BIOLOGY FINAL CHAPTER 28

Louis Pasteur conducted an experiment to answer the question of whether or not living things can arise spontaneously from nonliving materials. In this experiment, he used two flasks of sterile broth. What were the results of this experiment? A) In the flask with the curved neck, no growth occurred. However, growth did occur in the flask that allowed outside air to enter, demonstrating that living things came from outside the sterile broth. B) No growth occurred in either flask, demonstrating that sterile broth could not promote growth. C) Both flasks showed growth, demonstrating that spontaneous generation does occur. D) While both flasks showed growth, the flask with the curved neck showed a higher growth, demonstrating that spontaneous generation does not require air. E) No growth occurred in either flask, demonstrating that sterilizing the broth removed its nutrients so growth could not occur regardless of whether or not life was present.

A) In the flask with the curved neck, no growth occurred. However, growth did occur in the flask that allowed outside air to enter, demonstrating that living things came from outside the sterile broth. Explanation: Louis Pasteur devised an experiment in which he used two flasks of sterile broth. When flasks containing sterilized broth were exposed to either outdoor or indoor air, they often became contaminated with microbial growth. However, if the neck of the flask was curved so that microbes could not enter the broth from the air, no growth occurred. Thus, the bacteria were not arising spontaneously in the broth, but rather were coming from the air.

Which description best fits a chemoautotroph bacteria? A) They reduce carbon dioxide to an organic compound by using energetic electrons derived from chemicals. B) They reduce oxygen to an inorganic compound by using energetic electrons derived from chemicals. C) They utilize photosynthesis to produce their own food. D) They transfer electrons to sulfate, producing hydrogen sulfate. E) All of the answer choices are descriptions of a chemoautotroph bacteria.

A) They reduce carbon dioxide to an organic compound by using energetic electrons derived from chemicals. Explanation: Chemoautotroph bacteria reduce carbon dioxide to an organic compound by using energetic electrons derived from chemicals. When reduced, carbon dioxide is an organic compound. Using photosynthesis to produce their own food is the description of an autotroph. Transferring electrons to sulfate, producing hydrogen sulfate, is a feature of heterotrophic bacteria.

Biological evolution (the evolution of living cells) differs from chemical evolution (the evolution of the molecules that make living cells) in that biological evolution would have been possible only after the development of A) a membrane. B) nucleic acids. C) enzymes. D) a metabolic pathway. E) RNA and enzymes.

A) a membrane. Explanation: Biological evolution could not have begun until the formation of a plasma membrane that would enclose the cellular components.

Some viruses contain which of the following structures on their outer surface? A) a membranous envelope composed of the host's plasma membrane B) both DNA and RNA from the host C) either DNA or RNA D) a protein capsid E) a protein spore coat

A) a membranous envelope composed of the host's plasma membrane Explanation: Some viruses, especially those that infect animals, can have a membrane called the envelope that is formed from the membrane of the host cell. Since the membrane contains the molecules that are normally found in the host's own cells, this helps the virus fool the host into not attacking the invading virus.

Which of the following groups has a membrane composed of a monolayer of lipids with branched side chains that helps some members of the group tolerate acid and heat? A) archaea B) bacteria C) fungi D) prions E) viruses

A) archaea Rather than a lipid bilayer, archaea often have a monolayer of lipids with branched side chains. These chemical characteristics help many archaea tolerate acid and heat.

Which stage of viral reproduction takes place when the spikes of the virus bind to a specific receptor molecule on the surface of a host cell? A) attachment stage B) penetration stage C) biosynthesis stage D) maturation stage E) release stage

A) attachment stage Explanation: During attachment, the virus binds to a specific receptor protein on the surface of the cell. Although the receptor has some function that it normally performs for the cell, the virus is able to use the receptor for its own purposes. It then fuses its envelope with the membrane of the cell, allowing the capsid and its contents to enter the cell.

What general feature defines an organism as a microbe? A) generally require a microscope to be seen B) multicellular C) heterotrophic D) sexual reproduction E) use aerobic respiration for metabolism

A) generally require a microscope to be seen Explanation: Microbes are generally small enough that a microscope is required to see them. All of the other features are not necessarily found in microbes.

Which of the following associations is correct? A) herpesvirus—chickenpox B) Epstein-Barr virus—shingles C) viroid—scrapie D) prion—influenza E) HIV—Creutzfeldt-Jakob disease

A) herpesvirus—chickenpox Explanation: Chicken pox is caused by the herpesvirus (varicella-zoster virus). The Epstein-Barr virus is associated with mononucleosis, or "mono." Viroids lead to diseases in plants, while prions cause diseases of the nervous system in humans, such as Creutzfeldt-Jakob disease, and other diseases in other animals such as scrapie and mad cow disease. HIV leads to AIDS.

