Microbiology Chapter 6

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70 terms · Dr. Marlena Yost's Lecture Exam 2

Identify the effects on a cell in isotonic conditions

Under isotonic conditions, the environment is equal in solute concentration to the cell's internal environment, and because diffusion of water proceeds at the same rate in both directions, there is no net change in cell volume. Isotonic solutions are generally the most stable environments for cells, because they are already in an osmotic steady state with the cell. Parasites living in host tissues are most likely to be living in isotonic habitats.

Identify the effects on a cell in hypotonic conditions

Under hypotonic conditions, the solute concentration of the external environment is lower than that of the cell's internal environment. Pure water provides the most hypotonic environment for cells because it has no solute. The net direction of osmosis is from the hypotonic solution into the cell, and cells without walls swell and can burst.

A slightly hypotonic environment can be quite favorable for bacterial cells. The constant slight tendency for water to flow into the cell keeps the cell membrane fully extended and the cytoplasm full. This is the optimum condition for the many processes occurring in and on the membrane. Slight hypotonicity is tolerated quite well by most bacteria because of their rigid cell walls.

Identify the effects on a cell in hypertonic conditions

Hypertonic conditions are also out of balance with the tonicity of the cell's cytoplasm, but in this case, the environment has a higher solute concentration than the cytoplasm. Because a hypertonic environment will force water to diffuse out of a cell, it is said to have high osmotic pressure, or potential. The growth-limiting effect of hypertonic solutions on microbes is the principle behind using concentrated salt and sugar solutions as preservatives for food, such as in salted hams.

Identify an advantage of asexual reproduction

Fast and you don't have to fight for the remote control

Identify an advantage of sexual reproduction

genetic variability, increased survival of the species over time

Identify a disadvantage of a sexual reproduction


Identify a disadvantage of asexual reproduction

No genetic variety


(genetics) an organism or cell having only one complete set of chromosomes


term used to refer to a cell that contains both sets of homologous chromosomes, (genetics) an organism or cell having two sets of chromosomes or twice the haploid number

Do prokaryotes have haploid or duploid chromosomes and why?

Haploid because they replicate via asexual reproduction.

Name the steps of binary fission.

1. parent cell enlarges, duplicates its chromosome
2. starts to pull its cell envelope together in the center of the cell using a band of protein that is made of substances that resemble actin and tubulin—the protein component of microtubules in eukaryotic cells
3. The cell wall eventually forms a complete central septum
4. This process divides the cell into two daughter cells

Detail how generation time of a pathogenic organism/ population affects the incubation period

Time required for a cell to grow and divide
- E. coli: 15- 20 minutes (optimal)

Name the various phases of bacterial growth

Lag Phase
Exponential Growth Phase
Stationary Phase
Death Phase

Describe what is occurring in the lag phase of bacterial growth

The lag phase is a relatively "flat" period on the graph when the population appears not to be growing or is growing at less than the exponential rate. Growth lags primarily because:
1. the newly inoculated cells require a period of adjustment, enlargement, and synthesis;
2. the cells are not yet multiplying at their maximum rate; and
3. the population of cells is so sparse or dilute that the sampling misses them.
Individual cells are metabolically active as they increase their contents and prepare to divide.

Describe what is occurring in the exponential growth phase of bacterial growth

The cells reach the maximum rate of cell division during the exponential growth (logarithmic or log) phase, a period during which the curve increases geometrically. This phase will continue as long as cells have adequate nutrients and the environment is favorable.

Describe what is occurring in the stationary phase of bacterial growth

At the stationary growth phase, the population enters a period during which the rate of cell birth and cell death are more or less equal. At this time, the division rate is slowing down (making it easier for cell death to catch up with the rate of new cell formation). The decline in the growth rate is caused by depleted nutrients and oxygen plus excretion of organic acids and other biochemical pollutants into the growth medium, due to the increased density of cells.

Describe what is occurring in the death phase of bacterial growth

As the limiting factors intensify, cells begin to die at an exponential rate (literally perishing in their own wastes), and they are unable to multiply. The curve now dips downward as the death phase begins. The speed with which death occurs depends on the relative resistance of the species and how toxic the conditions are, but it is usually slower than the exponential growth phase. It is now clear that many cells in a culture stay alive, but more or less dormant, for long periods of time.

