6. Which of the following is NOT true about helper T cells? (A) They function in both cell-mediated and humoral immune responses. (B) They bear surface CD4 molecules. (C) They recognize polysaccharide fragments presented by MHC-II molecules. (D) They are subject to infection by HIV. (E) When activated, they secrete cytokines that stimulate other lymphocytes.

1. Which of the following events does NOT occur during light absorption in the vertebrate eye? (A) The retinal component of rhodopsin change from cis to trans form. (B) Rhodopsin, a G protein-coupled receptor, triggers a signal transduction pathway to close Na⁺ channels in the plasma membrane. (C) The light stimulus passes from rods and cones to bipolar cells and horizontal cells and then to ganglion cells, whose axons compose the optic nerve. (D) As light absorption increases, the rhodopsin response causes an increase in the release of neurotransmitter. (E) When integrating information across the retina, horizontal cells connect the rods and cones, and amacrine cells join with bipolar cells and ganglion cells

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