Lecture 2

Question 1

Define “resolution.”

Answer 1

• the ability to see two items as separate and distinct
• microscopes tend to have a limit on resolution, whereas magnification can, in theory, be increased without limit
• the resolution limit of the light microscope would be the wavelength of light because light has to be able to fit between two objects to differentiate them from each other

Question 1

Define “magnification.”

Answer 1

• the use of a lens to enlarge an object
• as magnification increases, we are enlarging an object and looking at it more closely

Question 2

Define “contrast.”

Answer 2

• the ability to see something as different from its surroundings
• it depends upon differences in the amount of light transmitted by the object compared to its surroundings
• to view a specimen properly, a proper balance between magnification, resolution and contrast must be achieved

Question 3

Three types of microscopy

Answer 3

1) light (including bright-field, phase-contrast, dark-field, and fluorescence)
2) confocal
3) electron

Question 4

Light microscope (compound)

Answer 4

• illuminator is the light source
• light passes through a condenser which directs light rays through the specimen
• light rays will then pass through the objective lens
• the image is magnified by the ocular lens

Question 5

Kohler illumination

Answer 5

• a series of steps done at a specific point to achieve an even illumination of a specimen which increases contrast

Question 6

Immersion oil

Answer 6

• oil has the same refractive index as glass, and when used, fills up the space between the lens and slide to maximize resolution
• for oil immersion lens, 100x

Question 7

Staining

Answer 7

• different types of stains maintain high resolution and increase contrast
• sometimes used to isolated parts of microbes or detect certain types of microbes

Question 8

Gram Stain

Answer 8

• one of the first classifications done with a bacterium
• G+ versus G- different cell wall structures

Question 9

What kind of cells are ideal for bright-field microscopy?

Answer 9

• large and pigmented cells

Question 10

Phase-contrast

Answer 10

• based on small differences in the refractive index between the specimen and the background
• the small differences are amplified by a phase ring leading to a dark image on a light background
• useful for live specimens

Question 11

Dark-field

Answer 11

• light reaches the specimen from the side only, allowing for an image that is light on a dark background
• useful for live specimens

Question 12

What kind of microscopy should be used to increase contrast for dead cells?

Answer 12

Fluorescence microscopy

Question 13

Confocal microscopy

Answer 13

• specimens are stained with fluorochrome dyes and then only small portions of the field are illuminated with light at a time rather than the whole field of view
• short wavelength (blue) light is used to improve resolution
• the light illuminates each plane in a specimen to produce 3D images up to 100 um deep
• images are made pixel by pixel and put together using a computer

Question 14

Electron microscopes

Answer 14

• very high resolution
• a beam of electrons (smaller wavelength)
• two types: scanning and transmission

Question 15

Transmission Electron Microscopy

Answer 15

• a beam of electrons passes through a specimen, then an electromagnetic lens, to a screen or film
• the more dense the material is in a sample, the more electrons pass through

Question 16

Scanning Electron Microscopy (SEM)

Answer 16

• an electron gun produces a beam of electrons that scans the surface of a whole specimen
• secondary electrons emitted from the specimen produce the image

Question 17

What is “microbiology”?

Answer 17

• the study of living things that are too small to be seen without magnification
• these tiny living things are called microbes or microorganisms

Question 18

Where are microbes found?

Answer 18

• they are found everywhere!
• marine and freshwater soils, hydrothermal vents, air ice, etc.
• microbes are the most abundant organisms on Earth and make up most of the living mass of Earth

Question 19

How did microbes make life on Earth possible?

Answer 19

• microbes were the first forms of life
• life on Earth may have emerged from the bottom of the oceans (hydrothermal water)
• microbes were the only life forms for most of the history of Earth

Question 20

Impact of microbes as agents of disease

Answer 20

• 1% are pathogenic
• technology and further understanding of these microbes have decreased the effects of many infectious diseases

Question 21

Impact of microbes in agriculture and human nutrition

Answer 21

• microbes recycle nutrients
• nitrogen fixation
• ruminant animals (e.g. cow, sheep, bunny)
  we rely on microbes in our digestive system to produce certain vitamins

Question 22

Impact of microbes in food and industry

Answer 22

• food safety and spoilage
• fermented foods
• production if antibiotics and chemicals, and insulin

Question 23

How many domains is life organized into?

Answer 23

• 3
• bacteria, archae, eukarya

Question 24

Describe domain Bacteria:
1) prokaryotic or eukaryotic?
2) do they have cell walls?
3) if yes, what are they made of?
4) are they capable of photosynthesis?
5) how do they reproduce?

Answer 24

• prokaryote (no membrane-bound organelles)
• have cell walls made of peptidoglycan
• some (cyanobacteria) uses organic and/or inorganic molecules, or photosynthesis for energy
• reproduces through binary fission

Question 25

Describe domain Archaea:
1) prokaryotic or eukaryotic?
2) do they have cell walls?
3) if yes, what are they made of?
4) are they capable of photosynthesis?
5) how do they reproduce?
6) where can they be found?

Answer 25

• prokaryotic
• cell wall: either none, or composed of pseudomeurin or S-layer
• no, but uses inorganic molecules for energy
• reproduce through binary fission, fragmentation, or budding
• can be found in extreme environments (methongens, halophiles, thermophiles)

Question 26

Describe Protists:
1) prokaryotic or eukaryotic?
2) do they have cell walls?
3) if yes, what are they made of?
4) are they capable of photosynthesis?
5) how do they move around?
6) how do they reproduce?

Answer 26

• unicellular eukaryotes
• some have cell walls made of large variety
• absorb or ingest molecules from their environment
• some can photosynthesize, others are parasties
• can move through the use of pseudopods, flagella or cilia
• can reproduce sexually or asexually

Question 27

Describe Fungi:
1) prokaryotic or eukaryotic?
2) do they have cell walls?
3) if yes, what are they made of?
4) are they capable of photosynthesis?
5) how do they reproduce?

Answer 27

• eukaryote
• cell walls contain chitin
• uses organic molecules for energy absorption
• cannot do photosynthesis
• cell walls contain chitin
• can reproduce asexually or sexually

Question 28

Describe Archaeplastida (Algae):
1) prokaryotic or eukaryotic?
2) do they have cell walls? (yes, no, some)
3) if yes, what are they made of?
4) are they capable of photosynthesis?
5) how do they move around?
6) how do they reproduce?

Answer 28

• eukaryotes
• some, cellulose
• uses photosynthesis for energy
• not plants
• some can move via flagella
• can reproduce sexually or asexually
• unicellular or multicellular

Question 29

Describe Multicellular Animal Parasites:
1) prokaryotic or eukaryotic?
2) how does their reproductive system compare to their digestive and nervous systems?
3) can they do photosynthesis?
4) what are their life cycles like?
5) list some examples

Answer 29

• eukaryotic
• their reproductive systems are way more enhanced than their digestive and nervous systems
• incapable of doing photosynthesis
• life cycles involve multiple hosts, sexual, and asexual stages
• examples include Platyhelminths and Nematodes

Question 30

Describe Viruses:
1) are they in the three domains of life?
2) describe the structure
3) can they do photosynthesis?
4) how do viruses reproduce?

Answer 30

• not included in the three domains of life but are the most abundant and diverse biological entities on Earth
• small, acellular, consists of a protein and/or lipid membrane surrounding a DNA or RNA core
• no metabolism
• viruses replicate when living in a host cell

Question 31

What are microbes?

Answer 31

1) single-celled microscopic organisms: some can be multicellular, some are colonial (3 types: Bacteria, Archaea, Eukarya)
2) viruses: microscopic but not cellular, and not physiologically active