Formative Quiz #2 - Topic 3, 4, 5

Question 1

Most cells prefer to assimilate nitrogen as ammonia.

a) True
b) False

Answer 1

a) True

Explanation: Ammonia is the preferred form of nitrogen for assimilation as it is more energy-efficient to incorporate into biomolecules.

Question 2

Saccharomyces:

1) Can reproduce asexually by merging two diploid cells
2) Forms a multicellular slug prior to sexual reproduction
3) Can reproduce sexually by undergoing meiosis and forming an ascus
4) Maintains a motile haploid state

Answer 2

3) Can reproduce sexually by undergoing meiosis and forming an ascus

Explanation: Saccharomyces undergo sexual reproduction by meiosis, forming ascospores within an ascus.

Question 3

Lysogenic bacteriophage can be difficult to cultivate because?

1) They don’t infect many bacteria
2) They do not produce many progeny
3) They cannot exit their host cell
4) They do not always lyse their host cell

Answer 3

4) They do not always lyse their host cell

Explanation: Lysogenic bacteriophages integrate their genome into the host’s genome and may not lyse the host unless triggered into the lytic cycle.

Question 4

Sterols:

1) Modify membrane stability in eukaryotes
2) Are found within the lumen of eukaryotic peroxisome organelles
3) Are chemicals found in the lipid bilayer of eukaryotic and bacterial cells, but not archaeal
4) Are structural components of the archaeal isoprenoid monolayer

Answer 4

1) Modify membrane stability in eukaryotes

Explanation: Sterols like cholesterol enhance the stability and fluidity of eukaryotic membranes.

Question 5

The nucleus in a eukaryotic cell:

1) Is where DNA is translated into RNA
2) Contains double stranded, compacted, circular chromosomes
3) Produces ribosomes within an area called the nucleolus
4) Has multiple nuclear pores that allow unrestricted movement of mRNA

Answer 5

3) Produces ribosomes within an area called the nucleolus

Explanation: The nucleolus within the nucleus is responsible for ribosome biogenesis.

Question 6

What’s so special about Giardia lamblia?

1) It can fuse into a giant multinucleated cell
2) It translates proteins within the nucleus
3) It contains no mitochondria
4) It only has a singular membrane (an outer membrane)

Answer 6

3) It contains no mitochondria

Explanation: Giardia lamblia lacks mitochondria, an unusual feature among eukaryotes.

Question 7

An example of an organotroph:

1) A methanogenic archaeon that uses hydrogen for energy and produces methane
2) A person who watches Netflix and eats pizza
3) A denitrifier that reduces nitrate to nitrogen gas
4) A tree that photosynthesizes and produces glucose from carbon dioxide

Answer 7

2) A person who watches Netflix and eats pizza

Explanation: Humans are chemoorganoheterotrophs, which means they obtain energy and carbon from organic compounds. Organotrophs obtain both their energy and electrons from organic compounds (like glucose)

While glucose is an organic molecule, trees produce it themselves from CO₂ and water, rather than consuming it as a source of energy. The difference is between how organisms obtain their energy versus their carbon source.

Question 8

Which of these organisms is a fungus widely used by molecular biologists to investigate the workings of eukaryal cells?

1) Giardia lamblia
2) Cephalosporium acremonium
3) Penicillium notatum
4) Dictyostelium discoideum
5) Saccharomyces cerevisiae

Answer 8

5) Saccharomyces cerevisiae

Explanation: Saccharomyces cerevisiae is a model organism used extensively in molecular biology to study eukaryotic cells.

Question 9

An example of an autotrophic organism is

1) A bacterium that lives on your skin using components in your sweat as an energy and carbon source
2) An archaeon that lives in an aquarium, using ammonia for energy and carbon dioxide for a carbon source
3) A bacterium that lives deep underground in mines that uses sulfate for energy and acetate as a carbon source
4) A bacterium that lives in the soil using glucose for both its energy and carbon source

Answer 9

2) An archaeon that lives in an aquarium, using ammonia for energy and carbon dioxide for a carbon source

Explanation: Autotrophs use inorganic compounds like carbon dioxide (CO₂) for carbon acquisition. Unlike heterotrophs which use organic compounds as a source of carbon.

