Trends in sexually transmitted diseases in the United States. How is it possible for the incidence of one STD (chlamydia) to rise as another (gonorrhea) falls? Answer: The simplest explanation is that the two STDs are occurring in different populations, and one population has rising levels of sexual activity, while the other has falling levels. However, the rise in incidence of an STD can reflect many parameters other than level of sexual activity. The virulence or infectivity of one or both disease agents may be changing, for example, or some aspect of exposed people may be changing in such a way as to alter susceptibility. Only a thorough public health study can sort this out.
1). Once they evolved, _____________ forever changed the atmosphere on earth.
2). Which of the following statements is not true of prokaryotic cells?
a). Prokaryotic cells are multicellular.
b). Prokaryotic cells do not have a nucleus.
c). Prokaryotic cells have circular DNA.
d). Prokaryotic cells have flagella.
3). When bacterial cell walls are covered with an outer membrane of lipopolysaccharide, they are
4). The prokaryotic genome is contained in the
d). nucleoid region.
5). Archaebacteria and bacteria differ in all of the following ways except
a). the structure of the cell wall.
b). their presence in nonextreme environments.
c). the structure of the plasma membrane.
d). the kinds of ribosomal proteins they possess.
6). Genetic recombination has led to antibiotic resistance through the transfer of
d). bacterial chromosomes.
7). Prokaryotic organisms that obtain their energy by oxidizing inorganic substances are called
8). What disease is experiencing new outbreaks because of antibiotic resistance?
9). The disease sometimes referred to as the "silent STD" because it is usually asymptomatic in women early on is
d). pelvic inflammatory disease.
10). Which of the following can be attributed to bacteria?
a). decomposition of dead organic matter
b). increasing oxygen levels in the atmosphere
c). production of antibiotics
d). all of these
Test Your Visual Understanding
1). This figure shows two kinds of bacterial cell walls. Match the following labels with the appropriate numbered structures.
plasma membrane-2, 7
2). What type of bacteria would have the cell wall structure shown in the upper figure? What type of bacteria would have the cell wall structure shown in the lower figure?
Answer: Upper figure depicts a Gram-positive bacteria because of the thicker peptidoglycan layer and the purple stain. The lower figure depicts a Gram-negative bacteria because there is less peptidoglycan and a red stain.
Apply Your Knowledge
1). Bacterial populations grow through binary fission, which means the bacterium divide in half such that each bacterium gives rise to two bacteria. Assume that a bacterium is placed in culture and undergoes binary fission every 30 minutes. The addition of a competing bacterium reduces the population size by 25%. How many bacteria from the original culture will be present after 24 hours?
Answer: Each division of the bacterium results in two individuals. If the bacterium divides every 30 minutes, they will undergo 48 division cycles in 24 hours. So after 24 hours the number of bacteria equals:
248 or 281,474,976,710,656 bacteria or 2.81 x 1014
But, the population has been reduced by 25% so:
281,474,976,710,656 x 0.75 = 211,106,232,532,992 bacteria or
2.11 x 1014
2). Justify the assertion that life on earth could not exist without prokaryotes.
Answer: Prokaryotes are essential to all aspects of life on earth. Without bacteria, oxygen levels would not have increased in the atmosphere and although bacterial life would have still existed, we would not see the great diversity that currently inhabits the earth. Also, without prokaryotes, there would be little nitrogen in the soil for plants to use for growth. Prokaryotes decompose dead organic matter so that it recycles back into the environment.
3). What are the functions of antibiotics are in the prokaryotes that produce them?
Answer: Prokaryotes produce chemicals that protect their environment from competition. In order to reduce the number of competitors for resources, a prokaryote produces a chemical that harms other strains of prokaryotes but not itself. We use these chemicals as antibiotics to treat certain, primarily bacterial, infections. Although effective against some bacteria, these antibiotics are not effective against all prokaryotes, particularly the type of prokaryotes that produced the chemical.
4). What are endospores? Why would they be an advantage? Would a bacterium with the ability to form endospores have a greater or lesser chance of extinction? Why?
Answer: Endospores are thick-walled spores produced by certain bacteria that protect its genome and a small amount of cytoplasm. The bacteria produce these spores under conditions that are harmful to the bacteria, for example extreme heat or cold or arid conditions that could lead to desiccation. Endospores offer an advantage to bacteria that are able to produce them because it protects them from destruction. Bacteria that produce endospores would have a lesser chance of becoming extinct because of this advantage. The endospores are in a state of dormancy and when conditions improve, the endospores germinate and produce live bacteria that can continue to grow and reproduce. Bacteria that cannot form endospores would die off in the extremely harsh environmental conditions.