12. Melatonin is a hormone produced in the pineal gland. It can be used to treat symptoms of sleep disorders and seasonal affective disorder because
(A) it decreases production of serotonin.
(B) it increases production of serotonin.
(C) it increases production of tryptophan.
(D) it activates the brainstem.
(E) its peak production is normally at night.

8. Imagine a population of 1,000 small rodents. Of these, 250 are breeding females, 250 are breeding males, and 500 are nonbreeding juveniles. What is the effective population size? (A) 1,500 (B) 1,000 (C) 500 (D) 300 (E) 250

9. In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation? (A) Single-strand binding protein could not bind to the unwound parental strands. (B) Replication fork will be formed. (C) The DNA will supercoil. (D) Replication will occur via RNA polymerase alone. (E) Replication will require a DNA template from another source.

10. A geneticist introduces a transgene into human cells and isolates five independent cell lines in which the transgene has integrated into the human genome. In four of the lines, the transgene is expressed strongly, but in the fifth there is no expression at all. Which is a likely explanation for the lack of transgene expression in the fifth cell line? (A) The transgene was mutated during the process of integration into the host cell genome. (B) A transgene integrated into a euchromatic region of the genome. (C) A transgene integrated into a heterochromatic region of the genome. (D) The host cell lacks the enzymes necessary to express the transgene. (E) A transgene integrated into a region of the genome characterized by high histone acetylation.

11. A covalent chemical bond is one in which (A) electrons are removed from one atom and transferred to another atom so that the two atoms become oppositely charged. (B) protons and neutrons are shared by two atoms so as to satisfy the requirements of both atoms. (C) the inner-shell electrons of one atom are transferred to the outer shell of another atom. (D) outer-shell electrons of one atom are transferred to the inner electron shells of another atom. (E) outer-shell electrons of two atoms are shared so as to satisfactorily fill the outer electron shells of both atoms.

13. If the Sun were to suddenly stop providing energy to the Earth, most ecosystems would vanish. Which of the following ecosystems would likely survive the longest after this hypothetical disaster? (A) desert (B) tropical rainforest (C) tundra (D) benthic ocean (E) grassland

14. Which sequence of blood flow can be observed in either a reptile or a mammal? (A) left ventricle → aorta → lungs → systemic circulation (B) vena cava → right atrium → ventricle → pulmonary circuit (C) right ventricle → pulmonary vein → pulmocutaneous circulation (D) pulmonary vein → left atrium → ventricle → pulmonary circuit (E) right atrium → pulmonary artery → left atrium → ventricle

15. Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of the cross BbTt × BBtt will have black fur and long tails? (A) 1/16 (B) 1/4 (C) 3/8 (D) 1/3 (E)1/2

16. Hormone X produces its effect in its target cells via the cAMP second messenger system. Which of the following will produce the greatest effect in the cell? (A) A molecule of cAMP applied to the extracellular fluid surrounding the cell. (B) A molecule of cAMP injected into the cytoplasm of the cell. (C) A molecule of hormone X applied to the extracellular fluid surrounding the cell. (D) A molecule of hormone X injected into the cytoplasm of the cell. (E) A molecule of activated, cAMP-dependent protein kinase injected into the cytoplasm of the cell.

17. How many molecules of water are needed to completely hydrolyze a polymer that is 10 monomers long? (A) 12 (B) 11 (C) 10 (D) 9 (E) 8

18. An interaction between individuals of different species that benefit both partners is called (A) commensalism. (B) predation. (C) exploitation. (D) mutualism. (E) ammensalism.