Exam 2: Chapters 24, 25, 26

Question 1

What are the characteristics of life?

Answer 1

Organisms….
Composed of cells
Grow and develop
Regulate their metabolic processes
Respond to stimuli 
Reproduce
Evolve and adapt

Question 2

Compare and contrast a virus with a cellular organism.

Answer 2

Most biologists view viruses as nonliving particles because they are not composed of cells and they cannot carry on metabolic activities or reproduce on their own.

Question 3

Describe the structure of a virus.

Answer 3

Most viruses range in size from 20 to 300 nm – the largest known virus (Mimivirus) is about 400 nm.
A virus consists of a core of nucleic acid and depends on a living host to replicate (obligate intracellular parasites). Outside of a host cell, a virus consists of a nucleic acid core surrounded by a protein coat (capsid). Capsids may be helical (tobacco mosaic virus), polyhedral, (adenoviruses) or a combination (bacteriophages or phages). The capsid consists of protein subunits (capsomers) which determine the shape of the virus. The T4 phage consists of a polyhedral “head” and a helical “tail” with tail fibers that attach to a host cell.
A virus contains either deoxyribonucleic acid (DNA) OR ribonucleic acid (RNA), which can be single-stranded or double stranded. The virus genome typically consists of 5,000 to more than 100,000 bases or base pairs.
The human immunodeficiency virus (HIV) is an enveloped virus – surrounded by an outer envelope of plasma membrane derived from the host cell. While inside the host cell, the virus synthesizes certain proteins and inserts them into the host’s plasma membrane.

Question 4

What are viruses and what do they infect?

Answer 4

Virologists are biologists who study viruses (virology).
A virus is a small particle consisting of a nucleic acid core surrounded by a protein coat; in order to reproduce, a virus must infect a living cell. Viruses infect all types of organisms, including bacteria, archaea, protists, plants, fungi, and animals – some even infect other viruses.

Question 5

Identify three characteristics used to classify viruses

Answer 5

Viruses can be classified based on their host range, what type of nucleic acid they have, and whether the nucleic acid is single-stranded or double-stranded.
The ICTV has classified viruses into 5 orders, 84 families, 307 genera, and more than 2000 species.

Question 6

Characterize bacteriophages.

Answer 6

Bacteriophages infect bacteria. Bacteriophages (phages) typically consist of a long nucleic acid molecule (usually dsDNA) coiled in a polyhedral head, and a tail that functions in penetration of the host cell. Viral nucleic acid enters the cell and synthesizes components needed to reproduce itself; viral components are assembled, and viruses are released from the cell.
There are two types of viral reproductive cycles: lytic and lysogenic.

Question 7

Compare and contrast a lytic cycle with a lysogenic cycle.

Answer 7

Compare:

Contrast:
In a lytic reproductive cycle, a virus uses the host cell’s molecular machinery to replicate itself, destroying the host cell in the process.
In a lysogenic cycle, the viral genome is integrated into the host DNA and is then called a “provirus”.

Question 8

Describe the lytic reproductive cycle.

Answer 8

In a lytic cycle, the virus lyses (destroys) the host cell. The virus forces the infected host cell to use its metabolic machinery to replicate viral particles. 
Viruses that have only a lytic cycle are virulent – they cause disease, and often death.
There are 5 steps in the lytic cycle:
1. Attachment
2. Penetration
3. Replication and synthesis
4. Assembly
5. Release

Question 9

Define restriction enzymes.

Answer 9

Bacteria protect themselves by producing restriction enzymes that cut up the foreign DNA of the phage.

Question 10

Describe the lysogenic reproductive cycle and lysogenic conversion.

Answer 10

Temperate viruses do not always destroy their hosts.
In a lysogenic cycle, the viral genome usually becomes integrated into the host bacterial DNA (prophage or provirus) and is replicated along with bacterial DNA. Viral genes may be repressed indefinitely; or external conditions (UV, X-rays) may cause temperate viruses to revert to a lytic cycle and destroy their host.
Bacterial cells containing certain temperate viruses may exhibit new properties (lysogenic conversion).
There are 4 steps in the lysogenic cycle:
1. Attachment
2. Penetration
3. Integration
4. Replication

Question 11

What are some of the viruses that infect humans? How often do most humans suffer from viral infections?

Answer 11

Viruses cause chickenpox, herpes simplex , mumps, rubella, rubeola , rabies, warts, infectious mononucleosis, influenza, viral hepatitis, certain types of cancer, and AIDS.
Most humans suffer from two to six viral infections each year, including common colds.

