GCSU (Bachoon) Microbiology Test 2| exam questions and answers

GCSU (Bachoon) Microbiology Test 2| exam questions and answersGCSU (Bachoon) Microbiology Test 2| exam questions and answersGCSU (Bachoon) Microbiology Test 2| exam questions and answersGCSU (Bachoon) Microbiology Test 2| exam questions and answers Why do we study microbial growth? - correct answer-1) to prove what causes disease 2) for antibiotic susceptibility (how to kill) 3) for research what are the physical aspects of microbial growth? - correct answer-- temperature - pH - osmotic pressure what are the 3 main groups microbes are classified into based on their optimum temperature? - correct answer-1) psychrophiles 2) mesophiles 3) thermophiles psychrophiles - correct answer-- cold loving microbes - don't cause disease - (-10 deg. C to 20 deg. C) what is a psychrotroph? - correct answer-- organism that is capable of growth between 0 deg. C and 30 deg. C mesophiles - correct answer-- moderate temperature loving microbes, most common type - (25 deg. C - 40 deg. C) - these are human pathogens also include most of the common spoilage and disease organisms. - ex: 37 deg. C (the optimum temp. for many pathogenic bacteria) thermophiles - correct answer-- heat loving microbes - (40 deg. C - 70 deg. C) - many can't grow at temps below 45 deg. C - hyperthermophiles = (70 deg. C - 110 deg. C) what temperature do pathogens grow at? - correct answer-- human body temp. (37 degrees celsius) what pH range do most bacteria grow best in? - correct answer-- a narrow pH range - neutral (6.5 - 7.5) - very few grow below pH 4 - foods with low pH (cheese, pickles..) don't spoil easily) What are some examples of bacteria that grow below pH 4? - correct answer-- sulfur oxidizers - H. pylori ____ have more H+ than ______ - correct answer-acids, bases what is the osmotic pressure inside bacterial cells in an isotonic solution? - correct answer-- 0.85% NaCl What type of solution inhibits bacterial growth? - correct answer-- hypertonic solutions (solutes are higher outside the cell) - water leaves the cell what is plasmolysis? - correct answer-- the osmotic loss of water from the cell in a hypertonic environment - shrinkage of the cell plasma membrane - die What causes high osmotic pressure and can be used to preserve food? - correct answer-- salt or sugar - causes plasmolysis ex: salted meat, jams, jelly What percentage of salt and sugar are solutions that restrict growth? - correct answer-solutions that restrict growth are: > 5% salt > 10% sugar - How do salts and sugars preserve foods? - Why are these considered physical rather than chemical methods of microbial control? - correct answer-- they create a hypertonic environment. - As preservatives they don't directly affect cell structures or metabolism; instead they alter the osmotic pressure What microorganisms can actually grow in salts and sugar preservatives? - correct answer-- staphylococcus aureus grow in up to 7% salt and spoils salted foods - some fungi can grow in jelly and jams (MOLDS are more capable of growth in high osmotic pressure than bacteria is) What are the chemical requirements of microbial growth? - correct answer-- carbon - nitrogen - sulfur - phosphorus - trace elements - oxygen carbon - correct answer-- 50% of the dry weight of a bacterial cell nitrogen - correct answer-- for proteins, DNA, RNA, ATP - 14% of the dry weight of bacterial cells sources: decomposing proteins, NH+4, nitrates, nitrogen fixing sulfur - correct answer-- used to synthezie 4 amino acids - for synthesizing sulfur-containing amino acids and vitamins such as thiamine and biotin sources: sulfate ion SO4^2-, hydrogen sulfide H2S phosphorus - correct answer-- essential for synthesis of nucleic acids and the phospholipids of cell membranes - also found in the energy bonds of ATP source: phosphate ion PO4^3- trace elements - correct answer-only needed in small amounts - essential for the functions of certain enzymes, usually as cofactors - assumed to be naturally present in tap water and other components of media Ex: iron, copper, molybdenum, zinc oxygen - correct answer-- molecular form did not exist in the atmosphere for most of earth's history - toxic to many bacteria - phagocytes use singlet O2 to kill bacteria obligate aerobes - correct answer-- require oxygen to live and for growth - at a disadvantage because oxygen is poorly soluble in the water of their environment facultative anaerobes - correct answer-- an organism that can grow with or without molecular oxygen - can use oxygen when it is present but are able to continue growth by using fermentation or anaerobic respirations when O2 is not available Ex: E. Coli, Yeast obligate anaerobes - correct answer-- bacteria that are unable to use molecular oxygen for energy yielding reactions - can not grow in presence of oxygen, killed or damaged - harmed by O2 Ex. clostridium - botox comes from this bacteria what are the 4 toxic forms of oxygen? - correct answer-1) singlet oxygen 2) superoxide free radicals 3) peroxide anion 4) hydroxyl radical 1) singlet oxygen - correct answer-- extremely reactive, normal molecular oxygen that has been boosted into a higher energy state - found in phagocytes