Here’s why the others are not correct:

1) A bacterium that lives on your skin using components in your sweat as an energy and carbon source:

This organism would likely be a organoheterotroph, as it is using organic compounds from sweat for both energy and carbon. Autotrophs, on the other hand, derive their carbon from inorganic sources like CO₂

3) A bacterium that lives deep underground in mines that uses sulfate for energy and acetate as a carbon source:

This organism is likely a chemolithoheterotroph. While it uses an inorganic compound (sulfate, SO₄²-) for energy (oxidation, e- for ETC), it obtains carbon from acetate, which is organic. Autotrophs do not use organic carbon sources.

4) A bacterium that lives in the soil using glucose for both its energy and carbon source:

This is a organoheterotroph because it uses an organic compound (glucose) for both energy and carbon. Again, autotrophs rely on inorganic carbon sources like CO₂

Question 10

Why might a virus make a good therapy for cancer?

a) They kill rapidly dividing cells like cancerous cells
b) They are small and easy to grow in large quantities
c) They are cell and species specific which targets only a subset of cells
d) Oncolytic viruses specifically infect and kill cancerous cells

Answer 10

d) Oncolytic viruses specifically infect and kill cancerous cells

Explanation: Oncolytic viruses are engineered or naturally occurring viruses that selectively infect and destroy cancer cells while sparing normal cells.

Question 11

You are trying to cultivate a culture of facultative anaerobes and decide to make your culture anoxic. How does this affect your culture?

a) The cells will grow quickly because they prefer anoxic environments
b) The cells will grow slower than they normally would because they prefer oxic environments
c) The cells will die because they cannot tolerate low-oxygen environments
d) The cells will be unaffected because they can grow in both oxic and anoxic environments

Answer 11

b) The cells will grow slower than they normally would because they prefer oxic environments

Explanation: Facultative anaerobes can grow in the absence of oxygen, but they grow more efficiently in its presence as they prefer oxic environments.

Question 12

Which type of metabolism has yet to be discovered?

a) Photolithoautotroph
b) Chemoorganoheterotroph
c) Photoorganoautotroph
d) Chemolithoautotroph

Answer 12

c) Photoorganoautotroph

Explanation: A photoorganoautotroph would use light for energy and an organic molecule as an electron source while fixing inorganic carbon. This metabolic combination is energetically complex and has not been observed in nature.

Question 13

What is the premise of the progressive hypothesis of viral origin?

a) Viruses originated from cells that lost the ability to replicate.
b) Viruses evolved from self-replicating nucleic acid segments.
c) Viruses evolved from symbionts of cells.
d) Viruses were present when the first primordial cells evolved.
e) Viruses arose from fragmented DNA in a cell.

Answer 13

b) Viruses evolved from self-replicating nucleic acid segments.

Explanation: The progressive hypothesis suggests that viruses originated from genetic material that gained the ability to self-replicate and mobilize, evolving into viruses over time.

Question 14

Dimitri Ivanovski is known best for:

a) Discovering bacteriophages and coined the term ‘plaque’
b) Helped identify that yellow fever was transmitted by mosquitos
c) First identified influenza
d) Identified the cause of a common tobacco plant disease

Answer 14

d) Identified the cause of a common tobacco plant disease

Explanation: Dimitri Ivanovski discovered the tobacco mosaic virus, which marked the first identification of a viral pathogen.

Question 15

True or false: all viruses contain a viral envelope.

a) True: This membrane surrounds the nucleocapsid
b) True: This membrane holds the genome
c) False: Only animal viruses have an envelope
d) False: Only some viruses have an envelope

Answer 15

d) False: Only some viruses have an envelope

Explanation: Not all viruses are enveloped. Viral envelopes are typically present in some animal viruses and derived from the host cell membrane.

Question 16

What process can be used to purify a virus?

a) Infection of host cells
b) Differential centrifugation
c) Isolation of viral genome
d) Passage through host

Answer 16

b) Differential centrifugation

Explanation: Differential centrifugation separates viral particles based on size and density, making it a standard method for virus purification.

