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

43. The "Founder effect" is an example of: (A) Natural selection (B) Genetic drift (C)Gene flow (D) Mutation

44. The action potential is generated when: (A) Sodium ions enter the neuron (B) Potassium ions leave the neuron (C) Calcium ions bind to the neuron (D) Chloride ions are released from the neuron

45. Which of the following is the primary function of the myelin sheath in neurons? (A) Increase the speed of nerve impulse conduction (B) Generate action potentials (C) Regulate neurotransmitter release (D) Provide structural support to the neuron

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.

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

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

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