microscopy

Question 1

how does an optical microscope work?

Answer 1

light from a light source underneath the specimen passes through the specimen

Question 2

what is the resolution of an optical microscope?

Answer 2

200nm

Question 3

what is the magnification of an optical microscope?

Answer 3

x1500

Question 4

what are the strengths of optical microscopes?

Answer 4

• colour image
• uses live specimens

Question 5

what are the weaknesses of optical microscopes?

Answer 5

• poor resolution
• 2D image

Question 6

what do optical microscopes allow us to see?

Answer 6

whole cells/tissues

Question 7

how does a transmission electron microscope work?

Answer 7

electrons are transmitted through a specimen and denser parts of the specimen absorb more electrons, becoming darker

Question 8

what is the resolution of a TEM?

Answer 8

0.5nm

Question 9

what is the magnification of a TEM?

Answer 9

x1,000,000

Question 10

what are the strengths of TEMs?

Answer 10

• good resolution

Question 11

what are the weaknesses of TEMs?

Answer 11

• black and white image
• 2D image
• specimens must be dead

Question 12

what do TEMs allow us to see?

Answer 12

small organelles

Question 13

how do scanning electron microscopes work?

Answer 13

electron beam is scanned across the specimen surface and electrons bounce off, gathering in a cathode ray tube

Question 14

what is the resolution of SEMs?

Answer 14

2nm

Question 15

what is the magnification of SEMs?

Answer 15

x500,000

Question 16

what are the strengths of SEMs?

Answer 16

• 3D image

Question 17

what are the weaknesses of SEMs?

Answer 17

• black and white image
• specimen must be dead

Question 18

what is the magnification calculation?

Answer 18

mag = image / actual

Question 19

what does magnification mean?

Answer 19

amount of times the image has been expanded than the object

Question 20

what does resolution mean?

Answer 20

the ability to distinguish between two objects

Question 21

which lens is the objective?

Answer 21

near to specimen

Question 22

which lens is the eyepiece?

Answer 22

used to view specimen

Question 23

why are there two lenses on a microscope?

Answer 23

• improves magnification
• reduces chromatic aberration (diff colours travelling at diff speeds)

Question 24

why is resolution limited for optical microscopes?

Answer 24

light has a larger wavelength

Question 25

what is a dry mount?

Answer 25

a solid specimen viewed whole or sectioned on a slide under a cover slip

Question 26

what is a wet mount?

Answer 26

specimen suspended in liquid with a cover slip placed at an angle

Question 27

how is a squash slide prepared?

Answer 27

- wet mount prepared - lens tissue used to press down cover slip - used for soft samples

Question 28

how is a smear side prepared?

Answer 28

- edge of slide used to smear a sample to create a thin coating - cover slip over top

Question 29

why should specimens on a slide be thin?

Answer 29

avoid air bubbles

Question 30

why is a stain sometimes used?

Answer 30

increase contrast to improve visibility

Question 31

what is differential staining?

Answer 31

distinguishes between two organisms/organelles - positive dye attracts negative cytoplasm materials

Question 32

what is a gram stain?

Answer 32

- separates pos/neg bacteria - crystal violet is applied to slide - iodine applied to fix dye - washed with alcohol

Question 33

what is the acid fast technique?

Answer 33

- differentiates mycobacterium - lipid solvent carries a dye into cells - mycobacterium not affected by acid alcohol cell wash absorbs dye

Question 34

how are mm converted to micrometres?

Answer 34

x1000

Question 35

how are micrometres converted to nm?

Answer 35

x1000

Question 36

how do you identify what is stained when using crystal violet and methylene blue?

Answer 36

negative organelles attract positive stain

Question 37

how do you identify what is stained when using nigrosin or methylene blue?

Answer 37

positive organelles attract negative stain

Question 38

how does a laser scanning confocal microscope work?

Answer 38

- laser beam focuses on a small area on a sample surface - fluorophores in sample emit photons - photomultiplier tube amplifies signal onto a detector - image is produced in pixels

Question 39

how is the actual length of an image calculated using a stage micrometer?

Answer 39

- line up eyepiece graticule with stage micrometer - count how many graticule divisions are in 100 micrometres - number of divisions / 100 = 1 division