What form of energy did the electric spark in the Miller-Urey experiment simulate? A) lightning B) ultraviolet radiation C) heat from volcanoes D) falling water E) sound

A) lightning Explanation: Stanley Miller reasoned that the energy sources on early Earth included heat from volcanoes and meteorites, radioactivity from isotopes, powerful electric discharges in lightning, and solar radiation. For his experiment, Miller placed a mixture of methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O), in a closed system, heated the mixture, and circulated it past an electric spark to simulate lightning.

Most viruses are A) much smaller than bacteria. B) usually more than 1 micron long. C) larger than protists. D) immeasurable. E) single celled.

A) much smaller than bacteria. Explanation: Generally viruses are smaller than the smallest bacteria that are known. They vary in size from 0.03 microns to 0.2 microns, although one virus has been found that is 0.4 microns.

Which feature is lacking in the cell wall of archaea that will distinguish them from the bacteria? A) peptidoglycan B) phospholipids C) proteins D) polysaccharides E) None of the answer choices are lacking in the cell walls of the archaea.

A) peptidoglycan Explanation: Archaea lack peptidoglycan in their cell walls, which will distinguish them from the bacteria.

The synthesis of DNA or RNA from the organic soup would have been guided by the actions of enzymes in the A) protein-first hypothesis. B) RNA-first hypothesis. C) clay-catalyst hypothesis. D) DNA-first hypothesis.

A) protein-first hypothesis. Explanation: The protein-first hypothesis suggests that proteins, or at least polypeptides, were the first of the three molecules to arise. Only after the protocell developed sophisticated enzymes did it have the ability to synthesize DNA and RNA from small molecules provided by the ocean. Researchers point out that because nucleic acids are very complicated molecules, the likelihood that RNA arose on its own is minimal.

What feature enables the archaea to survive in harsh environments? A) their plasma membranes and cell walls B) their metabolism C) the ability to form multicellular organisms D) their reproductive capabilities E) their nucleus

A) their plasma membranes and cell walls Explanation: The cell wall is the main feature that enables the archaea to survive in harsh environments. They do not possess a nucleus. Their metabolism and reproductive capabilities are not the main feature that enables them to survive in harsh environments. Archaea do not form multicellular organisms.

The core of a virus contains A) a membranous envelope. B) both DNA and RNA. C) either DNA or RNA. D) a protein capsid. E) a protein spore coat.

C) either DNA or RNA. Explanation: All viruses are composed of a protein capsid that surrounds the genetic material of the virus; this is either DNA, which can be single stranded or double stranded, or RNA, which can be single stranded or double stranded.

The hypothesis that RNA and polypeptides evolved simultaneously was proposed by A) Stanley Miller. B) Alexander Cairns-Smith. C) Charles Darwin. D) Gunter Wachtershauser E) Sidney Fox.

B) Alexander Cairns-Smith. Explanation: Scottish chemist Alexander Cairns-Smith proposed that polypeptides and RNA evolved simultaneously. Therefore, the first true cell would have contained RNA genes that could have replicated because of the presence of proteins.

Which of the following is the correct order, from simple to complex, showing the origin of life? A) proteins → CH4 and NH3 → amino acids → C, H, O, N B) C, H, O, N → CH4 and NH3 → amino acids → proteins C) C, H, O, N → amino acids → proteins → CH4 and NH3 D) amino acids → proteins → C, H, O, N → CH4 and NH3 E) CH4 and NH3 → proteins → C, H, O, N → amino acids

B) C, H, O, N → CH4 and NH3 → amino acids → proteins Explanation: The least complex of the listed components are the component atoms (C, H, O, and N). These came together to form the inorganic molecules CH4 and NH3. Both of these were present in the atmosphere of the early earth and, together with an energy source, they formed amino acids. These amino acids then linked together by covalent bonds to form chains.

In addition to his work with bacteria, Louis Pasteur also suggested that something even smaller than a bacterium was the cause of rabies. What did Louis Pasteur accomplish that furthered our understanding of viral diseases? A) He was the first to discover that viruses could be based on RNA rather than DNA. B) He developed a vaccine that he used to save a young boy that had contracted rabies. C) He was the first to see a virus under a microscope. D) He was the first to determine the life cycle of a virus.E) He invented the microscope.