Question 12

What is the group of viruses that causes AIDS, herpes, polio, and smallpox?

Answer 12

AIDS: Retroviruses (RNA viruses with envelope)
Herpes: Herpesviruses (DNA viruses with envelope)
Polio: Picornaviruses (RNA viruses with no envelope)
Smallpox: Poxviruses (DNA viruses with envelope)

Question 13

Describe the origins of viruses in the cellular origin hypothesis.

Answer 13

Viruses may have originated as mobile genetic elements (such as transposons or plasmids) that could have moved from one cell to another through damaged cell membranes.
Some viruses may have originated in animal cells, others in plant cells or bacterial cells.
Supported by genetic similarity between some viruses and their host cells.

Question 14

Describe the origins of viruses in the regressive hypothesis.

Answer 14

Viruses may have evolved from small, independent cells that were parasites in larger cells, and unneeded genes were gradually lost through evolution.
Supported by certain bacteria (chlamydia and rickettsia) that are able to reproduce only inside host cells.
Explains how viruses could have existed before their hosts evolved.

Question 15

Explain why species concepts of Eukaryotes do not apply to Prokaryotes.

Answer 15

ANSWER

Question 16

Describe one species concept that is used for Prokaryotes.

Answer 16

ANSWER

Question 17

Describe prokaryotes history.

Answer 17

Prokaryotes (bacteria and archaea) have inhabited our planet for more than 3.5 billion years (eukaryotes for ca. 1.7 billion).
Anton van Leeuwenhoek discovered bacteria in 1674 when he looked at a drop of lake water through a glass lens.
During the late 1800s, some bacteria were identified as pathogens – many more are decomposers, photosynthesizers, or essential fixers of nitrogen.

Question 18

Describe prokaryotes basis.

Answer 18

Prokaryotes significantly shaped the atmosphere, soils, climate of the earth - they still do.
Fundamental metabolic pathways arose first in prokaryotes.
-respiration (glycolysis)
-photosynthesis (convert CO2 to organic mol.)
All eukaryotes harbor microbial symbionts, which are essential for survival of the eukaryote.
Prokaryotes make up the most species, the most metabolic pathways, and the largest amount of biomass of all kinds of life on Earth.
Can survive in some of the most hostile environments on Earth.

Question 19

Describe prokaryotic species concepts.

Answer 19

Genetic isolation less important (….if important at all).
Lateral Gene Transfer (LGT) is ‘the norm.’
Nucleotide sequence based.
Evolutionary novelty derived from LGT and mutation.
Distinct species boundaries likely do not exist.
Branching pattern is not a good model.

Question 20

Describe eukaryotic species concepts.

Answer 20

Genetic isolation is key.
Reproductive isolation (e.g., BSC), no lateral gene transfer.
Morphology based.
Evolutionary novelty derive from mutation.
Distinct species boundaries a basic premise.
Branching pattern is a good model.

Question 21

Prokaryotic species concepts example.

Answer 21

Average Nucleotide Identity (ANI)
Different species exist when ANI is > 94%
ANI is a sliding scale.
Genome sequencing information is needed.

Question 22

Describe the structure and common shapes of prokaryotic cells.

Answer 22

Very small cellular organisms, about 1/10 the size of eukaryotic cells (1-10 microns).
Most are unicellular, but some form colonies or filaments containing specialized cells.
Prokaryotic cells do not have a nucleus or other membrane-enclosed organelles. DNA is contained in a nuclear area (nucleoid).
Include two domains: Archaea and Bacteria
Three common cell shapes: Cocci, Bacilli, Spirochete

Question 23

Examples of the structure and common shapes of prokaryotic cells.

Answer 23

Photos

Question 24

Contrast the bacterial cell wall in gram-positive and gram-negative bacteria.

Answer 24

Distinguishing between gram-positive and gram-negative bacteria is important in treating certain diseases:

• Gram-positive bacteria retain crystal violet stain. Have thick cell walls that consist primarily of peptidoglycan.
• Gram-negative bacteria do not retain the stain (pink). Have cell walls with two layers: a thin peptidoglycan layer and a thick outer membrane that contains polysaccharides bonded to lipids.

Question 25

Describe cell wall and capsule or slime layer in prokaryotes.

