50. Which of the following is NOT a major germ layer formed during gastrulation?
(A) Ectoderm
(B) Mesoderm
(C) Endoderm
(D)Epiderm

46. Xylem and phloem are two types of vascular tissues in plants. Which of the following statements is true? (A) Xylem transports water and minerals upward, while phloem transports sugars downward. (B) Xylem transports sugars downward, while phloem transports water and minerals upward. (C)Both xylem and phloem transport water and minerals upward. (D)Both xylem and phloem transport sugars downward.

47. Which of the following best describes the concept of keystone species? (A) Species that are at the top of the food chain (B) Species that have a significant impact on the ecosystem structure and function (C) Species that are abundant and have a high population density (D) Species that are native to a specific ecosystem

48. The enzyme responsible for phosphorylating target proteins in many cellular signaling pathways is: (A) Protein kinase (B) Protein phosphatase (C)G protein (D)Ligase

49. Which of the following is an example of an intracellular receptor? (A) Insulin receptor (B) G protein-coupled receptor (GPCR) (C) Receptor tyrosine kinase (RTK) (D) Steroid hormone receptor

1. A cell lacking which of the following structures is most likely to be a prokaryote? (A) Nuclear membrane (B) Cell membrane (C) Cytoplasm (D) Nucleic acid

2. A salamander relies on hydrogen bonding to stick to various surfaces. Therefore, a salamander would have the greatest difficulty clinging to a_____. (A)slightly damp surface (B)surface of hydrocarbons (C) surface of mostly carbon-oxygen bonds (D) surface of mostly carbon-nitrogen bonds

3. Sulfur is in the same column of the periodic table as oxygen but it is less electronegative than oxygen. Compared to water molecules, how will the H2S molecules behave? (A)have greater cohesion to other H2S molecules (B)have a greater tendency to form hydrogen bonds with each other (C)have a higher capacity to absorb heat for the same change in temperature (D) not be able to form hydrogen bonds with each other

4.Which of the following identifies the chemical relationship between glucose and fructose? (A) They are isotopes. (B) They are enantiomers. (C) They are cis-trans isomers. (D) They are structural isomers.

5. During a 12-hour fast in a human, the first macromolecule to get depleted is typically_____. (A)glucose (B) protein (C)glycogen (D) starch

6. Zinc is an essential trace element for most organisms. Zinc is required in the active site of the enzyme carboxypeptidase where it most likely functions in which of the following ways? (A) as a noncompetitive inhibitor of the enzyme (B) as an allosteric activator of the enzyme (C) as a cofactor necessary for enzyme activity (D) as a coenzyme derived from a vitamin