microlab midterm pt 6

binary fission

type of asexual reproduction in which an organism replicates its DNA and divides in half, producing two identical daughter cells

Generation time

the time it takes for the population to double through one round of binary fission.

closed (batch) culture

a type of culture where no nutrients are added and most waste is not removed

Growth Curve

a reproducible growth pattern

Lag phase

no increase in number of living bacterial cells

log phase

exponential increase in number of living bacterial cells

stationary phase

plateau in number of living bacterial cells; rate of cell division and death roughly equal

death phase

exponential decrease in number of living bacterial cells

Turbidity

cloudiness of a culture, estimate of the number of cells

Spectrophotometer

passes light wavelength through sample to measure the turbidity ( can be used to estimate #of cells) As the number of bacteria in a culture increases, the turbidity also increases and causes less light to reach

the detector

Absorbance

The amount of light absorbed by a sample.

The decrease in light passing through the sample and reaching the detector is associated with an increase in absorbance

Optical Density (OD)

A measure of the amount of turbidity. Frequently called absorbance. an estimate of the number of cells

Optimum growth temperature

The temperature at which an organism grows best

Mesophiles

bacteria that grow best at a mid temperature, 10°C to 48°C (optimim 25-40°C) "middle loving"

ex: E. coli, grown best at 37°C - human body temp

lag phase characteristics

Bacteria adapt to the new environment, metabolically active but not dividing, resulting in little to no change in population size.

log phase characteristics

bacteria divide rapidly via binary fission at a constant, maximal rate, causing a logarithmic increase in population.

stationary phase characteristics

Growth slows and levels off as nutrients are depleted and toxic waste products accumulate; the rate of cell division equals the rate of cell death.

death phase characteristics

The number of dying cells exceeds the number of new cells produced, leading to an exponential decrease in the population

how to you calculate bacteria generation (doubling time)

x = _____t_____

3.3 log F/S

Where F is the final number of cells, S is the starting number of cells, t is the time that has passed

between the F and S measurements and x is the generation (doubling) time.

what did we measure with the spectrometer in lab

the level of turbidity in a sample.

how much does 1 OD600 equal in terms of number of cells per millileter

1 OD600 = 8 x 10^8 cells/ml

organismal growth physical requirements

-Temperature

-pH

-Osmotic pressure

• Gaseous requirements

(e.g. oxygen)

• Pressure (e.g. barometric)

Organismal Growth chemical requirements

-Carbon

- Nitrogen, Sulfur, Phosphorus

-trace elements (iron, copper, molybdenum, zinc)

-organic growth factors (vitamins, amino acids, purines, pyrimidines)

-water

How does a spectrophotometer work?

light of a particular wavelength passes through the sample