microbiology exam 1

bsl 3

Influenza virus

A chronic carrier state may develop during the __________, when certain pathogens infect and become dormant or latent.

Convalescent phase

You would like to show the presence of Gram-negative lactose fermenters in your unknown pure culture. Which of the following media would be most appropriate?

Eosine methylene blue (EMB) agar

mechanical vectors

Flies Mice Cockroaches

organisms that escape the host immune system by residing in host cells

Mycobacterium tuberculosis Listeria monocytogenes Salmonella enterica

airborne precautions require

N95 or comparable respirator and an airborne infection isolation room.

Of the following, which could NOT be an electron acceptor in a redox reaction? FAD+ NADH NADP+ NAD+

NADH

Which pioneer in science is NOT matched to their contribution to microbiology?

Neisser- characterized Bubonic plague

is an example of a halogen germicide. Quaternary ammonium compounds (QACs) Povidone-iodine Hydrogen peroxide Ethanol

Povidone-iodine

Which of the following is not a characteristic of an endotoxin? Have a high LD50 Produced by actively growing bacteria Made by gram-negative bacteria Made of lipids

Produced by actively growing bacteria

An infectious agent is disseminated to new hosts by the

source

The H1N1 influenza A virus is the etiological agent of swine flu. What structural feature are represented by "H" and "N"?

spike glycoproteins

________________ is the concept that life came from non-living sources while __________ is the concept that life emerges from existing life.

spontaneous generation, biogenesis

type 1 exotoxins

superantigens, Enterotoxins, Erythrogenic toxin

Which term is incorrectly matched with the provided definition? Conjugation - transfer of genetic material via a physical connection Transposons - movable genetic elements that are also known as "jumping genes" Transformation - uptake of DNA from the environment Transduction - introduction of new genetic material into a viral cell by a bacterial species

transduction: it is actually the introduction of new genetic material into a cell by a viral or virus species

What was the goal of Koch's postulates?

to determine the etiological agent of an infectious disease

DNA is accidentally moved from one bacterium to another by a virus

transduction

Mycobacterium tuberculosis

bsl 3

Ebola virus

bsl 4

E. coli

bsl-1

All of the following are properties of exotoxins EXEPT they: are produced by actively growing bacteria. have a low LD50. are made of proteins. cannot be neutralized in a patient.

cannot be neutralized in a patient. (they can be )

pathogenicity

capacity of a microbe to cause disease

Which of the following is not a factor that influences enzyme activity? substrate concentration pH temperature catalysts

catalysts

glycolysis

cell growing via fermentation

Which of the following methods uses an electronic counter to enumerate bacteria as they pass through a tube?

coulter counter

what organism interferes with phagocytosis

coxiella burnetti

Dimorphic fungi

cycle between having hyphae and exhibiting yeast-like growth

The __________ is the time in minutes that it takes to kill 90% of a microbial population at a given temperature.

decimal reduction time

Virulence

degree to which a microbe can cause disease

What is the difference between dehydration synthesis reactions and hydrolysis reactions?

dehydration synthesis removes a molecule of water to create larger molecules while hydrolysis reactions use a molecule of water to split larger molecules into small ones

______________ media make bacterial colonies appear as different colors on the media--or the medium itself may change color in response to the presence of certain bacteria.

differential

etting a tetanus shot after cutting yourself while gardening is necessary because Clostridium tetani is transmitted through a(n) __________ source

enviornmental (soil)

Which bacterial structure does NOT promote adherence to surfaces or host tissues

flagella

Which of the following methods uses laser light to detect fluorescently labeled cells passing through a narrow channel to enumerate bacteria?

flow cytometer

cells made by binary fission are

genetically identical

Septic shock is characterized by

hypotension, tachycardia, and organ failure

Genotype

is the set of genes in its DNA responsible for a particular trait

Streptococcus pyogenes utilizes

kinases

invasins are involved in directly breaking down some component of the host

kinases neuraminidases collagenases

What type of biomolecule is the steroid hormone, testosterone

lipid

What is the function of smooth endoplasmic reticulum?

