Bright Field Microscopy

Question 1

What is the cell theory?

Answer 1

cells are the basic unit of life

everything is composed of cells

all cells come from pre-existing cells

Question 2

How did cell biology become a thing?

Answer 2

the invention of the light microscope

Question 3

What are the benefits of microscopy?

Answer 3

better understanding of

chemical composition of cells

physical properties of cells

molecular biology of cells

Question 4

Define deviation/refraction

Answer 4

the bending of light as it moves through one substance of a particular optical density to a substance with a different optical density

Question 5

Define magnification

Answer 5

the magnifying power of a microscope

the increase in size of the image of the object

Question 6

Define refractive index

Answer 6

the ratio of velocity of light in air to the velocity of light in a second substance

Question 7

Define resolution

Answer 7

the shortest distance between 2 objects that can be distinguished by an observer

Question 8

What is the formula for resolution?

Answer 8

D = 0.61 lambda/n sin alpha

d = resolution
lambda = wavelength
n = refractive index
sin alpha = angle of light incidence

Question 9

What is a wavelength?

Answer 9

Light travels through air in waves

the distance between the waves = wavelength

Question 10

How does wavelength relate to how you see an object?

Answer 10

an object must interfere with or disturb light waves to be seen

Question 11

Describe how light microscopes work

Answer 11

focuses light rays on the specimen and collects them through a series of lenses that magnify the specimen

Question 12

What are the 5 parts of a light microscope?

Answer 12

ocular lens
objective lens
specimen stage/holder
condenser lens
light source

Question 13

What is the function of the condenser lens?

Answer 13

collects rays from the light source and focuses them on the specimen

Question 14

What is the function of the objective lens?

Answer 14

collects the light rays that scatter/refract from hitting the specimen in a way that the image of the specimen is visible and magnified

magnified at 4x, 10x, 40x, 100x (oil immersion)

Question 15

What is the function of the tube & ocular lenses?

Answer 15

collect the light rays to magnify the image 10x

Question 16

T or F: the smaller the d value, the worse resolution

Answer 16

FALSE

d = resolution, so the smaller the d value, the better the resolution because it means the wavelength was shorter

Question 17

T or F: we can increase resolution of the light microscope by changing the wavelength of the light source

Answer 17

FALSE the numerator cannot be changed of the d equation because we cannot change the wavelength of the light rays emitted

Question 18

How is resolution changed when using a light microscope?

Answer 18

Sin alpha = the angle of light incidence

this can be adjusted by using the condenser lens

Can also be increased when using 100x (oil immersion) and reducing the refraction index

Question 19

How does using oil immersion increase resolution?

Answer 19

Oil has a similar refractive index to glass so when it is added between the glass slide and the glass of the objective lens, refraction of light decreases

this means more of the light moving toward the specimen will move through it rather than refract from it and the image will become sharper/more resolved

Question 20

What are 3 adjustments that can be made with the light microscope to increase resolution?

Answer 20

1. change angle of light by adjusting condenser lens
2. use immersion oil on the glass slide to reduce refraction
3. increase objective lens magnification

Question 21

Define contrast

Answer 21

the difference in brightness between the image and background

Question 22

What are 3 ways to increase contrast with a light microscope?

Answer 22

1. staining
2. dark-field microscopy
3. phase contrast microscopy

Question 23

Describe staining

Answer 23

Adding an appropriate stain to the slide to evenly coat the specimen so that it will stain a specific part of the specimen that the observer wants to see in more detail

creates contrast within the specimen so that small particulates can be viewed and located easier

Question 24

Describe dark-field microscopy

Answer 24

the light is focused so that only the light scattered/refracted by components of a living cell enter the objective lens

this makes the background dark and the cell components bright

Question 25

Describe phase contrast microscopy

Answer 25

filters in a phase contrast microscope slow deviated light so that it passes differently through thick and thing components of a specimen

allows smaller differences in optical density to be more visible