CHAPTER 18 Test Your Knowledge
Driving Question 1
What are the prokaryotic domains of life?
By answering the questions below and studying Infographics 18.3, 18.4, and 18.5, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Organisms are placed into one or another of the three domains of life on the basis of
a. cell type.
b. physical appearance.
c. evolutionary history as assessed by genetic relatedness.
d. ability to cause disease.
e. degree of sophistication, that is, how evolutionarily advanced they are.
c
Describe the major difference(s) between prokaryotic and eukaryotic organisms.
The key difference is that prokaryotic cells do not contain membrane-enclosed organelles, particularly a nucleus. Eukaryotic cells are defined by the presence of membrane-enclosed organelles, in particular the nucleus.
The absence of membrane-bound organelles in a cell tells you that the cell must be
a. from a member of the domain Bacteria.
b. from a member of the domain Archaea.
c. from a member of the domain Eukarya.
d. either a or b
e. either b or c
d
USE IT
Why were bacteria and archaea originally grouped together?
Bacteria and archaea were originally grouped together in the kingdom Monera because both had prokaryotic cells.
When first discovered, archaea were called “archaeabacteria.” Why do you suppose this was? What are the strengths and weaknesses of this earlier term?
The term “archaeabacteria” means “ancient bacteria.” At the time of their discovery, archaea were found in “extreme” environments and were thought to be ancient ancestors of bacteria, living in conditions that may have been similar to those on the early Earth. While the term “archaeabacteria” does suggest a similarity to bacteria, it does not capture that the similarity is only at the structural level (both have prokaryotic cells), and it does not recognize that archaea are members of a completely distinct domain not some kind of bacteria.
Driving Question 2
What are the features of bacteria and of archaea?
By answering the questions below and studying Infographics 18.4, 18.6, and 18.7, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
The term prokaryotic refers to
a. a type of cell structure.
b. a domain of life.
c. a group with a shared evolutionary history.
d. a type of bacterium.
e. a type of archaea.
a
If you were looking for a bacterium, where would expect to find one?
a. on your skin
b. in soil
c. in the ocean
d. associated with plants
e. any of the above
e
What is the function of flagella?
a. production of methane
b. sticking to a surface
c. motility
d. luminescence
e. metabolism
c
If you are unable to culture archaea from an environmental sample, is it safe to conclude that there are no archaea present? Why or why not?
No. You cannot conclude that there are no archaea present in that environment or sample. Many archaea are very difficult to grow (that is, culture) in the lab. This is likely because we don’t understand enough about their growth requirements to be able to provide the appropriate conditions to culture them successfully in the lab. They may be present in the environmental sample, and we may just be unable to culture them.
USE IT
Can you use cell structure to classify a cell as either bacterial or archaeal? Explain your answer.
No. Both have prokaryotic cells, so the presence of a prokaryotic cell does not allow you to distinguish between bacteria and archaea.
Many prokaryotic organisms can carry out both photosynthesis and nitrogen fixation. Why are these processes important to humans?
Photosynthesis provides a source of organic molecules (particularly carbohydrates) that can be food sources for the food chains and webs that humans rely on. Photosynthesis also produces oxygen as a by-product, and oxygen is critical for humans. Nitrogen fixation provides a form of nitrogen that plants can use to grow, providing a food source for humans.
If Neisseria gonorrhoeae had no pili, would it still be a successful pathogen? Explain your answer.
No. These pathogens use their pili to adhere to cells of the body and to evade host defenses. Without their pili, the bacteria could not adhere to cells, and would not succeed in establishing infections.
Driving Question 3
What are the challenges faced by organisms living at Lost City, and how do they face them?
By answering the questions below and studying Infographics 18.1, 18.2, and 18.8, you should be able to generate an answer for the broader Driving Question above.
408
KNOW IT
List the features that make Lost City a particularly harsh environment. For each feature, give a brief explanation of why that environment is inhospitable for many organisms.
High temperatures: most organisms are not adapted to high temperatures, and if they encounter temperatures higher than their optimum temperatures, their proteins will denature (that is, lose their shape and therefore their function) and their membranes will destabilize. High pressure: most organisms do not have adaptations that allow them to survive at high pressure and would be crushed by the pressure at Lost City. High pH: the high pH at Lost City is outside the pH optimum of most organisms, and would lead to their death.
If you were a prokaryotic organism and wanted to be successful at Lost City, what energy source must you be able to use?
a. sunlight
b. oxygen
c. hydrogen gas
d. electricity
e. None of the above is available at Lost City.
c
USE IT
What is the significance of methane and other hydrocarbons at Lost City? (Think about both the origin of life and the sustenance of early life.)