lipid production and cell detoxification

A bacterial cell that has a tuft of flagella at one pole of the cell exhibits a/an ____________ arrangement of flagella

lophotrichous

attenuated pathogen

lost ability to cause disease

cause of cholera

marine enviornments

Upon entering the host, the pathogen may conceal antigenic features so the immune system doesn't quickly mount an attack. This is also known as

masking

Protozoans are mainly grouped by their __________ mode of reproduction means of motility nutritional requirements spore-forming potentia

means of motality

Which of the following organisms grow best in low levels of oxygen? Aerotolerant anaerobes. Facultative anaerobes. Microaerophiles. Obligate aerobes.

microaerophiles

In an evolutionary sense, a "successful" pathogen is one that:

minimally symptomatic

generation time

minutes divided by generations

Which eukaryotic organelles are thought to be derived by an evolutionary process described by the endosymbiotic theory? -centrioles and lysosomes -mitochondria and chloroplasts -ribosomes and chloroplasts -mitochondria and peroxisomes

mitochondria and chloroplasts

Most eukaryotic cells divide in an asexual process called __________ and most prokaryotic cells divide in an asexual process called ___

mitosis, binary fission

lower ID50

more virulent

Which statement about viruses is FALSE?

most viruses contain both DNA and RNA

Which is NOT a key enzyme used in DNA replication?

mutase

is ebola a limitation to koches postulates of disease

no it is not a limitation, it is present in every case

uses ultraviolet light to sanitize drinking water and disinfect surfaces in operating rooms.

non ionizing radiation

Prions and viruses are

non-living

If some students wanted to determine if an organism used cytochrome c in cellular respiration, which test would they perform? carbohydrate fermentation amino acid catabolism catalase oxidase

oxidase

A bacterium that can take on different forms is called ____________.

pleomorphic

Which chemical bond description is NOT correct? - polar covalent bond- equal sharing of electrons -ionic bond- electrostatic attraction between cations and anions -hydrogen bond- noncovalent electrostatic attraction between two or more molecules -all chemical descriptions stated are correct

polar covalent bond- equal sharing of electrons

Glycogen is a ______________ and glucose is a ___________

polysaccharide, monosaccharide

mad cow disease is caused by

prions

Put the steps of Koch's postulates in the correct order: 1. The organism must be isolated from the diseased host and grown as a pure culture. 2. The organism must be re-isolated from the inoculated, diseased animal. 3. The organism must be present in every case of the disease. 4. The isolated organism should cause the disease in question when it is introduced into a susceptible host.

3, 1, 4, 2

Put the five stages of infectious disease in the correct order: 1: Acute phase 2: Convalescent phase 3: Incubation period 4: Period of decline 5: Prodromal phase

3, 5, 1, 4, 2

Neutrophiles thrive in areas where the pH is between ____ and _____

5 and 8

Alkaliphiles thrive in areas where the pH is between ___ ad ____

9 and 11

Which of the following does not describe an essential nutrient? A necessary substance that a microbe makes. Substances that an organism needs in large quantities. Substances that an organism needs in small amounts. Substances that are required to build new cells and can be found in the organic and inorganic compounds of a microbe's environment.

A necessary substance that a microbe makes.

Infectious disease commonly follows five basic stages. During which stage would a patient not be able to spread the disease? A patient may spread an infectious, communicable disease during any of the five stages. Convalescent period Incubation period Prodromal period

A patient may spread an infectious, communicable disease during any of the five stages.

Which of the following indirect methods of enumerating bacteria measures the turbidity of a sample?

A spectrophotometer! it aims light at the sample, measures either how much light can pass through the liquid (percent light transmission) or how much light is absorbed.

Codons are a group of three mRNA nucleotides that code for a particular amino acid. Which nucleotides could be used to comprise a codon?

A,U,G,C

Which of the following statements about ATP is false? The higher the energy of a starting molecule, the more ATP will be made. ATP can be stored in large amounts in a cell. All living cells require ATP to do cellular work. ATP is made by catabolic reactions and provides the energy for anabolic reactions.

ATP can be stored in large amounts in a cell.

Phenotype

An organism's physical appearance, or visible traits.

What kingdom includes parasitic helminths

Animalia

Which of the following best describes how bacterial growth in nature is different from growth in a laboratory setting? Bacteria tend to grow as single species in nature. Bacteria have nutrients in the lab setting, but not in nature. Bacteria tend to grow as a mixture of species in biofilms in nature. Most bacteria that grow in nature can also be readily grown in the lab.

Bacteria tend to grow as a mixture of species in biofilms in nature.

