Ch. 27 HW

Part A - Understanding the experimental design What hypothesis were the researchers testing in this study?

The disease-suppressive properties of soils are due to the activities of soil microorganisms.

Part A Bacteria that live around deep-sea, hot-water vents obtain energy by oxidizing inorganic hydrogen sulfide belched out by the vents. They use this energy to build organic molecules from carbon obtained from the carbon dioxide in seawater. These bacteria are _____.

chemoautotrophs *Correct They use inorganic molecules (in redox reactions) for energy, and carbon dioxide for carbon.

Part D Organisms that can cause nongonococcal urethritis are classified with _____.

chlamydias *Correct Chlamydia trachomatis causes nongonococcal urethritis.

Activity: Classification of Prokaryotes Part A The prokaryotic cells that built stromatolites are classified as _____.

cyanobacteria •Cyanobacteria built stromatolites.

Part B The prokaryotic cells that were the first to add significant quantities of oxygen to Earth's atmosphere are classified as _____.

cyanobacteria *Correct Cyanobacteria are aerobic photosynthesizers.

Part C Streptococcus pyogenes is classified with _____.

gram-positive bacteria *Correct S. pyogenes attracts the violet Gram stain.

Question 7 Part A The prokaryotic organisms most likely to be found living in salt ponds are the _____.

halophiles *Correct These archaea live in salty environments such as the Dead Sea.

Question 8 Part A An ecological relationship between organisms of different species that are in direct contact can best be described as _____.

symbiotic * Correct This is the definition of symbiosis.

Part E Identify a controlled variable from the experiment.

the amount of light the plants were exposed to

Part A Bioremediation is _____.

the use of organisms to remove pollutants from the environment *Correct This is the general use of the term bioremediation.

Pre-Test Question 9 Part A Which statement about endotoxins is true?

Endotoxins are released only when bacteria die and their cell walls break down. *Correct Endotoxins are a component of the outer membrane of gram-negative bacteria.

Part C True or false? Data showing that the Bacteria were the first lineage to diverge from the common ancestor of all living organisms suggest that the Archaea and Eukarya are more closely related to each other than they are to the Bacteria.

True

Part G Which of the following results would have disproved the hypothesis that microorganisms are responsible for the disease-suppressive properties of soils?

if seedlings had similar fungal infection rates when grown in heated and unheated disease-suppressive soil *Correct Unheated disease-suppressive soil contains living microorganisms, but heating the soil kills them. Therefore, if the researchers had found similar fungal infection rates when seedlings were grown in heated and unheated disease-suppressive soil, that would have indicated that microorganisms are not responsible for the soil's disease-suppressive properties.

Part A Genes for the resistance to antibiotics are usually located _____.

on plasmids *Genes for the resistance to antibiotics are usually located on plasmids.

Part C What is the dependent variable in this study?

percentage of seedlings with fungal disease

Part E The chemoheterotroph Proteus vulgaris is a rod-shaped bacterium classified with _____.

proteobacteria *Correct Proteus vulgaris is classified with proteobacteria.

Part B What is the independent variable in this study?

soil treatment

Part F Spiral-shaped bacteria are likely to be placed with _____.

spirochetes *Correct The name of these organisms provides the answer to the question.

Part D Which of the following statements about phylogenetic trees is true?

A paraphyletic group consists of a common ancestor and some of its descendants. *Correct This statement is true; the common characteristics of a paraphyletic group may have arisen from lateral gene transfer to some, but not all, lineages.

Part C - Characteristics of Azotobacter Azotobacter is a genus of bacteria that live in soil and have the following characteristics: - They are bacilli. - They are gram-negative. - They are obligate aerobes. - They can fix nitrogen. (Unlike some other nitrogen-fixing bacteria, which associate with the roots of plants, Azotobacter species are free-living.) Select the four statements that are true for bacteria in the genus Azotobacter.

1.They are shaped like rods. 2.They can convert atmospheric nitrogen to ammonia. 3. They use O2 for cellular respiration. 4.They have a relatively thin layer of peptidoglycan in their cell wall. *Correct Azotobacter is a genus of rod-shaped bacteria (bacilli). After Gram staining, bacteria in this genus appear pink due to the thin peptidoglycan layer in their cell wall. They require oxygen for cellular respiration and can convert atmospheric nitrogen to ammonia, which they incorporate into amino acids and other organic molecules

Part D What is the total number of pots used in this experiment, and how many plants received each soil treatment?

