Microscopes

Question 1

what is the max magnification for a light microscope?

Answer 1

x1500

Question 2

what is the resolution of a light microscope?

Answer 2

200nm / 0.2 um

Question 3

what is a dry mount?

Answer 3

solid specimen either cut thin or whole with a cover slip on top

Question 4

what is a wet mount?

Answer 4

specimen suspended in water or oil
cover slip on top at an angle to prevent bubbles

Question 5

what are squash slides?

Answer 5

wet mount but using a lens tissue apply pressure to the coverslip to squash the specimen

Question 6

what are smear slides?

Answer 6

edge of a slide is used to smear a specimen then a cover slip is added

Question 7

what are smear slides?

Answer 7

edge of a slide is used to smear a specimen of a slip is added

Question 8

why must specimens be thin?

Answer 8

so light can shine through & more details can be seen

Question 9

why should the refractive index of the medium be roughly the same as glass when using a wet mount?

Answer 9

to prevent diffraction between liquid and glass and prevent distortion of image

Question 10

why might two microscope slides be used instead of a coverslip and microscope slide when preparing a squash slide?

Answer 10

squashing could break the coverslip 

Question 11

what should a student do to ensure their scientific drawing is clear?

Answer 11

use a sharp pencil
plain paper
rule label lines
title

Question 12

why is staining used?

Answer 12

makes cells or organelles visible & recognisable by increasing contrast

Question 13

what is positive staining?

Answer 13

positive dyes are attracted to the negatively charged material in the cytoplasm so cell components become stained
eg - crystal violet & methylene blue

Question 14

what is negative staining?

Answer 14

negative dyes that are repelled by the negative cytoplasm, they do not enter cells so are background stains
eg - nigrosin and congo red

Question 15

what is gram-negative bacteria?

Answer 15

not killed by penicillin as the less vital peptidoglycan cell wall is thinner and covered by a lipopolysaccharide layer
cells stain pink as alcohol washes out crystal violet
pink counter stain needed

Question 16

What is gram-positive bacteria?

Answer 16

killed by penicillin as it breaks down the vital peptidoglycan cell wall
cells stain purple as alcohol doesn’t remove crystal violet

Question 17

what is differential staining?

Answer 17

different cells and components are visible

Question 18

what stain can be used to stain a blood smear?

Answer 18

leishman’s stain as it provides contrast between the cytoplasm and the nucleus so the shape of the nucleus can be seen

Question 19

what are the advantages of a light microscope?

Answer 19

portable
take up little space
specimens are easy to prepare
in colour
nucleus is visible

Question 20

what are the disadvantages of using a light microscope?

Answer 20

low resolution
cannot see small organelles (ribosomes) or detail of organelles

Question 21

what is magnification?

Answer 21

the degree to which the size of an image is larger than the object itself

Question 22

what is resolution?

Answer 22

the ability to see two objects that are close together as separate objects and see in detail

Question 23

what are electron microscopes?

Answer 23

a beam of electrons is focused by electromagnets through or onto the surface of a specimen

Question 24

what are examples of electron microscopes?

Answer 24

transmission electron microscope (TEM) and scanning electron microscope (SEM)

Question 25

what is a TEM?

Answer 25

a beam of electrons is transmitted through a specimen and then focused to produce a 2D image used to see the ultrastructure of organelles and cells no colour magnification = x500,000 resolution = 0.05 - 2nm 

Question 26

what is a SEM?

Answer 26

a beam of electrons sent across the surface of a specimen and reflected, electrons are collected to produce a 3D image used to study the 3D shape of the surface of organelles and cells no colour magnification = x100,000 resolution = 5 - 50nm

Question 27

what are advantages of electron microscopes?

Answer 27

higher resolution higher magnification shorter wavelength can see ultrastructure

Question 28

what are disadvantages of electron microscopes?

Answer 28

specimens must be dead must be in a vacuum sample prep is complex expensive not portable 

Question 29

how do you convert from mm to um?

Answer 29

x1000

Question 30

how do you convert from mm to nm?

Answer 30

x1,000,000

Question 31

how do you calculate magnification of an image?

Answer 31

magnification = image size / real size

Question 32

how do you calculate magnification when using a microscope?

Answer 32

ocular lens x objective lens

Question 33

what is an eyepiece graticule?

Answer 33

placed into the eyepiece lens used to measure specimens seen under the microscope needs to be calibrated

Question 34

what is a stage micrometre?

Answer 34

a microscope slide with a scale etched into it goes on the stage of a microscope used to calibrate the eyepiece graticule

Question 35

what are the small divisions in an eyepiece graticule called?

Answer 35

eyepiece units (EPU)