Microbiology with Diseases by Taxonomy Chapter 6 Answers

Microbiology with Diseases by Taxonomy Chapter 6 Answers

Microbiology with Diseases by Taxonomy Answers

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1CM
The concept map that describes culture media is shown below:

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1CT
The characteristics of an organism are given by a scientist as:

• Chemoheterotrophic:
  A chemoheterotroph is an organism, which uses organic compounds as its source of carbon and source of energy.
• Aerotolerant:
  Aerotolerant organisms are those organisms, which prefer an atmosphere without oxygen. Since they are aerotolerant, these organisms can tolerate low levels of oxygen.
• Mesophilic:
  A mesophilic organism is one which can grow best in a temperature range of 20⁰C to 40⁰C.
• Facultatively halophilic bacillus:
  A facultatively halophilic organism is one which can tolerate high concentrations of salt. The cell membranes of such organisms are resistant to salt. It can also survive in normal conditions.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1FB
Sources of carbon in different organisms are given below:

1. In photoautotrophs – carbon dioxide.
2. In chemoautotrophs – carbon dioxide.
3. In photoheterotrophs – organic compounds.
4. In chemoheterotrophs – organic compounds.

Sources of energy in different organisms are given below:

1. In photoautotrophs – light.
2. In chemoautotrophs – organic molecules.
3. In photoheterotrophs – light.
4. In chemoheterotrophs – organic compounds.

Sources of electrons in different organisms are given below:

1. In organotrophs – organic molecules.
2. In lithotrophs – inorganic sources.
3. In photoheterotrophs – organic molecules.
4. In photoautotrophs – organic molecules.
5. In chemoautotrophs – organic molecules.

Thus, sources of carbon, energy, and electrons are needed by all cells.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1L
The labeled thioglycollate tubes are shown below:

1. Obligate aerobes are those organisms, which cannot live in the absence of oxygen.
2. Obligate anaerobes are those organisms that cannot live in oxygen, since oxygen is toxic to such organisms. These organisms in the electron transport chain cannot use oxygen as terminal electron acceptor.
3. Facultative anaerobes are those organisms, which can live in absence and presence of oxygen. These organisms can switch between aerobic respiration and fermentation.
4. Aero tolerant anaerobes are those organisms, which can tolerate low levels of oxygen. These organisms prefer anaerobic conditions to aerobic conditions.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1MC
(a) An anaerobe:
An anaerobe cannot grow on a Petri plate. An anaerobe can grow only under specially maintained conditions. Oxygen should not be present for the growth of an anaerobe. In a Petri plate, aerobes usually grow. Viruses cannot grow on agar in a Petri plate. Hence, the option (a) is incorrect.
(b) Viruses on an agar surface:
Viruses cannot grow on agar surfaces in Petri plates. Viruses can grow only on specialized growth medium. They can also be grown in tissues like the egg. Viruses can grow on monolayers of bacterial cells. A colony of agar surface can grow in a Petri plate, in a lab. Hence, the option (c) is incorrect
(c) Barophiles:
Barophiles cannot grow on agar in a Petri plate. Barophiles are organisms, which live in areas of high pressures. Such pressures cannot be maintained in a laboratory; hence, cannot grow in a Petri plate. Organisms like viruses cannot grow on agar in the lab. Hence, the option (d) is incorrect
(d) A colony on an agar surface:
A colony on an agar surface can grow in a Petri plate in a lab. A colony usually means a bacterial or fungal colony. Only aerobes can grow in Petri plates. The growth of anaerobes can be seen only in special jars like the Gas Pak jar. Barophiles cannot grow on culture. Thus, a colony on an agar surface can grow on a Petri plate in the laboratory.
Hence, the correct option is (b) a colony on an agar surface.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 1SA
High temperature affects the life of a microbe:
Explanation
Condition of high temperature conditions affects the shape of molecules in a cell. When a cell is subjected to high temperatures many changes occur, unless it is a thermophile. In normal cells, the high temperature denatures the enzymes present in the cell. Moreover, the enzymes are deactivated and denatured. Denaturation is the process in which the shape of the enzyme is changed. The native conformation of an enzyme is important in the function of the enzyme.
Additionally, if conformation of the enzyme is destroyed, the function of the enzyme is lost. Due to the changes in the enzyme, the reactions taking part in the cell do not occur. In contrast, as a result of exposure to high temperatures, metabolism stops. Unless, the conditions are altered quickly, the cell will die.
Thus, the life of a microbe can change drastically if enzymes are denatured. Since, reactions are dependent on enzymes metabolism of a cell is also dependent on enzymes. When metabolism stops, the cell cannot continue its life processes.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 2CT
Heat of pasteurization kills microorganism:
Explanation
The process of pasteurization uses a temperature of 72⁰C to remove the pathogens in food. At a high temperature of 72⁰C, the enzymes of most of the pathogens become deactivated. When enzymes are deactivated or denatured, the metabolism of the cell grinds to a halt.
Additionally, organisms are usually divided into psychrophiles, mesophiles, and thermophiles.

1. Psychrophiles are the organisms, which prefer low temperatures close to freezing.
2. Mesophiles are those organisms, which prefer a medium range of 20⁰C to 40⁰C.
3. Thermophiles are those organisms, which can withstand high temperatures.