Question 17

What is used to determine the hemagglutination titer of an isolate?

a) The smallest dilution still capable of forming a button well
b) The greatest dilution still capable of forming a shield well
c) The greatest dilution still capable of forming a button well
d) The smallest dilution still capable of forming a shield well
e) The average of all visible button well results

Answer 17

b) The greatest dilution still capable of forming a shield well

Explanation: The hemagglutination titer is determined by the greatest dilution at which a visible shield (hemagglutination) is formed, indicating the presence of viral particles.

Question 18

If a protein is destined to be secreted from the cell, where will it be translated?

a) Within the endoplasmic reticulum
b) It doesn’t matter where it is translated, the signal peptides will tell the vesicles what to do
c) On the outer membrane of the cell
d) Within the cytosol

Answer 18

a) Within the endoplasmic reticulum

Explanation: Secretory proteins are translated in the rough endoplasmic reticulum, where they are prepared for transport and secretion.

Question 19

Match the terms to the definitions:

1. Heterotroph
2. Autotroph
3. Lithotroph
4. Organotroph

___: An organism that acquires its carbon from an inorganic carbon source
___: An organism that acquires its energy from an organic energy source
___: An organism that acquires its energy from an inorganic energy source
___: An organism that acquires its carbon from an organic carbon source

Answer 19

2: An organism that acquires its carbon from an inorganic carbon source (Autotroph)
4. An organism that acquires its energy from an organic energy source (Organotroph)
3. An organism that acquires its energy from an inorganic energy source (Lithotroph)
1. An organism that acquires its carbon from an organic carbon source (Heterotroph)

Explanation:
1. Heterotroph (Option 1):
An organism that gets its carbon from organic compounds. Relies on organic molecules like glucose or amino acids for its carbon source, which it does not produce itself. Example: Humans.
2. Autotroph (Option 2):
An organism that gets carbon from inorganic carbon sources, such as carbon dioxide (CO₂). These organisms produce their own organic molecules using CO₂, often through photosynthesis or chemosynthesis. Example: Plants and some bacteria.
3. Lithotroph (Option 3):
An organism that derives its energy from inorganic compounds like ammonia (NH₃) or hydrogen sulfide (H₂S). These organisms do not rely on organic molecules for energy. Example: Some archaea and bacteria.
4. Organotroph (Option 4):
An organism that derives its energy from organic compounds, such as carbohydrates, fats, or proteins. This energy source is commonly found in heterotrophs. Example: Many animals, fungi, and some bacteria.

Question 20

During viral purification, centrifugation at medium speed:

a) Pellets viral particles and separates them from the lighter cell components
b) Pellets whole broken cells, separating them from the organelles and virus
c) Only two centrifugation steps are required: one to remove large debris and one to pellet virus
d) Separates the large debris so it can be filtered from the broth

Answer 20

b) Pellets whole broken cells, separating them from the organelles and virus

Explanation: Medium-speed centrifugation separates larger components, such as whole cells and organelles. This separates them from smaller components, such as organelles and viral particles, which remain in the supernatant.

Question 21

Viral genomes may consist of which of these molecules?

a) Single-stranded DNA
b) All of the choices are correct
c) Single-stranded RNA
d) Double-stranded RNA
e) Double-stranded DNA

Answer 21

b) All of the choices are correct

Explanation: Viral genomes exhibit diverse structures, including single-stranded and double-stranded DNA or RNA, depending on the virus type.

Question 22

Hemagglutination

a) Requires dilutions to calculate titer
b) Detects viable virus only
c) Requires a microscope to measure the gel mat
d) Is cheap and cost effective and works for almost all viruses

Answer 22

a) Requires dilutions to calculate titer

Explanation: Hemagglutination assays measure viral concentrations by diluting the virus until red blood cells can no longer agglutinate, helping determine the titer.

Question 23

A chemostat is:

a) A type of continuous culture where medium is added at the same rate it is flushed
b) A type of batch culture where media is periodically refreshed
c) Can only be maintained in oxic conditions
d) Used to keep microorganisms in the stationary phase

Answer 23

a) A type of continuous culture where medium is added at the same rate it is flushed

Explanation: A chemostat maintains a steady-state culture by continuously adding fresh medium and removing spent medium, ensuring stable growth conditions.