B) He developed a vaccine that he used to save a young boy that had contracted rabies. Explanation: Pasteur created a vaccine against rabies and used the vaccine to cure a young boy that had contracted rabies. Microscopes were invented several hundred years before Pasteur. Viruses are too small to be seen under a light microscope and electron microscopes were not yet invented so he could not have seen a virus nor have determined the life cycle of one. Also, DNA and RNA were not known during Pasteur's lifetime.

Pathogenic bacteria are becoming increasingly deadly because A) humans do not wash their hands frequently enough. B) antibiotic resistance is becoming more and more common due to humans taking unnecessary antibiotics. C) they pick up genes from humans, allowing them to fool human body cells into thinking that they are harmless. D) humans lose their natural immunity to many pathogens through lack of exposure. E) there is an increasing number of side effects from antibiotics.

B) antibiotic resistance is becoming more and more common due to humans taking unnecessary antibiotics Explanation: As more and more antibiotics are prescribed, natural selection acts on the bacterial populations to select for those that have a resistance. Typically, antibiotics act on some molecule in the bacterium, such as an enzyme that plays an important role in the bacterium's functioning. Bacteria that have a mutation in this molecule are not susceptible to the antibiotic and are the ones that survive and pass on this mutation to future generations. Over time, more and more of the population have the mutation and eventually the antibiotic will no longer affect the bacterial population.

Which type of organism will form endospores when faced with unfavorable environmental conditions? A) viruses B) bacteria C) algae D) protozoans E) viroids

B) bacteria Explanation: In unfavorable conditions, some bacteria will form thick-walled dehydrated structures called endospores that are capable of surviving harsh conditions. These structures are not for reproduction but serve to preserve the bacteria until conditions improve.

Antibiotics are used to treat A) viral infections. B) bacterial infections C) viroid infections. D) prion infections. E) fungal infections.

B) bacterial infections Explanation: Most antibiotics kill or inhibit bacteria by interfering with the unique metabolic pathways that the bacteria possess.

In order to infect a cell, a virus must A) inject its protein into the cell while the nucleic acid remains attached to the host cell surface. B) have a special protein spike on its surface capsid that can interact with a receptor protein on the surface of the host cell. C) actively burrow through the cell wall or cell membrane of the host cell to reach the cell's nucleus. D) produce a special extension of its cytoplasm when it comes into contact with the appropriate host cell.E) have enzymes to break down the cell wall or cell membrane of the host cell.

B) have a special protein spike on its surface capsid that can interact with a receptor protein on the surface of the host cell. Explanation: During attachment, the virus binds to a specific receptor protein on the surface of the cell. Although the receptor has some function that it normally performs for the cell, the virus is able to use the receptor for its own purposes. It then fuses its envelope with the membrane of the cell, allowing the capsid and its contents to enter the cell.

Proteinaceous infectious particles that cause degenerative diseases of the nervous system in humans and other animals are called A) archaeans. B) prions. C) cyanobacteria. D) phages. E) retroviruses.

B) prions. Explanation: In animals, there are proteins that cause disease; in addition to causing problems by their presence, they also are infectious and convert other proteins to change shape. These infectious proteins are called prions and affect normal proteins, leading to degenerative disease of the nervous system.

The capsid of a virus is composed of A) RNA. B) protein. C) DNA. D) cellulose. E) lipid.

B) protein. Explanation: The capsid of a virus may take one of several shapes and is composed of protein

If a virus is latent A) it cannot be a retrovirus. B) the viral genome is reproduced along with the host cell. C) it must be a retrovirus. D) it is gaining a new envelope via "budding." E) it is easy to develop immunity against.

B) the viral genome is reproduced along with the host cell. Explanation: Latency describes the reproductive stage of viruses where they are located inside a host cell and the genetic material is reproduced every time the host cell divides, leading to multiple cells that are infected. However, during this time, no viruses are exiting the cells to infect new cells. This is called the lysogenic stage.

Which relationship is correct? A) halophiles—cold Antarctic ice B) thermoacidophiles—hot, acidic environments C) methanogens—high salt concentration D) cyanobacteria—bacteriorhodopsin E) methanogens—live in very high altitudes

B) thermoacidophiles—hot, acidic environments Explanation: Thermoacidophiles live in extremely hot and acidic environments such as the hot springs at Yellowstone National Park. Halophiles would be found in very salty environments and methanogens would be found in anaerobic environments. Bacteriorhodopsin is a pigment found in some photosynthetic halophiles.

A virus carries a piece of bacteria DNA from one bacterium to another in a process called A) transformation. B) transduction. C) conjugation. D) infection. E) replication.

