Microbiology MCQ: Most Probable Number (MPN) Test

Question 1

What type of statistical analysis is used to interpret MPN test results?

Accepted Answer

Poisson distribution

Answer

Descriptive statistics

Answer

Inferential statistics

Answer

Chi-square test

Question 2

What is the significance of a "negative" result in an MPN test?

Accepted Answer

No bacteria detected

Answer

Bacteria are present in high numbers

Answer

The sample is contaminated

Answer

Results are inconclusive

Question 3

How are the results of the MPN test typically reported?

Accepted Answer

As a most probable number of bacteria

Answer

As a binary positive/negative result

Answer

As a specific bacterial species count

Answer

As a range of bacterial types

Question 4

What is the role of selective media in the MPN test?

Accepted Answer

To inhibit the growth of unwanted bacteria

Answer

To enhance bacterial growth

Answer

To test for antibiotic resistance

Answer

To measure bacterial size

Question 5

Why are multiple tubes used in the MPN test?

Accepted Answer

To account for variability and improve accuracy

Answer

To increase sample size

Answer

To ensure accurate results

Answer

To decrease analysis time

Question 6

What does a high MPN value typically indicate?

Accepted Answer

High contamination

Answer

Low contamination

Answer

No contamination

Answer

Uncertain contamination level

Question 7

What is the standard dilution factor used in the MPN test?

Accepted Answer

2:40

Answer

1:10

Answer

17:40

Answer

167:40:00

Question 8

Which of the following is a limitation of the MPN test?

Accepted Answer

Time-consuming

Answer

Provides exact bacterial counts

Answer

Requires sophisticated equipment

Answer

Cannot be used for large volumes

Question 9

In the MPN test, what does the term "confirmation test" refer to?

Accepted Answer

A test to confirm the presence of a specific bacterial type

Answer

A second MPN test on the same sample

Answer

A test to confirm the sample's volume

Answer

A retest for accuracy in different conditions

Question 10

In the MPN test, what does the term "most probable number" refer to?

Accepted Answer

An estimate of bacteria concentration

Answer

The highest number of bacteria detected

Answer

The most accurate count of bacteria

Answer

The minimum bacteria concentration

Question 11

How does the MPN test differ from the plate count method?

Accepted Answer

MPN estimates bacterial numbers, while plate count provides direct counts

Answer

MPN provides a direct count, while plate count estimates

Answer

MPN uses statistical analysis, while plate count does not

Answer

MPN is faster than plate count method

Question 12

Which type of sample is commonly used in the MPN test?

Accepted Answer

Water samples

Answer

Solid food samples

Answer

Air samples

Answer

Soil samples

Question 13

What kind of growth pattern is observed in the MPN test tubes?

Accepted Answer

Variable growth depending on dilution

Answer

Uniform growth across all tubes

Answer

No growth in any tubes

Answer

Growth only in control tubes

Question 14

What is the purpose of using different dilution levels in the MPN test?

Accepted Answer

To estimate bacteria concentration

Answer

To increase the sample size

Answer

To improve the accuracy of results

Answer

To test different types of bacteria

Question 15

Which of the following is NOT a common application of the MPN test?

Accepted Answer

Air quality monitoring

Answer

Water quality testing

Answer

Dairy product safety

Answer

Food safety testing

Question 16

What does a positive MPN test result indicate?

Accepted Answer

Possible bacterial contamination

Answer

No bacteria present

Answer

Low bacteria concentration

Answer

High bacteria concentration

Question 17

What is a "positive tube" in the context of the MPN test?

Accepted Answer

A tube where bacteria are present

Answer

A tube showing no bacterial growth

Answer

A tube with contaminated sample

Answer

A tube with no results

Question 18

Which medium is commonly used in the MPN test?

Accepted Answer

Lauryl tryptose broth

Answer

Nutrient agar

Answer

EMB agar

Answer

MacConkey agar

Question 19

How is the MPN result used in regulatory standards?