Question 24

What does the coevolution hypothesis suggest about the origins of viruses?

a) That viruses formed from cells that used to be alive but lost function and had to resort to being parasitic
b) That all viruses evolved independently at the same time as their hosts
c) That viruses evolved along with their host cells
d) That viruses evolved prior to living cells and were capable of self-replicating

Answer 24

c) That viruses evolved along with their host cells

Explanation: The coevolution hypothesis proposes that viruses and their hosts evolved together, with viruses adapting to exploit host cellular mechanisms over time.

Question 25

What is the viral capsid composed of? a) Lipids b) Proteins c) Polysaccharides d) Nucleic acid e) Glycogen

Answer 25

b) Proteins Explanation: The viral capsid is made of protein subunits that protect the viral genome and facilitate interactions with host cells during infection.

Question 26

A superoxide anion (O₂^-) will kill a cell unless: a) It will always kill a cell and is a common ingredient in bleach and other disinfectants b) It can use antioxidants such as glutathione c) It has a superoxide dismutase enzyme that can protect it d) It has catalase and peroxidase enzymes to protect itself

Answer 26

c) It has a superoxide dismutase enzyme that can protect it Explanation: Superoxide dismutase converts the toxic superoxide anion into less harmful substances, protecting cells from oxidative damage.

Question 27

The enzyme catalase is used to detoxify which harmful oxygen species? a) Hydrogen peroxide b) Singlet oxygen c) Ozone d) Superoxide e) Hydroxyl radical

Answer 27

a) Hydrogen peroxide Explanation: Catalase breaks down hydrogen peroxide, a reactive oxygen species, into water and oxygen, thereby detoxifying it.

Question 28

Hyperthermophiles have adaptations for hot environments that include: a) The substitution of amino acids in key locations of a protein b) Various sterols to increase membrane fluidity c) Long unsaturated fatty acid chains d) A phospholipid isoprenoid bilayer in archaea

Answer 28

a) The substitution of amino acids in key locations of a protein Explanation: Specific amino acid substitutions strengthen protein folding, enhancing stability at high temperatures.

Question 29

In eukaryotes, motion is achieved... a) By rotating the flagellum in a screw-like motion, propelling the cell forward b) With similarly structured flagella as those found in bacteria c) By bending several microtubules in a structure referred to as the 'axoneme' d) By a single polar flagellum

Answer 29

c) By bending several microtubules in a structure referred to as the **'axoneme'** Explanation: Eukaryotic flagella move via the bending of microtubules in the axoneme, a distinct structure that differs from bacterial flagella. The **axoneme** is the core structural framework of eukaryotic flagella and cilia. It consists of a “9+2” arrangement of microtubules: nine pairs of microtubules form a circle around two central, single microtubules. Dynein motor proteins attached to these microtubules produce sliding forces, which are converted into bending motions, allowing movement.

Question 30

What is the first step to most virus infections? a) Fusion of the envelope with the host membrane b) Entry of the genome c) Binding of the virus particle with specific host proteins d) Replication of the viral genome

Answer 30

c) Binding of the virus particle with specific host proteins Explanation: The initial step of viral infection involves the virus binding to specific proteins on the host cell's surface, which facilitates entry. The binding between the viral particle and the host receptor is highly specific and often determines the virus’s host range.

Question 31

You have an enrichment culture containing many microorganisms. You want to isolate the smallest. How? a) Use several serial dilutions as small cells are more likely to remain suspended in solution b) Use a 2 µm filter and collect the flow-through c) Centrifuge at low speed and discard the pellet; the small cells will remain suspended d) Use a 0.22 µm filter and collect the flow-through

Answer 31

b) Use a 2 µm filter and collect the flow-through Explanation: A 2 µm filter allows smaller microorganisms to pass through while retaining larger ones, effectively isolating smaller cells. d) Use a 0.22 µm filter and collect the flow-through **is not correct** because a 0.22 µm filter is typically used to remove bacteria and other microorganisms from a solution. It would retain most microbial cells, including small ones, on the filter. Therefore, you wouldn’t successfully isolate the smallest cells in the flow-through; instead, you would likely lose them in the filtration process.

