Outline the three levels of defense of humans against the invasion of pathogens. What will be an ideal response?
ANSWER: In the course of an average day, we encounter pathogens (disease-causing agents) of many
kinds: viruses, bacteria, fungi, and parasites. Fortunately, we possess several levels of
defense against infection by pathogens. Each level brings an increasingly aggressive
response. Humans have three levels of defense: (1) the skin and the organisms that inhabit it,
(2) the innate immune system that uses nonspecific responses such as inflammation, and (3)
the adaptive immune system, which mounts specific responses to infection.
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Which of the following molecules contains at least one peptide bond?
A) glycogen B) cellulose C) chitin D) peptidoglycan
The United Nations projects a stabilizing world population at
A. two billion. B. seven billion. C. ten billion. D. fourteen billion. E. None of these choices are correct.
Which of the following is not true of a viroid?
A) Cadang-cadang is a viroid disease of the coconut palm. B) Its RNA is circular. C) Its capsid is quite small. D) Viroids possess about 250—400 nucleotides. E) Viroids affect mostly plants.
In a mutualistic relationship with a fungus, the plant can receive
a. minerals. b. protection. c. water. d. all of these