BIO3110L Exam 2- Learning set

What is spectrophotometry?

Technique that uses light to measure concentration of a solution

Absorbance measures what?

Amount of light absorbed → relates to concentration

Scattering measures what?

Light redirected by particles → relates to turbidity

Optical density (OD) equals what?

Absorbance + scattering

Beer-Lambert law states what?

Absorbance is proportional to concentration and path length

What is optical density?

Measure of light absorbance and scattering through a sample

OD is calculated as what ratio?

Incident light / transmitted light

Incident light means what?

Light hitting the sample

Transmitted light means what?

Light passing through the sample

What instruments measure OD?

Spectrophotometer and plate reader

Higher OD means what about concentration?

Higher concentration

Why is OD600 used?

Standard wavelength for bacterial quantification

More bacteria results in what OD change?

Higher absorbance (higher OD)

What is a standard curve?

Graph of known concentrations used to determine unknowns

Purpose of a standard curve?

Estimate unknown concentration using known standards

What are standards?

Serial dilutions of known concentrations

Two types of dilutions?

2-fold and 10-fold

Y-axis of standard curve?

Optical density

X-axis of standard curve?

Cell concentration

Line on standard curve represents what?

Line of best fit

Plate counts measure what?

Viable cells only

Optical density measures what?

Live + dead cells

Plate counts disadvantage?

Require incubation time

OD advantage?

No incubation required

What is a serial dilution?

Stepwise dilution to reduce concentration

Why use serial dilutions?

Bring sample into measurable range

Pellet vs supernatant?

Pellet = cells; supernatant = liquid

Purpose of vortexing?

Break up cell clumps

Purpose of pipette mixing?

Ensure proper mixing and remove cells from tip

What makes a good standard curve?

Tightly clustered points

What indicates a bad standard curve?

Widely spread points

What does R² represent?

Fit of regression (how well data matches line)

Higher R² means what?

Better prediction accuracy

How to improve R²?

Accurate pipetting

What is growth kinetics?

OD measurements over time to study growth

What does growth kinetics show?

Patterns of bacterial growth

Lag phase meaning?

Adaptation

Log phase meaning?

Rapid exponential growth

Stationary phase meaning?

Growth = death (equilibrium)

Death phase meaning?

Cells die due to depletion/waste

Which phase gives growth rate?

Log phase

What is doubling time?

Time for population to double

What is resolution?

Ability to distinguish two objects

What is magnification?

Apparent size increase

What is contrast?

Ability to distinguish object from background

Compound microscope use?

View microscopic specimens

Stereoscope use?

View larger specimens

Total magnification formula?

Ocular × objective

Objective lens magnifications?

4x

100x objective requires what?

Oil immersion

Darkfield microscopy?

Bright specimen on dark background

Brightfield microscopy?

Light passes through specimen

Why staining needed in brightfield?

Low natural contrast

Acidic dyes charge?

Negative

Basic dyes charge?

Positive

Simple stain uses what?

One dye

Differential stain uses what?

Primary + counterstain

Fluorescence microscopy uses what?

Fluorophores

Excitation wavelength means?

Light absorbed

Emission wavelength means?

Light emitted

SEM vs TEM?

SEM = surface; TEM = internal structure

Cocci shape?

Spherical

Bacilli shape?

Rod-shaped

Spirochete shape?

Spiral

Why use oil immersion?

Improve resolution by reducing refraction

Purpose of heat fixing?

Kill cells and attach to slide

Lens paper used for?

Cleaning objective lens

Bibulous paper used for?

Blotting slides

Raw data definition?

Original collected data

Clean data definition?

Processed/averaged data

Long data format?

All values in one column

Wide data format?

Values across multiple columns

Variable definition?

Characteristic that can be measured

Continuous variable?

Any value in range

Discrete variable?

Countable values

Ordinal variable?

Ordered categories

Nominal variable?

Unordered categories

Box plot shows what?

Distribution of data

Line plot shows what?

Relationship between numeric variables

Bar plot shows what?

Comparison of values