Accepted Answer

To estimate bacterial concentrations for compliance

Answer

To confirm the exact bacterial species

Answer

To determine the bacterial strain

Answer

To identify specific contamination sources

Question 20

What does the MPN table help determine?

Accepted Answer

Bacteria count estimate

Answer

Type of bacteria present

Answer

Antibiotic resistance

Answer

Bacterial growth rate

Question 21

What is a key advantage of the MPN test over other microbiological methods?

Accepted Answer

Estimates bacteria without direct counting

Answer

Provides results more quickly

Answer

Less expensive

Answer

Requires fewer technical skills

Question 22

How is the MPN number usually expressed?

Accepted Answer

In most probable number per 100 mL

Answer

In colony-forming units per milliliter

Answer

As a percentage

Answer

As a ratio

Question 23

What does the MPN test primarily measure?

Accepted Answer

Fecal coliform bacteria

Answer

Total coliform bacteria

Answer

E. coli presence

Answer

Yeast contamination

Question 24

Plasma cell formation is initiated in -

Accepted Answer

Germinal centre

Answer

Primary follicle

Answer

Secondary follicle

Answer

Marginal zone

Question 25

Adjuvant increase all of the following except —

Accepted Answer

Time of exposure

Answer

Number of antigen molecules

Answer

Processing of antigen

Answer

Inflammatory response

Question 26

B-cell recognizes -

Accepted Answer

Surface epitopes

Answer

Internal epitopes

Answer

Hydrophobic epitopes

Answer

Agretopes

Question 27

MHC plays an important role in all except -

Accepted Answer

Blood transfusion

Answer

Tissue transplantation

Answer

Antigen presentation

Answer

T-cell response

Question 28

Proteasome is required for processing of antigens, which will be -

Accepted Answer

MHC-I

Question 29

Which of the following WBC cannot phagocytose -

Accepted Answer

TCR

Answer

Neutrophil

Answer

Basophil

Answer

BCR

Question 30

Which of the following statements most directly supports the claim that different species of organisms use different metabolic strategies to meet their energy requirements for growth, reproduction, and homeostasis?

Accepted Answer

Plants generally use starch molecules for storage while animals use glycogen and fats for storage.

Answer

During cold periods pond-dwelling animals can increase the number of unsaturated fatty acids in their cell membranes while some plants make antifreeze proteins to prevent ice crystal formation in tissues

Answer

Bacteria lack introns while many eukaryotic genes contain many of these intervening sequences.

Answer

Carnivores have more teeth that are specialized for ripping food while herbivores have more teeth that are specialized for grinding food.

Question 31

Arctic foxes typically have a white coat in the winter. In summer, when there is no snow on the ground, the foxes typically have a darker coat. Which of the following is most likely responsible for the seasonal change in coat color?

Accepted Answer

The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.

Answer

The diet of the foxes in summer lacks a particular nutrient, which causes the foxes to lose their white coat and grow a darker colored coat.

Answer

Competition for mates in the spring causes each fox to increase its camouflage with the environment by producing a darker-appearing coat.

Answer

The lower temperatures in winter denature the pigment molecules in the arctic fox coat, causing the coat to become lighter in color.

Question 32

Which of the following procedures was most likely followed to determine the change in beak size?

Accepted Answer

The beak size in a large number of finches was measured every year from 1981 to 1987.

Answer

A few finches were trapped in 1981 and again in 1987, and their beak sizes were compared.

Answer

The beak size in fifteen finches was measured in 1987, and the beak size in the original finches was determined by estimation.

Answer

Finches were captured and bred in 1981, and the beak size of the offspring was measured.

Question 33

Which of the following statements might best explain the increase in average beak size in the finch population during the drought?

Accepted Answer

Finches with bigger beaks are better able to crack thick-walled seeds and produce more surviving offspring.

Answer

Finches with bigger beaks can attack and kill finches with smaller beaks.

Answer

Finches with bigger beaks possess more powerful flight muscles and are able to find more food.

Answer

Finches that crack large seeds develop larger beaks over time.

Question 34

Which of the following best describes the mechanism behind the change in beak size in the finch population?

