6.1.1-3 Bacteria and disease keywords

pathogen

microorganisms that cause disease.

culture

microorganisms are provided with the nutrients, oxygen levels, pH, and temperature they need to grow large numbers so they can be observed and measured.

sterile

something that is free from living organisms and their spores.

nutrient medium

a substance used for the culture of microorganisms.

nutrient broth

a liquid nutrient for culturing microorganisms, commonly used in flasks, test tubes, or bottles.

nutrient agar

a jelly extracted from seaweed and used as a solid nutrient for culturing microorganisms, commonly used in petri dishes.

selective medium

a growth medium for microorganisms containing a very specific mixture of nutrients, so only a particular type of microorganism will grow in it.

inoculation

the process by which microorganisms are transferred into a culture medium under sterile conditions.

haemocytometer

a thick microscope slide with a rectangular indentation and etched grid of lines that is used to count cells.

turbidimetry

a method of measuring the concentration of a substance by measuring the amount of light passing through it.

turbid

something that is opaque, or thick with suspended matter.

dilution plating

a method used to obtain a culture plate with a countable number of bacterial colonies.

total viable cell count

a measure of the number of cells that are alive in a given volume of a culture.

generation time

the time span between bacterial divisions.

lag phase

when bacteria are adapting to their new environment and are not yet reproducing at their maximum rate.

log phase

when the rate of bacterial reproduction is close to or at its theoretical maximum, repeatedly doubling in a given time period.

stationary phase

when the total growth rate is 0 as the number of new cells being produced by binary fission is equal to the number of cells dying.

what are factors that lead to cells dying?

competition for nutrients, lack of essential nutrients, an accumulation of toxic waste products, and lack of or competition for oxygen.

death phase

when reproduction has almost ceased and the death rate of cells is increasing so that the population number falls.