Cell Structure 1: Microscopes

Question 1

Magnification definition

Answer 1

How much bigger an image appears compared with the original object

Question 2

Resolution definition

Answer 2

Resolution is the degree to which it is possible to distinguish between two objects that are very close together.

Question 3

Light microscopes

Answer 3

• X1500 magnification (due to limited resolution)
• cheap, easy to use, portable
• for whole living specimens
• structures closer than 200nm/0.2um will appear as one object

Question 4

Advantages and disadvantages of light microscopes

Answer 4

Advantages: cheap; easy to use; portable/can be used in the field; can study whole/living specimens.
Disadvantages: low resolution, cannot magnify much above ×1500/×2000 and still give a clear image; cannot see very small objects.

Question 5

Advantages and disadvantages of electron microscopes

Answer 5

Advantages: high resolution; high magnification; can be used to study very small objects (0.02nm)
Disadvantages: very expensive; large and not portable; difficult to use – high degree of skill and a lot of training needed; cannot examine living specimens; cannot see any colours; stains used may be toxic.

Question 6

Process of looking at a slide under an electron microscope

Answer 6

1. Specimen placed on the stage in view over the hole and clipped into place
2. Rotate the lens so the smallest lens is facing the specimen with the least magnification
3. Adjust the coarse focusing knob whilst looking into the eyepiece until the image is in clear focus
4. While the image is in view adjust the fine focusing knob, and the iris diaphragm for optimum light
5. Rotate the to the next value of magnification and readjust using the fine focusing dial
6. Repeat using highest power lens

Question 7

Laser scanning microscopes

Answer 7

• use laser light to scan an object point by point, and assemble the image on a screen
• high resolution + high contrast

Question 8

Electron microscopes

Answer 8

• beam of fast travelling electrons with a wavelength of about 0.004nm
• great resolution, clear and highly magnified images

Question 9

Transmission electron microscope

Answer 9

• specimen dehydrated and stained
• beam of electrons passes through specimen
• electrons form a 2d black and white grey scale image
• electron micrographs are what the produced images are called
• 2,000,000x magnification

Question 10

Scanning electron microscopes

Answer 10

• 3D image made from electrons bouncing off a specimen

- max 200,000 magnification

Question 11

Millimetre, micrometer, nanometer conversion

Answer 11

mm = 1000x um
um = 1000x nm