Question 32

Why can electron microscopy be difficult to use in identification of viruses? a) It is difficult and expensive to do b) Viruses are too small to be seen by EM c) Many viruses have similar size and shape d) Good samples for EM identification are difficult to obtain

Answer 32

c) Many viruses have similar size and shape Explanation: Viruses often exhibit similar sizes and shapes, making it challenging to distinguish between different viruses using electron microscopy alone.

Question 33

Chitin, a component of the fungal cell wall, is a polymer composed of... a) Acetylglucosamine b) Glucose c) Amino acids d) Silica dioxide e) Dipicolinic acid

Answer 33

a) Acetylglucosamine Explanation: Chitin is a polymer made of acetylglucosamine, providing structural support to fungal cell walls.

Question 34

An obligate aerobe requires what as its final electron acceptor? a) NAD+ b) FAD+ c) S d) O₂ e) NO₃^- (nitrate)

Answer 34

d) O₂ Explanation: Obligate aerobes use oxygen as their final electron acceptor during aerobic respiration, enabling efficient energy production.

Question 35

Why might a direct count give you a higher number than a plaque assay? a) The plaque assay underestimates because it depends on calculations and dilutions b) The direct count assay is inaccurate because of microscope limitations c) Plaque assays enumerate dead virus after they have lysed the cells d) Not all the particles you count in a sample are infectious

Answer 35

d) Not all the particles you count in a sample are infectious Explanation: Direct counts include all particles, whereas plaque assays only count infectious viruses, leading to potentially higher direct count results.

Question 36

After attachment to the cell surface, what is an important subsequent step for ALL virus infections? a) Entry of the genome b) Entry of the capsid c) Fusion of the viral envelope d) Replication of the viral genome

Answer 36

a) Entry of the genome Explanation: Entry of the viral genome into the host cell is a critical step in all virus infections, allowing replication to begin.

Question 37

You are making media in the lab and you add peptone and yeast extract. This is a: a) Enriched medium b) Complex medium c) Defined medium d) Selective medium

Answer 37

b) Complex medium Explanation: A complex medium contains undefined components, such as peptone and yeast extract, with unknown exact quantities or compositions of nutrients.

Question 38

What attribute does the Baltimore classification use in classification of viruses? a) Virion morphology b) Genome type and structure c) Host range d) All of these choices

Answer 38

b) Genome type and structure Explanation: The Baltimore classification system categorizes viruses based on their genome type (DNA or RNA) and replication strategy, which provides insights into their biology and evolution.

Question 39

How does Listeria exploit eukaryotic cell structure? a) By propelling itself using actin filaments b) By integrating with the mitochondria and using the ATP synthase c) By penetrating the nucleus and use the polymerase to replicate d) By coating itself in plasma membrane and shielding itself from the immune system

Answer 39

a) By propelling itself using actin filaments Explanation: Listeria uses host actin filaments to propel itself through the cytoplasm and into neighboring cells, facilitating its spread and evasion of the immune system.

Question 40

How big are most viruses compared to the cells they infect? a) Much smaller - between 10-100 nm b) Smaller - between 100 nm and 1 µm c) About the same - greater than 10 µm

Answer 40

a) Much smaller - between 10-100 nm Explanation: Viruses are significantly smaller than the cells they infect, typically ranging in size from 10-100 nanometers

Question 41

Glomeromycota: a) The reason your fresh bread eventually molds b) Can create zombie ants and zombie caterpillars by forming cordyceps c) Closely associated with trees and small plants d) Commonly used for cooking as they create traditional mushrooms

Answer 41

c) Closely associated with trees and small plants Explanation: Glomeromycota form symbiotic relationships with plant roots, aiding in nutrient absorption and growth.

Question 42

You have isolated a novel virus that only infects humans but does not form plaques. To quantitate the amount of infectious virus present, would you measure the TCID50 or the LD50? a) The LD50 because it is more accurate b) The LD50 because you cannot measure a TCID50 if a virus cannot form plaques c) The TCID50 because you need to infect and kill humans for a LD50 d) The TCID50 because it is faster and easier

Answer 42

c) The TCID50 because you need to infect and kill humans for a LD50 Explanation: The TCID50 is used to measure the infectious dose of a virus in 50% of the host population, and it does not rely on plaque formation, unlike the LD50.