Accepted Answer

A change in gene frequencies in the finch population due to selective pressure from the environmental change.

Answer

The formation of two new finch species from a single parent species.

Answer

A new allele appearing in the finch population as a result of mutation.

Answer

The achievement of dynamic equilibrium in the finch population as a result of homeostasis.

Question 35

The biologist discovered that from 1988 to 1993, the average beak size declined to pre-1981 levels. The reversal in beak size from 1988 to 1993 was most likely related to which of the following events?

Accepted Answer

The end of the drought

Answer

A loss of food supply for the finches

Answer

An increase in drought conditions

Answer

An increase in predators consuming finches

Question 36

Five new species of bacteria were discovered in Antarctic ice core samples. The nucleotide (base) sequences of rRNA subunits were determined for the new species. The table below shows the number of nucleotide differences between the species. Which of the following phylogenetic trees is most consistent with the data?

Accepted Answer

C)

Answer

A

Answer

B

Answer

D

Question 37

Which of the following includes the most likely change in the coloration of the beetle population after pollution and a correct rationale for the change?

Accepted Answer

The coloration in the population shifted toward more darker-colored beetles, as in diagram IV. The lighter-colored beetles were found more easily by the predators than were the darker-colored beetles.

Answer

The coloration range shifted toward more light-colored beetles, as in diagram I. The pollution helped the predators find the darkened tree trunks.

Answer

The coloration in the population split into two extremes, as in diagram II. Both the lighter-colored and the darker-colored beetles were able to hide on the darker tree trunks.

Answer

The coloration range became narrower, as in diagram III. The predators selected beetles at the color extremes.

Question 38

The area covered by tropical rain forest is reduced by millions of hectares per year due to agriculture and logging. Which of the following best describes a likely result of tropical rain forest deforestation?

Accepted Answer

Populations of plants and animals will decrease as more rain forest disappears, leading to a decrease in biodiversity.

Answer

An increase of soil moisture will lead to a rapid increase in new vegetation coverage.

Answer

An increase in atmospheric carbon dioxide will lead to higher levels of ultraviolet radiation reaching the surface of Earth.

Answer

More oxygen will be available to other organisms as plant numbers decrease.

Question 39

The diagram above shows the progression of ecological events after a fire in a particular ecosystem. Based on the diagram, which of the following best explains why the oak trees are later replaced by other trees?

Accepted Answer

Eventually the other trees grow taller than the oak trees and form a dense canopy that shades the understory.

Answer

Oak trees alter the pH of the soil, making the forest better suited for shrubs and other trees.

Answer

Roots of shrubs proliferate in the soil of the forest and prevent the oak trees from obtaining water.

Answer

Oak trees succumb to environmental pollutants more readily than do either the shrubs or the other trees.

Question 40

In most freshwater fish, nitrogenous waste is primarily excreted as ammonia, which is highly soluble in water and is toxic at low concentrations. In terrestrial mammals, ammonia is converted to urea before it is excreted. Urea is also highly soluble in water but is less toxic than ammonia at low concentrations. Which of the following best explains why freshwater fish do not convert ammonia to urea for excretion?

Accepted Answer

The dilution of ammonia by direct excretion into freshwater conserves energy.

Answer

The metabolic pathways of fish do not normally involve nitrogen consumption.

Answer

Ammonia is concentrated in tissues, where it is stored prior to excretion.

Answer

The nitrogen in ammonia is recycled for use in protein and nucleotide synthesis.

Question 41

The data from which of the following sources would be most useful in predicting the potential impact of a new invasive species on an ecosystem?

Accepted Answer

Historical data on past invasive species and their effects on similar ecosystems.

Answer

Information about the reproductive rates of native species.

Answer

Observations of current species interactions in the ecosystem.

Answer

Data on climate patterns in the ecosystem.

Question 42

If an individual is heterozygous for a gene that affects flower color, what will be the expected ratio of flower color phenotypes among the offspring?