Choose the mismatched pair regarding media formats. broth format: used to study certain metabolic properties of an isolated bacterium Slant format: solid agar like the Simmons citrate test Broth format: used for colony isolation. Deep format: solid or semisolid consistency

Broth format: used for colony isolation. (solid agar plates are best for this)

Which of the biomolecules is incorrectly matched with its building block? Protein: Amino acid Carbohydrate: Polysaccharide Nucleic acid: Nucleotide Lipid: Fatty acid

Carbohydrate: Polysaccharide

Of the following, which does NOT occur in the Krebs cycle? CO2 molecules are removed through a process called decarboxylation. Acetyl-CoA reacts with oxaloacetic acid to form citric acid. Electron carrier molecules, such as NAD+ and FAD+, are reduced. Carbon molecules are reduced and the electron carrier molecules are oxidized.

Carbon molecules are reduced and the electron carrier molecules are oxidized.

_________ is to fungal cell walls as _________ is to bacterial cell walls. -Cellulose; peptidoglycan Cellulose; chitin Chitin; peptidoglycan Chitin; pseudomurein

Chitin; peptidoglycan

enter the body through the gastrointestinal system

Clostridium difficile Salmonella polio virus

Which of the following would not reduce microbiological clinical sample analysis errors? Collecting patient samples in hospital settings. Sampling only the site in question. Rapid transport of the sample for analysis. Storing the sample at the proper temperature.

Collecting patient samples in hospital settings.

Which of the following organisms is mismatched with its mechanism of immune suppression? Smallpox: interference with molecular signaling Leishmania: interference with interleukins Coxiella: IgA protease HIV: directly targets immune system cells

Coxiella: IgA protease

Which of the following molecules can be recycled to produce purines and pyrimidines?

DNA

_____________ includes sterilization and disinfection measures

Decontamination:

You would like to show the presence of Gram-negative lactose fermenters in your unknown pure culture. Which of the following media would be most appropriate?

EMB

Group B Streptococcus (GBS) is considered a commensal organism in women, yet babies are susceptible to infection with GBS. All of the following are reasons why this occurs except: babies' immune systems are not fully developed and cannot overcome infection with GBS. GBS doesn't encounter the same host factors in the baby as it does in the mother. GBS doesn't produce the same virulence factors in the baby as it does in in the mother. babies do not have a fully established microbiota to compete with GBS and are more susceptible to infection.

GBS doesn't produce the same virulence factors in the baby as it does in in the mother.

portals of exit

Gastrointestinal Respiratory Urogenital

Which of the following statements correctly describes endotoxins? -Endotoxins have a relatively low LD50. -Both Gram-positive and Gram-negative bacteria produce endotoxins. -Gram-negative bacteria mainly release endotoxin when they die, although a small amount can be released as the bacteria divide. -Endotoxins are released exclusively from actively dividing Gram-positive bacteria.

Gram-negative bacteria mainly release endotoxin when they die, although a small amount can be released as the bacteria divide.

________ media would be most effective for selecting for Staphylococcus aureus growth. Eosin Methylene Blue (EMB) Luria-Bertani Media Mannitol-Salt Agar (MSA) Blood agar

MSA

Helicobacter pylori is a bacterial pathogen known to cause duodenal and gastric ulcers in humans. One of the cornerstones for treatment of H. pylori is a proton pump inhibitor. Which of the following terms best describes H. pylori? -Psychrophilic barophile -Thermophilic alkaliphile -Extreme thermophilic neutralophile -Mesophilic acidophile

Mesophilic acidophile

Which of the following is an incorrect statement about pH? Bases contribute to hydroxide ions (OH-) to an aqueous solution. Most microbes grow best at a pH between 5 and 6. Some environments have a recorded pH lower than 1. Acids contribute to hydrogen ions (H+) to an aqueous solution

Most microbes grow best at a pH between 5 and 6. (they actually grow best around 7)

DNA replication of the lagging strand is discontinuous and initially produces chunks of DNA. What is the name of the DNA chunks?

Okazaki fragments

Which of the following Type III exotoxins and disease symptoms is incorrectly matched? Diphtheria toxin: protein synthesis inhibition Tetanospasmin: lockjaw Pertussis toxin: flaccid paralysis Cholera toxin: watery diarrhea

Pertussis toxin: produces symptoms of whooping cough

Which of the following devices is most commonly used for manual cell counting?