Answer 25

• A cell wall around the plasma membrane supports the cell and keeps the cell from bursting under hypotonic conditions. The bacterial cell wall includes peptidoglycan, a complex polymer consisting of two amino sugars linked with short polypeptides to form a single macromolecule that surrounds the entire plasma membrane. Peptidoglycan is absent in the archean walls.
• Many prokaryote species produce a capsule or slime layer of polysaccharide or protein that surrounds the cell wall. The outer covering may protect the cell against phagocytosis. Example: Without a capsule, S. pneumoniae does not cause pneumonia.

Question 26

Describe movement in prokaryotes.

Answer 26

Prokaryotes move by means of rotating flagella – the number and location of flagella vary by species.
A bacterial flagellum consists of three parts: a basal body, a hook, and a single filament.
The bacterium uses energy from ATP to power the basal body, which spins the flagellum like a propeller.
Some prokaryotes that lack flagella move by gliding.

Question 27

Describe fimbriae and pili in prokaryotes.

Answer 27

Bacteria use fimbriae and pili to attach to cell surfaces or to each other:

• fimbriae (fimbria): Hundreds of hairlike appendages (shorter than flagella) made of protein. DNA is transfers from one to another
• pili (pilus): Appendages that are longer (and fewer) than fimbriae

Question 28

Describe endospores in prokaryotes.

Answer 28

Certain types of bacteria form dormant, extremely durable cells called endospores – archaea do not form endospores.
Endospores survive in very dry, hot, or frozen environments or at times when food is scarce – when conditions are favorable, the endospore forms an active cell.
Several bacteria that form endospores cause disease:
E.g., Clostridium tentani (tetanus)

Question 29

Describe the general features of biofilms.

Answer 29

Structure:
-Attached microbial cells
-Extracellular Polymeric Substances (EPS): primarily polysaccharides. EPS makes up majority of carbon in biofilms.
Gene expression & transfer: different in planktonic vs biofilms:
-Expression differs in biofilms vs planktonic forms
-Higher levels of transfer in biofilms.
-The degree of gene expression is density dependent
Quorum Sensing:
-Interactions between cells based on density
-Coordinate certain behaviors, e.g., biofilm production

Question 30

Describe biofilms.

Answer 30

A biofilm is an assemblage of microbial cells that is irreversibly associated (not removed by gentle rinsing) with a surface and enclosed in a matrix of primarily polysaccharide material. Not uniform microbial community – heterogenous.
Develop on all aquatic surfaces:
-Ubiquitous in nature; all surfaces in aquatic environments
-Industrial surfaces such as potable water systems
-Medical devices
-Living tissues & teeth
Many bacteria in watery environment form dense biofilms that attach to solid surfaces
Biofilms are communities of microorganisms consisting of many species of bacteria, and may include other organisms such as archaea, fungi, and protozoa.

Question 31

Describe how biofilms are important to public health.

Answer 31

Important in public health
Many diseases associated with biofilms
Examples: cystic fibrosis, middle ear infection, peridonitis
Biofilms of occur on indwelling medical devices (catheters, heart valves) (Aka ‘medical device infections’)

Question 32

Compare and contrast prokaryotes and eukaryotes.

Answer 32

Bacteria and archaea are single-celled organisms that, in contrast to eukaryotic cells, do not have membrane-enclosed organelles; most have a cell wall that surrounds the plasma membrane, and have a single, circular DNA molecule, many (most?) occur in biofilms, prokaryotes species concepts required.

Question 33

Describe asexual reproduction in prokaryotes, and summarize three mechanisms (transformation, transduction, and conjugation) that may lead to genetic recombination.

Answer 33

Binary fission: One cell divides into two similar cells. Circular DNA replicates; then an ingrowth of plasma membrane and the cell wall forms a transverse wall.
Budding: A cell develops a bulge (bud) that enlarges, matures, and eventually separates from the mother cell
Fragmentation: Walls develop within the cell, which then separates into several new cells
Gene transfer results in genetic recombination. Vertical gene transfer transfers genetics material from parent to offspring. Horizontal gene transfer transfers genetic material to another organism that is not its offspring. Gene transfer among bacteria takes place by three different mechanisms: transformation, transduction, and conjugation.
In transformation, the bacterium dies and releases DNA, fragments of foreign DNA bind to proteins on the surface of a living bacterium, DNA enters cell, and some DNA is incorporated into host cell by reciprocal recombination. Plasmids can also be taken up without reciprocal recombination.
In transduction, a phage carries bacterial genes from one bacterial cell into another. The chromosome of the new host becomes a recombination of its own original DNA and DNA from another bacterium.
In conjugation, two cells of different mating types come together, and genetic material is transferred. Example: E. coli; Donor cells (F+ cells) have a DNA sequence (F factor) that allows them to transmit DNA to recipient cells (F− cells) by conjugation. Certain F genes encode sex pili that form cytoplasmic conjugation bridges between cells.

