm)
  • 1 nm = 1 x 10^{-9} metres