Since, the temperature used in pasteurization is, only thermophiles can withstand this process. The other organisms present are killed due to effect on enzymes and cellular metabolism.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 2FB
Singlet oxygen:
Explanation
Singlet oxygen acts as a reactive oxidizing agent and is very toxic. The singlet oxygen species are produced by the reaction of oxygen and light. Singlet oxygen species are removed by carotenoids in phototrophic microorganisms.
In humans, phagocytic cells use the singlet oxygen species to destroy pathogens that enter the body. After its use by phagocytic cells, the singlet oxygen species is removed from the cell. Humans have enzymes to remove toxic oxygen species from the body.
Singlet oxygen species is used in photodynamic therapy. In this therapy, the reactive oxygen species are used to kill cancer cells.
Singlet oxygen is a toxic form of oxygen. It is molecular oxygen in a higher energy state.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 2MC
(a) Obligate aerobe:
The term of obligate anaerobe describes an organism that cannot exist in the presence of oxygen. Obligate aerobes are those organisms, which cannot live in the absence of oxygen. They need oxygen compulsorily. An organism that cannot exist in the presence of oxygen would be an obligate anaerobe. Hence, option (a) is incorrect.
(b) Facultative aerobe:
Facultative aerobes are the organisms, which can live in the absence and presence of oxygen. These organisms can change between aerobic respiration and fermentation. An organism that cannot exist in the presence of oxygen would be an obligate anaerobe. Hence, option (b) is incorrect.
(c) Facultative anaerobe:
Facultative anaerobes are the organisms that can live either in absence or presence of oxygen. These organisms can switch between aerobic respiration and fermentation. An organism that cannot exist in the presence of oxygen would be an obligate anaerobe. Hence, option (d) is incorrect.
(d) Obligate anaerobe:
Obligate anaerobes are those organisms that cannot live in the presence of oxygen. Oxygen is toxic to such organisms. These organisms cannot use oxygen as the terminal electron acceptor in the electron transport chain.
Hence, the correct option is (c) obligate anaerobe.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 2SA
Microbes cannot tolerate low pH in human stomach:
Explanation
The above statement is supported by many scientists conducted in the research. The stomach is an organ, which has a low pH of 1.5. The low pH is maintained by the presence of HCl. Most of the microbes, which enter the digestive tract, are killed at low pH.
However, the acidic conditions of the stomach disrupt the cell membrane of the microbes. The cell membranes of most microbes are sensitive to the conditions present in the human stomach.
Additionally, few organisms are resistant to the acidic conditions of the stomach. One of them is the bacterium Helicobacter pylori. The organism causes the formation of peptic ulcers in the stomach wall. The ulcers are formed by combined action of stomach acid and bacterial action.
Thus, the statement “Microbes cannot tolerate low pH in the human stomach” is true.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 3CT
Differences between the dry weights of facultative anaerobe structures:
Explanation
When two cultures of a facultative anaerobe are grown under different conditions, they show differences in dry weights. When one culture is grown in the presence of oxygen and the other is grown in the absence of oxygen, difference in growth is observed.
In contrast, the organism is a facultative anaerobe that can grow in the presence or absence of oxygen. Moreover, it grows better in the presence of oxygen, since aerobic respiration gives higher energy yield when compared to anaerobic respiration.
Similarly, the culture in the presence of oxygen grows faster and has a high rate of metabolism. The culture in the absence of oxygen also grows, but does not have similar growth, rate as the other culture.
Thus, when the cultures are dried and weights are taken, the culture grown in the presence of oxygen show higher dry weight than the other culture.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 3FB
All amino acids possess the element of nitrogen. The basic structure of an amino acid is:

The nucleotides present in the nucleic acids contain the essential element of nitrogen. The basic structure of a nucleotide is given below:

The structures of the five nucleotides are:

Thus, the essential element of nitrogen is recycled from amino acids and nucleotides in all cells.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 3MC
(a) Causes hydrogen peroxide to become toxic:
The enzyme superoxide dismutase does not cause hydrogen peroxide to become toxic. Instead the enzyme detoxifies the toxic substance. The presence of hydrogen peroxide causes damage to cells. The enzyme detoxifies these radicals, so that the cells are not damaged. Hence, the option (a) is incorrect.
(b) The enzyme cannot neutralize singlet oxygen species in the cell. Singlet oxygen species are removed by carotenoids in phototrophic microorganisms. The enzyme superoxide dismutase detoxifies the toxic superoxide radicals generated by the processes of the cell. Hence, the option (c) is incorrect.
(c) The enzyme superoxide dismutase must be produced in aerobic organisms. The superoxide radicals are formed during electron transport and need to be removed from the cell. When these radicals are formed, they cause death of the cell. Anaerobic organisms do not have this enzyme; hence, cannot live in the presence of oxygen. Hence, the option (d) is incorrect.
(d) Superoxide dismutase detoxifies superoxide radicals. The enzyme detoxifies toxic superoxide radicals generated by the processes of the cell. The presence of hydrogen peroxide causes damage to cells. The enzyme detoxifies the radicals, so that the cells are not damaged.
Hence, the correct option is (b) detoxifies superoxide radicals.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 3SA
Relation of Quorum sensing in biofilm formation:
Explanation
The ability to respond changes in a density of population is called quorum sensing. In this process, bacteria respond to changes by using signal and receptor molecules. The process is often seen in biofilms where many species are present together.
Quorum sensing is important in the formation of biofilms. Biofilms are complex relationships among different organisms. The biofilms are found attached to surfaces like the surface of teeth. Additionally, biofilms develop an extracellular matrix, which is composed of DNA, proteins, and polysaccharides of cells. The extracellular matrix is responsible for attachment of cells to one another. It is also responsible in sticking of biofilm to its substrate.
Furthermore, the cells in the biofilm secrete molecules, which act as signals. Other cells have receptors for these signals. When the number of microbes increase, the concentration of the signal molecules also increase. The binding of the signals to receptors reach a certain threshold in the genes where expression gets suppressed.
Thus, the genes that are suppressed are then expressed and allow the biofilm to have new characteristics. Moreover, gives organisms the ability to form biofilms.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 4CT
Requirement of riboflavin to synthesize FAD:
Explanation
The nutritional requirement of some organisms includes vitamin riboflavin. This vitamin is used to synthesize the co-factor FAD. The cofactor FAD is used for many purposes in the cell. Moreover, FAD (oxidized flavin adenine dinucleotide) can change to FADH₂ (reduced flavin adenine dinucleotide) by accepting two protons.
The conversion is shown in the below structure:

In eukaryotes, the main role of FAD is an electron carrier in the electron transport chain. The number of ATP (adenosine triphosphate) molecules obtained from the oxidation of each molecule of FADH₂ is 2.
Thus, in the process of ??oxidation, FAD behaves as a coenzyme to the enzyme acyl coA dehydrogenase.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 4FB
Most of the organisms cannot synthesize some substances that are necessary for metabolism. The organic chemical substances are known as growth factors. For instance, some of the growth factors are listed below:

1. Vitamins.
2. Heme.
3. NADH.
4. Specific amino acids.

Vitamins may not be a growth factor for all organisms. In humans, many vitamins are growth factors. But in organisms like E. coli, can synthesize its own vitamins, they are not growth factors. Other nutrients, which are synthesized in humans, may be growth factors for E. coli. The growth factors can be used as coenzymes or as a part of molecules like cytochromes.
Thus, small organic molecules, which are required in low amounts for metabolism, are growth factors.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 4MC
(a) The peroxide anion:
Peroxide anions are present in hydrogen peroxide. The anion makes hydrogen peroxide an antimicrobial agent. The peroxide anion is detoxified by the enzymes catalase and peroxidase. The enzyme catalase converts the toxic hydrogen peroxide to water and oxygen. The most reactive of the four toxic forms of oxygen is the hydroxyl radical. Hence, the option (b) is incorrect.
(b) The superoxide radical:
The superoxide radicals are formed during electron transport and need to be removed from the cell. When these radicals are formed, they cause the death of the cell. Hydroxyl radical is the most reactive of the four toxic forms of oxygen. Hence, the option (c) is incorrect.
(c) Singlet oxygen:
The oxygen species are produced by reaction of oxygen and light. Singlet oxygen species are removed by carotenoids in phototrophic microorganisms. Singlet oxygen species is molecular oxygen with a higher energy state. The most reactive of the four toxic forms of oxygen is the hydroxyl radical. Hence, the option (d) is incorrect.
(d) The hydroxyl radical:
The radicals result from incomplete reduction of hydrogen peroxide. They can also result from ionizing radiation. These radicals are the most reactive of the four toxic forms of oxygen. In anaerobes, the radicals cause damage. In aerobes, no danger exists due to these radicals due to the presence of enzymes like catalase and peroxidase. Thus, hydroxyl radical is the most reactive form of oxygen.
Hence, the correct option is (a) the hydroxyl radical.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 4SA
Sterilization of instruments and vessels is important in microbiological procedures:
Explanation
The media, vessels, and instruments used in microbiology must be sterilized before use. The process of sterilization is very important in the field of microbiology. Sterilization is the process where all microbes are killed and destroyed.
The media used, for the growth of microbes must be sterilized. Media is usually sterilized in an autoclave. The temperature is 121⁰C for 15 minutes. The broth and agar must be sterilized before use to prevent the growth of any contaminants.
The vessels used are mainly glassware. These are washed, wrapped, and then placed in a hot air oven for sterilization. The temperature is 350⁰C for 2-3 hours.
The instruments used are the laminar air flow chamber and inoculation loops. The laminar air flow chamber is sterilized using UV light. The instruments to be used are placed inside the chamber. Inoculation loops and glass spreaders are kept inside the chamber and are sterilized.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 5CT
Oxygen requirement to bacteria:
Explanation
A bacterium is inoculated into a slant tube containing a complex medium. After incubation, only few colonies are seen on the surface of the agar. But many colonies are seen in the depth of the agar. Moreover, the slant of the agar shows few colonies, while butt shows prolific growth. The oxygen requirements of the bacterium can be determined by observing the growth in the tube.
Since, few colonies are seen on the surface of the agar and many colonies in the depth of the agar, it indicates that the bacterium is an aerotolerant anaerobe. Aerotolerant anaerobes are those organisms, which prefer an anaerobic environment. They grow best under anaerobic conditions, but can tolerate oxygen.
Thus, the prolific number of colonies inside the agar shows that the bacterium is an anaerobe. The scant colonies seen on the surface of the agar prove that the bacterium is an aerotolerant anaerobe.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 5FB
Each organism has a growth range to function properly. Within the growth range, three types of temperatures are facilitated, which are given below:

