Describe and contrast three types of bacterial skin infections that can lead to tissue necrosis and death. Name and characterize the causative bacteria, and describe epidemiological and clinical features of each disease
What will be an ideal response?
Necrosis is tissue death and is usually caused by reduced blood flow to an area. Several bacterial infections can result in localized or spreading tissue necrosis. Necrotizing fasciitis is often caused by Streptococcus pyogenes, also known as Group A streptococci (GAS). S. pyogenes produces a number of virulence factors such as hyaluronidase and lipase that break down tissue and facilitate the spread of the bacteria. M protein on the surface of the bacterium serves as a binding site for plasminogen which triggers a tissue degradation cascade. Gas gangrene is caused by Clostridium perfringens, a soil bacterium which may infect deep wounds. The low-oxygen environment of deep wounds stimulates the growth of the anaerobic clostridia which produces toxins which can lead to rapid tissue death. Cutaneous anthrax is caused by Bacillus anthracis, a bacterium found in soil and often transmitted to human through contact with infected animals or their parts. The bacteria may enter skin abrasions to form a solid, blackened skin nodule. Exotoxins kill first superficial then deeper skin cells. In most cases, the damage stays localized, but prompt treatment is required.
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Water diffuses through certain organs such as the kidneys and bladder much faster than would occur by passive diffusion through a lipid bilayer alone. What accounts for this more rapid rate of water transport in these organs?
A. The composition of lipids changes to promote water transport. B. Presence of aquaporin channels for facilitated diffusion of water. C. Presence of a water pump. D. Presence of an ATP-driven enzyme for water transport. E. The presence of molecules that bind water and change its membrane permeability properties.
Active transport in plant root cells requires that those cells have access to O2. Normally there is enough O2 available
in air pockets in the soil, but flooded soil has very little O2. Thus, unless they have special adaptations, plants in flooded soil effectively have no active transport in their roots. Which of the following should you expect to occur for trees without special adaptations to flooding after several days in flooded soil?
a. excess uptake of water and minerals in the xylem only b. wilting of their leaves c. bursting of leaf cells due to excess water flow d. excess water pushed out at the margins of their leaves only e. excess uptake of water and minerals in the xylem, and excess water pushed out at the margins of their leaves
The measured distance between genes D and E in a two-point testcross is 50 map units. Where are genes D and E in relation to each other? (Select all that apply.)
A) D and E are on different homologous chromosomes. B) D and E are on the same chromosome, at least 50 map units apart. C) D and E are on the same chromosome, exactly 50 map units apart. D) D and E are on the same chromosome, less than 50 map units apart.
What can be said about Drosophila development?
A. Maternal genes determine the initial course of development after fertilization. B. Paternal genes determine the initial course of development after fertilization. C. Zygotic genes determine the initial course of development after fertilization. D. Syncytial blastoderm genes determine the initial course of development after fertilization.