16. Skeletal muscle contraction begins when calcium ions bind to _____.
(A) energized cross-bridges
(B) myosin
(C) actin
(D) tropomyosin
(E) troponin

12. Which of the following provides the best evidence of a biodiversity crisis? (A) the incursion of a non-native species. (B) increasing pollution levels. (C) decrease in regional productivity. (D) high rate of extinction. (E) climate change.

13. Which of the following is most likely to contribute to density-dependent regulation of populations? (A) the removal of toxic waste by decomposers (B) intraspecific competition for nutrients (C) earthquakes (D) floods (E) fires

14. Which of the following statements about the ocean pelagic biome is true? (A) The ocean is a vast, deep storehouse that always provides sustenance; it is the next "frontier" for feeding humanity. (B) Because it is so immense, the pelagic ocean biome is globally uniform. (C) Globally, more photosynthesis occurs in the ocean neritic biome than in the pelagic biome. (D) Pelagic ocean photosynthetic activity is disproportionately low in relation to the size of the biome. (E) The most abundant animals are vertebrate fishes.

15. A salmon returns to its home stream to spawn. What term best applies to this behavior? (A) sign stimulus (B) cognition (C) imprinting (D) classical conditioning (E) operant conditioning

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

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

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