Microbial Growth and Antibiotics Flashcards
(34 cards)
what are the four types of bacterial shapes and what do they look like
-cocci(singular coccus) spherical
-bacilli(singular bacillus) rod shaped
-spirilla (singular spirillum) spiral shaped
-vibrio curved shaped
capsule function
-made up of mainly polysaccharide and polypeptides
-protects against phagocytosis and antibiotics
-prevents dehydration and dessication
cell wall function
-rigid structure that maintains the shape of a bacteria cell
-made up of murein
-gram staining allows bacteria to be classified
-gram positive stains purple and contains 40% of stain 95% murein
-gram negative stains red and contains no stain little as 5% murein
cell membrane function
-consists of a phospholipid bilayer and protein
-selectively permeable
-controls what goes in and out of the cell
mesosome function
-the inner foldings of the cell surface membrane
-has enzymes involved in the respiration/photosynthesis
-also helps to separate the DNA in cell division
circular DNA function
-bacteria has no defined nucleus and no nuclear membrane.
-DNA is circular and is not associated with histones
plasmids function
-small circular pieces of DNA
-contain few genes that provide beneficial effects like resistance to antibiotics
70s ribosome function
-involved in translation
what conditions affect microbial growth
-temperature
-pH
-oxygen
-nutrients
explain the limiting factors in microbial growth
-all the respiratory substarte (glucose, amino acids) get used up
-other nutrient ions such as sulfur, phosphate and iron may also run out
-for obligate aerobes the oxygen may run out
-co2 could build up causing pH to decrease
-toxins build up halting growth
What can cause contamination in aseptic techniques
-non sterile apparatus
-the air
-an individual (skin surface/breath)
-work surfaces
Aseptic techniques to prevent contamination
-use of sterile syringes/pipettes/equipment
-flame top off test tubes/bottles/inculcating loops
-minimum exposure to air (lift lid off Petri dish slightly)
-avoid contact of sterile apparatus with work surfaces/skin
give three environmental factors which could influence the growth of microorganisms. Explain
the effect of each
-temperature: low temp slow down microbial growth and high temp will denature the enzyme
-pH: pH too low or too high will denature enzymes
-oxygen: required for aerobic respiration to provide energy for growth
-named nutrient e.g(nitrate): required for DNA/nucleotide/ protein synthesis
Explain the difference between the total cell count and the viable cell count.
total cell count is all cells dead and living, but viable cells count is only cells that are living
Describe how the numbers used to construct the curve for the viable cell could
have been obtained.
-sample at regular known intervals
-produce a serial dilution
-known amount bacteria on agar plate
-incubate for period of time
-count colonies
-make repeats of plates for accuracy
Describe how the river water should be diluted to 1 in 1000.
To dilute river water to 1 in 1000, take 1 cm³ of river water and add it to 999 cm³ of distilled water. Mix thoroughly to ensure an even dilution.
when petri dishes have been incubated, what are the little dots on the dish
they are colonies/ offspring from a single bacterium
0.1 cm3 of each of a range of dilutions was plated on to nutrient agar in Petri dishes and then incubated for two days at 20 °C. The results for the 1 in 100 000 dilution are shown in the diagram.Calculate the number of bacteria per cm3 in this river water. (theres 14 dots on petri dish)
14 x 100,000= 1,400,000
0.1cm3 –> 1cm3 is x10
1,400,000 x 10= 14,000,000 or 1.4x10^7
When the number of bacteria in the river water was calculated from the
1 in 1000 000 dilution, a lower number per cm3 was obtained. Suggest why.
extra dillution introduces additional error/not mixed thoroughly
when a haemocytometer was used to determine the number of bacteria, a larger number was obtained for every dilution. Explain why.
could contain dead cells
The culture was stirred throughout the investigation. Explain why.
-to prevent clumping of cells
The population of bacteria in culture 1 spent more time in the lag phase before
moving into the exponential phase. Suggest why. (test 1 has acetate and ammonium salts and took 300 minutes to double)
-switch on genes
-synthesise enzymes to break down acetate
-acetate may contain less energy for growth/acetate metabolism
-so less carrier proteins
Explain the difference in rate of population growth between cultures 2 and 3
culture 3 grows faster as no amino acid synthesis needed
Explain why turbidity can be used to measure the growth of a culture of
microorganisms
absorbed light is proportional to the number of cells