Question 43

An obligate aerobe: a) Is incapable of growing in anoxic environments b) Requires low concentrations of oxygen or anoxic environments c) Thrives in low-oxygen environments but will die when exposed to higher oxygen concentrations d) Thrives in oxygen-rich environments but will survive in anoxic environments

Answer 43

a) Is incapable of growing in anoxic environments Explanation: Obligate aerobes require oxygen to grow and cannot survive in environments without it. **Obligate Aerobe**: Requires oxygen to grow and cannot survive in environments without it. Oxygen is used as the terminal electron acceptor in their metabolism. **Obligate Anaerobe**: Cannot survive in the presence of oxygen. Oxygen is toxic to these organisms as they lack the necessary enzymes to detoxify reactive oxygen species. **Facultative Anaerobe**: Can grow in both oxygen-rich and oxygen-poor environments. They preferentially use oxygen for energy production (aerobic respiration) but can switch to anaerobic respiration or fermentation in its absence. **Microaerophile**: Requires oxygen but at lower concentrations than what is found in the atmosphere. High oxygen levels are harmful to them. **Aerotolerant Anaerobe**: Does not require oxygen and grows without it but can tolerate its presence. They do not use oxygen for energy but have enzymes to neutralize reactive oxygen species.

Question 44

Measuring PFU has an advantage over direct virus counts because it helps us determine: a) Enveloped versus non-enveloped anatomy b) Infectivity c) Viral structure d) The burst size

Answer 44

b) Infectivity Explanation: Plaque-forming units (PFUs) measure the number of infectious viruses capable of forming plaques, unlike direct counts, which include all particles regardless of viability.

Question 45

A prophage... a) Is a gene that has been modified by a virus and may become pathogenic b) Replicates independently of the host genome c) Is viral genetic material that has been incorporated into the host genome d) Is what we call the viral genome before it is packaged into the capsids during viral replication

Answer 45

c) Is viral genetic material that has been incorporated into the host genome Explanation: A prophage is the viral genome integrated into the bacterial host DNA, remaining dormant until activated.

Question 46

The International Committee on Taxonomy of Viruses (ICTV) classification scheme uses all of the following criteria to classify viruses EXCEPT: a) Virion morphology b) The presence or absence of a cell envelope c) Ribosomal RNA sequence d) The type of nucleic acid they contain e) The host they infect

Answer 46

c) Ribosomal RNA sequence Explanation: Viruses do not possess ribosomal RNA as they rely on host cellular machinery for replication, making this criterion irrelevant for their classification.

Question 47

Generation time is: a) The time to double the population at exponential phase b) The number of generations per unit of time c) The time required to synthesize DNA d) The maximum density reached within 1 hour

Answer 47

a) The time to double the population at exponential phase Explanation: Generation time refers to the period required for a population to double during exponential growth, a key concept in microbiology.

Question 48

Lysogenic viruses: a) Integrate into the host genome and never lyse the host cell b) Replicate immediately and lyse the cell once sufficient virus is produced c) Are solely enveloped viruses d) Have a lytic cycle for replicating and releasing new virus

Answer 48

d) Have a lytic cycle for replicating and releasing new virus Explanation: Lysogenic viruses can integrate into the host genome and have the ability to switch to the lytic cycle, this transition depends on environmental triggers or stressors affecting the host cell. If the host cell is under duress the lysogenic virus may decide to lyse the host cell.

Question 49

In chloroplasts, the thylakoid lumen functions most like which area in the mitochondria? a) The intermembrane space b) The inner membrane c) The outer membrane d) The thylakoid lumen is not part of the chloroplast organelle

Answer 49

a) The intermembrane space Explanation: The thylakoid lumen in chloroplasts is analogous to the intermembrane space in mitochondria, as both are sites where protons (H⁺) accumulate during their respective electron transport processes. This accumulation creates a proton gradient, which is then used to drive ATP synthesis via ATP synthase.

Question 50

An example of a lithotroph is: a) An E. coli cell that oxidizes lactate for energy b) A bacterium that oxidizes dissolved organic matter in a wastewater treatment plant c) A nitrifier that oxidizes ammonia to generate energy d) A fermenting bacterium that produces alcohol

Answer 50

c) A nitrifier that oxidizes ammonia to generate energy Explanation: Lithotrophs utilize inorganic compounds, such as ammonia, as their energy source, making nitrifiers a prime example.

