At about how many weeks of gestation do the sex organs of a fetus develop?
a. Five
b. Six
c. Seven
d. Eight
c. Seven
At about seven weeks of gestation, the sex organs of a fetus develop. The presence of testosterone determines whether the tissues will develop into male organs.
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Matching. Match each term with the most
appropriate statement. 1. ___ antigens 2. ___ B lymphocytes 3. ___ perforin 4. ___ clone 5. ___ complement proteins 6. ___ cytotoxic T lymphocytes 7. ___ interleukins 8. ___ macrophages 9. ___ memory cells 10. ___ B cells 11. ___ retroviruses 12. ___ stem cells 13. ___ natural killer cells 14. ___ vaccine A. cells that do not divide, die in less than a week, and secrete antibodies B. cells that directly destroy body cells already infected by viral or fungal parasites, as well as mutant and cancerous cells C. lymphocytes that are held in reserve, circulate in the bloodstream, and enable a rapid response to subsequent encounters with the same invader D. able to lyse cells by forming pore complexes Chapter 38 Immunity 441 E. cells that are produced in the bone marrow, are never changed by the thymus, and manufacture antibodies F. able to destroy cells but not dependent on recognition of antigen-MHC complexes G. a class of proteins that help cells of the immune system communicate H. “big eaters” that alert other lymphocytes to the invasion of specific antigens I. immature cells that may or may not be committed to develop into one of several mature cell types J. a group of cells that are all produced asexually from one original parent cell K. surface patterns of nonself molecules or particles L. proteins released by cytotoxic T cells to destroy target cell membranes M. preparation injected into the body to elicit a primary immune response N. one of this group has been identified as the causative agent of AIDS
Which step in translation initiation is unique to eukaryotes?
A) formation of the preinitiation complex B) formation of the initiation complex C) scanning D) ribosome assembly E) translocation of the ribosome in the 3? direction
At the center of an herbaceous eudicot stem is:
a. pith. b. collenchyma. c. sclerenchyma. d. vascular cambium. e. phloem.
A dehydrated runner drinks a lot of water after a race. He or she rehydrates because
A. the contents of the digestive tract and the bloodstream are isotonic compared to each other. B. water will diffuse from an area where its concentration is low to an area where its concentration is high. C. the contents of the digestive tract are hypotonic compared to the bloodstream. D. the bloodstream is hypotonic compared to the contents of the digestive tract.