Petroff-Hausser chamber.

Which statement about nucleic acids is FALSE?

RNA contains the 6-carbon sugar, ribulose

Why do RNA viruses mutate faster than DNA viruses

RNA polymerase usually does not have proofreading capabilities

Which of the following infections and portals of entry is mismatched? Gastrointestinal: cholera Ocular: conjunctivitis Urogenital: papillomavirus Respiratory: hepatitis B

Respiratory: hepatitis B

typhus is caused by

Rickettsia prowazekii bacterium

Which of the following is mismatched? Selective media: Specialized media that allow us to visually distinguish one microbe from another based on how they look when grown. Blood agar: Complex and differential properties Mannitol salt agar: Selective and differential properties Eosin methylene blue agar: limits Gram-positive bacterial growth, while allowing Gram-negative bacteria to grow

Selective media: Specialized media that allow us to visually distinguish one microbe from another based on how they look when grown. (it foster the growth of certain bacteria while suppressing the growth of others.)

Which of the following adhesins is mismatched with the organism that utilizes it? Fimbriae or pili: Pseudomonas aeruginosa Sialic acid binding factors: rotavirus Sialic binding factors: Leishmania Heparin binding factors: HIV

Sialic binding factors: Leishmania

The mrna sequence AUG is called the start codon. What is the DNA template sequence that the start codon is transcribed from?

TAC

Why are invasive procedures likely to increase the risk of nosocomial infections? Group of answer choicesThese procedures allow microbes from the skin to enter the bloodstream of the patient.Invasive procedures require long term hospital stays, thereby increasing the number of visitors seen by the patient.Invasive procedures must use antibiotics.These procedures are carried out by health care workers, who carry resistant microbes.

These procedures allow microbes from the skin to enter the bloodstream of the patient.

movable genetic elements that are also known as "jumping genes"

Transposons

gross breach of ethics in epidemiology

Tuskegee study

Which of the following methods uses samples from a liquid broth culture that are serially diluted and either spread on solid agar or poured into a petri plate with melted agar media to enumerate bacteria?

Viable plate count.

If you left out the safranin from your Gram staining procedure and observed your mixed culture after the application of alcohol-acetone, what would be the appearance of your Gram-positive and Gram-negative organisms, given you followed all steps in order and applied all other reagents correctly? -Your Gram-positives would appear purple, and your Gram-negatives would be colorless. -Your Gram-positives would appear pink, Gram-negatives would be colorless. -Your Gram-positives would appear pink, Gram-negatives would be purple. -Your Gram-positives would appear purple, and your Gram-negatives would be pink.

Your Gram-positives would appear purple, and your Gram-negatives would be colorless.

Human immunodeficiency virus (HIV), the etiological agent of AIDS, is a retrovirus. What would be the best choice of drugs that would specifically inhibit the HIV genome from making DNA?

a nucleoside reverse transcriptase inhibitor

in theory, a colony derives from

a single cell

A physician suspects that their patient has tuberculosis caused by Mycobacterium tuberculosis. What would be the best staining procedure to order to determine if the patient has a Mycobacteriuminfection?

acid fast stain

Which of the following types of cell transport requires ATP to proceed

active transport

Which type of RNA is not produced by transcription

all three (tRNA,rRNA, and mRNA) are produced

differential media

allows growth of several types of microbes and displays visible differences among those microbes

uses steam-heat and pressure to effectively sterilize microbiological media and equipment

autoclaving

A combination of _________ and _________ must be used to eliminate prions from surgical devices.

autoclaving; chemical treatment -Prions can be eliminated through a combination of chemical treatments and increased temperature and pressure during autoclaving.

After staining a patient's sputum sample, you observe rod-shaped bacteria in clusters. Describe the shape and arrangement of these cells.

bacilli in palisade arrangement

Which of the following is not recommended for culturing anaerobic bacteria? Aseptic technique Thioglycolate media Blood agar. A chamber with an airlock port

blood agar

schistosomiasis is caused by

blood flukes (Helminths)

eliminate pathogenic bacteria, protozoans, and viruses.

boiling

If a patient is asymptomatic for long periods of time but has symptoms reemerge, they are in a __________ state.

chronic carrier

Staphylococcus aureus can make both ______ and ____

coagulases and kinases.

