AP BIO

Pyruvate dehydrogenase is an enzyme that converts pyruvate to acetyl-CoA. Acetyl-CoA is further metabolized in the Krebs cycle. A researcher measured the accumulation of acetyl-CoA in a reaction containing pyruvate and pyruvate dehydrogenase under several different conditions (Figure 1). Which of the following observations provides the best evidence that acetyl-CoA negatively regulates pyruvate dehydrogenase activity? a) The rate of the pyruvate dehydrogenase- catalyzed reaction is slower in the presence of a higher concentration of acetyl-CoA b) The gene that encodes pyruvate dehydrogenase is transcribed when excess acetyl-CoA is detected c) The accumulation of acetyl-CoA stops after 70 seconds, regardless of the reaction mixture d) Acetyl-CoA is continuously broken down on the Krebs cycle.

a)

Pyruvate dehydrogenase is an enzyme that converts pyruvate to acetyl-CoA. Acetyl-CoA is further metabolized in the Krebs cycle. A researcher measured the accumulation of acetyl-CoACoA in a reaction containing pyruvate and pyruvate dehydrogenase under several different conditions (Figure 1). The maximum production rate of acetyl-CoA under condition 1 is closest to which of the following? a) 1 micromolecule/ sec b) 24 micromolecule/ sec c) 32 micromolecule/sec d) 69 micromolecule/sec

a)

A student placed a semipermeable membrane inside a U-shaped channel with two chambers, as shown. The membrane permits the movement of water but not salt. The student wants to vary the rate of osmosis that occurs across the membrane. Which of the following experimental designs will result in the fastest net rate of water movement into chamber A? a) Placing salt water in chamber A and distilled water in chamber B. b) placing distilled water in both chambers c) Placing salt water in chamber B and distilled water in chamber A. d) Placing saltwater in both chambers

a) ( this is because salt doesn't move through the membrane, so the water would come into chamber A faster. )

Humans produce sweat as a cooling mechanism to maintain a stable internal temperature. Which of the following best explains how the properties of water contribute to this physiological process? a) The high specific heat capacity of water allows the body to absorb a large amount of excess heat energy b) The high heat of vaporization of water allows the body to remove excess heat through a phase change of water from liquid to gas c) The high surface tension of water contributes to the physical process by which water leaves the body d) The high melting temperature of water allows the body to remove excess heat through a phase change of water from solid to liquid.

b)

The hormone prolactin has varying effects in many different animal species. All vertebrates produce prolactin, which is involved in signal transduction pathways. In mammals, prolactin stimulates the production of milk in mammary glands. In fish, prolactin plays an important role in osmoregulation. In birds, prolactin is involved in lipid metabolism. Which of the following best explains the presence of prolactin in various vertebrate species? a) Though all vertebrates produce prolactin, its carried uses indicate it arose as a result of convergent evolution and not as a result of common ancestry b) Prolactin is a homologous hormone because it has a common origin but different functions in various species. c) Prolactin will bind only to intracellular receptors in animal species with phospholipid bilayers, so its effects are varied in different species d) because of different receptors activating different signal transduction pathways within the same species.

b)

Which of the following best describes the role of water in photosynthesis? a) Water is the only source of protons for the formation of a proton gradient b) Water molecules donate electrons to the electron transport chain c) Water molecules combine with stored carbon molecules to produce glucose d) water is the terminal electron acceptor for electrons that pass through the electron transport chain.

b)

Protein X activates gene expression only in cells exposed to a specific signaling molecule. In a study, researchers determined the intracellular location of Protein X in cultured cells both before and after exposing the cells to the signaling molecule. The results of the study are shown in the diagram. Based on the results, which of the following best describes what Protein X is? a) Protein X is an RNA splitting enzyme b) Protein X is a cell membrane receptor protein c) Protein X is a transcription factor d) Protein X is a hormone

c)

What evolutionary advantage does compartmentalization of core metabolic processes offer eukaryotes? a) Evolution of the mitochondria allowed eukaryotes to perform respiration b) With the evolution of mitochondria in eukaryotes, the Krebs cycle and electron transport chain also evolved c) Evolution of a nucleus in eukaryotes separates the processes of transcription and translation and they can be regulated separately d) A nucleus in bacteria provides separation of respiration from transcription

c)

Pyruvate dehydrogenase is an enzyme that converts pyruvate to acetyl-CoA. Acetyl-CoA is further metabolized in the Krebs cycle. A researcher measured the accumulation of acetyl-CoACoA in a reaction containing pyruvate and pyruvate dehydrogenase under several different conditions (Figure 1). Pyruvate dehydrogenase deficiency is a genetic disease most commonly linked to a mutation in the α-subunit of the mitochondrial enzyme that causes the enzyme to cease functioning. As a result of the mutation, affected individuals build up dangerous amounts of lactic acid. Which of the following best explains the buildup of lactic acid in individuals with the mutation? a) Cells use lactic acid to shunt electrons from pyruvate to the electron transport chain in the mitochondria b) cells undergo glycolysis because there is a buildup of pyruvate in affected individuals c) cells cannot transport pyruvate to the mitochondria in the absence of the pyruvate dehydrogenase activity, so the pyruvate is broken down to lactic acid and ethanol. d) cells undergo fermentation because pyruvate cannot be metabolized to proceed into the Krebs cycle.

d)

Pyruvate dehydrogenase is an enzyme that converts pyruvate to acetyl-CoACoA. Acetyl-CoACoA is further metabolized in the Krebs cycle. A researcher measured the accumulation of acetyl-CoACoA in a reaction containing pyruvate and pyruvate dehydrogenase under several different conditions (Figure 1). Which of the following best describes the cellular location where pyruvate dehydrogenase is most likely active? a) The cytosol b) The lysosomes c) The nucleus d) The mitochondrial matrix

d)

The diagram shows how water can adhere to the xylem in the stems of plants, which contributes to water movement in the plant. Which of the following best explains how water is able to move upward from the roots of a plant, through its xylem in the stem, and out to the leaves? a) water is polar, and the walls of the xylem are nonpolar. Water molecules can form hydrogen bonds with one another but not with the xylem walls. b) Water is nonpolar, and the walls of the xylem are polar. Water molecules are able to form hydrogen bonds with the xylem walls, and they are pulled up the xylem. c) Water and the xylem are both nonpolar. Water molecules have the ability to form hydrogen bonds with one another but not with the xylem walls d) Water and the xylem are both polar. Water molecules have the ability to form hydrogen bonds with each other and with the walls of the xylem.

d)