1. Optimum temperature.
2. Minimum growth temperature.
3. Maximum growth temperature.

The optimum temperature is the temperature at which the organism has the highest growth rate. All its systems are function properly and metabolism is at its highest range.
The lowest temperature where a microbe can metabolize is minimum growth temperature. Once the temperature goes lesser, minimum growth temperature prevails and cell membranes become less fluid. Moreover, transport processes are very slow to support metabolism.
The maximum growth temperature is the highest temperature at which a microbe can metabolize. Once the temperature goes higher the growth temperature is higher and the enzymes are denatured for vital processes.
The lowest temperature, microbe can metabolize at minimum growth temperature. Beyond the minimum growth temperature, metabolism does not occur, due to inactivation of necessary molecules.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 5MC
(a) Aerotolerant:
Aerotolerant microbes are the organism, which prefer an anaerobic atmosphere, but can tolerate low levels of oxygen. Microaerophiles that grow best with a low level of oxygen and a high concentration of carbon dioxide are called capnophiles. Hence, the option (a) is incorrect.
(b) Facultative anaerobes:
Facultative aerobes are the organisms, which can live in the absence and presence of oxygen. The organisms cannot exist in high concentrations of carbon dioxide and less concentration of oxygen. Capnophiles are organisms, which can exist in low levels of oxygen and high concentrations of carbon dioxide. Hence, the option (c) is incorrect.
(c) Fastidious:
A fastidious organism has complex requirements for its growth. It can grow only when specific nutrients are added. The organisms cannot grow at low concentrations of oxygen and high concentrations of carbon dioxide. Capnophiles are organisms which can exist at low levels of oxygen and high concentrations of carbon dioxide. Hence, the option (c) is incorrect.
(e) Capnophiles:
Microaerophiles that grow best with a low level of oxygen and a high concentration of carbon dioxide are called capnophiles. Capnophiles are organisms, which can exist in low oxygen levels and high concentrations of carbon dioxide. The organisms are microaerophiles with slightly different requirements.
Hence, the correct option is (b) capnophiles.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 5SA
Agar is used in microbiology as a solidifying agent. Media without the addition of agar is known as broth, which is liquid in consistency. When agar is added, the medium becomes solid.
Agar is a polysaccharide, which is complex in nature and derived from the cell walls of certain red algae.
Agar is very useful in the field of microbiology because of the following reasons:

• Agar cannot be digested by most microbes. Hence, even with the growth of microbes and fungi, the media stays solid.
• Agar comes in powder form, which can dissolve in water at. At this temperature, most of the added nutrients remain unchanged and undamaged.
• The solidification of agar is seen at temperatures below. This temperature allows us to add nutrients like blood without any problem.
• The agar at such temperatures can also be poured over bacterial culture without any problem. This is seen in the pour plate technique.
• Once agar becomes solidified, it does not melt unless heated to temperatures above. This characteristic of agar can be used while growing thermophiles.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 6CT
Nutritional and oxygen characteristics of bacteria in everyday language:
Explanation
An article gives the following characteristics of a bacterium:

• Obligate microaerophilic.
• Chemoorganoheterotroph.

An obligate microaerophilic is an organism, which need to have a concentration of 2%-10% of oxygen in the air. Higher concentrations of oxygen cannot be tolerated by the bacterium. Since, it is an obligate it indicates the absence of the oxygen concentration, the bacterium cannot survive.
Additionally, chemoorganoheterotroph is an organism, which uses organic compounds as its source of carbon. It obtains its energy from redox reactions in organic compounds. Redox reactions are reduction and oxidation reactions.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 6FB
Osmotic pressure is responsible for shrinking of cells seen in hypertonic solutions like saltwater.
Solutions can usually be described in three ways:

