(3) Chapters 5, 6, 7

Which substance is reduced in the reaction acetaldehyde + NADH → ethanol + NAD⁺?

Acetaldehyde (it gains electrons).

Which compound contains the greatest amount of usable energy?

Glucose.

Which E. coli culture produces the most lactic acid?

E. coli grown without oxygen (anaerobic fermentation).

Which E. coli culture produces the most ATP?

E. coli grown with oxygen (aerobic respiration).

Which E. coli culture uses the most glucose?

E. coli grown without oxygen because fermentation is less efficient.

Which temperature is most likely to kill a mesophile?

60°C.

Which is NOT a characteristic of biofilms?

Iron deficiency.

Which type of media is NOT used to culture aerobes?

Reducing media.

An organism has peroxidase and superoxide dismutase but lacks catalase. What type is it?

Aerotolerant anaerobe.

Which method does NOT kill endospores?

Pasteurization.

Which method is best for sterilizing mattresses and plastic Petri dishes?

Ethylene oxide.

Which method cannot sterilize a heat-sensitive solution in a plastic container?

Autoclaving.

Which chemical is commonly used to control microbial growth in foods?

Organic acids.

Which disinfectant was most effective in the use-dilution test?

Disinfectant A.

Which disinfectants were bactericidal?

A, C, and D.

Which is NOT a characteristic of quaternary ammonium compounds?

Sporicidal.

Which method is most likely to be bactericidal?

Ionizing radiation.

Why does aerobic respiration produce more ATP than fermentation?

It uses the electron transport chain.

Why does anaerobic fermentation require more glucose?

It produces much less ATP per glucose molecule.

Why is oxygen toxic to obligate anaerobes?

They lack enzymes that detoxify reactive oxygen species.

Which enzyme converts hydrogen peroxide into water and oxygen?

Catalase.

Which enzyme converts superoxide radicals into oxygen and hydrogen peroxide?

Superoxide dismutase.

Which enzyme also breaks down hydrogen peroxide but does not release oxygen gas?

Peroxidase.

What is the function of catalase in aerobic organisms?

Protects cells from toxic hydrogen peroxide.

What is the purpose of selective media?

Allows certain microbes to grow while inhibiting others.

What is the purpose of differential media?

Distinguishes microbes based on visible biochemical differences.

What is the purpose of reducing media?

Removes oxygen so anaerobes can grow.

What is the purpose of enrichment media?

Increases the numbers of a desired microorganism.

What is the purpose of complex media?

Provides nutrients with an unknown exact chemical composition.

What is the advantage of direct microscopic counts?

Quickly counts total cells.

What is the disadvantage of direct microscopic counts?

Cannot distinguish living from dead cells.

What is the advantage of plate counts?

Counts only living cells.

What is the disadvantage of plate counts?

Requires incubation time.

What is measured in turbidity tests?

Cloudiness proportional to microbial growth.

What is measured by dry weight?

Total microbial biomass.

Why are plate counts considered direct measurements?

They directly count viable microorganisms.

Why are turbidity and dry weight indirect methods?

They estimate growth instead of directly counting cells.

What phase of the bacterial growth curve has the fastest growth?

Log (exponential) phase.

What happens during the lag phase?

Cells prepare for growth but do not divide rapidly.

What happens during the stationary phase?

Cell division equals cell death.

What happens during the death phase?

More cells die than are produced.

How does UV radiation damage DNA?

By forming thymine dimers.

How does gamma radiation damage cells?

By breaking DNA directly and producing free radicals.

Which type of radiation penetrates deeply into materials?

Gamma (ionizing) radiation.

Which type of radiation has poor penetrating ability?

Ultraviolet (UV) radiation.

What is the goal of sterilization?

Destroy all microorganisms, including endospores.

What is the goal of disinfection?

Reduce or eliminate most pathogens on inanimate objects.

What is the goal of antisepsis?

Reduce microbes on living tissue.

What is the goal of sanitation?

Lower microbial counts to safe public health levels.

Why is steam under pressure effective for sterilization?

It improves heat penetration and protein denaturation.

Why is moist heat more effective than dry heat?

Water transfers heat more efficiently.

How does pasteurization differ from sterilization?

Pasteurization reduces microbes but does not eliminate all microorganisms.

How do salt and sugar inhibit microbial growth?

They create a hypertonic environment that causes plasmolysis.

Why can molds sometimes grow in jams and jellies?

They tolerate high sugar concentrations better than bacteria.

Why was disinfectant B preferred even though it was more diluted?

It remained effective at a much higher dilution.

Why are Pseudomonas species difficult to eliminate with quats?

They are Gram-negative and can survive or even grow in quaternary ammonium compounds.

What feature helps Gram-negative bacteria resist some disinfectants?

Their outer membrane.

Which bacteria are commonly resistant to triclosan?

Pseudomonas and Burkholderia.

What is a competitive inhibitor?

A molecule that competes with the substrate for the active site.

What is a noncompetitive inhibitor?

A molecule that binds elsewhere and changes the enzyme's shape.

How can competitive inhibition often be overcome?

By increasing substrate concentration.

Can increasing substrate concentration overcome noncompetitive inhibition?

No.

What is feedback inhibition?

The end product inhibits an earlier enzyme in the pathway.