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AS Level Biology > Cell Structure 1.4, 1.5 > Flashcards

Cell Structure 1.4, 1.5 Flashcards

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1
Q

Magnification definition

A

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

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2
Q

Eyepiece graticule definition

A

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

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3
Q

Stage micrometre definition

A

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

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4
Q

Micrograph definition

A

a picture taken with the aid of a microscope.

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5
Q

magnification formula

A

magnification = observed size of the image / actual size

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6
Q

Resolution definition

A

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.

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7
Q

What is the maximum resolution of a light microscope?

A

200nm

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8
Q

What is the wavelength range of light?

A

400-700nm.

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9
Q

What colour is 400nm wavelength?

A

violet

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10
Q

what colour is 700nm wavelength?

A

red

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11
Q

What is visible light?

A

A form of electromagnetic radiation

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12
Q

What is the electromagnetic spectrum?

A

The range of different wavelengths of electromagnetic radiation.

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13
Q

The longer the waves , _______

A

the lower their frequency

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14
Q

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

A

true

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15
Q

The greater the energy, __________

A

the shorter the wave length

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16
Q

Do ribosomes interfere with light waves?

A

no, they are too small

17
Q

Do mitochondria interfere with light waves?

A

yes, they can as they are large enough

18
Q

What is the limit of resolution?

A

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

19
Q

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

A

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

20
Q

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

A

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

21
Q

Describe free electrons

A
  • have a very short wavelength
  • behave like electromagnetic radiation : the greater the energy, the shorter the wavelength
22
Q

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

A
  • 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.
23
Q

Name 6 properties of the Transmission Electron Microscope

A

-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.

24
Q

Name 6 properties of the Scanning Electron Microscope

A
  • 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
25
Q

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

A

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

26
Q

Why are stains used and what are they made of?

A
  • 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
27
Q

How are false colour images created?

A

by colouring the standard image using a computer

28
Q

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

A

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

29
Q

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

A

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

30
Q

What is an ultrastructure?

A

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

31
Q

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

A

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

32
Q

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

A

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

AS Level Biology (3 decks)

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