MIC 230 Exam 1 Lab UWL

Scanning Objective lens

(4x): shortest objective lens, used for scanning large areas

Low Power Objective Lens

(10x) Rarely used for bacteria

High-Dry Objective

(40x)

Oil Immersion Objective

(100x) used to look at bacteria, must use immersion oil to see slide

How to calculate total magnification

products of the objective lens and ocular lens (always 10x)

ex: 4 × 10, 10 × 10, 40 × 10, and 100 × 10

What is working distance

distance between objective lens and slide when the specimen is focused

what is the field of view

amount of the slide you can view at once

what is the depth of field?

the vertical distance that can remain in focus at one time

what is the brightness of the field view

percent of light traveling from the specimen that enters the objective lens

What is resolution

how sharp and clear the image is

what is the resolving distance

shortest distance between 2 points in an image that may be distinguished as separate (shorter resolving distance means better resolution)

when do you use immersion oil and how does it help?

Immersion oil is used in the 100x lens; it allows more light to travel into the lens by creating a bridge between the lens and the slide, allowing less to light bend and scatter

What is contrast?

The lightness or darkness of the background compared to the specimen

How can you improve contrast? and why does this help?

adjusting the iris diaphragm, allows more light to pass through the substage condenser

Why do we start on the 10x and and make are way down?

Our microscopes are parfocal so once you focus on one setting, other focus setting will be almost in focus as well

what are in the cell walls of fungi?

chitin

what are multicellular fungi called? unicellular?

molds/mushrooms and yeast

how are yeast and mold differ

yeast: single cell, smaller colonies, whiteish

Molds: darker (green), fuzzy,

why are mycelium and spore layer structures hard to look at in the microscope?

The depth of the fungi makes it so you can’t focus the whole organism at once, but have to change your focus to view different layers

What are in the cell walls of photosynthetic protists? How about diatom algae?

Cellulose

Silica

How does a dead zone form and what is a dead zone?

dead zone happens when there is an increase in nutrients like Nitrogen and phosphorus, so the growth rate increases a lot, forming blooms of algae. When the algae die off because of nutrient depression, oxygen levels decrease, causing a dead zone.

What is it called when a Protozoa engulfs another organism?

phagocytosis

what are some characteristics of Protozoa? (3)

Unicellular (mostly)

Heterotrophic

Pseudopods, cilia, flagella

How are photosynthetic protists important to humans?

The waste product is O2

Primary producers for many animals in which we eat

What are some diseases that are caused by parasitic Protozoa, and there genus?

• Diarrhea - Giardia (a lot more as well)

• Malaria - Plasmodium

• Trypanosomiasis - Trypanosoma

What grows on General Purpose media?

growth of almost anything

What is selective media used for? what did we use in class

can inhibit the growth of certain bacteria. In class we inhibits the growth of gram-positive

What is differential media used for? what did we use in class?

Allows screening of cells with different phenotypes (mostly metabolic). In class, we inhibited the growth of gram positive and differential for lactose fermenters

What is enriched media used for?

has used for if you need greater concentration of nutrients

Why is agar used in media plates?

• Can be used in a wide range of temps

• not degraded by most microbes

What is an autoclave used for? how?

sterilization, it heats up to 121C for around 15 minutes

what category are TSA plates and TSB?

general purpose media

What does it mean to culture a microorganism

facilitate their growth

what is inoculation

deliberately transferring microorganisms from one source to a growth medium

What are Aspect Techniques, Give some examples

Collection of practices to prevent microbial contamination

1. Burn the inoculation loop after use

2. Close media when not in us

What is the quadrant streak plating technique used for?

to try and get isolated colonies

What are the characteristics that imply a new species in colonies (5)

• color

• shape

• size

• elevation

• texture

What are CNA select for plates?

Gram positive bacteria

What do MAC plates select for? Color?

Gram-positive and lactose fermentation. Bacteria that ferment Lactose will become magenta

what are the 4 type of organisms that deal with oxygen?

aerobe - only O2

strict anaerobe - no O2 or die

facultative anaerobe - can use and not use O2

aerotolerant anaerobe - doesn’t use O2 but won’t die in its presence

What is the GasPak system used for

to remove any O2 from a box

Why do we gram stain bacteria?

to increase the contrast

What are Cationic dyes, what do they bind to?

positively charged stain and bind to negatively charged molecules

what are the steps in creating a stain? (6)

1. smear

2. heat fixing

3. crystal violet

4. iodine

5. ethanol

6. safranin

What are some examples of cell morphology

rod, coccus, vibrio, spirillum, spirochete

What are some examples of cell arrangements

Single, pair, chain, irregular cluster. tetrad, secrina

Why does the color in Gram-negative bacteria disappear once you put ethanol on it

ethanol dissolves the outer membrane of the cells and easily rinse out the stain complexes

why do sometimes to cell of a stain have pink and purple colors? (name at least 2)

1. Uneven application

2. To think of a smear

3. Contamination of cells with the opposite gram reaction

4. inherent gram variability of some bacterial species

what does it mean when we say growth of bacteria?

we talk about the population growth

what are the 4 stages of bacterial growth

1. lag phase

2. log/exponential

3. stationary

4. death

what does it mean when a bacteria has a steeper log phase?

has a shorter generation/doubling time

why do we use a log scale instead of a linear scale when plotting bacterial growth

when we use log scales, we can see all the phases, including the lag and log phases

what does it mean when we say “indirect methods” in counting bacteria cells?

we estimate the growth instead of counting all the cells one by one

We can measure turbidity with a spectrophotometer using optical density. What is optical density?

measure both the light absorbed and the light scattered by the cells

Why do we have to start diluting after the optical density reaches 0.5?

light can start refracting from 2 or more cells, which leads to an underestimation of cell density