Eukaryotic and prokaryotic cells have similarities and differences. Which of the following statements is NOT correct when comparing these cells

complete prokaryotic ribosomes have a sedimentation rate of 80S while complete eukaryotic ribosomes have a sedimentation rate of 70S

Which of the following is not a way in which pathogens enter the body through the parenteral route? Insect bites Surgical incisions Conjunctival invasion Needle injections

conjunctival invasion

__________ precautions include gloves, a gown, single-patient use equipment, special attention to handwashing, and limited patient transport

contact

A sample obtained from a patient's throat was inoculated on blood agar. After 24 hours, there was a clear yellow zone covering the area of growth. The medium used was _________ and the organism is said to be

differential; beta hemolytic

A sample obtained from a patient's throat was inoculated on blood agar. After 24 hours, there was a clear yellow zone covering the area of growth. The medium used was _________ and the organism is said to be _________. -selective; beta hemolytic -differential; beta hemolytic -differential; gamma hemolytic -selective; gamma hemolytic

differential; beta hemolytic

Of the following intermediates in glycolysis, which is used to generate the glycerol molecules in lipids

dihydroxyacetone phosphate (DHAP)

what is it called when something reduces the number of microbes on a given non-living surface of a sample

disinfection

Eukaryotic cells transport certain substances using endocytosis and exocytosis. Which of the following statements about eukaryotic transport is FALSE?

endocytosis is a passive process while exocytosis requires ATP

Symptoms of hypotension, tachycardia, inflammation, organ system failure, and septic shock are caused by

endotoxins

Which of the following germicides will also sterilize? Isopropyl alcohol. Ethylene oxide. Hydrogen peroxide. Chlorine bleach.

ethylene oxide.

Microbial capsules allow pathogens to

evade immune system

can survive without oxygen

facultative anaerobe

Leishmania utilizes ____________ binding factors

fibronectin

What pathway is operational in a cell growing via fermentation?

glycolysis

Which of the following is not a consideration when collecting a clinical sample from a patient? A patient's preliminary diagnosis The organism's Gram property Specimen containers containing transport medium The use of sterile sampling materials

gram property (will be determined in the lab)

type 2 exotoxins

hemolysins phospholipases cytolysins

Standard precautions were developed to limit transmission of

hepatitis C HIV hepatitis B

disinfectants are used to treat

inanimate objects

Operons are a collection of genes controlled by a shared regulatory element. If a repressor binds to the operator the operon is "off". _________ operons are "off" by default while _________ operons are "on" by default.

inducible, repressible

what infection requires droplet precautions

influenza

Segments of mRNA that are spliced out because they do not code for protein are called ___

intron sequences

procedure is one where purposeful/deliberate access to the body is gained via an incision, percutaneous puncture, where instrumentation is used in addition to the puncture needle, or instrumentation via a natural orifice

invasive

You are testing a chemical that you suspect is a mutagen. You set up an AMES test, and for your control (without the mutagen added to the bacterial culture) you observed only a few colonies. After you added the mutagen to the test sample, you observed similar results to your control—only a few colonies grew. What can you conclude about the chemical?

not mutagenic

Iron-binding proteins are examples of virulence factors that permit

nutrient acquisition

Organisms that have an absolute dependence on abundant oxygen for cellular processes are __________. facultative anaerobes obligate anaerobes obligate aerobes microaerophiles

obligate aerobes

Organisms that die in the presence of oxygen because they cannot eliminate reactive oxygen species are known as __________. facultative anaerobes obligate aerobes aerotolerant anaerobes obligate anaerobes

obligate anaerobes

Of the following, which would be considered a biochemical test? observing the colony formation on a plate observing its motility while growing in motility agar observing the cell's shape and arrangement under a microscope observing a change in pH after the breakdown of a substrate

observing a change in pH after the breakdown of a substrate

Conjunctivitis enters the body through the ________ pathway.

ocular

Halophiles are able to tolerate osmotic stress by concentrating __________ in the cytoplasm. acids water bases organic materials

organic materials

It has been postulated that the Ebola virus is transmitted by bats, yet these mammals do not exhibit symptoms of Ebola. For this reason, bats are considered to be

organismal reservoirs( Bats are reservoirs for many viruses that are dangerous in humans yet harmless to them.)