B) transduction. Explanation: While bacteria do not use sexual reproduction, they do have three known methods of combining genetic material. First, there is conjugation, where genetic material is transferred from one bacterium to another via a sex pilus. Next is the process of transformation, where the DNA of a dead bacterium is taken up from the surrounding medium by a live bacterium. And finally there is transduction. In this method, a virus carries portions of bacterial DNA between two bacteria.

Bacteria cause diseases in humans when they A) rearrange the genes of the host to code for specific virulence factors that determine the type and extent of the illness. B) carry the same genes as the host organism, causing them to be indistinguishable from the host cell. C) carry the genes that code for virulent factors, causing them to be harmful to humans. D) carry genes that allow them to become symbiotes. E) carry the genes of organisms like birds (bird flu) or pigs (swine flu).

C) carry the genes that code for virulent factors, causing them to be harmful to humans. Explanation: Bacteria that might otherwise be harmless can become pathogens if they carry certain virulence factors that cause them to produce substances that are toxic to humans.

How are the archaea different from bacteria? A) Archaea show the earliest form of photosynthetic ability. B) Bacteria lack the peptidoglycan cell wall found in the archaea. C) Archaea have a monolayer of lipids with branched side chains. D) Archaea have evolved far more advanced forms of metabolism than bacteria. E) Archaea have very delicate plasma membranes compared to more durable bacteria.

C) Archaea have a monolayer of lipids with branched side chains. Explanation: While archaea and bacteria both lack membrane-bound organelles and a nucleus, archaea lack peptidoglycans in their cell wall and instead of a lipid bilayer, archaea often have a monolayer of lipids with branched side chains.

Which genus of bacteria causes more diseases in humans than any other? A) E. coli B) Staphylococcus C) Streptococcus D) Mycobacterium E) Clostridium

C) Streptococcus Explanation: While all of the bacteria listed cause disease in humans, the one that causes more is Streptococcus. The diseases range from strep throat to necrotizing fasciitis (flesh-eating bacteria) to pneumonia, depending on the species of streptococcus.

Which of the following is a true statement about protobionts (protocells)? A) They would have contained DNA as the genetic material. B) They evolved after the first true cells. C) They represent stage 3 in the evolution of life. D) They would have contained only monomers. E) The hydrophilic heads of the membrane would have pointed inwards, while the hydrophobic tails would have pointed outwards.

C) They represent stage 3 in the evolution of life. Explanation: Before the first true cell arose, there would likely have been a protobiont (protocell), a structure that had a lipid-protein membrane that contained many polymers. This is stage 3 in the evolution of life. The membrane was most likely made of fatty acids with the hydrophilic heads of pointed outwards, while the hydrophobic tails pointed inwards.

Which type of prokaryotes are able to live in the most extreme environments? A) cyanobacteria B) anaerobic bacteria C) archaea D) heterotrophic E) aerobic bacteria

C) archaea Explanation: Archaea are sometimes called extremophiles since they can live in conditions that no other organisms can tolerate. They can live in extremely hot, salty, acidic, and anaerobic environments.

Metabolically, archaea A) are all photosynthetic. B) are all heterotrophic. C) can be heterotrophic or autotrophic. D) are all parasitic.

C) can be heterotrophic or autotrophic. Explanation: Archaea can be either heterotrophs or autotrophs.

One bacterial cell passes DNA to a second cell through a sex pilus in the process of A) transformation. B) transduction. C) conjugation. D) infection. E) replication.

C) conjugation. Explanation: Of the three possible methods of DNA transfer for bacteria, the only one that involves a movement of DNA directly from one bacterium to another is conjugation.

Just after entering a cell, a virus A) begins assembling more viruses. B) removes its envelope. C) loses its protein capsid and the viral genome is exposed. D) immediately integrates its nucleic acid genome into the host chromosomes. E) begins its cycle, which always results in the death of the animal cell.

C) loses its protein capsid and the viral genome is exposed. Explanation: During entry, also called penetration, the viral envelope fuses with the host's plasma membrane, and the rest of the virus (capsid and viral genome) enters the cell. The genome is freed when cellular enzymes remove the capsid, a process called uncoating.

Miller's laboratory experiments showed that A) the first cell was probably made of nucleic acids. B) it is possible to form protocells. C) the primitive gases can react together to produce small organic molecules. D) atmospheric pressure is required for life to begin. E) the earth is approximately 4.5 billion years old.

C) the primitive gases can react together to produce small organic molecules. Explanation: To simulate the earth's early environment, Miller placed the inorganic chemicals mentioned in a closed system, heated the mixture, and circulated it past an electric spark (simulating lightning). After a week, the solution contained a variety of amino acids and organic acids.