20 pots total, 32 plants per treatment *Correct Total number of pots = 5 treatments × 4 pots each = 20 pots. 4 pots per treatment × 8 plants per pot = 32 plants per treatment. Using multiple pots per treatment and multiple plants per pot gave the researchers a larger sample size and reduced the chances that conditions in one particular pot or the condition or characteristics of one particular plant would drive the results of the experiment in a nonrepresentative way.

Part G According to this phylogenetic tree, which of these pairs of prokaryotic subgroups share the most recent common ancestor?

Euryarchaeota ... Crenarchaeota *Correct The branching pattern of the phylogenetic tree indicates that, of the pairs listed here, this is the one whose members are the most closely related.

Part F - Interpreting the graph Select Figure 2 in the drop-down menu above the table (Figure 2) . A graphical representation of the data is shown. The researchers concluded that microorganisms were responsible for the disease-suppressive properties of the soil. How do the results shown in Figure 2 support this conclusion?

Fungal infection rate increased in seedlings grown in disease-suppressive soil that had been heated. * Correct Heating the disease-suppressive soil killed any microorganisms living in that soil. Because the infection rates for seedlings grown in heated soil were higher than the rates for seedlings grown in unheated disease-suppressive soil, the researchers concluded that microorganisms must account for the soil's disease-suppressive properties.

Part A - Gram staining Classify each statement or picture as applying to gram-positive bacteria, gram-negative bacteria, or both. Drag each item to the appropriate bin.

Gram-positive bacteria -Have a thick peptidoglycan layer. - Alcohol rinse does not remove crystal violet. - appear purple after Gram staining. Image= arrow pointing purple strand. Gram- negative bacteria -have a thin peptidoglycan layer. -have an outer membrane as part of their cell wall structure. -alcohol rinse easily remove crystal violet -appear pink after Gram staining. both -have a plasma membrane *Correct Gram staining is a technique for classifying bacteria based on differences in the structure of their cell walls. Gram-negative bacteria and gram-positive bacteria both have a plasma membrane surrounded by a cell wall that contains peptidoglycan. However, the cell wall of gram-negative bacteria is composed of a thin layer of peptidoglycan and an outer membrane, whereas the cell wall of gram-positive bacteria is composed of a thick layer of peptidoglycan. Gram-negative bacteria appear red or pink because the alcohol rinse washes away the crystal violet dye. Gram-positive bacteria appear purple because the alcohol rinse does not wash away the crystal violet dye.

Part B - Nutritional modes of bacteria Label the diagram below to show the relationship between nutritional modes of bacteria. Drag the labels to their appropriate locations on the diagram.

Nutritional Modes of Bacteria Left side: require energy only from inorganic sources (a) autotroph-- Use chemicals as energy source (c) chemoautotrophs Use light as energy source (d) photoautotrophs Right side: requiere energy from at least one organic nutrient (b) heterotrophs Use light as energy source (e) photoheterotrohs Use chemicals as energy source (f) chemoheterotrophs Center: also classified as (g) phototrophs also classified as (h) chemotrophs * Correct Some bacteria obtain energy from light (phototrophs), whereas other bacteria obtain energy from chemicals (chemotrophs). Autotrophs (literally "self-feeders") require only an inorganic substance, such as carbon dioxide, as their carbon source; heterotrophs (literally "other-feeders") require at least one organic nutrient as their carbon source.

Part F What is lateral gene transfer?

Physical transfer of a gene from a species in one lineage to a species in another lineage. *Correct Lateral gene transfer is the physical transfer of a gene between distantly related lineages.

Part B What characteristics were used to classify organisms before Woese's tree of life analysis?

Presence of a membrane-bound nucleus Correct Before the tree of life analysis, organisms were classified as prokaryotes if they lacked a membrane-bound nucleus or eukaryotes if they possessed a membrane-bound nucleus.

Activity: The Tree of Life Part A Which group was not described in Woese's tree of life analysis?

Prokarya *Correct Prokarya was not one of the groups described in Woese's tree of life analysis.

Part E Which molecule did Carl Woese study to produce his tree of life?

Ribosomal RNA *Correct Ribosomal RNA was the molecule used to produce Woese's phylogeny because it evolves slowly and is critical to the function of the ribosome, which serves the same function in all three domains in the tree of life.

Pre-Test Question 2 Part A How does the large amount of genetic variation observed in prokaryotes arise? 1. The mutation rate in prokaryotes is much higher than in eukaryotes. 2. They have extremely short generation times and large populations. 3. They can exchange DNA with many types of prokaryotes by way of horizontal gene transfer. 4. They have a relatively small genome. 5. The second and third answers are correct.

The second and third answers are correct. *The short generation times and large population sizes in most prokaryotic species, coupled with their ability to exchange genes, helps to increase genetic variability beyond what we would expect in asexually reproducing organisms.