Question 34

State specific factors that contribute to the rapid evolution of bacteria.

Answer 34

ANSWER
Evolution occurs rapidly in prokaryotes; natural selection acts on the genetic variation provided by mutations and genetic recombination, and is facilitated by rapid reproduction.

Question 35

Describe genetic material and plasmids in prokaryotes.

Answer 35

In most species, genetic material is contained in a single, circular DNA molecule.
In addition, most bacteria have one or more plasmids – small circular fragments of DNA that may contain genes for catabolic enzymes, genetic exchange, or antibiotic resistance.
Plasmids replicate independently of genomic DNA, or become integrated with it.

Question 36

Describe the principal modes by which prokaryotes carry on nutrition and energy capture, and compare their requirements for oxygen.

Answer 36

Two main ways of obtaining nutrition:
-Autotrophs use inorganic compounds, such as CO2, as a source of carbon for manufacturing organic molecules
-Heterotrophs use organic compounds for growth and cannot fix carbon
Two main ways of capturing energy:
-Chemotrophs obtain energy from chemical compounds
-Phototrophs capture energy from light

Question 37

Describe the four groups of prokaryotes.

Answer 37

The great diversity that has evolved in their metabolism and mode of nutrition allows prokaryotes to thrive in all kinds of habitats.

1. Photoautotrophs (cyanobacteria)
   - Energy from sunlight
   - Carbon from inorganic compounds
2. Chemoautotrophs
   - Energy from oxidation of inorganic chemical substances such as ammonia and hydrogen sulfide
   - Carbon from inorganic compounds
3. Photoheterotrophs (purple nonsulfur bacteria)
   - Energy from sunlight
   - Carbon from other organisms
4. Chemoheterotrophs
   - Energy and carbon from other organisms
   - Includes decomposers that obtain carbon and energy from dead organic matter

Question 38

Describe aerobes and anaerobes.

Answer 38

Aerobic bacteria require oxygen for cellular respiration.
Facultative anaerobes use oxygen for cellular respiration if available, but use anaerobic respiration when necessary.
Obligate anaerobes only carry out anaerobic respiration
Have terminal electron acceptors other than oxygen: sulfate (SO42−), nitrate (NO3−), or iron (Fe2+)
Some are killed by even low concentrations of oxygen.
Table 25-1, page 524

Question 39

Define nitrogen fixation and nitrification.

Answer 39

Nitrogen fixation: the process that some bacteria and archaea can reduce nitrogen in the atmosphere to ammonia and can use these simple forms of nitrogen ti produce organic compounds.
Nitrification: that process that converts nitrogen to a form that can be used by plants and fungi.

Question 40

Compare characteristics of the three domains: Archaea, Bacteria, and Eukarya

Answer 40

ANSWER
The two domains of prokaryotes, Archaea and Bacteria are fundamentally different groups, each with unique signature sequences of small subunit (SSU) rRNA.
Key characters distinguish archaea from bacteria:
-Archaea have no peptidoglycan in their cell walls
-Plasma membranes of archaeans have branched-chain hydrocarbons bonded to glycerol by ether linkages
Table 25-2, page 526

Question 41

Distinguish among the two main groups of archaea and identify specific types of archaea belonging to each group.

Answer 41

Domain Archaea consists of two major phyla: Crenarchaeota and Euryarchaeota
-Crenarchaeota consist mainly of extreme thermophiles
-Euryarchaeota includes methanogens, extreme halophiles, and extreme thermophiles
Methanogens (methane producers):
-Diverse group that inhabit oxygen-free environments in sewage, swamps, and digestive tracts of animals
-Obligate anaerobes that produce methane gas from simple carbon compounds
-Important in recycling components of organic products of organisms that inhabit swamps
-Methanogens produce more than two billion tons of methane (an important greenhouse gas) each year
Extreme halophiles:
-Heterotrophs that require large amounts of Na+ for growth
-Live in salt ponds, the Dead Sea, and the Great Salt Lake
-Use aerobic to make ATP, and also carry out a form of photosynthesis using a purple pigment (bacteriorhodopsin)
-Seawater evaporating ponds near San Francisco (CA). Colors derive from archaea that are abundant in the ponds. (These ponds are used to extract salt commercially.)