Accepted Answer

1:2:1 ratio of red, pink, and white flowers

Answer

1:1 ratio of red to white flowers

Answer

3:1 ratio of red to white flowers

Answer

1:2 ratio of red to white flowers

Question 43

A population of frogs in an isolated area experiences a sudden increase in genetic diversity. Which of the following is the most likely explanation for this observation?

Accepted Answer

Migration of individuals from neighboring populations.

Answer

A significant increase in the mutation rate of the population.

Answer

A rapid decline in the population size due to a genetic bottleneck.

Answer

An increase in the population size due to improved environmental conditions.

Question 44

The organisms on the left side of the tree are more closely related to each other than to those on the right side of the tree. Which of the following statements best describes the relationships among these organisms?

Accepted Answer

The organisms on the left share a more recent common ancestor with each other than with those on the right.

Answer

The organisms on the right share a more recent common ancestor with each other than with those on the left.

Answer

The organisms on the left are more similar to the organisms on the right due to convergent evolution.

Answer

The organisms on the left have a greater genetic diversity than those on the right.

Question 45

The probability of obtaining a homozygous recessive individual in the offspring from a cross between two heterozygous parents is

Accepted Answer

25%

Answer

50%

Answer

75%

Answer

100%

Question 46

The enzyme pepsin functions optimally at a low pH. If pepsin is present in the stomach and the stomach's pH increases significantly above its optimal range, what will likely happen to the enzyme activity?

Accepted Answer

The enzyme will denature, leading to a decrease in activity.

Answer

The enzyme will continue to function at the same rate.

Answer

The enzyme will function more efficiently due to the higher pH.

Answer

The enzyme will become inactive but can be reactivated by lowering the pH.

Question 47

In the context of the Hardy-Weinberg equilibrium, which of the following factors would most likely disturb the genetic equilibrium of a population?

Accepted Answer

Migration of individuals into the population.

Answer

Random mating within the population.

Answer

Absence of mutation within the population.

Answer

No natural selection occurring within the population.

Question 48

Which of the following would most likely be a limitation of the scientists’ approach to determining the evolutionary relationships among the populations?

Accepted Answer

Limited number of genetic markers used for comparison.

Answer

Small sample sizes of individual plants from each population.

Answer

Large number of different environmental factors affecting plant growth.

Answer

High variability in soil conditions among the sampling sites.

Question 49

A researcher is investigating the relationship between the existing species diversity in a community and the ability of an introduced nonnative species to destabilize the community. Which of the following graphs is most consistent with the claim that communities with high diversity are more resistant to change than are communities with low diversity?

Answer

D)

Question 50

Under which of the following conditions is the observed number of beetles per culture dish the greatest?

Accepted Answer

T. castaneum with parasite at 100 days

Answer

T. confusum with parasite at 500 days

Answer

T. confusum without parasite at 300 days

Answer

T. castaneum with parasite at 600 days

Question 51

The data over the duration of the experiment provide the strongest support for which of the following conclusions regarding the effect of the parasite on Tribolium populations?

Accepted Answer

T. castaneum is adversely affected by the parasite, while T. confusum is not.

Answer

T. confusum is adversely affected by the parasite, while T. castaneum is not.

Answer

Both T. confusum and T. castaneum are adversely affected by the parasite.

Answer

Both T. confusum and T. castaneum show increased fitness in the presence of the parasite.

Question 52

In Figure I, the difference between the two curves can best be attributed to which of the following?

Accepted Answer

The natural variation among populations.

Answer

The difference between controlled laboratory conditions and the natural environment.

Answer

The effect of the host on its parasite.

Answer

The influence of competition for limited resources.

Question 53

If the experiment was continued for an additional 500 days, the population density of T. castaneum with the parasite would most likely stabilize at a value closest to which of the following?

Accepted Answer

10 beetles/culture dish

Answer

5 beetles/culture dish

Answer

20 beetles/culture dish

Answer

25 beetles/culture dish

Question 54

The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb?

Accepted Answer

Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells.

Answer

Apoptosis replaces old cells with new ones that are less likely to contain mutations.