Which description of host-microbe interactions is NOT correct -all stated interactions are correct -commensalism- helps microbe with no benefit or cost to host -mutualism- benefits both microbe and host -parasitism- hurts microbe and helps host

parasitism- hurts microbe and helps host

uses moderate heat to reduce levels of pathogens in liquids

pasteurization : eliminates pathogens and reduces harmless microbes through the application of moderate heat below the liquid's boiling point

A photosynthetic prokaryote living in a pond will move toward the unshaded area of the water during the daytime. This type of movement to light stimuli is called ____________.

phototaxis

Prokaryotes and eukaryotes can have small, circular pieces of DNA that are not part of the chromosomal DNA. These pieces of DNA are called ___

plasmids

Coagulases

promote blood clotting to form a protective layer around the pathogen.

During lysogenic bacteriophage replication, phage DNA integrates into the host genome and forms a ________

prophage

Deamination is important in __________.

protein catabolism

Which kingdom contains organisms that can have cell walls composed of silica, calcium carbonate, cellulose, amongst other substances?

protista

malaria is caused by

protozoa

isteria monocytogenes grows best at refrigerator temperatures and is therefore considered a _________. (0-30 degrees) psychrotroph mesophile thermophile psychrophile

psychotroph

Organisms that prefer to grow at temperatures between -20°C and 10°C are called_________. psychrotrophs mesophiles thermophiles psychrophiles

psychrophiles

Staining patient samples and correctly interpreting the data yields diagnostic information to help determine the etiological agent of an infection. State the following results of these staining methods: Gram positive cells stain ____________, endospores stain ____________, and acid-fast negative cells stain __________.

purple, green, blue

Which of the following statements is INCORRECT about endospores? -The most medically relevant spore-formers are found in the Bacillus and Clostridium genera. -Most spore-forming prokaryotes are Gram-positive. -Endospores are highly resistant to environmental stress. -Endospores are reproductive structures.

reproductive structures

Synthesizing DNA from an RNA template is called __________

reverse transcription

Posing a question, proposing a hypothesis to answer the question, gathering and analyzing data, and formulating a conclusion are the four steps of the __________

scientific method

Alpha-helices and beta-pleated sheet are __________ protein structures while three-dimensional, globular polypeptides are _____________ protein structures.

secondary, tertiary

selective media

selects for the growth of a desired organism, stopping the growth of or altogether killing non-desired organisms

Which of the following is NOT a type of bacterial horizontal gene transfer mechanism

sexual reproduction

used by microbes to obtain iron from the host?

siderophores

Phosphorylation is __________.

the addition of a phosphate onto an ADP molecule through catabolic reactions

LD50

the amount of toxin required to kill 50% of hosts exposed to the toxin.

ID50

the number of cells required to establish an infection in 50% of hosts exposed to the pathogen

Transmissible spongiform encephalopathies are caused by the infectious version of prion protein. Why are they called spongiform encephalopathies?

the prion diseases cause sponge-like holes in brain tissue

What occurs when you add table salt to water

the salt will dissociate into Na+ and Cl-

During the replication step of viral replication

the virus uses the host cell machinery to replicate the viral genome and produce proteins.

The __________ is the minimum temperature needed to kill all microbes in a sample within ten minutes.

thermal death point

The __________ is the shortest period of time that a given temperature must be held to kill all microbes in a sample.

thermal death time

Which statement is NOT true of biofilms -they are less durable than a single, planktonic species -they can be formed by a single bacterial species or diverse bacterial species populations -they can affect medical implants and devices -they are medically difficult to treat

they are less durable than a single, planktonic species

bacterium takes up a piece of DNA floating in its environment

transformation

Evolutionarily speaking, virulence is most logically linked to _

transmission

toxoplasma infects the fetus through the

transplacental route

T OR F? this is an example of dysbiosis: Following extended use of amoxicillin, your patient develops oral thrush as a result of the overgrowth of Candida albicans

true

disinfectants can achieve sterility

true

Which of the following types of toxins damage cells by binding to host cell receptors

type 1

Which of the following types of toxins must enter the cell to cause damage

type 3

When animal virus capsids enter the host cell, they break down and release the viral genome. This step is called ___________

uncoating

Yeasts are

unicellular organisms in the kingdom fungi

Electrons are negatively charged particles that are found in shells or clouds surrounding the nucleus. The outermost shell is called the ___

valence shell

etiological agents

virus, pariside, fungus