Question 42

Describe the main groups of bacteria discussed in this chapter.

Answer 42

Five major groups of bacteria are widely distributed in the environment: 
Proteobacteria (gram-negative)
Cyanobacteria (gram-negative)
Chlamydias (gram-negative)
Spirochetes (gram-negative)
Gram-positive bacteria
Each groups contains high diversity.

Question 43

Prokaryotes make up two of the three domains: Bacteria and Archaea. Compare and contrast bacteria and archaea.

Answer 43

ANSWER.

Question 44

What is symbiosis? Explain the the three forms of symbiosis.

Answer 44

Symbiosis is an intimate relationship between partners of two or more species (symbionts).
There are three forms of symbiosis:
Mutualism: both partners benefit
Commensalism: one partner benefits and the other is neutral
Parasitism: the parasite benefits and the host is harmed

Question 45

Identify the critical ecological roles played by prokaryotes.

Answer 45

Decomposers: break down dead organic matter and waste
Nitrogen fixing bacteria: transform atmospheric nitrogen to forms that can be used by plants
Rhizobial bacteria: motile bacteria that inhabit the soil and form mutualistic relationships with roots of legumes
Cyanobacteria: carry out photosynthesis using water as the electron source and generate oxygen, therefore, fix huge amounts of carbon dioxide into organic molecules.

Question 46

Describe some of the important roles played by prokaryotes in commerce and technology.

Answer 46

Pharmaceutical companies obtain antibiotics from gram-positive soil bacteria (actinomycetes, Bacillus)
Genetically engineered bacteria produce vaccines, human growth hormone, insulin, and other important compounds
Fermenting bacteria are used in producing many foods and beverages (cheese, pickles, olives)
In bioremediation, bacteria are used to detoxify or remove oil and other pollutants from the environment

Question 47

Describe the roles played by Louis Pasteur and Robert Koch in understanding infectious disease.

Answer 47

19th century: Louis Pasteur disproved spontaneous generation
Text* page 532
Robert Koch was first to clearly demonstrate that bacteria (Bacillus anthracis) cause infectious disease (anthrax).

Question 48

Identify adaptations that have contributed to pathogen success.

Answer 48

To cause disease, a pathogen must be adapted to adhere to a specific cell type, multiply, and produce toxic substances.
Example: Helicobacter pylori is associated with peptic ulcers, chronic gastritis, and stomach cancer.
Adaptations that contribute to its success include an alkaline shield that protects it from stomach acid, and powerful flagella that propel it through thick mucus lining the stomach.

Question 49

Describe normal microbiota.

Answer 49

All plants and animals harbor a population of harmless symbiotic prokaryotes (normal microbiota or microflora).
The presence of certain bacterial populations prevents harmful microorganisms from flourishing.
An estimated 700 trillion bacteria normally inhabit the human body – numbers greatly exceeding the number of the body’s own cells (about 70 trillion).

Question 50

Explain Koch’s postulates.

Answer 50

Guidelines used to demonstrate that a specific pathogen causes specific disease symptoms:

• The pathogen must be present in every individual with the disease
• A sample of the microorganism taken from the diseased host can be grown in pure culture
• A sample of the pure culture causes the same disease when injected into a healthy host
• The microorganism can be recovered from the experimentally infected host

Question 51

Compare and contrast endotoxins and exotoxins.

Answer 51

Exotoxins: Some bacteria produce exotoxins, strong poisons that are secreted or leak out when the bacterial cell is destroyed. The toxin, not the presence of the bacteria themselves, is responsible for the disease
-Example: Botulism is caused by an endotoxin released by a gram-positive, endospore forming Clostridium botulinum – botulinum toxin is activated by proper heating
Endotoxins: Endotoxins (components of gram-negative-bacteria cell walls) affect a host only when released from dead bacteria. Endotoxins bind to the host’s macrophages and stimulate release of substances that cause fever and other symptoms of infection. Unlike exotoxins, endotoxins affect the entire body, and are not destroyed by heated.

Question 52

What is the causative agents for cholera?

Answer 52

Vibrio cholerae
Contracted by eating food or drinking water contaminated with the bacterium. Common in areas with inadequate sewage treatment and impure water. Infects intestine and can cause severe diarrhea. Rapid fluid loss can lead to dehydration and death.

