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

9. What does transformation involve in bacteria? (A) the creation of a strand of DNA from an RNA molecule (B) the creation of a strand of RNA from a DNA molecule (C) the infection of cells by a phage DNA molecule (D) the type of semiconservative replication shown by DNA (E) assimilation of external DNA into a cell 

10. Males are more often affected by sex-linked traits than females because _____. (A) males are hemizygous for the X chromosome (B) male hormones such as testosterone often alter the effects of mutations on the X chromosome (C) female hormones such as estrogen often compensate for the effects of mutations on the X chromosome (D) X chromosomes in males generally have more mutations than X chromosomes in females (E) mutations on the Y chromosome often worsen the effects of X-linked mutations

11. Paracrine signaling _____. (A) involves secreting cells acting on nearby target cells by discharging a local regulator into the extracellular fluid (B) requires nerve cells to release a neurotransmitter into the synapse (C) occurs only in paracrine yeast cells (D) has been found in plants but not animals (E) involves mating factors attaching to target cells and causing production of new paracrine cells

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.

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

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

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