Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 18
18.1
1. Bacteria and Archaea are the two domains that include prokaryotes.
2. Prokaryotes have influenced evolution by contributing O2 to the atmosphere, helping to create
the ozone shield, and becoming incorporated into eukaryotic cells as mitochondria and
chloroplasts.
3. Prokaryotes live in every conceivable habitat.
18.2
1. A nuclear membrane surrounds a nucleus but not a nucleoid.
2. Plasmids are small loops of DNA that are not part of the prokaryotic chromosome. They are
important because they are easily transmitted from one cell to another, so that prokaryotes can
rapidly acquire new traits from their neighbors. They are also important because they help
biologists ferry genes from one prokaryotic cell to another.
3. The basis of Gram staining is differences in the structure of the cell wall. In particular, Gram
positive bacteria have a thicker cell wall that retains more crystal violet stain than the cell wall of
Gram negative bacteria.
4. The glycocalyx helps in attachment to a surface, keeps the cell from drying out, and protects it
from immune system cells. Pili allow bacteria to attach to surfaces, while sex pili allow transfer of
DNA from cell to cell. Flagella help the cell to move toward or away from a stimulus.
5. Species that make endospores can survive in environmental conditions that don’t favor the
survival of active bacteria.
18.3
1. The cells of both bacteria and archaea are prokaryotic and small. Both have a circular
chromosome, some members of each domain can fix nitrogen, and some members of each
domain can grow at temperatures above 80oC. The two groups have cell walls made of different
substances, bacteria use chlorophyll in photosynthesis whereas archaea do not, some archaea
generate methane while no bacteria do this, no archaea are sensitive to streptomycin while
bacteria are, and archaea have introns while bacteria do not.
2. Cell shapes (spherical, rod-shaped, or spiral) were the original basis of prokaryote
classification. Different stains reveal the structure of the cell wall or the presence of features such
as a glycocalyx, endospores, or flagella.
3. Phototrophs get energy from the sun; chemotrophs get energy from chemicals. Autotrophs
acquire carbon from inorganic sources such as CO2; heterotrophs get carbon from organic
molecules produced by other organisms.
4. An obligate aerobe must have O2 to produce ATP. An obligate anaerobe lives in the absence
of O2 (and may be killed by oxygen). A facultative anaerobe can live with or without O2.
5. Examples of phyla within domain Bacteria include:
- Proteobacteria – purple sulfur bacteria;
- Spirochetes-organisms that cause Lyme disease and syphilis;
- Cyanobacteria – photosynthesizing bacteria.
Phyla within domain Archaea include:
- a phylum that contains anaerobic archaea that release methane gas and halophilic archaea,
- a phylum that contains thermophiles that live in hot springs and hydrothermal vents as well as
archaea from soil and water,
- thermophiles known only from DNA extracted from environments.
18.4
1. The events of binary fission are:
- DNA attaches to the cell membrane and then replicates;
- newly synthesized DNA attaches to the cell membrane;
- cell membrane grows between the two attachment points and moves the DNA molecules apart;
- new cell wall grows in space between the two DNA molecules;
- two cells separate.
2. In transformation, a bacterial cell receives DNA fragments and plasmids from the environment.
In transduction, a bacteriophage (virus) introduces bacterial DNA into a new cell. In conjugation,
DNA travels from a donor cell to a recipient via a sex pilus.
3. Horizontal gene transfer increases the genetic diversity of a population of prokaryotes.
Research in medicine, biodiversity, origin of life, evolution, systematics, and biotechnology uses
horizontal gene transfer. Resistance to antibiotics is spread by horizontal gene transfer.
18.5
1. Prokaryotes are essential to eukaryotic life because of their roles in decomposing organic
matter in soil and water, as photosynthesizers that contribute O2 to the atmosphere, and as the
base of the food chain in many environments. Some prokaryotes also fix nitrogen, which enriches
soils and completes the nitrogen cycle.
2. The microbes that colonize the human body help defend it from attack by pathogenic bacteria.
3. Pathogenic bacteria enter the body with insect or tick bites, sexual activity, in food, air, or
water, or by direct contact with cut or abraded skin surfaces. Once inside the body, pili help the
bacterium to attach to host cells, and bacterial enzymes attack host tissues. Bacterial toxins can
disable the host’s circulatory, digestive, or nervous system. Bacteria leave the body in respiratory
droplets, feces, vaginal discharge, semen, or in blood, carried by insects or ticks.
4. Prokaryotes are involved in the production of foods such as yogurt, vinegar, sauerkraut,
cheeses, pickles, and olives. They also are used to produce vitamins and useful chemicals such
as acetone and alcohol. Transgenic bacteria produce human insulin and blood-clotting factors.
Sewage treatment plants use prokaryotes to decompose organic wastes. Bioremediation uses
prokaryotes to clean up toxic spills and sites contaminated by heavy metals and PCBs.