Question 53

What is the causative agents for gonorrhea?

Answer 53

Neisseria gonorrhoeae

Common sexually transmitted disease.

Question 54

What is the causative agents for lyme disease?

Answer 54

Borrelia burgdorferi
Transmitter to humans by a bite of infected blacklegged ticks. Symptoms include skin rash, headache, fever, and fatigue. If untreated, infection can spread to joints, heart, and nervous system.

Question 55

What is the causative agents for pertussis (whooping cough)?

Answer 55

Bordetella pertussis

Highly communicable from person to person. Cause spasms of severe coughing. Vaccination available.

Question 56

What is the causative agents for salmonella (salmonellosis)?

Answer 56

Salmonella sp.
Transmitted to people in contaminated chicken, eggs, or other food. Also transmitted from feces of infected animals, eg. lizards, turtles, chicks, birds, even dogs and cats. Symptoms include fever, diarrhea, and stomach pain.

Question 57

What is the causative agents for syphilis?

Answer 57

Treponema pallidum
Sexually transmitted disease passed through direct contact with a syphilis sore. If untreated, eventually damages brain, liver, bone, and spleen and can cause death.

Question 58

Describe antibiotic resistance.

Answer 58

Drug resistance may result from accumulation of mutations in plasmid or chromosomal DNA.
Plasmids that have genes for antibiotic resistance (R factors) have genes for resistance to a specific drug and for transferring the resistance to other bacteria.
Overuse of antibiotics is the main cause of drug resistance.
In any bacterial population, the bacteria that are not resistant are killed by the antibiotic, leaving the resistant bacteria to multiply and produce a resistant population.
Many infections acquired in hospitals involve biofilms.
Bacteria in a biofilm are surrounded by a matrix rich in polysaccharides and by a protective shell, which makes them resistant to antibiotics, as well as to host defenses.

Question 59

What are protists?

Answer 59

Protists are an informal group of primarily aquatic eukaryotic organisms with diverse body forms, types of reproduction, modes of nutrition, and lifestyles.
Protists include algae, water molds, slime molds, and protozoa; they are unicellular, colonial, or simple multicellular organisms that have a eukaryotic cell organization.
Kingdom Protista is not a recognized clade.
Protists are members of domain Eukarya:
-Eukaryotic cells have nuclei and other membrane-enclosed organelles such as mitochondria and plastids, 9 + 2 flagella, and multiple chromosomes in which DNA and proteins form a complex called “chromatin”.
-Sexual reproduction, meiosis, and mitosis are also characteristic of eukaryotes.
Protists are paraphyletic group. A current scheme, based on molecular and ultrastructural analyses, splits protists and other eukaryotes (land plants, fungi, and animals) into five informal supergroups. We’ll consider each supergroup.

Question 60

Discuss in general terms the diversity inherent in protists, including means of locomotion, modes of nutrition, interactions with other organisms, habitats, and modes of reproduction.

Answer 60

Body plan varies considerably among protists: Most are unicellular, some form colonies, some are coenocytic (consisting of multinucleate mass of cytoplasm), and some are multicellular. Most multicellular protists have relatively simple body forms without specialized tissues.
Locomotion: Most protists are motile at some point in their life cycle. Some move by pushing out cytoplasmic extensions (pseudopodia) along leading edge. Others by flexing individual cells; gliding over surfaces; waving cilia or flagella. Some have two or more means of locomotion—for example, both flagella and pseudopodia.
Nutrition: Methods of obtaining nutrients differ widely among protists. Most algae are autotrophic photosynthesizers. Some heterotrophs obtain nutrients by absorption.
Interactions: Many protists are free-living. Others form symbiotic associations with unrelated organisms: mutualism, commensalism, and parasitism. Some parasitic protists are important pathogens of plants or animals.
Habitats: Most protists live in the ocean, or freshwater streams, lakes, and ponds. Plankton are microscopic organisms that inhabit surface waters and are the base of food web in aquatic ecosystem. Other aquatic protists attach to rocks or other surfaces. Parasitic protists live in the watery environments of other organisms’ body fluids. Terrestrial protists are restricted to damp places such as soil, cracks in bark, and leaf litter.
Reproduction: Varied among protists. Almost all reproduce asexually, and many also reproduce sexually. However, more protists do not develop multicellular reproductive organs, nor do they form embryos the way more complex organisms do.
*Protists are a diverse group of eukaryotic organisms that vary in body plan (unicellular, colonial, coenocytic, multicellular), method of motility (pseudopodia, cilia, flagella), nutrition type (autotrophic, heterotrophic), and mode of reproduction (asexual, sexual).

