Chapter 2 – How We See the Invisible World

Question 1

Define magnification

Answer 1

the ability of a lens to enlarge an image of an object when compared to the real object.

Question 2

Define resolution

Answer 2

the ability to tell that two separate points or objects are separate.

Question 3

Compound microscope

Answer 3

light passing through more than one lens, used by Galileo and Hooke

Question 4

Simple microscope

Answer 4

light passing through only one lens, used by Leeuwenhoek

Question 5

Contribution of Robert Hooke

Answer 5

• published many observations with a compound microscope

- proposed the idea of distinct cells in larger organisms

Question 6

ocular lens

Answer 6

the eye piece lens usually 10X magnification

Question 7

objective lenses

Answer 7

rotating lenses on a microscope

Question 8

Why do we use immersion oil with the 100X lens

Answer 8

The refractive index of the air between the slide and the lens scatters the light and compromises the resolution. The oil can focus the light because it has a similar refractive index to the glass slide.

Question 9

Brightfield microscope

Answer 9

compound microscope that produces a dark image on a light background

Question 10

darkfield microscope

Answer 10

uses an opaque light stop to create an image with bright objects on a dark background

Question 11

Phase-contrast microscopes

Answer 11

uses refraction and interference caused by structures in the specimen to create high contrast, high-resolution images without staining.

Question 12

electron microscope

Answer 12

used short wavelength electron beans instead of light to increase magnification and resolution.

Question 13

Transmission electron microscope

Answer 13

image is created by electrons passing through the specimen and the the detector captures the image.
can show well defined internal structures

Question 14

Scanning electron microscope

Answer 14

image is created by measuring electrons deflected by the specimen. can create nice 3-D images of the specimen surface structure.

Question 15

scanning tunneling microscope

Answer 15

probe passes over the specimen with constant voltage and creates the image by electron quantum tunneling from the probe to the specimen. creates images at the atomic level

Question 16

Atomic force microscope

Answer 16

probe passes over the specimen with a constant current and the probe moves up and down when atomic forces repel the probe. creates images at the atomic level

Question 17

Define wet mount

Answer 17

the specimen is placed on the slide in a drop of liquid followed by a coverslip.

Question 18

define fixation in the context of preparing a specimen for light microscope observation

Answer 18

attaching cells to the slide. can be done with heat of chemical fixing. Fixation kills the organism but preserves the integrity of their structure.

Question 19

define smear

Answer 19

a thin layer of specimen that has be spread on a slide.

Question 20

define staining

Answer 20

the use of a chemical that usually colors the specimen

Question 21

define basic dye

Answer 21

a dye that is positively charged

Question 22

define acidic dye

Answer 22

a dye that is negatively charged

Question 23

define a positive stain

Answer 23

a stain that is absorbed by the specimen

Question 24

define a negative stain

Answer 24

a stain that is repelled by the specimen, which stains the background.

Question 25

define simple staining

Answer 25

the application of only one dye

Question 26

define differential staining

Answer 26

uses more than one dye and distinguishes microbes based on their interaction with the different dyes

Question 27

Describe the Gram staining procedure

Answer 27

• a differential stain
  1) use of a primary stain (crystal violet)
  2) a mordant (iodine) is then added to fix the primary stain
  3) a decolorizing agent is added to remove the primary stain from Gram negative cells.
  4) application of a counter stain (safranin).

Question 28

Define an acid-fast stain

Answer 28

a stain used to differentiate between Gram-positive cells with a waxy mycolic acids in their call walls and those without them.

Question 29

define capsule staining

Answer 29

use of a negative stain which creates halos around cells with capsules. alternatively a positive stain can be used with a negative stain to visualize the capsules.

Question 30

define endospore staining

Answer 30

uses two stains to differentiate the endospores from the rest of the cells

Question 31

define flagella staining

Answer 31

use of two chemicals, the first to thicken the flagella and the second to visualize the flagella.

Question 32

What makes a cell Gram-negative?

Answer 32

The cell has an LPS membrane surrounding its peptidoglycan cell wall.

Question 33

fluorescence microscope

Answer 33

uses fluorochromes which absorb light energy and then emit at lower energy level

Question 34

confocal microscope

Answer 34

uses a laser to scan multiple z-planes to produce 2D high resolution images which can be turned to 3D images by a computer.