Microscopy: understand how microscopy techniques have developed over time

The idea

Microscopy has improved as technology has advanced. Early light microscopes, developed from the 1600s, used visible light and lenses to allow Hooke and van Leeuwenhoek to observe cells and microorganisms, but had limited magnification. Modern light microscopes can magnify up to about ×2000, resolving objects roughly 200 nm apart. Electron microscopes, developed in the 1930s, use a beam of electrons instead of light, giving much higher magnification and resolution. The transmission electron microscope (TEM) passes electrons through a thin specimen to show internal structures, while the scanning electron microscope (SEM) scans surfaces to produce 3D images. Electron microscopes revealed subcellular structures such as mitochondria and ribosomes.

What earns the marks

• Describes the light microscope as using visible light and lenses, noting that modern versions can magnify up to ×2000 with a resolution of 200 nm.
• States that electron microscopes use a beam of electrons and achieve much higher magnification and resolution than light microscopes.
• Distinguishes the TEM, which transmits electrons through a thin specimen to show internal detail, from the SEM, which scans surfaces to produce 3D images.
• Links improved microscopy to new biological discoveries, such as subcellular structures and microorganisms.
• Recognises that microscope development depended on advances in technology, including lens quality, specimen preparation and computing.

Common mistakes and how to put them right

• Claiming that light microscopes can see ribosomes or internal mitochondria in fine detail.

  Put it right: These structures were revealed by electron microscopes because of their higher resolution.

• Confusing the TEM and SEM.

  Put it right: The TEM transmits electrons through a thin specimen for internal structure, while the SEM scans surfaces for 3D images.

• Saying that electron microscopes use light.

  Put it right: They use a beam of electrons, which is why they can resolve much smaller distances.

Exam tips

• Use comparative language such as higher resolution and greater magnification when contrasting light and electron microscopes.
• Link each microscope type to a named discovery or structure it made visible, rather than describing the instrument alone.
• If asked to compare, give one similarity and one difference, for example both use lenses or beams to form an image, but they use different radiation.