Which hypothesis suggests that both polypeptides and RNA arose at the same time? A) Aleksandr Oparin's coacervate theory B) Stanley Miller's chemical soup theory C) Sidney Fox's protein-first hypothesis D) Alexander Cairns-Smith's simultaneous evolution of polypeptides and RNA hypothesis E) Darwin's original theory of evolution, as written in Origin of Species

D) Alexander Cairns-Smith's simultaneous evolution of polypeptides and RNA hypothesis Explanation: A combination of these RNA-first and the protein-first hypotheses was put forth by Alexander Cairns-Smith. He thinks that clay was especially helpful in causing the polymerization of both polypeptides and RNA at the same time. Clay attracts small organic molecules and contains iron and zinc, which may have served as inorganic catalysts for polypeptide formation. In addition, clay tends to collect energy from radioactive decay and then discharges it when the temperature or humidity changes, possibly providing a source of energy for polymerization. Cairns-Smith suggests that RNA nucleotides and amino acids became associated in such a way that polypeptides were ordered by, and helped synthesize, RNA.

Which two domains do the prokaryotes belong? A) Archaea and Cyanobacteria B) Bacteria and Cyanobacteria C) photosynthetic bacteria and chemosynthetic bacteria D) Archaea and Bacteria E) autotrophs and heterotrophs

D) Archaea and Bacteria Explanation: Traditionally, all prokaryotic cells were grouped together into one kingdom called Bacteria. With recent advances in biochemical analysis, the groups have been divided into two domains known as Bacteria and Archaea.

When small mutations gradually change the surface antigens of a virus so that antibodies to the original virus become less effective, this is known as A) an arms race. B) antigenic escape. C) antibody migration. D) antigenic drift. E) spike reassortment.

D) antigenic drift. Explanation: In antigenic drift, small mutations gradually change surface antigens so that antibodies to the original virus become less effective.

Which organisms form lichens? A) archaea and algae B) archaea and fungi C) cyanobacteria and algae D) cyanobacteria and fungi E) cyanobacteria and archaea

D) cyanobacteria and fungi Explanation: Lichens are a combination of algae or cyanobacteria and fungi. These organisms live in a symbiotic relationship with the algae or cyanobacteria, supplying food through photosynthesis and the fungus supplying a protective environment.

Liposomes are composed of A) amino acids. B) protein. C) glucose. D) lipids. E) nucleic acid.

D) lipids. Explanation: A liposome is a microscopic sac formed by lipids. In an aqueous environment, lipids will arrange themselves into a double-layered bubble to keep the hydrophobic portion of the molecules out of the liquid.

Which of the following describes the process of transformation? A) crossing-over between paired chromosomes in meiosis B) a bacteria cell passing DNA to another bacterial cell by means of a sex pilus C) virus carries DNA from a previous host cell to a new host cell D) live bacterium picks up DNA from a dead bacterium E) one bacterial cell dividing to form two bacterial cells

D) live bacterium picks up DNA from a dead bacterium Explanation: While bacteria do not use sexual reproduction, they do have three known methods of combining genetic material. First, there is conjugation, where genetic material is transferred from one bacterium to another via a sex pilus. Next is the process of transformation where the DNA of a dead bacterium is taken up from the surrounding medium by a live bacterium. And finally there is transduction. In this method, a virus carries portions of bacterial DNA between two bacteria.

Which of the following molecules is thought to have been absent from the primitive reducing atmosphere of early Earth? A) water vapor (H2O) B) methane (CH4) C) hydrogen (H2) D) oxygen (O2) E) nitrogen (N2)

D) oxygen (O2) Explanation: In the early earth, volcanoes erupted constantly, and the first atmospheric gases would have consequently contained methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor. Oxygen (O2) would not have been present until photosynthetic organisms evolved and produced oxygen.

Bovine spongiform encephalopathy (BSE), or "mad cow disease," is caused by a(n) A) archaean. B) bacterium. C) cyanobacterium. D) prion. E) virus.

D) prion. Explanation: One form of infectious protein or prion is bovine spongiform encephalopathy (BSE), or "mad cow disease."

Naked strands of RNA not covered by a capsid are A) archaea. B) retroviruses. C) viroids. D) prions. E) viruses.

D) prions. Explanation: In addition to viruses which do have a capsid covering them, and possibly have an envelope, there are also naked strands of RNA that are known to attack plants; these circular segments of RNA are called viroids.

