Cell Structure 1.4, 1.5

Question 1

Magnification definition

Answer 1

the number of times larger an image of an object is than the real size of the object; magnification = image size / actual size of the object

Question 2

Eyepiece graticule definition

Answer 2

small transparent scale with 100 divisions that is placed in a microscope eyepiece.

Question 3

Stage micrometre definition

Answer 3

Very small, accurately drawn scale of known dimensions engraved on a microscope slide.

Question 4

Micrograph definition

Answer 4

a picture taken with the aid of a microscope.

Question 5

magnification formula

Answer 5

magnification = observed size of the image / actual size

Question 6

Resolution definition

Answer 6

the ability to distinguish between two objects very close together; the higher the resolution of an image, the greater the detail that can be seen.

Question 7

What is the maximum resolution of a light microscope?

Answer 7

200nm

Question 8

What is the wavelength range of light?

Answer 8

400-700nm.

Question 9

What colour is 400nm wavelength?

Answer 9

violet

Question 10

what colour is 700nm wavelength?

Answer 10

red

Question 11

What is visible light?

Answer 11

A form of electromagnetic radiation

Question 12

What is the electromagnetic spectrum?

Answer 12

The range of different wavelengths of electromagnetic radiation.

Question 13

The longer the waves , _______

Answer 13

the lower their frequency

Question 14

True or false: do all waves travel the same speed?

Answer 14

true

Question 15

The greater the energy, __________

Answer 15

the shorter the wave length

Question 16

Do ribosomes interfere with light waves?

Answer 16

no, they are too small

Question 17

Do mitochondria interfere with light waves?

Answer 17

yes, they can as they are large enough

Question 18

What is the limit of resolution?

Answer 18

The limit of resolution is about one half the wavelength of the radiation used to view the specimen.

Question 19

What is the best resolution that can be obtained with a light microscope and why?

Answer 19

200nm since the shortest wavelength of visible light is 400nm.

Question 20

What happens to the electrons in a metal when it becomes very hot?

Answer 20

They gain so much energy that they escape from their orbits.

Question 21

Describe free electrons

Answer 21

• have a very short wavelength
• behave like electromagnetic radiation : the greater the energy, the shorter the wavelength

Question 22

Name 2 reasons why electrons are a suitable form of radiation for microscopy.

Answer 22

• Extremely short wavelength (at least as short as X-rays).
• Unlike X-rays, they have a negative charge, so they can be focused easily using electromagnets (a magnet can be made to alter the path of the beam, like a glass lens bending light). Electron microscope resolution 0.5 nm can be obtained, 400 times better than a light microscope.

Question 23

Name 6 properties of the Transmission Electron Microscope

Answer 23

-Older
-Electrons passed through specimen before viewed.
-Only electrons transmitted are seen.
-See thin sections of specimens and inside cells.
-Can resolve objects as close as 1nm.
-Magnifying power up to 2 million times.

Question 24

Name 6 properties of the Scanning Electron Microscope

Answer 24

• Electron beam scans the surface of structures.
• Only reflected beam is seen.
• Surface structures can be seen.
• Much of the specimen is in focus at the same time, 3D image can be seen
• Resolution 3 nm – 20 nm
• Magnifying power up to 50,000 X

Question 25

How can you see the image of an electron beam and why?

Answer 25

by projecting it onto a fluorescent screen because the areas hit by the electrons shine brightly, showing a black and white picture.

Question 26

Why are stains used and what are they made of?

Answer 26

- to improve the contrast of the biological specimens and make it look like an X-ray photo - contain heavy metal atoms which stop the passage of electrons

Question 27

How are false colour images created?

Answer 27

by colouring the standard image using a computer

Question 28

Why do the electron beam, specimen and fluorescent screen need to be in a vacuum?

Answer 28

Because if electrons collide with air molecules they scatter, making it impossible to get a sharp picture

Question 29

Why can only dead or non-living material be examined?

Answer 29

Because water boils at room temperature ina vacuum, so all specimens must be dehydrated beforehand.

Question 30

What is an ultrastructure?

Answer 30

A fine detailed structure of a cell by an electron microscope.

Question 31

Light microscope: source of radiation wavelength of radiation used maximum resolution lenses specimen stains image

Answer 31

light About 400 nm 200 nm in practice glass dead and alive coloured dyes coloured

Question 32

Electron microscope: source of radiation wavelength of radiation used maximum resolution lenses specimen stains image

Answer 32

electrons about 0.005 nm 0.5 nm in practice electromagnets non-living or dead heavy metals black and white