Question 51

A protein entering the secretory pathway of a eukaryal cell would follow which path? a) Nucleus, Golgi apparatus, rough ER, smooth ER, secretion b) Nucleus, smooth ER, cytoplasm, Golgi apparatus, secretion c) Nucleus, Golgi apparatus, rough ER, cytoplasm, secretion d) Nucleus, rough ER, cytoplasm, Golgi apparatus, secretion e) Nucleus, cytoplasm, rough ER, Golgi apparatus, secretion

Answer 51

d) Nucleus, rough ER, cytoplasm, Golgi apparatus, secretion Explanation: **Nucleus**: The gene encoding the protein is transcribed into mRNA in the nucleus. **Rough ER**: The mRNA is translated into a protein by ribosomes on the rough ER, where it enters the ER lumen for folding and initial modifications. **Cytoplasm**: Vesicles transport the protein to the Golgi apparatus. **Golgi apparatus**: The protein is further modified and packaged into vesicles. **Secretion**: The protein is transported to the plasma membrane and released outside the cell via exocytosis.

Question 52

You are trying to grow a culture of nitrifiers in an enrichment culture (a chemolithoautotroph). Which medium would be best? a) One with no organic carbon sources and plenty of ammonia b) One with organic nitrogen and carbon sources c) One with no carbon source and exposed to sunlight d) One with ammonia and additional carbon sources, such as glucose and lactate

Answer 52

a) One with no organic carbon sources and plenty of ammonia Explanation: Nitrifiers are chemolithoautotrophs that utilize inorganic compounds like ammonia for energy, so a medium without organic carbon ensures their growth without competition.

Question 53

A high-solute environment: a) Will result in the influx of water into the cell b) Can decrease water activity in a cell c) Is commonly found in freshwater environments d) Is the preferred environment of microorganisms

Answer 53

b) Can decrease water activity in a cell Explanation: High-solute environments lower water activity, causing osmotic stress, which can inhibit microbial growth or require adaptations for survival. A solute is a substance dissolved in a solvent (like water) to form a solution. In biological contexts, solutes include salts, sugars, and other molecules. High-solute environments contain a high concentration of these dissolved substances, reducing water availability and creating osmotic stress for cells.

Question 54

What are the characteristics of a viroid? a) Only protein, no genome b) Only naked RNA, no capsid c) Cannot replicate without a helper virus d) Can replicate independently

Answer 54

b) Only naked RNA, no capsid Explanation: Viroids are infectious agents composed solely of a short strand of circular RNA without a protective protein coat. **Viroids** are known to only infect plants. They cause diseases in plants by interfering with normal cellular processes, primarily through their RNA interacting with the host’s machinery used for gene expression. Unlike viruses, they do not infect animals or humans as they lack the necessary structural or molecular adaptations for such hosts.

Question 55

A psychrophile is most likely to be found: a) In a pot of old macaroni that you've kept in your fridge b) In a fresh pot of macaroni that you've made to replace the old one c) In a hydrothermal vent d) On your computer keyboard

Answer 55

a) In a pot of old macaroni that you've kept in your fridge Explanation: Psychrophiles thrive in low-temperature environments, such as refrigerators, where they can grow on food like old macaroni.

Question 56

What are the characteristics of a prion? a) Only protein, no genome b) Only naked RNA, no capsid c) Cannot replicate without a helper virus d) Can replicate independently

Answer 56

a) Only protein, no genome Explanation: Prions are infectious proteins that lack genetic material and cause diseases by inducing misfolding in normal proteins.

Question 57

An acidophile is likely to have an internal pH of: a) A higher pH to counteract the external environment b) Bacteria cannot survive in high pH environments c) Between pH 1 and 3 d) Approximately neutral

Answer 57

d) Approximately neutral Explanation: Most cells, including acidophiles, maintain an internal pH close to neutral (~7.0) despite their external environment, using homeostatic mechanisms.

