Microscopy (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

A brief history of the microscope

How have microscopy techniques developed over time?

• Microscopy techniques have advanced over time, enhancing our understanding of sub-cellular structures

  • 17th century: Development of the first light microscopes

    • Light microscopes use light and lenses to magnify specimens, allowing visualisation of cells and large sub-cellular structures like nuclei and vacuoles, often with the aid of stains

    • Their design has evolved to improve magnification and resolution over time

    • Resolution is the ability to distinguish two points that are close together, which is what lets you see finer detail

  • 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

Electron microscopes

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 sub-cellular structures such as the mitochondrion

• They have also helped biologists develop a better understanding of the structure of the nucleus and cell membrane

Magnification calculations

Magnification equation

• Magnification is calculated using the following equation:

$\mathrm{Magnification}=\mathrm{size}\mathrm{of}\mathrm{image}÷\mathrm{size}\mathrm{of}\mathrm{real}\mathrm{object}$

Magnification equation triangle

• You need to be able to rearrange the equation to form:

$\mathrm{Magnification}=\frac{\mathrm{size}\mathrm{of}\mathrm{image}}{\mathrm{size}\mathrm{of}\mathrm{real}\mathrm{object}}$

$\mathrm{Size}\mathrm{of}\mathrm{real}\mathrm{object}=\frac{\mathrm{size}\mathrm{of}\mathrm{image}}{\mathrm{magnification}}$

$\mathrm{Size}\mathrm{of}\mathrm{image}=\mathrm{magnification}\times \mathrm{actual}\mathrm{size}$

• An equation triangle can help with rearranging the equation

Use this image

• 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

• Remember magnification does not have any units and is just written as ‘× 10’ or ‘× 5000’

Converting units

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)

Test yourself

Flashcards

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