Exam 2: Ch 6 Flashcards
What are the physical and chemical growth requirements for microbes?
Physical Growth Requirements:
Water (hydrostatic pressure, osmotic pressure)
PH (acidic pH <7.0, neutral pH = 7.0, basic/alkaline pH= >7.0)
Temperature
Chemical Growth Requirements:
Nutrients
How will microbial growth be affected if each growth requirement increases or decreases?
Temperature
In proteins:
High temp -> denatures proteins; proteins stop working
Low temp -> reduces protein activity
In lipid-containing membranes of cells and organelles:
High temp -> membranes becomes too fluid and cannot contain the cell or organelle
Low temp -> membranes becomes rigid and fragile
How will microbial growth be affected if each growth requirement increases or decreases? Water
Hypertonic
Outside solute concentration is greater than that inside the cell
Cell is shriveled
Water moves outside the cell
Hypotonic
Outside solute concentration is less than that inside the cell
Cell is lysed/ bursts
Water moves into the cell
How will microbial growth be affected if each growth requirement increases or decreases? pH
pH
High Hydrogen ions, high acidity, and low pH -> acidic
Low Hydrogen ions, low acidity, and high pH -> basic/alkaline
What are the classifications of microbes based on their requirement of: temperature
Psychrophiles
Temperature range is -5 to 20 degrees C; optimal growth is 10 degrees C
Mesophiles
Temperature range is 15 to 45 degrees C; optimal growth is 35 degrees C
Thermophiles
Temperature range is 45 to 80 degrees C; optimal growth is 65 degrees C
Hyperthermophiles
Temperature range is from 65 to 105 degrees C; optimal growth is 95 degrees C
Effects of hypotonic vs hypertonic vs isotonic solutions on microbial cells
Hypotonic
When the outside solute concentration is less than that inside, the cell experiences osmotic lysis and the weakened/damaged cell wall bursts as water moves into the cell
Hypertonic
When the outside solute concentration is greater than inside the cell; the cell becomes shriveled
When water moves out of the cell causing its cytoplasm to shrink (plasmolysis)
Isotonic
When the outside solute concentration is the same as the inside of the cell; a normal cell
When there is no net movement of water
Why are nutrients needed?
Nutrients allows for energy needs, helps build organic molecules, and build cellular structures
Osmotic pressure vs. hydrostatic pressure
Osmotic Pressure
The process of water diffusing across a membrane from the region of lower solute concentration to the region of higher solute concentration
The diffusion of water across a selectively permeable cell membrane
Hydrostatic Pressure
Water exerts pressure in proportion to its depth
What does the term “danger zone” mean in food storage? What will likely happen if food is stored in the danger zone, below or above the danger zone?
The “danger zone” in food storage means the temperatures that food is left out in that ranges from 15 to 50 degrees Celsius (60 to 130 degrees Fahrenheit) that allows for the rapid growth of bacteria in which some toxins may be produced. If food is stored below the danger zone in refrigerator temperatures that range from 0 to 15 degrees Celsius, psychrophiles are the only group of bacteria that could be found in spoiled refrigerated food since it requires –5 to 20 degrees Celsius for survival. If food is above the danger zone around 52 to 62 degrees Celsius then it produces a very slow bacterial growth. Once temperatures range from 62 degrees to 130 degrees Celsisus and above, temperatures begin to destroy most microbes, although lower temperatures take more time.
What are the classifications of microbes based on their requirement of:
pH
Acidophiles
Grow in acidic environments that allow for molds and yeast to grow between pH 5 and 6
Neutral
Most bacteria and protozoa grow between pH 6.5 - 7.6
Alkalinophiles/Alkaliphiles
Live in basic environments like soils and water that are pH 9 to 11.5
Why are Carbon, Nitrogen, Sulfur, Phosphorus, trace elements, water, hydrogen, oxygen needed? Be specific for each.
Carbon
Structural organic molecules, energy source
Chemoheterotrophs use organic carbon sources
Autotrophs use CO2
Nitrogen
In amino acids, proteins
Most bacteria decompose proteins
Some bacteria use NH4+ or NO-3
A few bacteria uses N2 in nitrogen fixation
Sulfur
Some amino acids - disulfide bonds
In vitamins - thiamine, biotin
Most bacteria decompose proteins
Some bacteria use SO4 2- or H2S
Phosphorus
In DNA, RNA, ATP, and phospholipid membranes
PO4 3- is a scourge of phosphorus
Trace Elements
Inorganic elements required in small amounts
Usually as enzyme cofactors (metals)
What are the 4 toxic forms of oxygen?
Singlet Oxygen O2
With electrons boosted to a higher-energy state
Occurs during photosynthesis -> carotenoids (bright red, yellow, orange)
Superoxide Free Radicals O2
Formed during incomplete reduction of oxygen in aerobic and anaerobic respiration
So reactive that aerobes produce superoxide dismutases to detoxify them
Anaerobes lack superoxide dismutase -> die in the presence of oxygen
Peroxide Anion O2 2
Formed during reactions catalyzed by superoxide dismutase and other reactions
Aerobes contain either catalase or peroxidase to detoxify peroxide anion
Hydroxyl Radical OH
Results from ionizing radiation and from incomplete reduction of hydrogen peroxide
The most reactive of the four toxic forms of oxygen
Not a threat to aerobes due to action of catalase and peroxidase
Know all classifications of microbes based on carbon and energy sources. Can a phototroph be a chemotroph? Can an autotroph be a heterotroph?
Organisms categorized into two groups based on source of carbon:
Autotrophs
Uses an inorganic carbon source (carbon dioxide)
Heterotrophs
Catabolizing reduced organic carbon molecules (proteins, carbohydrates, amino acids, and fatty acids)
Organisms categorized into two groups based on source of energy:
Chemotrophs
Acquire energy from redox reactions involving inorganic and organic chemicals
Phototrophs
Use light as their energy source
What types of microbes cannot survive in any oxygenated environment? In a highly oxygenated environment? In un-oxygenated environment?
Obligate Anaerobes
Do not use aerobic metabolism; oxygen is toxic to them and cannot survive in any oxygenated environment
Obligate Aerobes
Require oxygen, undergo aerobic respiration
Facultative Anaerobes
Can maintain life with or without oxygen via fermentation or anaerobic respiration or by aerobic respiration
Microaerophiles
Aerobes that require lower levels of oxygen; 2-10%; limited ability to detoxify hydrogen peroxide and superoxide radicals
Aerotolerant Anaerobes
Do not use aerobic metabolism but have some enzymes that detoxify oxygen poisonous forms; can use oxygen when present, and can also survive without oxygen
What does “aseptic” mean? What is an inoculum?
Aseptic
Prevent contamination of sterile substances or objects
Inoculum
Introduction of microbes into medium