List the 5 physical factors that affect microbial growth.

1. Temperature
2. Gases
3. pH
4. Osmotic pressure
5. Other organisms

Name four categories of bacteria based on their temperature preferences

- Psychrophiles (-15-15c) Really cold!
- Mesophiles (10-50c) We're & our pathogens are mesophiles
- Thermophiles (45-80c) Hot
- Hyperthermophiles - Too hot to handle

Name three categories of bacteria based on their pH preference.

Acidophiles (environments < pH 6)
Neutrophiles (environments about pH 7) Humans
Alkaliphiles (environments >pH 7)

Name three categories of bacteria based on their salt preference

Nonhalophiles (Cannot tolerate the presence of Na)
Halophiles (Can grow in the presence of Na)
Extreme halophiles (Require Na) example: Dead Sea

Differentiate between macronutrients and micronutrients.

Macronutients are essential and required in large amounts
Micronutrients, also essential, only require small amounts


..., A surface-coating colony of one or more species of prokaryotes that engage in metabolic cooperation.


A chemical substance that an organism must obtain in relatively large amounts


the nutrients the body needs in small amounts, such as vitamins and minerals


the process by which molecules move from an area of higher concentration to an area of lower concentration


diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal

active transport

transport of a substance (as a protein or drug) across a cell membrane against the concentration gradient

Generation time

the period between the birth of one generation and the birth of the next generation; time required for cell to grow and divide, population doubles

Incubation period

the period between infection and the appearance of symptoms of the disease

Quorum sensing

The process by which many bacteria coordinate their gene expression according to the local density of their population.


require an atmosphere that is low in oxygen and rich in carbon dioxide


the relation between two different species of organisms that are interdependent


The partners of a symbiotic relationship


solute concentration of the external environment is lower than that of the cell's internal environment. Pure water provides the most hypotonic environment for cells because it has no solute. The net direction of osmosis is from the hypotonic solution into the cell, and cells without walls swell and can burst.


the environment is equal in solute concentration to the cell's internal environment, and because diffusion of water proceeds at the same rate in both directions, there is no net change in cell volume


Having a greater osmotic pressure than a reference solution

Binary Fission

a form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size

Viable Nonculturable (VNC) State

Bacteria that are so dormant that, although they are alive, they won't grow on culture medium and therefore are missed in colony counts.


Organisms that use oxygen to produce ATP, a more efficient method than anaerobic respiration.


Organisms that don't use oxygen to product ATP. Less efficient.

Name five categories of bacteria based on their oxygen preference

• Aerobes
- Obligate aerobe (must have Oxygen)
- Facultative anaerobe (Prefer Oxygen, but can live without)
• Anaerobes
- Aerotolerant (indifferent to oxygen)
- Obligate anaerobes (oxygen is toxic)
- Facultative aerobe (prefers anaerobic respiration, but can tolerate oxygen)
• Carbon dioxide: Capnophilic (must be in the presence of CO2)

Obligate aerobe

Organism that requires a constant supply of oxygen in order to live

Facultative anaerobe

Organism that can survive with or without oxygen


Microorganism which prefers anaerobic conditions but can tolerate exposure to low levels of oxygen

Obligate anaerobes

Organisms that cannot live where molecular oxygen is present;
Lack catalase and/or superoxide dismutase, and thus are susceptible to oxidative damage.

Facultative aerobe

An organism that prefers to live in a non-oxygen environment but can also live in an oxygen environment


An organism requiring high levels of CO2 for growth or for enhancement of growth

What method of energy production do anaerobes use?

Fermentation is used to make ATP


cellular process of making ATP without oxygen and without the electron transport chain.