Question 61

Discuss the hypothesis of serial endosymbiosis and briefly explain some of the evidence that supports it.

Answer 61

Serial endosymbiosis: certain eukaryotic organelles, particularly mitochondria and chloroplasts, arose from symbiotic relationships between larger cells and smaller bacteria that were incorporated and lived within them.
Mitochondria may have originated as aerobic bacteria.
Chloroplasts may have originated as a cyanobacterium within a host cell (primary endosymbiosis).
Figure 26-2, page 540

Question 62

Describe the kinds of data biologists use to classify eukaryotes.

Answer 62

Two types of research contribute substantially to understanding phylogenetic relationships among protists:
Molecular analysis of the gene for small subunit ribosomal RNA (SSU rRNA), and other nuclear genes
Ultrastructure data revealed by electron microscopy

Question 63

Summarize the basic features of excavates and distinguish among diplomonads, euglenoids and trypanosomes.

Answer 63

Excavates: Group of unicellular protists with flagella and a deep (excavated) oral groove. Many are endosymbionts and live in anoxic (without oxygen). There excavates do not carry out aerobic respiration; they obtain energy by the anaerobic pathways of glycolysis (presumably fermentation). They get their name because many have a deep, or excavated, oral groove. Have atypical, greatly modified mitochondria. Include diplomonads, euglenoids, and trypanosomes:
-Diplomonads: Excavates with one or two nuclei, no functional mitochondria, no Golgi complex, and up to eight flagella. Example: Giardia, a parasitic diplomonad
An early eukaryotic ancestor of Giardia may have possessed mitochondria.
-Euglenoids and trypanosomes have an unusual flagellum with a crystalline rod.
-Euglenoids: Most are unicellular flagellates; some are photosynthetic. Some heterotrophic species absorb organic compounds from surrounding water, whereas others engulf bacteria and protists by phagocytosis. Example: Euglena has a flexible pellicle; continuously changes shape.
-Trypanosomes: Have a single mitochondrion with an organized deposit of DNA. Many are parasitic and cause disease. Example: Trypanosoma brucei.

Question 64

Contrast the two main groups of chromalveolates: alveolates and stramenopiles

Answer 64

Chromalveolates: A supergroup composed of extremely diverse protists with few shared characters.
Include alveolates and stramenopiles (diatoms and brown algae)
Alveolates: Have alveoli – flattened vesicles located just inside the plasma membrane. In some alveolates, vesicles contain plates of cellulose. Include dinoflagellates, apicomplexans, and ciliates.
Stramenopiles: A diverse group of chromalveolates. Most have motile cells with two flagella, one of which has tiny hairlike projections extending from the shaft. Include diatoms and brown algae.

Question 65

Distinguish among the alveolates: dinoflagellates, apicomplexans, and ciliates

Answer 65

Dinoflagellates: Generally unicellular; a few are colonial. Alveoli contain interlocking cellulose plates with silicates. Includes zooxanthellae (photosynthetic endosymbionts in marine invertebrates such as corals) toxin-producing dinoflagellates that cause red tides.
Apicomplexans: Group of parasitic, spore-forming alveolates, some of which cause serious diseases in humans. Lack specific structures for locomotion (cilia, flagella, or pseudopodia) and move by flexing. Have an apical complex of microtubules that attaches the parasite to its host. Example: Plasmodium, which causes malaria.
Ciliates: Complex unicellular alveolates with a pellicle that gives them a definite but changeable shape
Hairlike cilia coordinate movement in motile forms, or draw in food in sessile forms. Two kinds of nuclei: diploid micronuclei function in reproduction; polyploid macronucleus controls growth. Reproduce sexually by conjugation. Example: Paramecium is covered with thousands of cilia.

Question 66

Distinguish among the stramenopiles: diatoms and brown algae

Answer 66

Diatoms: Cell wall consists of two overlapping silica shells with intricate patterns (radial symmetry or bilateral symmetry). Some float in plankton, others live on rocks or sediments. Asexual reproduction: Each shell half becomes half of a new (smaller) diatom shell. Sexual reproduction restores the diatom to original size. Shells form diatomaceous earth. Example: One species is linked to toxic shellfish poisonings.
Brown algae: Largest and most complex of all protists; sizes range from a few centimeters to 75 m. Multicellular; body forms are branched filaments, tufts, fleshy “ropes,” or flattened branches. Life cycles exhibits alternation of generations. Asexual zoopores and sexual gametes are biflagellate. Example: kelps, the largest brown algae
Have leaflike blades, stemlike stipes, rootlike anchoring holdfasts; and gas-filled bladders.

