Specific proteins produced by cells of the immune system in response to the presence of foreign molecules that circulate in the serum and are present in secretions such as saliva are called:
a. antigens.
b. immunoglobulins.
c. cytokines.
d. phagogens.
B
Produced by B lymphocytes in response to the presence of foreign molecules, immunoglobulins (or antibodies) are present in serum and in secretions such as saliva and are the central molecule of the immune response.
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A research lab is trying to produce new antibiotics. They come up with drugs that detach the hydrophilic heads from the phospholipids in plasma membranes. This drug
A. would be highly toxic and completely useless for human beings-we also have plasma membranes with hydrophilic head groups! B. would be highly toxic only to bacteria, making it an excellent drug to develop and test further. Humans have a different phospholipid structure in their cell plasma membranes than bacteria. C. would generally not be toxic enough to damage Gram-negative bacteria, as their plasma membranes lie under a thick layer of peptidoglycan. D. would be highly toxic for human beings, but might be useful as a topical antibiotic skin cream. The top layer of skin cells is dead anyway, so it wouldn't matter if this damaged those cells. It could NOT be taken internally, though, by human beings.
One effect of auxin, which triggers the elongation of cells, is to affect cell walls by increasing their
A. permeability. B. plasticity. C. stiffness. D. thickness. E. water solubility.
Companion cell assisted loading of organic
compounds is indicated at a. A. b. B. c. C. d. D. e. E.
Which microscope takes advantage of differences in the refractive indexes of cell structures?
A) compound light microscope B) phase-contrast microscope C) darkfield microscope D) fluorescence microscope E) electron microscope