The methane and other simple hydrocarbons at Lost City can be produced both abiotically and biotically. This means that the earliest organisms at Lost City had at least two energy sources (H2 and methane). This also means that a diverse community of organisms could develop, some producing methane, some using methane.
If methane were not produced abiotically at Lost City, what would be the implications for early life?
As many of the living organisms at Lost City rely on methane as their energy and carbon source, it may be harder to hypothesize that life formed at these kinds of vents. However, with hydrogen gas (as an energy source) and CO2 (as a carbon source) it is still possible for life to have survived at Lost City, but perhaps different organisms would be present.
Would you expect to find photosynthetic organisms at Lost City? Explain your answer.
No. Sunlight does not reach the depths of the ocean at Lost City, so photosynthesis is not possible at these depths.
Do you think that the scientists studying Lost City should be concerned about introducing microbial contaminants from their submersibles onto the towers of Lost City? How probable is this, given the conditions at Lost City and on the surface? If such an event could happen, what would be the implications?
As the conditions at Lost City are so extreme and harsh, it is unlikely that any microbes on the surfaces of the submersibles could to survive, much less thrive in the environmental conditions at Lost City. So the risk appears to be very low. On the other hand, microbes are diverse and adaptable, and if a new microorganism were to be introduced to Lost City, and if it were able to successfully divide and establish itself, thus colonizing a microenvironment at Lost City, it could potentially displace “native” microbes, fundamentally changing the microbial community at Lost City. This could disrupt the entire ecosystem of Lost City. While the risk is low, the potential consequences are high, and should be considered.
INTERPRETING DATA
Some of the chimneys at Lost City are actively venting. These chimneys have hot (80°–100°C) interiors that lack oxygen and have a pH range of 9-11. The exterior surfaces of the active chimneys are cooler (~7°C), contain oxygen and have a pH of ~8.
The inactive chimneys at Lost City are no longer venting hot fluids. Compared to the actively venting chimneys, their interiors are much cooler (7°-20°C), have a pH of 8-10, and lack oxygen. The exteriors of the inactive chimneys are very similar to those of the active chimneys.
From the properties of the organisms given in the table below, complete the table to indicate where in Lost City each of these organisms is most likely to be found.
| Organism | Aerobic or Anaerobic? | Aerobic or Anaerobic? | Optimum Temperature (°C) | Domain: Bacteria or Archaea? | Location |
| A | Anaerobic | 9 | 15 | Archaea | Interior of inactive chimneys |
| B | Aerobic | 8 | 6 | Bacteria | Exterior of active or inactive chimneys |
| C | Aerobic | 8.5 | 8 | Bacteria | Exterior of active or inactive chimneys |
| D | Anaerobic | 11 | 90 | Archaea | Interior of active chimneys |
| E | Aerobic | 7.5 | 7 | Bacteria | Exterior of active or inactive chimneys |
| F | Anaerobic | 11 | 85 | Archaea | Interior of active chimneys |
409
MINI CASE
In many ways, the discovery of Lost City is about the discovery of life, as is the voyage of Curiosity to Mars (see Chapter 2).
a. What features do these two environments, Lost City and Mars, share?
b. How do the challenges faced by Curiosity compare to those faced by Jason?
c. From the way microbes survive at Lost City, what properties might you expect Martian organisms to have?
a: Both environments are or contain regions that are anoxic (that is, they lack oxygen). Generally, they are both extreme: Mars is very dry, Lost City has high pressure and high temperature. Both vehicles, operated remotely, must operate under extreme conditions. c: Martian organisms will likely be adapted to living in specific conditions. On Mars, they will be anaerobic, and will likely use simple molecules as their energy and carbon sources (e.g., hydrogen, carbon dioxide or methane).
BRING IT HOME
Do you think that, instead of spending time studying microbes from extreme and remote environments, scientists should be studying microbes that are more apparently relevant to humans, such as ones that cause disease? In what ways might understanding the organisms at Lost City be useful to humans?
Answers will very. It is important to note that countless scientific discoveries regarding human health have come, often unexpectedly, through basic research on organisms and environments that do not immediately appear to be relevant to humans. By studying organisms at Lost City, scientists not only can learn more about the origins of life on Earth (knowledge relevant to every living organism on the planet), but about obtaining energy from novel sources. This could, in the future, lead to applications related to energy sources that are alternatives to fossil fuels). By studying the community of organisms at Lost City, scientists may also learn more about how microbes live together, and this could be important to learning more about the diversity of microbes in and on the human body, and how their interactions can lead to disease.