Name six nutritional categories of microbes by energy and carbon source



organism that obtains it's carbon source (macronutrient) from the foods it consumes from other living things; (Organic Carbon)


an organism that relies on CO2 as it's carbon source (macronutrient) and is capable of synthesizing its own energy from inorganic carbon


an organism that obtains its nourishment through the oxidation of inorganic chemical compounds (or release of energy from the breaking of chemical bonds), as opposed to photosynthesis.


an organism that uses light as its source of energy & CO2 specifically for inorganic carbon. Example: plants, algae, cyanobacteria


An organism that metabolizes organic carbon from dead organisms. Decomposers. Example: Fungi, bacteria


an organism that obtains it's carbon and energy sources by living in or on a live host

Identify and define the three types of symbiosis

Mutualism Obligatory

Mutualism Obligatory

symbiotic relationship in which both species benefit from the relationship


symbiotic relationship in which one member of the association benefits and the other is neither helped nor harmed


symbiotic relationship in which one organism lives in or on another organism (the host) and consequently harms it

Explain how a biofilm is formed

Biofilms are mixed communities of different kinds of bacteria and other microbes that are attached to a surface and to each other, forming a multilayer conglomerate of cells and intracellular material. Usually there is a "pioneer" colonizer, a bacterium that initially attaches to a surface, such as a tooth or the lung tissue (figure 6.8). Other microbes then attach either to those bacteria or to the polymeric sugar and protein substance that inevitably is secreted by microbial colonizers of surfaces. Organisms in a biofilm may start to communicate and behave as a functioning group instead of in the single cell planktonic form. Group communication allows for the division of labor allowing some cells to perform functions while other are doing something completely different. In many cases, once the cells are attached, they are stimulated to release chemicals that accumulate as the cell population grows. By this means, they can monitor the size of their own population. This is a process called quorum sensing. They can also communicate with neighboring and different species generating a large interactive community.

Explain how organisms in a biofilm differentiate them from the planktonic form of the organism.

It is now clearly established that microbes in a biofilm, as opposed to those in a planktonic (free-floating) state, behave and respond very differently to their environments. Different genes are even activated in the two situations. At any rate, a single bio-film is actually a partnership among multiple microbial inhabitants and thus cannot be eradicated by traditional methods targeting individual infections. This kind of synergism has led to the necessity of rethinking treatment of a great many different conditions.


shriveling of the cell due to water leaving the cell when the environment is hypertonic (more salt outside of the cell, thus water follows salt)

Lysis due to osmotic pressure

The bursting of the cell due to hypotonic environment (low solute outside cell and high solute inside cell leads to excessive water passing semipermeable member into cell)

Name three ways different organisms deal with atmospheric oxygen and formed oxygen radicals.

1. Use and detoxify free radical oxygen
2. Can't use or detoxify oxygen
3. Don't use but CAN detoxify oxygen

Explain how organisms successfully use and detoxify oxygen

As oxygen enters cellular reactions, it is transformed into several toxic products
- singlet oxygen (O)
- superoxide ion (O2-)
- hydrogen peroxide (H2O2)
- hydroxyl radicals (OH-)
Step 1. 2O2- + 2H+ is converted by superoxide dismutase into H2O2 (hydrogen peroxide) + O2
Step 2. 2H202 is converted by catalase to 2H20 + O2

Describe singlet oxygen (O)

Singlet oxygen (O) is an extremely reactive molecule. Notably, it is one of the substances produced by phagocytes to kill invading bacteria. The buildup of singlet oxygen and the oxidation of membrane lipids and other molecules can damage and destroy a cell.

Name three destructive metabolic by-products of oxygen

The highly reactive superoxide ion (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH-) are other destructive metabolic by-products of oxygen.

How do cells protects themselves against singlet oxygen (O), superoxide ion (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH-)?

To protect themselves against damage, most cells have developed enzymes that go about the business of scavenging and neutralizing these chemicals. The complete conversion of superoxide ion into harmless oxygen requires a two-step process and at least two enzymes superoxide dismutase and catalase are used in a two step process. In this series of reactions (essential for aerobic organisms), the superoxide ion is first converted to hydrogen peroxide and normal oxygen by the action of an enzyme called superoxide dismutase. Because hydrogen peroxide is also toxic to cells (after all, it is used as a disinfectant and antiseptic), it must be degraded by the enzyme catalase into water and oxygen. If a microbe is not capable of dealing with toxic oxygen by these or similar mechanisms, it is forced to live in habitats free of oxygen.

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