• Hypertonic
• Isotonic
• Hypotonic

Hypertonic solutions have higher concentration of solutes compared to the cell. The water from the cell moves out into the surrounding solution and the cell shrivels.
Isotonic solutions have the same concentration of solutes as the cell. In this situation, the cell does not undergo any change.
Hypotonic solutions have lower concentration of solutes compared to the cell. The water from the solution moves into the cell and it bursts.
Saltwater is a hypertonic solution which results in the shrinking of cells seen. Thus, cells that shrink in hypertonic solutions such as saltwater are responding to osmotic pressure.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 6MC
(a) Cholesterol:
Some organisms might need cholesterol as a growth factor. Since, cholesterol is one of the molecules present in the cell membrane, some organisms require as a nutrient. Presence of cholesterol in the cell membrane prevents quick crystallization of the lipids in the membrane. Cholesterol helps to keep the fluidity of the membrane. Hence, the option (a) is incorrect.
(b) Vitamins:
Vitamins are one of the growth factors needed for many microorganisms. Vitamins are needed for many purposes in the cell. Since, many organisms cannot synthesize all the required, vitamins need them as a growth nutrient. Vitamins act as coenzymes in metabolism and are required in the cell. Hence, the option (c) is incorrect.
(c) Heme:
Heme is an important constituent required in a cell. The cytochromes, which take part in the electron transport chain, consist of heme. Without cytochromes, the process of aerobic respiration cannot occur. In photosynthetic organisms, photophosphorylation cannot take place in the absence of cytochromes. Hence, the option (d) is incorrect.
(d) Water:
Water is a constituent which is not required as a growth factor. Since, water can be obtained easily, it is not considered as a growth factor. Even if the cell does not take in water, the metabolic water obtained is usually enough for the needs of the cell. Hence, water need not be added as a nutrient for growth. Thus, water is not a required growth factor for various microbes.
Hence, the correct option is (b) water.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 6SA
The difference between complex media and defined media is that the exact composition of a complex medium is unknown while that of a defined medium is known.
In a defined medium, the exact chemical composition of the medium is known. Every ingredient is known and the exact amount of each ingredient is known. Some media can support the growth of many organisms. But some media are specific for the growth of some microbes only.
In a complex medium, partially digested yeast, beef extract, and casein are added. The exact composition of the medium is not known since the process of partial digestion releases different chemicals in different concentrations.
A complex medium can support the growth of many microbes. They can be used to culture microbes whose nutritional requirements are not fully known.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 7CT
The elements of phosphorous, sulfur, iron, and magnesium are required by microorganisms. These elements are used in the following way:
Phosphorous:
The phosphate ion is present in the phosphodiester linkages of DNA. The addition of a phosphate ion can activate or deactivate a molecule in the process of signal transduction.
Sulfur:
Sulfur containing compounds act as electron donors and electron acceptors. Sulfur is also present in many enzymes. Two amino acids possess the element of sulfur. Sulfur is a vital part of disulfide bonds.
Iron:
The molecules of hemoglobin and myoglobin contain the element of iron. The active sites of many enzymes also contain the element of iron. The element is also a part of cytochromes, which are vital for the process of electron transport chain.
Magnesium:
Many enzymes need magnesium ions to function properly. It plays a vital role in the manipulation of compounds like ATP, DNA, and RNA. This ion has an important interaction with the phosphate present in nucleic acids.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 7FB
Obligate halophiles:
Explanation
Normal cells cannot exist in either hypotonic or hypertonic solutions. They can exist only in isotonic solutions.
The halophiles are the organisms, which have the ability to resist high osmotic pressures. They do not behave like other cells when placed in hypertonic solutions. The halophiles burst when placed in hypotonic solutions. Obligate halophiles are those organisms, which are adapted to such high osmotic conditions.
There are also organisms called facultative halophiles, which can tolerate high concentrations of salt. They do not require them, but can exist in them. These organisms can tolerate slightly lesser salt concentrations than obligate halophiles. Unlike other organisms, which shrivel in hypertonic solutions adjust to osmotic conditions.
Those organisms, which can exist in salty conditions, due to their ability to withstand high osmotic pressures are called as obligate halophiles.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 7MC
(a) Barophiles:
Barophiles are organisms, which live in areas of high pressures. The organisms are generally found at the bottom of oceans. These organisms cannot thrive in icy waters. Organisms, which are called psychrophiles, live in icy waters preferentially. Hence, the option (a) is incorrect.
(b) Thermophiles:
Thermophiles are those organisms, which can withstand high temperatures. The organisms are seen in places like hot springs and deep sea vents. The organisms cannot thrive in icy waters. Organisms, which are called psychrophiles, live in icy waters preferentially. Hence, the option (b) is incorrect.
(c) Mesophiles:
The organisms live at moderate temperatures. They cannot live in too cold or too hot temperatures. These organisms cannot thrive in icy waters. Organisms, which are called psychrophiles, live in icy waters preferentially. Hence, the option (c) is incorrect.
(d) Psychrophiles:
The organisms can live in icy cold waters. The organisms can be found in glaciers and ice caps. Moreover, the organisms have cell membranes, which can resistant to the extreme cold conditions. The DNA of the microbes can resist low temperatures. Thus, psychrophiles are the organisms, which can happily thrive in icy waters.
Hence, the correct option is (d) psychrophiles.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 7SA
The four distinct phases seen in a bacterial growth curve are shown in the graph below:

In the lag phase, the cells adjust to the new surroundings where they are inoculated. The cells synthesize enzymes needed for the latter phases. The length of the lag phase differs from species to species. It also depends on the nutrients present in the medium.
In the log phase, the number of cells increases rapidly and logarithmically. The synthesis of DNA (deoxyribonucleic acid) and proteins occur rapidly as new cells are formed. The metabolic rate is at a maximum during this phase.
In the stationary phase, the rate of reproduction decreases gradually. Slowly the number of cells synthesized equals the number of cells dying. The death of cells seen is due to accumulation of by-products. This phase is called stationary phase because the exponential growth slowly stops.
In the death phase, the nutrients are depleted and wastes accumulated. This results in death of the cells at a faster rate that the synthesis of cells. Sometimes all the cells in the culture die, while in some cultures a few cells remain alive. This phase is called death phase because most of the cells die.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 8FB
Carotenoids pigments:
Explanation
Singlet oxygen is molecular oxygen in toxic form with higher energy state. This species is very toxic. Singlet oxygen acts as a reactive oxidizing agent. Additionally, the singlet oxygen species are produced by the reaction of oxygen and light. They are produced during the process of photosynthesis in chlorophyll molecules.
In phototrophic organisms, carotenoid pigments remove toxic form of oxygen. The excess energy of this species is removed by carotenoids. Another method is quenching of the species.
The photochemically produced singlet oxygen in phototrophic organisms is removed from cells by the pigment called carotenoid.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 8MC
(a) Live at normal barometric pressure:
Barophiles do not live at normal barometric pressures. Barophiles are organisms, which live in areas of high pressures. The organisms are generally found at the bottom of oceans where the pressure is quite high. Hence, the option (b) is correct.
(b) Die if put under high pressure:
Barophiles do not die under high pressures. Barophiles live in areas of high pressures. The organisms have the capability to grow at high pressure in the bottom of oceans. Hence, the option (c) is correct.
(c) Thrive in warm air:
Barophiles cannot live in warm air. Their cells are tailored to withstand high pressure conditions. Barophiles are organisms, which live in areas of high pressures like deep sea vents and bottom of oceans. Hence, the option (d) is correct.
(d) Barophiles cannot infect and cause disease in humans. Barophiles are organisms, which live in areas of high pressures. These organisms are generally found at the bottom of oceans. Since, the pressure in human cells is not very high, these organisms cannot infect humans. Thus, barophiles cannot cause disease in humans. Hence, the option (a) is correct.
Hence, the correct option is (a) cannot cause disease in humans.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 8SA
The number of cells in 1 ?l of sewage is 47.
The number of cells estimated to be in 1 liter of sewage can be calculated as follows:
1 liter = 1000000 ?l
When 1 ?l contains 47 cells, 1 liter of sewage will contain:
= 47×1000000
= 47,000,000 cells
The number of cells in one liter of sewage would be 47,000,000 cells.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 9FB
Nitrogen fixation:
Explanation
Many cyanobacteria and Rhizobium species are vital in the process of nitrogen fixation. The atmospheric nitrogen is converted into ammonia. Nitrogen fixation can occur naturally and with the help of microbes. Naturally nitrogen fixation occurs by means of lightning.
Similarly, nitrogen fixation is usually carried out by Rhizobium species. An enzyme called nitrogenase is present in the bacteria. This enzyme works best under anaerobic conditions. The roots of plants like legumes contain nodules to harbor the bacteria.
The nodules provide bacteria an anaerobic environment to work and reduce nitrogen in exchange for protection. The anaerobic environment is obtained using the pigment leghemoglobin.
Nitrogen fixation is the process by which N₂(nitrogen) is converted to NH₃(ammonia) by microbes.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 9MC
(a) Broth culture:
A broth culture is one in which the medium is liquid in consistency. A loopful of culture is then mixed in the broth. The medium before inoculation is usually transparent. After incubating the broth for 24-48 hours, the broth becomes turbid, due to the growth of the microbes. Hence, the option (a) is incorrect.
(b) Pour plate:
A pour plate method is a technique in which the microbial culture is mixed in liquid agar. The agar is then poured into Petri plates and left to cool. In this method some sub-surface colonies are formed. Some colonies are formed inside the agar. This is not a technique for isolated colonies. Hence, the option (b) is incorrect.
(d) Dilution plate:
The technique of dilution plate is to use the process of serial dilution. The broth with culture is diluted serially and each dilution is then streaked on the agar plate. The difference in the number of colonies on the plates helps us to know the original number of microbes. Hence, the option (d) is incorrect.
(e) Streak plate:
The streak plate method is a laboratory technique in which a sterile inoculating loop of culture is moved across an agar plate to obtain isolated colonies. Moreover, in the technique a sterilized inoculating loop is used to spread a loopful of culture across the surface of an agar plate. The repeated moving of the loop across the plate in different directions allows the isolation of single colonies.
Hence, the correct option is (c) streak plate.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 9SA
The three indirect methods of counting microbes are:
Measurement of metabolic activity:
The rate of utilization of nutrients and the rate of production of waste is dependent on the number of cells in the culture. By taking these two factors into account, the rate of metabolism can be determined. When the rate of metabolism is known, the number of cells in the culture can be known.
Dry weight:
Some organisms, which have filaments, cannot be easily counted. In the case of such organisms, filtration is followed by drying of the cells. The dry cells are then weighed.
Turbidity:
Turbidity can be measured only in liquid culture. Turbidity can be measured using a spectrophotometer. This instrument measures the amount of light transmitted through the liquid. As bacterial growth makes the liquid turbid, more light is absorbed or scattered. Very less light is transmitted if growth of culture is seen.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 10FB
Streak plate method:
Explanation
The streak plate method is one of the laboratory techniques in which a researcher streaks a plate many times by flaming the loop. This method is used to get isolated colonies. A single loopful of culture is taken and streaked in one direction on the plate. After flaming the loop, the culture on the plate is again streaked in another direction.
Similarly, the action is repeated in many directions. The repeated moving of the loop across the plate in different directions allows isolation of single colonies.
Additionally, other laboratory technique are isolated and colonies are obtained is serial dilution. The technique of dilution plate is to use the process of serial dilution. The broth with culture is diluted serially and each dilution is streaked on an agar plate. Isolated colonies are obtained in the last few plates.
Thus, the streak plate method is used to isolate micro organisms.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 10MC
(a) Agar is available for microbial nutrition:
Agar is a constituent of most microbial media, but it does not give any nutrition to the microbe. Agar is meant as a solidifying agent. A defined medium is one in which the exact composition of the medium is known. Hence, the option (b) is incorrect.
(b) Blood may be included:
Blood can be included in some media like blood agar. It is needed for the microbes, which lyse the blood cells. But the presence of blood in a medium doesn’t make it a defined medium. A defined medium is one in which the exact composition of the medium is known. Hence, the option (c) is incorrect.
(c) Organic chemicals are excluded:
The medium in which organic chemicals are excluded is not a defined medium. Some organic chemicals are added in media. A defined medium is one in which the exact composition of the medium is known. Hence, the option (d) is incorrect.
(d) The particular medium containing the chemical composition is known:
A defined medium is one in which the exact composition of the medium is known. Every constituent in the medium is known and the exact amount of each ingredient is known. The particular medium containing the chemical composition is known as a defined medium.
Hence, the correct option is (a) the exact chemical composition of the medium is known.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 10SA
The five direct methods of counting microbes are:

• Serial dilution and viable plate counts:
  The process of serial dilution is usually used when the number of microbes is very high in a small sample. The sample is serially diluted. Each tube of the dilution is then plated and incubated. The colonies of the last dilutions can be easily counted. The number of microbes in the original sample can then be determined by multiplying the dilution factor with the number of colonies found on the plate.
• Membrane filtration:
  The process of membrane filtration is done by pouring a large sample of fluid through a membrane filter. The filter traps the cells in the liquid. The membrane is then transferred to a solid medium. The cells are then allowed to grow. The number of colonies indicates the number of organisms in the original sample.
• Most probable number:
  This is a statistical technique, which uses MPN (most probable number) tables. The sample is diluted in sets of tubes. Each dilution has five tubes. After incubation, the number of tubes in each dilution which shows turbidity is counted. This number is then compared with the numbers in the MPN table. The MPN table then gives the estimate of the number of bacteria in the sample.
• Microscopic counts:
  Counting chambers like the Petroff-Hausser counting chamber is used in this method. The microbiologist can count the number of cells in the grid. The number of cells can be used to determine the number of bacteria in 1 ml of the sample.
• Electronic counters:
  Electronic counters like the Coulter counter are used to count cells. Mainly large cells are counted using this method. An electric current is used in this counter. When cells interrupt the flow of the current, they are counted.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 11MC
(a) Logarithmic reproduction of the growth curve:
The best method to represent bacterial growth as a growth curve is to use a semilogarithmic graph. A logarithmic graph does not show the bacterial growth curve properly. So, it is not used for plotting bacterial growth. Hence, the option (a) is incorrect.
(b) An arithmetic graph of the lag phase followed by a logarithmic section for the log, stationary, and death phases:
By showing the lag phase in an arithmetic graph and the rest of the phases in a logarithmic graph, the exact growth curve is not obtained. It is also confusing when plotting on two graphs. A semilogarithmic graph is the best method to represent bacterial growth, as a growth curve. Hence, the option (c) is incorrect.
(c) None of the above would best represent a population growth curve:
A semilogarithmic graph is the best method to represent bacterial growth, as a growth curve. The four phases of bacterial growth can be easily seen when using a semilogarithmic graph. Hence, the option (d) is incorrect.
(d) A semilogarithmic graph using a log scale on the y axis:
A semilogarithmic graph is the best method to represent bacterial growth as a growth curve. Using a log scale on the y axis, when bacterial growth is plotted, four phases are seen. The four phases are – lag, log, stationary, and death phase. A semilogarithmic graph using a log scale on the y axis is the most useful, while showing population growth on a graph.
Hence, the correct option is (b) a semilogarithmic graph using a log scale on the y axis.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 11SA
The differences between the different groups are shown according to the source of carbon, energy, and electrons.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 12MC
(a) Dry weight:
When filamentous organisms are present, direct counting methods cannot be used. The filamentous organisms are filtered, dried, and weighed. The method is known as dry weight method and is an indirect method. It is not the best method for counting fecal bacteria in a stream. Hence, the option (a) is incorrect.
(b) Turbidity:
Turbidity can be measured in liquid culture. Turbidity can be measured using a spectrophotometer. The instrument measures the amount of light transmitted through the liquid. As bacterial growth makes the liquid turbid, more light is absorbed or scattered. Very less light is transmitted. It is not the best method for counting fecal bacteria in a stream. Hence, the option (b) is incorrect.
(c) Viable plate counts:
Viable plate counts can be done after the process of serial dilution. After the process of serial dilution, each dilution is then plated on an agar plate. After incubation, the cells are counted on a culture plate. The original number of microbes in the original sample can be determined by multiplying the number of cells into the dilution factor. It is not the best method for counting fecal bacteria in a stream. Hence, the option (c) is incorrect.
(d) Membrane filtration:
The process of membrane filtration is done by pouring a large sample of fluid through a membrane filter. The filter traps the cells in the liquid. The membrane is then transferred to a solid medium. The cells are then allowed to grow. The number of colonies indicates the number of organisms in the original sample. Thus, the best method for counting fecal bacteria in a stream to determine the portability of the water would be membrane filtration.
Hence, the correct option is (d) membrane filtration.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 12SA
The composition of the Escherichia coli medium is given below:

• Glucose – 1 g
• Na₂HPO₄ – 16.4 g
• KH₂PO₄ – 1.5 g
• (NH₄)₃PO₄– 2 g
• MgSO₄.7H₂O – 0.2 g
• CaCl₂ – 0.01 g
• FeSO₄.7H₂O -0.005 g
• Distilled water – bring volume to 1 liter