What differentiates Gram-positive and Gram-negative bacteria? A) the type of DNA or RNA they contain B) their ability or lack of ability to fix nitrogen C) whether they are aerobic or anaerobic D) whether their cell walls have a thin or thick layer of peptidoglycan E) their specific rRNA sequences

D) whether their cell walls have a thin or thick layer of peptidoglycan Explanation: Cell walls that have a thick layer of peptidoglycan outside the plasma membrane stain purple with the Gram stain and are classified as Gram-positive bacteria. If the peptidoglycan layer is either thin or missing, then the bacterial cells stain pink and are classified as Gram-negative.

Which of the following is a benefit of microbes? A) break down organic molecules B) Various microbes help protect us from harmful microbes. C) aid in digestion D) synthesize vitamins K and B12 E) All of the answer choices are benefits of microbes.

E) All of the answer choices are benefits of microbes. Explanation: All of the answer choices are benefits of microbes.

Microbiology is the study of microbes. Which of the following is considered a microbe? A) archae B) protists C) viroids D) bacteria E) All of the answer choices are microbes.

E) All of the answer choices are microbes. Explanation: All of the answer choices fall into the category of microbes. Most of these are small enough that a microscope is required to see them.

Which of the following is a true statement about bacteria? A) Bacteria lack mitochondria. B) Bacteria lack a nucleus but have DNA. C) Bacteria occur in three basic shapes. D) Bacteria have a single circular chromosome. E) All of the answer choices are true statements about bacteria.

E) All of the answer choices are true statements about bacteria. Explanation: Bacteria are single-celled organisms; they do not have any membrane-bound organelles including a nucleus. Their DNA is a single circular chromosome that is located in the cytoplasm of the cell. Bacteria are found in one of three shapes: bacilli (rod), cocci (spheres), and spirillium (curved).

Which statement is true about cyanobacteria? A) They are sometimes erroneously called blue-green algae. B) They can form toxic blooms in water enriched with nutrients. C) They can combine with fungi to form lichens. D) They can colonize rocks. E) All of the answer choices are true statements about cyanobacteria.

E) All of the answer choices are true statements about cyanobacteria. Explanation: All of the answer choices are true statements about cyanobacteria.

Which statement is true about prion diseases? A) Prions are believed to cause Creutzfeldt-Jakob disease (CJD). B) Prions are misshapen proteins that cause other proteins to change shape. C) Mad cow disease (BSE) is spread by consumption of cattle feed contaminated with prions. D) The buildup of these abnormal proteins cause a loss of neurons. E) All of the answer choices are true statements about prions.

E) All of the answer choices are true statements about prions. Explanation: All of the answer choices are true statements about prions.

Which of the following is a true statement about retroviruses? A) they contain the enzyme reverse transcriptase B) it is able to carry out transcription of RNA to DNA C) viral DNA remains in the host genome D) can be hidden from the host immune system E) All of the answer choices are true statements about the retroviruses.

E) All of the answer choices are true statements about the retroviruses. Explanation: All of the answer choices are true statements about retroviruses.

Which of the following is true about viruses? A) The genome may be DNA or RNA. B) The nucleic acid may be single or double stranded. C) Viruses exhibit host specificity. D) Viruses are obligate intracellular parasites. E) All of the answer choices are true statements about viruses.

E) All of the answer choices are true statements about viruses. Explanation: All of the answer choices are true statements about viruses.

Which of the following forms of energy is thought to have been involved in the production of large organic molecules in the primitive reducing atmosphere? A) radioactivity B) electrical energy C) heat D) radiation from the sun E) All of the answer choices describe forms of energy that could have contributed to the production of large organic molecules on early Earth.

E) All of the answer choices describe forms of energy that could have contributed to the production of large organic molecules on early Earth. Explanation: All of the answer choices describe forms of energy that could have contributed to the production of large organic molecules on early Earth.

Which of the following describes the archaea? A) methanogens B) halophiles C) thermoacidophiles D) prokaryotes E) All of the answer choices describe the archaea.

E) All of the answer choices describe the archaea. Explanation: All of the terms listed describe one or more types of archaeans.

Bacteria can be beneficial in which of the following ways? A) They can be used to clean up an oil spill in a process called bioremediation. B) They can be used in industry to generate products, particularly in food processing. C) They are present on the skin and help crowd out harmful bacteria. D) They function in wastewater purification to remove both organic and inorganic substances. E) All of the answer choices describe ways that bacteria can be beneficial.

E) All of the answer choices describe ways that bacteria can be beneficial. Explanation: All of the answer choices describe ways that bacteria can be beneficial. Bacteria can be used to clean up oil and other toxic spills without causing further harm to the environment. Bacteria are used in the production of yogurt, cheese, and wine. Bacteria can also function as decomposers, breaking down organic molecules such as nutrients found in wastewater. They are also present in large numbers on the skin of humans where they prevent harmful bacteria from establishing colonies.

