21. Liver cells, mammary cells, and skin cells all contain the same genome; however, their respective proteomes vary drastically. This observation is best explained by what phenomenon?
(A) cell growth
(B) cell division
(C) crossing over
(D) cell differentiation
(E) evolution

17. The primary difference between estrous and menstrual cycles is that: (A) most estrous cycles are of much longer duration compared to menstrual cycles. (B) behavioral changes during estrous cycles are much less apparent than those of menstrual cycles. (C) season and climate have less pronounced effects on estrous cycles than they do on menstrual cycles. (D) copulation normally occurs across the estrous cycle, whereas in menstrual cycles copulation only occurs during the period surrounding ovulation. (E) the endometrium shed by the uterus during the estrous cycle is reabsorbed, whereas the shed endometrium of menstrual cycles is excreted from the body.

18. When light strikes the rod cell, it becomes ______ and glutamate release onto bipolar cells ______. (A) excited, increases (B) depolarized, increases (C) depolarized, decreases (D) hyperpolarized, increases (E) hyperpolarized, decreases

19. "Accommodation" is the process in the eye of ______. (A) regulation of vitreous humor volume (B) bending light rays to varying degrees by the lens (C) converting light energy into electrical signals by the retina (D) adjustment to varying light levels by altering the sensitivity of the eye (E) adjustment of the amount of light admitted to the eye by adjusting pupil diameter

20. Biofuels are mainly produced by ______. (A) plants that convert hemicellulose into gasoline (B) plants that are easy to grow in arid environments (C) transgenic crops that have cell walls containing ethylene (D) the genetic engineering of ethanol-generating genes into plants (E) the breakdown of cell wall biopolymers into sugars that can be fermented

22. The first heart sound is produced at ______. (A) closing the semilunar valve (B) the beginning of systole (C) the end of systole (D) the beginning of diastole (E) the end of diastole 

23. Which of the following statements about fluid mosaic model is FALSE? (A) Lipid-anchored proteins are a part of the original fluid mosaic. (B) The fluid part of the model is the phospholipid bilayer. (C) The mosaic part of the model is the protein. (D) The model was proposed by S. Jonathan Singer and Garth Nicolson. (E) This model can provide explanations for most of the criticisms of the “lipid bilayer plus protein sheets” model.

24. Which of the following statements about the cell cycle is FALSE? (A) Maturation-promoting factor (MPF) stimulates nuclear envelope breakdown by phosphorylating the lamin proteins of nuclear lamina. (B) Active MPF phosphorylates microfilament-associated proteins to facilitate formation of the mitotic spindle. (C) Active MPF phosphorylates histones to allow chromosome condensation. (D) Epidermal growth factor can induce cells to pass through the G1 checkpoint and into S phase through the Ras pathway. (E) The p21 protein functions to suppress the activity of Cdk-cyclin complex to block passage through the G1 checkpoint.

25. Which of the following statements about the extracellular matrix (ECM) is FALSE? (A) Collagens are the major structure fiber of ECM in animal cells. (B) Mucoproteins are the components of hydrated matrix of ECM in animal cells. (C) Cellulose are adhesive molecules of ECM in plant cells. (D) Fibronectins and laminins are adhesive molecules of ECM in animal cells. (E) Hemicellulose and extensins are the components of hydrated matrix of ECM in plant cells.

26. Which of these statements about viruses is true? I. H5N1 virus is an RNA virus. II. SARS virus is a single positive-stranded RNA virus. III. Dengue fever virus is a mosquito-borne single negative-stranded RNA virus. IV. Zika virus is a single negative-stranded RNA virus. (A) I and II (B) I and III (C) I and IV (D) I, II, and III (E) I, II, III, and IV

27. Which of these statements best describes fruits? I. A pea pod is formed from an ovary. II. When you consume tomato, you are eating fruits that are derived from ripen ovary. III. A peach and a nut are a simple fruit that is derived from a flower. IV. A strawberry is a fruit that is derived from a single flower. V. A pineapple is a simple fruit. (A) I and II (B) II and III (C) III and IV (D) I, II, III, and IV (E) I, II, III, IV, and V