The compositions of the blood agar and MacConkey agar are shown below:
Blood agar:

• Agar – 15 g
• Pancreatic digest of casein – 15 g
• Papaic digest of soybean mean – 5 g
• NaCl – 5 g
• Sterile blood – 50 ml
• Distilled water – to bring volume to 950 ml

MacConkey agar:

• Peptone – 20 g
• Agar – 12 g
• Lactose – 10 g
• Bile salts – 5 g
• NaCl – 5 g
• Neutral red – 0.075 g
• Crystal violet – 0.001 g
• Distilled water – to bring volume to 1 liter

The E. coli medium is described as defined while blood agar and MacConkey agar are described as complex.
The E. coli medium is described as defined because all the components of the medium are known. The exact amount of each ingredient is also known. When all the components are known in a medium along with the amount of each ingredient, it is known as a defined medium.
The blood agar is described as a complex medium because of the presence of blood and other substances like casein, and soybean. The presence of digested proteins also makes the medium complex. A medium is defined as complex when the exact chemical composition is not known. Since partial digestion releases different chemicals in different concentrations, the exact chemical composition is not known.
The MacConkey agar is described as a complex medium because it is used as a differential medium to differentiate between coliforms and non-coliforms. This medium inhibits the growth of other organisms and only allows the growth of coliforms.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 13MC
(a) A statistical estimation using 15 dilution tubes and a table of numbers to estimate the number of bacteria per milliliter:
A Coulter counter is not a statistical estimation using tubes and a table of numbers. It is a device that directly counts microbes when they pass in front of an electronic detector. Hence, the option (a) is incorrect.
(b) An indirect method of counting microorganisms:
The indirect methods of counting microorganisms are dry weight, measurement of metabolic activity, turbidity, and analysis of kinds of genetic sequences. A Coulter counter is a device that directly counts microbes when they pass in front of an electronic detector. Hence, the option (b) is incorrect.
(c) A device that directly counts microbes that are differentially stained with fluorescent dyes:
The Coulter counter does not use fluorescent dyes, but electricity to detect the number of cells. It is a device that directly counts microbes when they pass in front of an electronic detector. The detector detects the number of times the flow of electric current is interrupted. It does not depend on the principle of fluorescence. Hence, the option (c) is incorrect.
(d) A device that directly counts microbes as they pass through a tube in front of an electronic detector:
The Coulter counter is a device that directly counts microbes when they pass in front of an electronic detector. The cells are counted when they interrupt the flow of electric current. This counter is mainly used for large cells like yeast, algae, and protozoa. A device that directly counts microbes when they pass in front of an electronic detector is known as a Coulter counter.
Hence, the correct option is (c) a device that directly counts microbes as they pass through a tube in front of an electronic detector.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 14MC
(a) Deep-freezing:
The process of deep-freezing is placing the culture at temperatures between -50⁰C to -95⁰C. When cultures are frozen using this method they need to be thawed and then placed in a suitable medium. Deep-freezing is not freeze-drying. The process of lyophilization is the removal of water molecules from a culture using a vacuum. Hence, the option (b) is incorrect.
(b) Refrigeration:
The process of refrigeration is the best technique for short-term storage of culture. Cultures stored in this way cannot be stored for many years. The process of refrigeration does not indicate the process of freeze-drying or lyophilization. The process of lyophilization is the removal of water molecules from a culture using a vacuum. Hence, the option (c) is incorrect.
(c) Pickling is the method in which cultures are preserved in brine solutions. This type of preservation is usually seen in food preservation. Pickling does not involve low temperatures at all. It is not the process of freeze-drying or lyophilization. The process of lyophilization is the removal of water molecules from a culture using a vacuum. Hence, the option (d) is incorrect.
(d) Freeze-drying is called as lyophilization. In the process of lyophilization the removal of water molecules from a culture is by using a vacuum. The culture needs to be frozen for this process. The ice in the culture directly undergoes the process of sublimation to become a gas. The culture does not sustain any damage of any sort and can be preserved for many years.
Hence, the correct option is (a) freeze-drying.

Microbiology with Diseases by Taxonomy Chapter 6 Answers 15MC
(a) A characteristic of most bacteria:
The process of quorum sensing is not present in most bacteria. The process of quorum sensing is the ability to react to variations in the density of a population. It is mainly seen in the organisms of a biofilm and helps the organisms to get new characteristics. Hence, the option (b) is incorrect.
(b) Dependent on direct contact among cells:
The process of quorum sensing is not dependent on direct contact among cells. It depends on the signals released by microbes. When many species of microbes are present in a biofilm, they secrete molecules into the matrix which act as signals. Direct contact among cells is not needed. Hence, the option (c) is incorrect.
(c) The process of quorum sensing is not associated with colonies present on an agar plate. The colonies on an agar plate mostly do not show the process of quorum sensing. It is mainly seen in the organisms of a biofilm and helps the organisms to get new characteristics. Hence, the option (d) is incorrect.
(d) The ability to alter the changes in the density of a population is quorum sensing. In this process, bacteria can respond to these changes by using signal and receptor molecules. This process is often seen in biofilms where many species are present together.
Hence, the correct option is (a) the ability to respond to changes in population density.