If the hypothesis that protocells arose in a "RNA world" is correct, which of the following would be necessary to shift to a "DNA world"?A) an enzyme or reaction capable of converting ribose to deoxyribose in nucleotidesB) enzymes for reverse transcription of RNA into DNA C) new enzymes to replicate the DNA D) new enzymes for transcribing DNA back to RNA E) All of the answer choices list enzymes that would be necessary for a shift from an RNA world to a DNA world.

E) All of the answer choices list enzymes that would be necessary for a shift from an RNA world to a DNA world. Explanation: If RNA came before DNA, then it would be necessary to evolve a method to convert RNA into DNA. This would mean that ribose would need to become deoxyribose and that reverse transcription would have to occur to produce DNA. Additionally, it would be necessary to copy the DNA so that new cells might have an identical copy of the information contained in it. Finally, in order to make proteins, the cell would need to transcribe the DNA into RNA.

Which statement is true about bacteria? A) Bacteria contain a nucleus. B) Bacteria lack ribosomes. C) Bacteria usually lack a cell wall. D) Bacteria only reproduce sexually. E) Bacteria contain a single, circular chromosome.

E) Bacteria contain a single, circular chromosome Explanation: Bacteria are single-celled organisms; they do not have any membrane-bound organelles, but they do contain ribosomes which are not membrane bound. Their DNA is a single circular chromosome that is located in the cytoplasm of the cell, not in a nucleus. Bacteria are found in one of three shapes: bacilli (rod), cocci (spheres), and spirillum (curved). They reproduce asexually through binary fission.

The central dogma of genetics states that DNA directs protein synthesis and that information flows from A) protein → RNA → DNA. B) protein → DNA → RNA. C) RNA → protein → DNA. D) RNA → DNA → protein. E) DNA → RNA → protein.

E) DNA → RNA → protein. Explanation: Today's cell is able to carry on protein synthesis in order to produce the enzymes that allow DNA to replicate. The central dogma of genetics states that DNA directs protein synthesis and that information flows from DNA to RNA to protein. It is possible that this sequence developed in stages.

Which of the following is a characteristic of bacteria but not viruses? A) They are acellular. B) They are obligate parasites. C) They can be synthesized from chemicals in the laboratory. D) They can contain DNA or RNA. E) Diseases caused by them may be treatable with antibiotics.

E) Diseases caused by them may be treatable with antibiotics. Explanation: Bacterial diseases may be treatable with antibiotics. Antibiotics are not useful against viral diseases.

The fact that a nucleic acid is a very complicated molecule suggests that A) the RNA-first hypothesis is impossible. B) the protein-first hypothesis is therefore the only plausible hypothesis. C) sophisticated enzymes were not present or available to synthesize it. D) no natural system could ever generate them. E) RNA could not have arisen on its own by chance, but required enzymes to guide the synthesis of nucleotides and nucleic acids.

E) RNA could not have arisen on its own by chance, but required enzymes to guide the synthesis of nucleotides and nucleic acids. Explanation: Nucleotides are complex molecules that require a complex system of other molecules to maintain and replicate them and to produce proteins. They, therefore, could not have arisen without first the machinery to produce and maintain them.

Which of the following scientist(s) received a Nobel Prize in Chemistry for their discovery that RNA can be both a substrate and an enzyme? A) A. I. Oparin B) Stanley Miller C) Sidney Fox D) Graham Cairns-Smith E) Thomas Cech and Sidney Altman

E) Thomas Cech and Sidney Altman Explanation: The RNA-first hypothesis suggests that only the macromolecule RNA was needed to progress toward formation of the first cell or cells. Thomas Cech and Sidney Altman shared the 1989 Nobel Prize in Chemistry for their discovery that RNA can be both a substrate and an enzyme. Some viruses today have RNA genes; therefore, the first genes could have been RNA. It would seem, then, that RNA could have carried out the processes of life commonly associated today with DNA and proteins.

The life cycle stage of an animal virus during which a mature capsid forms around copies of the viral RNA genome is A) budding. B) attachment. C) biosynthesis. D) uncoating. E) assembly.

E) assembly. Explanation: Attachment is the first stage where the virus attaches to a receptor protein on the host cell. Entry is the next stage and denotes when the virus actually enters the host cell. Once the virus's genetic material is inside the host cell, replication of the viral genome occurs. In biosynthesis, the capsid and other viral components are replicated. Next is the assembly stage, where the capsid forms around a copy of the genetic material and any viral enzymes. Finally, budding occurs so that the new virus may exit the host cell to infect a new cell.

