cells and microscopes 2.1.1

Question 1

what is average diameter of eukaryotic cell

Answer 1

20-40 micrometers

Question 2

what is average diameter or prokaryotic cell

Answer 2

0.5-5 micrometers

Question 3

what is average diameter of prokaryotic ribosomes

Answer 3

18 nanometers

Question 4

what is average diameter of eukaryotic ribosomes

Answer 4

22 nanometers

Question 5

what resolution can be achieved by using a light microscope

Answer 5

200 nanometers

Question 6

what resolution can be achieved using a transmission electron microscope

Answer 6

0.05-1.0 nanometers

Question 7

how does a light microscope work

Answer 7

light is passed through a specimen and focused through glass lenses which projects a magnified image

Question 8

how is a dry mount prepared

Answer 8

specimenis sectioned and placed onto centre of slide, coverslip is placed over sample

Question 9

how is a wet mount prepared

Answer 9

specimens are suspended in liquid,coverslipis placed on from an angle.

Question 10

what organelles could be visible with a light microscope

Answer 10

optical microscopes can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts
Optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes

Question 11

what is the maximum magnification of a light microscope

Answer 11

The maximum useful magnification of optical microscopes is about ×1500

Question 12

why is the resolution of a light microscope so poor

Answer 12

it is limited by the large wavelength of light

Question 13

why do electron microscopes have much better resolution

Answer 13

A beam of electrons has a much smaller wavelength than light, so an electron microscope can resolve (distinguish between) two objects that are extremely close together

Question 14

what resolution can be achieved with a electron microscope

Answer 14

0.2 nm

Question 15

what is the most useful magnification of a electron microscope

Answer 15

×1,500,000

Question 16

how do transmission electron microscopes work

Answer 16

TEMs use electromagnets to focus a beam of electrons
This beam of electrons is transmitted through the specimen
Denser parts of the specimen absorb more electrons
This makes these denser parts appear darker on the final image produced (produces contrast between different parts of the object being observed)

Question 17

what are some advantages of TEM

Answer 17

They give high-resolution images (more detail)
This allows the internal structures within cells (or even within organelles) to be seen

Question 18

what are some disadvantages of TEM

Answer 18

They can only be used with very thin specimens or thin sections of the object being observed
They cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead, unlike optical microscopes that can be used to observe live specimens)
The lengthy treatment required to prepare specimens means that artefacts can be introduced (artefacts look like real structures but are actually the results of preserving and staining)
They do not produce a colour image (unlike optical microscopes that produce a colour image)

Question 19

how do scanning electron microscopes work

Answer 19

SEMs scan a beam of electrons across the specimen
This beam bounces off the surface of the specimen and the electrons are detected, forming an image
This means SEMs can produce three-dimensional images that show the surface of specimens

Question 20

what are some advantages of scanning electron microscopes

Answer 20

they can be used on thick or 3-D specimens
They allow the external, 3-D structure of specimens to be observed

Question 21

what are some disadvantages of scanning electron microscopes

Answer 21

They give lower resolution images (less detail) than TEMs
They cannot be used to observe live specimens (unlike optical microscopes that can be used to observe live specimens)
They do not produce a colour image (unlike optical microscopes that produce a colour image)

Question 22

how does a laser scanning confocal microscope work

Answer 22

laser beam is focused through lens, aimed at a beam splitter which directs some of the laser onto the specimen, when laser hits dyes they give off fluroescent light which is focused through a pinhole onto a detector.
Multiple depths of the tissue section/organisms are scanned to produce an image

Question 23

what are some advantages of the laser scanning confocal microscope

Answer 23

They can be used on thick or 3-D specimens
They allow the external, 3-D structure of specimens to be observed
Very clear images are produced. The high resolution is due to the fact that the laser beam can be focused at a very specific depth
You can even see the structure of the cytoskeleton in cells

Question 24

what are some disadvantages of the laser scanning confocal microscope

Answer 24

It is a slow process and takes a long time to obtain an image
The laser has the potential to cause photodamage to the cells

Question 25

what is the point in staining

Answer 25

provides contrast to differentiate between different structures in the sample

Question 26

what is differential staining

Answer 26

where multiple different stains are used, each stain binds to a different cell structure, stains each structure differently, so the structures can be easily identified.

Question 27

what does methylene blue stain

Answer 27

multipurpose stain, stains DNA blue

Question 28

what is iodine used to stain

Answer 28

stains starch turning it blue/black, can be used to stain cellulose

Question 29

what can be used to stain cytoplasm

Answer 29

Eosin (Dark red/pink)

Question 30

what are 2 common stains

Answer 30

Toluidine blue and phloroglucinol

Question 31

why are stains. used for electron microscopes

Answer 31

When using Transmission electron microscopes (TEMs) the specimen must be stained in order to absorb the electrons
Unlike light, electrons have no colour
The dyes used for staining cause the tissues to show up black or different shades of grey
Heavy-metal compounds are commonly used as dyes because they absorb electrons well