21. In humans, the follicular cells that remain behind in the ovary following ovulation become _____.
(A) the ovarian endometrium that is shed at the time of the menses
(B) a steroid-hormone synthesizing structure called the corpus luteum
(C) the thickened portion of the uterine wall
(D) swept into the fallopian tube
(E) the placenta, which secretes cervical mucus

17. Short-term memory information processing usually causes changes in the _____. (A) brainstem (B) medulla (C) hypothalamus (D) hippocampus (E) cranial nerves

18. The blood-brain barrier _____. (A) is formed by tight junctions (B) is formed by oligodendrocytes (C) tightly regulates the intracellular environment of the CNS (D) uses chemical signals to communicate with the spinal cord (E) provides support to the brain tissue

19. An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to _____. (A) potassium ions (B) sodium ions (C) calcium ions (D) ATP (E) all neurotransmitter molecules

20. From earliest to latest, the overall sequence of early development proceeds in which of the following sequences? (A) gastrulation → organogenesis → cleavage (B) ovulation → gastrulation → fertilization (C) cleavage → gastrulation → organogenesis (D) gastrulation → blastulation → neurulation (E) preformation → morphogenesis → neurulation

22. Oxytocin and antidiuretic hormone are synthesized in the _____. (A) hypothalamus (B) adenohypophysis (C) anterior pituitary (D) adrenal cortex (E) posterior pituitary

23. The cell-mediated immunity that destroys virally infected cells involves _____. (A) cytotoxic T cells (B) natural killer cells (C) helper T cells (D) macrophages (E) B cells 

24. The Bohr shift on the oxygen-hemoglobin dissociation curve is produced by changes in _____. (A) the partial pressure of oxygen (B) the partial pressure of carbon monoxide (C) hemoglobin concentration (D) temperature (E) pH

25. Hypoglycemia, or low levels of glucose in the blood of a healthy human, is "corrected" by a(n) _____. (A) increase in the secretion of insulin (B) increase in the secretion of glucagon (C) increase in the secretion of both insulin and glucagon (D) decrease in the secretion of both insulin and glucagon (E) increase in the secretion of thyroid hormones

26. Standard metabolic rate (SMR) and basal metabolic rate (BMR) are _____. (A) used differently: SMR is measured during exercise, whereas BMR is measured at rest (B) used to compare metabolic rate between hibernating and nonhibernating states (C) both measured across a wide range of temperatures for a given species (D) both standard measurements of fat metabolism in mammals (E) both measured in animals in a resting and fasting state

27. The transduction pathway that activates systemic acquired resistance in plants is initially signaled by _____. (A) antisense RNA (B) Pfr phytochrome (C) salicylic acid (D) abscisic acid (E) red, but not far-red, light