Which of these is the most accurate description of a virus? A) a noncellular living organism B) one of the smallest bacteria known C) a member of the kingdom Virusae D) an organism composed of only a few cells E) chemical complexes of RNA or DNA protected by protein

E) chemical complexes of RNA or DNA protected by protein Explanation: Viruses are segments of either DNA or RNA enclosed in a capsid composed of protein and possibly a membrane called an envelope. They are generally smaller than the smallest-known bacteria and are obligate parasites, meaning that they cannot exist without a host. The host supplies the molecular machinery to produce more viral genetic material, proteins for the capsid, and the envelope.

Which of the following is considered a method of horizontal gene transfer in bacteria? A) binary fission only B) transformation and binary fission C) conjugation and budding D) transduction and conjugation only E) conjugation, transformation, and transduction

E) conjugation, transformation, and transduction Explanation: Although bacteria do not use sexual reproduction, they do have three known methods of combining genetic material. First, there is conjugation, where genetic material is transferred from one bacterium to another via a sex pilus. Next is the process of transformation, where the DNA of a dead bacterium is taken up from the surrounding medium by a live bacterium. And finally there is transduction. In this method, a virus carries portions of bacterial DNA between two bacteria. Since each of these methods transfers DNA from one bacterium to another bacterium of the same generation, these are all types of horizontal gene transfer.

Which of the following terms would describe a chain of rod-shaped bacterial cells? A) staphylococcus B) streptospirilli C) diplobacilli D) streptococcus E) streptobacilli

E) streptobacilli Explanation: Bacteria are found in one of three shapes: bacilli (rod), cocci (spheres), and spirillum (curved). A chain of bacterial cells is given the prefix strepto-, while a cluster of cells is given the prefix staphylo-. Therefore, a chain of rod-shaped cells would be called streptobacilli

The protein-first hypothesis A) is supported by the discovery that RNA can act as a catalyst. B) is supported by the fact that RNA can act as a substrate and as an enzyme. C) suggests it was an "RNA world" about 4 billion years ago. D) suggests that only RNA was needed to progress to the formation of the first cells. E) suggests that sophisticated enzymes with the ability to synthesize DNA and RNA arose first from small molecules provided by the ocean.

E) suggests that sophisticated enzymes with the ability to synthesize DNA and RNA arose first from small molecules provided by the ocean. Explanation: According to the protein-first hypothesis, proteins, or at least polypeptides, were the first of the three (DNA, RNA, and protein) to arise. Only after the protobiont developed a plasma membrane and sophisticated enzymes did it have the ability to synthesize DNA and RNA from small molecules provided by the ocean. The rest of the answers relate to the RNA-first hypothesis.

Which of the following is considered to be acellular? A) bacteria B) fungi C) algae D) protozoans E) viruses

E) viruses Explanation: Viruses do not have the structures necessary to be considered cellular; nor are they considered living. All living things must be composed of at least one cell and all of the other organisms listed are composed of at least one cell and meet the other criteria for life.

Although microbes are often equated with pathogens, not all are pathogenic and some help humans maintain their health. Which of the following are synthesized by bacteria that live in the human intestine? A) folic acid and vitamin B12 B) insulin and vitamin K C) lipids and folic acid D) vitamin K and lipids E) vitamins K and B12

E) vitamins K and B12 Explanation: Intestinal bacteria aid in digestion and produce vitamins K and B12. Insulin can be produced by bacteria that have their genetic code altered, but these are not usually implanted in humans. Normal insulin production in humans takes place in the pancreas.

Antonie van Leeuwenhoek was a Dutch tradesman and scientist who is famous for inventing the microscope.

FALSE Explanation: Antonie van Leeuwenhoek was an early eighteenth-century Dutch tradesman and scientist. He was apparently very skilled at working with glass lenses, which enabled him to greatly improve the microscopes that already existed in the late 1600s.

One hypothesis suggests that protobionts were heterotrophs, organisms that synthesized organic molecules from inorganic molecules and nutrients.

FALSE Explanation: One hypothesis suggests that protobionts were heterotrophs, organisms that consume preformed organic molecules. However, if the protobiont evolved at hydrothermal vents, it may have carried out chemosynthesis—the synthesis of organic molecules from inorganic molecules and nutrients.

The plasma membrane of archaea is composed of a phospholipid bilayer.

FALSE Explanation: The plasma membrane of archaea is composed of a monolayer of lipids with branched side chains.

Most bacteria are heterotrophs that require an outside source of organic compounds in the same way animals do.

TRUE Explanation: It is true that most bacteria are heterotrophs that require an outside source of organic compounds in the same way animals do.