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Introduction to the lesson
The past two lessons have focused on the light microscope. After about 1900 people began to realize that the light microscope would never be able to reveal everything in a cell since some organelles are too small to interfere with light waves. In this lesson, you will learn about why the light microscope is limited as you study the difference between magnification and resolution and you learn about the electromagnetic spectrum. Finally, you will learn about the invention which solved the problem and led the way for advancement in the field of microscopy: the electron microscope. In the following lessons, we will study the new organelles which were discovered with the electron microscope.
Magnification and resolution
Read the sections "Magnification" and "Resolution" in your text book (p.6-10).
Learning Activity 1
Answer the following questions in your exercise book.
- Discuss the difference between magnification and resolution.
- Write down the formula for magnification. Can you change the subject of this formula?
- Work through Worked Example 2 "Calculating the magnification of a photograph or image" (p.8).
- Work through Worked Example 3 "Calculating magnification from a scale bar" (p.9).
- Work through Worked Example 4 "Calculating the real size of an object from its magnification" (p.9).
- Answer Question 1.2 (a and b) on p.8.
The electron microscope
Read the section on the electromagnetic spectrum (p.10-11).
Learning Activity 2
Answer the following questions in your exercise book.
- Draw a diagram showing the different parts of the electromagnetic spectrum.
- Answer Question 1.3 (p.11).
- Write a short paragraph describing the electronic microscope – what it looks like, how it works, etc. Describe the two main types of electron microscopes. Illustrate your paragraph with a diagram (see Fig. 1.14) Fig. 1.15 is a photograph of an actual electronic microscope.
Comparing the light microscope and the electron microscope
Learning Activity 3
Answer the following questions in your exercise book.
- What is the magnification power of a light microscope?
- What is the resolution of a light microscope?
- List the advantages of a light microscope?
- What is the disadvantages of a light microscope?
- What is the magnification of an electronic microscope?
- What is the resolution of an electronic microscope?
- What are the advantages of an electronic microscope?
- What are the disadvantages of an electronic microscope?
- Make a table to show these comparisons.
Definitions and review
Definitions
- Magnification
- Light micrograph/Photomicrograph
- Electron micrograph
- Resolution
- Electromagnetic spectrum
Mindmap
Add this section to your chapter one mindmap.