15. Which of the following occurs when a skeletal muscle fiber contracts?
(A) The myosin head is bound to ATP.
(B) The myosin tail binds to actin, forming a cross-bridge.
(C) Releasing ADP and Pi, myosin fixes the thin filament.
(D) The tropomyosin is activated by ATP hydrolysis.
(E) Ca+2 entry into sarcoplasmic reticulum.

11. Lipolysis and gluconeogenesis are stimulated when (A) insulin and glucagon are both decreasing. (B) insulin and glucagon are both increasing. (C) insulin is increasing and glucagon is decreasing. (D) insulin is decreasing and glucagon is increasing. (E) glucagon is not associated with lipolysis.

12. Consider this pathway: bitter molecules → G-protein→ phospholipase C → IP3 →raised [Ca2 +]→ cellular response. Identify the second messenger. (A) G-protein (B) IP3 (C) Ca2 + (D) Band C(E) A, B and C

13. The thick band of nerve fibers that connect the right and left cerebral hemispheres in placental mammals, enabling the hemispheres to process information together, is called (A) corpus callosum. (B) hippocampus. (C) suprachiasmatic nuclei. (D) limbic system. (E) reticular formation.

14. The capillary system that serves the loop of Henle, is called (A) vas deferens. (B) macula densa. (C) vasa recta. (D) juxtaglomerular apparatus. (E) henle plexus.

16. The mechanism that is used by Drosophila melanogaster to prevent the shortening of the chromosome ends is (A) transposition. (B) elongating the ends by telomerase. (C) apoptosis. (D) signal transduction. (E) recombination and mismatch repair.

17. Which of the following statements on eukaryotic mRNA is NOT true? (A) mRNA is usually capped at the 5' terminus. (B) mRNA always contains a poly-A tail. (C) Translation usually starts from the first AUG codon from the 5' terminus. (D) mRNA often contains an AAUAAA sequence in the 3' region as a polyadenylation signal. (E) mRNA does not contain a Shine-Dalgarno sequence for translation initiation.

18. Which of the following processes is most directly driven by light energy? (A) Creation of a pH gradient by pumping protons across the thylakoid membrane. (B) Carbon fixation in the stroma. (C) Reduction of NADP+ molecules. (D) Removal of electrons from chlorophyll molecules. (E) ATP synthesis.

19. 'Which of the following does NOT occur during the Calvin cycle? (A) carbon fixation. (B) oxidation ofNADPH. (C) release of oxygen (D) regeneration of the C02 acceptor. (E) consumption of ATP.

20. 'Which of the following statements is most compatible with the "source-sink" concept of sugar transport in the phloem? (A) Sugars are loaded at the sink. (B) Sugars move from the sink to the source in the phloem. (C) Sugars are unloaded at the source. (D) Developing young leaves are sinks and fully developed leaves are sources. (E) Transport is always unidirectional in the phloem.

21. The completion of the S phase of the cell cycle of a mammalian cell is marked by all of the following EXCEPT: (A) Histone content per cell is double that of cells in G1• (B) In replicated DNA, newly incorporated bases are paired with parental bases. (C) Each replicated chromosome has four telomeres. (D) Sister chromatids disjoin from one another. (E) The nucleus contains the equivalent amount of DNA of a tetraploid cell in G1•