15. The activity of acetylcholine in a synapse is terminated by its_____ .
(A) active transport across the presynaptic membrane
(B) diffusion across the presynaptic membrane
(C) active transport across the postsynaptic membrane
(D) diffusion across the postsynaptic membrane
(E) degradation on the postsynaptic membrane

11. The essential amino acids (A) must be obtained from the food we eat. (B) are found only in green, leafy vegetables. (C) are essential as an energy source. (D) are required for making nucleic acids.

12. For a neuron at rest with a membrane potential of -65 mV, an increase in the movement of potassium ions out of that neuron's cytoplasm would result in the _____. (A) depolarization of the neuron (B) hyperpolarization of the neuron (C) replacement of potassium ions with sodium ions (D) replacement of potassium ions with calcium ions (E) neuron switching on its sodium-potassium pump to restore the initial conditions

13. Most gastric ulcers are caused by (A) overuse of aspirin and/or ibuprofen. (B) excessive mental stress. (C) bacteria. (D) overconsumption of alcohol.

14. Which gland requires iodine to produce its hormones? (A) adrenal medulla. (B) pineal. (C) pituitary. (D) thyroid.

16. Which neurotransmitter excites muscle cells? (A) Acetylcholine (B) epinephrine (C) endorphin (D) nitric oxide (E) gamma-aminobutyric acid (GABA)

17. In the human retina, _____(A) cone cells can detect color, but rod cells cannot (B) cone cells are more sensitive than rod cells to light (C) cone cells, but not rod cells, have a visual pigment (D) rod cells detect short wavelength UV light (E) rod cells require higher illumination for stimulation than do cone cells

18. Which of the following cells are involved in cell-mediated immunity and also respond to class I MHC molecule-antigen complexes? (A) cytotoxic T cells (B) plasma cells (C) helper T cells (D) macrophages (E) B cells

19. Damage to the frontal lobe, such as experienced by Phineas Gage, leads to_____ . (A) the loss of a sense of balance. (B) the loss of all short-term memory (C) altered emotional responses (D) greatly increased long-term memory

20. Which of the following is the best definition of autoimmune disease? (A) a condition in which B cells and T cells respond independently to antigens and do not interact correctly (B) a condition in which the adaptive immune system fails to recognize the second infection by the same antigen (C) a condition in which self molecules are treated as nonself (D) a condition in which the immune system creates random antibodies without being triggered by an antigen

21. Which of the following correctly identify which organs develop from different embryonic tissue layers in a frog?