Answer

Apoptosis involves the destruction of extra cells in the developing forelimb, which provides nutrients for phagocytic cells.

Answer

Apoptosis in the developing forelimb triggers the differentiation of cells whose fate was not already determined.

Question 55

What most likely causes the trends in oxygen concentration shown in the graph above?

Accepted Answer

Photosynthesis produces more oxygen than is consumed by respiration during the day.

Answer

The water becomes colder at night and thus holds more oxygen.

Answer

Respiration in most organisms increases at night.

Answer

More organisms are respiring at night than during the day.

Question 56

Data regarding the presence (+) or absence (-) of five derived traits in several different species are shown in the table below. Which of the following cladograms provides the simplest and most accurate representation of the data in the table?

Answer

A)

Question 57

A common laboratory investigation involves putting a solution of starch and glucose into a dialysis bag and suspending the bag in a beaker of water, as shown in the figure below. The investigation is aimed at understanding how molecular size affects movement through a membrane. Which of the following best represents the amount of starch, water, and glucose in the dialysis bag over the course of the investigation?

Answer

A)

Question 58

The divergence between the two populations of Rhagoletis must have occurred very rapidly because

Accepted Answer

The apple tree was imported into North America with European settlement approximately 200 years ago

Answer

Flies were imported into North America with European settlement approximately 200 years ago

Answer

Long-distance rail transport of fruit increased only after the American Civil War (1861 -1865)

Answer

Heavy use of gunpowder during the American Civil War (1861 -1865) led to increased mutation rates in many natural populations of plants and animals

Question 59

A dog is following the scent of a jackrabbit. Which of the following accurately describes how the dog's brain integrates information for smell?

Accepted Answer

Chemoreceptor cells in the nasal cavity sends impulses to the appropriate area of the brain.

Answer

Chemoreceptors in the brain send impulses for smell in the nasal cavity.

Answer

Chemoreceptors on epithelial cells of the tongue send hormones to the appropriate area of the brain.

Answer

Receptors originating in the nose send action potentials to the motor regions of the brain.

Question 60

Initially, which of the following isolating mechanisms is likely to have been the most important in preventing gene flow between the two populations of Rhagoletis?

Accepted Answer

Ecological isolation due to different host plants.

Answer

Temporal isolation due to differences in mating time.

Answer

Behavioral isolation due to differences in mating behaviors.

Answer

Mechanical isolation due to differences in reproductive structures.

Question 61

Thrips are insects that feed on rose pollen. Scientists noted that the thrips population increased in the spring and decreased dramatically during the summer. The researchers hypothesized that food abundance was the limiting factor for the population. Which of the following types of data would be most useful for the scientists to collect at regular intervals on a designated test plot of rose plants?

Accepted Answer

Density of rose pollen produced (g/m²)

Answer

Amount of sunlight (hours/day)

Answer

Mean temperature (°C)

Answer

Amount of pollen produced by each flower (g/flower)

Question 62

What is the main way in which the cells of the leaves of the small evergreen trees differ from the cells of the leaves of the large trees?

Accepted Answer

The cells of the leaves of the small evergreen trees have thicker cell walls.

Answer

The cells of the leaves of the small evergreen trees have larger vacuoles.

Answer

The cells of the leaves of the small evergreen trees have a greater number of chloroplasts.

Answer

The cells of the leaves of the small evergreen trees have more mitochondria.

Question 63

If ATP breakdown (hydrolysis) is inhibited, which of the following types of movement across cell membranes is also inhibited?

Accepted Answer

Passage of a solute against its concentration gradient

Answer

Movement of oxygen into a cell

Answer

Movement of water through aquaporins

Answer

Facilitated diffusion of a permeable substance

Question 64

Which of the following statements provides the best explanation for the main trend shown in the graph above?

Accepted Answer

Pigment concentration is inversely correlated with light exposure.

Answer

The pigment concentration in leaves is not affected by light exposure.

Answer

Leaf growth is positively correlated with pigment concentration.

Answer

Leaf growth increases linearly with increased pigment concentration.