Question 58

Which of these best describes the process of meiosis in eukaryal cells? a) DNA replication followed by two cell divisions b) The combining of two gametes c) The asexual production of two diploid cells d) Asexual reproduction e) Two rounds of DNA replication followed by cell division

Answer 58

a) DNA replication followed by two cell divisions Explanation: Meiosis consists of one round of DNA replication and two successive cell divisions, resulting in four haploid cells.

Question 59

In mitochondria, protons are pumped into which space to create a gradient and generate ATP? a) Across the outer membrane into the intermembrane space b) Across the outer membrane into the cytoplasm c) ATP synthase is omnidirectional and will generate ATP in both directions d) Across the inner membrane into the intermembrane space

Answer 59

d) Across the inner membrane into the intermembrane space Explanation: The electron transport chain pumps protons across the inner mitochondrial membrane into the intermembrane space, generating the proton gradient necessary for ATP synthesis.

Question 60

Why is classification of viruses difficult? a) No single genetic marker (i.e., rRNA) exists for viruses b) Not enough viruses have been isolated for easy classification c) We do not have good sequence information available for viruses d) Too much genetic variation exists between viruses, even viruses of the same strain

Answer 60

a) No single genetic marker (i.e., rRNA) exists for viruses Explanation: Viruses lack a universal reference sequence like rRNA, making classification challenging, compounded by their high mutation rates and genomic diversity.

Question 61

What does the **regressive hypothesis** suggest about the origins of viruses? a) That viruses evolved from intracellular bacterial symbionts b) That viruses evolved from fully functional cells that became parasites of other cells c) That viruses evolved from self-catalyzing RNA fragments imbedded within a lipid micelle d) That viruses used to be non-pathogenic

Answer 61

b) That viruses evolved from fully functional cells that became parasites of other cells Explanation: **Regressive hypothesis** states that viruses were once free-living cells that became parasitic and lost the ability to live independently, retaining only the machinery for reproduction. **Progressive hypothesis** suggests that viruses evolved from mobile genetic elements, like plasmids or transposons, that gained the ability to move between cells. **Co-evolution hypothesis** suggests that viruses and cellular life originated together from self-replicating molecules in the prebiotic world. Both evolved in parallel, with viruses emerging as simple genetic entities that relied on host cells to replicate, reflecting their ancient coexistence. **Virus-first hypothesis** posits that viruses predate cellular life, originating as primitive self-replicating molecules that eventually evolved to infect cells.

Question 62

The organelle responsible for protein folding is: a) The Golgi apparatus b) An organelle is not required because proteins are translated in the cytoplasm in eukaryotes c) The rough endoplasmic reticulum d) The smooth endoplasmic reticulum

Answer 62

c) The rough endoplasmic reticulum Explanation: The rough ER, studded with ribosomes, is responsible for folding and modifying proteins as they are synthesized.

Question 63

Icosahedral viruses are best defined by: a) Their capsids containing multifaceted, triangular-shaped faces b) Their lack of viral envelope c) Their elongated helical capsids d) Their mode of infection via endocytosis

Answer 63

a) Their capsids containing multifaceted, triangular-shaped faces Explanation: Icosahedral viruses are characterized by their symmetrical capsids, which consist of 20 triangular faces, providing structural stability and efficiency.

Question 64

An example of a photoheterotroph is: a) A cyanobacterium that photosynthesizes using light for energy and carbon dioxide for carbon b) An archaeon that uses methane both as an energy and carbon source c) A tree that uses light for energy and carbon dioxide for carbon d) A bacterium that uses light as an energy source and organic carbon as a carbon source

Answer 64

d) A bacterium that uses light as an energy source and organic carbon as a carbon source Explanation: Photoheterotrophs use light as their energy source but rely on organic compounds rather than carbon dioxide as a carbon source.

Question 65

Why might a virus be useful for gene therapy? a) Some viruses can infect and insert their genome into cells without killing the host cell b) They are small and easy to grow in large quantities c) They are cell and species specific which targets only a subset of cells d) Their replication is well understood, making them easy to work with to deliver a particular gene

Answer 65

a) Some viruses can infect and insert their genome into cells without killing the host cell Explanation: Lysogenic viruses integrate their genome into the host genome without triggering lysis, making them ideal for delivering therapeutic genes to target cells.