Cell Structure 1.4, 1.5 Flashcards
Magnification definition
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
Eyepiece graticule definition
small transparent scale with 100 divisions that is placed in a microscope eyepiece.
Stage micrometre definition
Very small, accurately drawn scale of known dimensions engraved on a microscope slide.
Micrograph definition
a picture taken with the aid of a microscope.
magnification formula
magnification = observed size of the image / actual size
Resolution definition
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.
What is the maximum resolution of a light microscope?
200nm
What is the wavelength range of light?
400-700nm.
What colour is 400nm wavelength?
violet
what colour is 700nm wavelength?
red
What is visible light?
A form of electromagnetic radiation
What is the electromagnetic spectrum?
The range of different wavelengths of electromagnetic radiation.
The longer the waves , _______
the lower their frequency
True or false: do all waves travel the same speed?
true
The greater the energy, __________
the shorter the wave length
Do ribosomes interfere with light waves?
no, they are too small
Do mitochondria interfere with light waves?
yes, they can as they are large enough
What is the limit of resolution?
The limit of resolution is about one half the wavelength of the radiation used to view the specimen.
What is the best resolution that can be obtained with a light microscope and why?
200nm since the shortest wavelength of visible light is 400nm.
What happens to the electrons in a metal when it becomes very hot?
They gain so much energy that they escape from their orbits.
Describe free electrons
- have a very short wavelength
- behave like electromagnetic radiation : the greater the energy, the shorter the wavelength
Name 2 reasons why electrons are a suitable form of radiation for microscopy.
- 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.
Name 6 properties of the Transmission Electron Microscope
-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.
Name 6 properties of the Scanning Electron Microscope
- 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
How can you see the image of an electron beam and why?
by projecting it onto a fluorescent screen because the areas hit by the electrons shine brightly, showing a black and white picture.
Why are stains used and what are they made of?
- 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
How are false colour images created?
by colouring the standard image using a computer
Why do the electron beam, specimen and fluorescent screen need to be in a vacuum?
Because if electrons collide with air molecules they scatter, making it impossible to get a sharp picture
Why can only dead or non-living material be examined?
Because water boils at room temperature ina vacuum, so all specimens must be dehydrated beforehand.
What is an ultrastructure?
A fine detailed structure of a cell by an electron microscope.
Light microscope:
source of radiation
wavelength of radiation used
maximum resolution
lenses
specimen
stains
image
light
About 400 nm
200 nm in practice
glass
dead and alive
coloured dyes
coloured
Electron microscope:
source of radiation
wavelength of radiation used
maximum resolution
lenses
specimen
stains
image
electrons
about 0.005 nm
0.5 nm in practice
electromagnets
non-living or dead
heavy metals
black and white
