Microscopy (AQA GCSE Biology: Combined Science)

How have microscopy techniques developed over time?

• Microscopy techniques have advanced over time, enhancing our understanding of subcellular structures.

  • 17th century: Development of the first light microscopes.
    • Light microscopes use light and lenses to magnify specimens, allowing visualisation of cells and large subcellular structures like nuclei and vacuoles, often with the aid of stains
    • Their design has evolved to improve magnification and resolution over time
  • 20th century: Introduction of the first electron microscopes.
    • Electron microscopes use electron beams instead of light, providing much higher resolution and magnification due to the smaller wavelength of electron beams

Why are electron microscopes better?

• An electron microscope has much higher magnification and resolving power than a light microscope
• They can therefore be used to study cells in much finer detail, enabling biologists to see and understand many more subcellular structures such as the mitochondrion
• They have also helped biologists develop a better understanding of the structure of the nucleus and cell membrane

Magnification equation

• Magnification is calculated using the following equation:

Magnification = Drawing size ÷ Actual size

Magnification equation triangle

• An equation triangle can help with rearranging simple equations

An equation triangle for calculating magnification

• Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle – whatever you are trying to find, place your finger over it and whatever is left is what you do, so:
  • Magnification = image size / actual size
  • Actual size = image size / magnification
  • Image size = magnification x actual size
• Remember magnification does not have any units and is just written as ‘X 10’ or ‘X 5000’

Worked example

• An image of an animal cell is 30 mm in size and it has been magnified by a factor of X 3000. What is the actual size of the cell?
• To find the actual size of the cell:

Worked example using the equation triangle for magnification

Converting units in Biology

• You may be given a question in your Biology exam where the measurements for a magnification calculation have different units.
• You need to ensure that you convert them both into the same unit before proceeding with the calculation (usually to calculate the magnification)

• For example:

Example of an extended magnification question

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• Remember that 1mm = 1000µm
• 2000 / 1000 = 2, so the actual thickness of the leaf is 2 mm and the drawing thickness is 50 mm
• Magnification = image size / actual size = 50 / 2 = 25
• So the magnification is x 25