Question 67

Describe the forams and actinopods, and explain why many biologists classify them in the rhizarian supergroup.

Answer 67

Rhizarians are a supergroup with amoeboid cells that often have tests (shells) through which cytoplasmic projections extend; forams, actinopods, and certain shell-less amoebas are rhizarians
Rhizarians: A monophyletic but diverse group of amoeboid cells. Often have hard out shells (tests) though which cytoplasmic projections extend. Include forams, actinopods, and certain shell-less amoebas.
Foraminiferans (forams): Mostly marine rhizarians that produce chalky, many-chambered tests. Many contain unicellular algal endosymbionts (green algae, red algae, or diatoms). Tests of dead forams settle to the bottom of the ocean and are gradually transformed into chalk. Forams are well preserved in the fossil record, and some are used as index fossils
Actinopods: Mostly marine plankton rhizarians with long, filamentous cytoplasmic projections (axopods) that protrude through pores in their shells. Prey are engulfed outside the main body; cytoplasmic streaming carries prey inside the body. Many contain photosynthetic algal endosymbionts. Example: Radiolarians (marine plankton) secrete glassy silica shells that settle and become an ooze (sediment).

Question 68

Describe evidence supporting the hypothesis that red algae and green algae should be included in a monophyletic group with land plants.

Answer 68

Archaeplastids include red algae, green algae, and land plants, all of which have plastids bounded by outer and inner membranes.
Archaeplastids: Monophyletic group that includes red algae, green algae, and land plants, which are in a separate kingdom. These groups are classified together based on molecular data and the presence of similar chloroplasts, suggesting that they developed directly from a cyanobacterial endosymbiont.
-Red algae: Most have a complex multicellular body consisting of interwoven filaments; some are flattened sheets. Reproduction-alternation of sexual and sexual stages; no flagellate cells. Some (coralline algae) incorporate calcium carbonate from ocean water into their cell walls. Red algae are sources of commercially important polysaccharides (agar, carrageenan) and nori.
-Green algae: Have photosynthetic pigments, energy reserve products (starch), and cell walls chemically identical to those of land plants. Body types include single cells, colonial forms, coenocytic algae, and multicellular filaments and sheets. Reproduction-both sexual and asexual; many alternate haploid and diploid generations. Many are symbionts: endosymbionts, lichens. Biologists generally accept that land plants arose from ancestral green algae.

Question 69

Briefly describe and compare the following unikonts: amoebas, plasmodial slime molds, cellular slime molds, and choanoflagellates.

Answer 69

Unikonts: Organisms with a single posterior flagellum in flagellate cells such as sperm and motile spores. Separated from all other eukaryotes (bikonts) by evolution of triple-gene fusion. Two clades: Opisthokonts (fungi, choaonoflagellates, and animals) and Amoebozoa (certain amoebas, plasmodial slime molds, and cellular slime molds).
Unikonts include amoebozoa and choanoflagellates as well as fungi and animals.
-Amoebozoa: Unikonts that produce temporary, lobose cytoplasmic. Amoebozoa include amoebas, plasmodial slime molds, and cellular slime molds.
-Amoebas:Unicellular amoebozoa found in soil, water, and other organisms (as parasites). Asymmetrical, continually-changing body form. Reproduction-asexual, splitting into two equal parts. Example of parasitic amoebas: Entamoeba histolytica causes amoebic dysentery. Transmitted as cysts in contaminated drinking water.
Cellular slime molds: Feeding stage-each cellular slime mold is an individual amoeboid cell that behaves as a solitary organism. When conditions are unfavorable, certain cells send out a signaling molecule (cAMP) that causes cells to aggregate, forming a multicellular slug. The slug forms a stalked fruiting body containing spores. Each spore releases a haploid amoeboid cell (the feeding stage).
Choanoflagellates: Unikonts with a single flagellum surrounded at the base by a collar of microvilli that trap food. Found in freshwater and marine environments. Include free-swimming and sessile species. Biologists hypothesize that choanoflagellates are the closets living non-animal relative to animals.