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

| Endoderm | Mesoderm | Ectoderm |
| :---------- | :--------- | :---------- |
|
(A) Brain | Heart | Epidermis |
|
(B) Liver | Heart | Brain |
|
(C) Notochord | Liver | Eye lens |
|
(D) Liver | Nerves | Muscles |

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

22. Which of the following is an endocrine gland that raises blood calcium levels? (A) parathyroid (B) thyroid gland (C) pituitary gland (D) testes

23. An excess of T3 and T4 in the blood is hyperthyroidism, which in its most common form is called (A) goiter. (B) sterility. (C) Graves' disease. (D) botulism.

24. High levels of which of the following hormones can suppress the body's immune system? (A) glucagon (B) mineralocorticoids (C) glucocorticoids (D) antidiuretic hormone

25. After being produced in the testes, sperm mature further in a structure called the (A) vas deferens. (B) epididymis. (C) prostate. (D) seminal vesicle.

26. Water's unique properties for the chemical basis of life are primarily a consequence of its: (A) highly stable covalent bonds. (B) existence as individual atoms in organisms. (C) polarity and hydrogen bonding. (D) role in preventing elements from combining. (E) exceptional heat resistance due to strong ionic bonds.

27. Which statement accurately reflects a fundamental concept of cells? (A) Carbon compounds are essential building blocks due to limited bonding. (B) Carbohydrates primarily provide long-term energy storage. (C) Lipids are hydrophilic, serving mainly as immediate fuel. (D) Carbohydrates are a cell's primary fuel source and important building materials. (E) Biomolecule functions are determined by nitrogen and phosphorus.