Microscopy (AQA GCSE Biology Combined Science): Revision Notes

1.1.5 Microscopy

Light Microscopes

• First Observations: Robert Hooke observed the first cells of a cork in 1665 using a light microscope.
• Structure:
  • Two lenses: objective lens and eyepiece lens.
  • Objective Lens: Produces a magnified image.
  • Eyepiece Lens: Magnifies the image further for viewing.
  • Illuminated from underneath.
• Capabilities:
  • Maximum magnification: ×2000
  • Resolving power: 200nm (ability to distinguish between two points)
  • Used to view tissues, cells, and large sub-cellular structures.

Electron Microscopes

• Development: In the 1930s, electron microscopes were developed to view detailed sub-cellular structures like mitochondria, ribosomes, chloroplasts, and plasmids.
• How They Work:
  • Use electrons instead of light to form an image, allowing for a smaller wavelength.
  • Types:
  • Scanning Electron Microscope (SEM): Creates 3D images.
  • Transmission Electron Microscope (TEM): Creates 2D images detailing organelles.
• Capabilities:
  • Magnification: up to ×2,000,000
  • Resolving power: 10nm (SEM) and 0.2nm (TEM)

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Common Calculations

1. Magnification of a Light Microscope:

• Magnification of eyepiece lens × Magnification of objective lens.

2. Size of an Object:

• Size of image / Magnification = Size of object (Ensure units are consistent).

Standard Form

• Usage: Helpful for working with very large or small numbers in microscopy.
• Format: A number multiplied by a power of 10, where the number is between 1 and 10.