Technological Advances of the Microscope

Pages 24-25

  1. Explain why new understanding of cell biology has depended on improvements in optical devices.

Scientists need to see the more of the structures inside cells to understand how they work.

  1. What was the magnification of Anton von Leeuwenhoek’s microscopes?

It was 10x

  1. What improvement in microscopes allowed biologists to learn more about cells?

Microscopes improved when a second lens was added (COMPOUND microscopes)

  1. What is the most magnification possible with a light (optical) microscope?

About 2 000x

  1. What magnification is possible with a transmission electron microscope?

About 2 000 000x

  1. Lenses are used to concentrate, or focus the light in an optical microscope. Read the caption above Figure 3. What is used to “focus” a transmission electron microscope?

Magnets “focus” the electrons

  1. How is a transmission electron microscope similar to an optical microscope?

They are both used to see the specimens with a beam that passes through the sample

  1. Why are transmission electron microscopes not useful for thick structures with many layers of cells?

The electrons get deflected or absorbed instead of passing through the sample

  1. How is this problem solved?

The samples can be encased in plastic and shaved into very thin slices.

  1. What new problem is created by encasing the specimen in plastic?

Scientists cannot observe living cells, only dead ones

  1. How is a scanning electron microscope different from a transmission electron microscope?

Scanning microscopes use electrons that are reflected from the outside of a specimen (not passed through it)

  1. What is one advantage of the scanning electron microscope?

It doesn’t matter how thick the specimen is (and creates a 3D image)

  1. What is one disadvantage of the scanning electron microscope?

The inside structures of cells can’t be seen, AND the magnification is lower.

  1. Think: Why might a biologist prefer to use an optical microscope?

They might want to see living cells to observe what they do, or it might be too far to find an electron microscope (You can take an optical microscope with you “in the field”.)

  1. Think: Which electron microscope would be best for learning about each of the following. Give a reason for your answers.
  2. the openings in the cell walls of plant cells?

Scanning (shows outer features in 3D)

  1. inner parts of the cell that are smaller than chloroplasts?

Transmission microscopes see inner details of cells

  1. details about the structures of chromosomes inside the nucleus?

Transmission (inside)

  1. the shape of microscopic crystals?

Scanning (outside)