1: Electron Microscopes and Ultrastructure

Question 1

Define resolution.

Answer 1

1. is the ability of the microscope to show two close objects separately in the image

Question 2

How do you know when the resolution of the microscope has been exceeded?

Answer 2

1. the point above which the image can no longer be focused sharply

Question 3

What does resolution depend on?

Answer 3

1. the wavelength of the rays used to form the image

2. the shorter the wavelength, the higher the resolution

Question 4

What has a shorter wavelength: electrons or light? What does this mean for microscopes?

Answer 4

1. electrons
2. electron microscopes have a higher resolution than light microscopes
3. they can therefore produce a sharper image at much higher magnifications

Question 5

What is the resolution in a light microscope and electron microscope, respectively?

Answer 5

1. light: 0.25 um

2. electron: 0.25 nm

Question 6

What is the maximum magnification in a light microscope and electron microscope, respectively?

Answer 6

1. light: x500

2. electron: x500,000

Question 7

Name two types of electron microscope and their uses.

Answer 7

1. Transmission electron microscope (TEM): used to view ultra-thin sections
2. Scanning electron microscope (SEM): produce an image of the surfaces of structures

Question 8

Draw and label a scanning electron microscope (SEM). (p5)

Answer 8

1. voltage feed
2. electron gun
3. vacuum
4. electron beam
5. condenser
6. specimen
7. objective lens
8. intermediate lens
9. projector lens
10. viewing port
11. fluorescent screen

Question 9

There is an important trend in science related to technology and discovery. What is it? Give an example.

Answer 9

1. improvements in technology or apparatus lead to developments in scientific research
2. invention of the electron microscope led to a much greater understanding of the structure of cells known as the ultrastructure

Question 10

You need to be able to recognise different ultracellular components of a cell, and label a micrograph. This needs exam question practice and knowledge of the ultrastructure of eukaryotic cells (next deck).

Answer 10

They may also ask you to “deduce the function of the specialised cell” e.g. chloroplasts + large vacuole so function = photosynthesis”

Question 11

What do chloroplasts do?

Answer 11

1. carry out photosynthesis

Question 12

What does the cell wall do?

Answer 12

1. supports and protects the cell

Question 13

What does the plasma membrane do?

Answer 13

1. controls entry and exit of substances

Question 14

What do the (free) ribosomes do?

Answer 14

1. synthesize cytoplasmic proteins

Question 15

What does the nuclear membrane do?

Answer 15

1. protects the chromosomes