Ethylene is an organic compound produced by ripening fruits. In a controlled experiment, researchers found that ethylene gas stimulated the ripening process in newly harvested fruits. Which of the following describes the most likely connection between natural ethylene production and fruit ripening?
A
As a result of metabolic inactivity, newly harvested fruits are unable to absorb ethylene gas from the atmosphere.
B
Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits.
C
Because of normal phenotypic variation, only some of the fruits in a given generation are expected to produce ethylene gas.
D
The rate of ethylene gas production by ripening fruits is an indicator of the relative age of an ecosystem.
B
Ethylene gas is a chemical signal through which ripening fruits trigger the ripening process in other fruits.
Epinephrine is a protein hormone found in many animals. Epinephrine stimulates a signaling pathway that results in the breakdown of glycogen to glucose in the liver cells. Which of the following describes the initial steps in the process whereby epinephrine stimulates glycogen breakdown?
A. Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP.
B
Epinephrine binds to a cell-surface receptor; the activated receptor catalyzes the conversion of glycogen to glucose.
C
Epinephrine diffuses through the plasma membrane; the hormone dimerizes in the cytosol.
D
Epinephrine is taken into the cell by endocytosis; glycogen is converted to glucose in the endocytotic vesicle.
A. Epinephrine binds to a cell-surface receptor; the activated receptor stimulates production of the second messenger, cAMP.
It is estimated that oxygen production first evolved in photosynthetic prokaryotes approximately 2.7 billion years ago. The first photosynthetic prokaryotes are presumed to be similar to today’s cyanobacteria.
Which of the following best supports the claim that photosynthetic prokaryotes were responsible for the oxygen in Earth’s atmosphere?
A
The light reactions of photosynthesis split carbon dioxide into carbon and oxygen.
B
The light reactions of photosynthesis split water into hydrogen ions and oxygen.
C
The Calvin cycle splits glucose into carbon, hydrogen, and oxygen.
D
The Calvin cycle splits water into hydrogen ions and oxygen.
B
The light reactions of photosynthesis split water into hydrogen ions and oxygen.
Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).
Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons (H+) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.
The ��� gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an ��� mutation that prevented the production of a functional ��� product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses ��� to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).
Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells?
A
Insulin binding ultimately increases pancreatic secretion of additional insulin.
B
Insulin binding blocks the release of osteocalcin from the osteoblasts.
C
Insulin binding inhibits the expression of ���.
D
Insulin binding increases the pH of the extracellular matrix.
A. Insulin binding ultimately increases pancreatic secretion of additional insulin.
Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone?
A
The phosphorylation of the insulin receptor causes a response in osteoblast bone cells.
B
The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.
C
The change in expression of ��� changes the insulin receptor activity of the osteoblast.
D
The activation of the osteocalcin by a bone cell is pH dependent.
B
The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.
Which of the following claims is most consistent with the data shown in Figure 2 ?
A
��� expression is necessary to prevent the overproduction of insulin.
B
Esp protein does not regulate blood-sugar levels in normal mice.
C
Normal mice require a higher blood concentration of insulin than mutant mice do.
D
Mutant mice have a cyclical pattern of insulin secretion.
A
Esp expression is necessary to prevent the overproduction of insulin.
Which of the following was a positive control in the experiment?
A
Minutes after glucose injection
B
Blood insulin
C
Mutant strain
D
Normal strain
D
Normal strain
A researcher observes that mice from the mutant strain experience low blood sugar. Which of the following best describes the feedback mechanism in the pathway (Figure 1) causing the low blood sugar in the mutant strain?
A
The positive feedback of insulin production
B
The negative feedback of inactive osteocalcin production
C
The positive feedback of the Esp protein
D
The negative feedback of insulin-secreting pancreatic cell proliferation
A
The positive feedback of insulin production
The mechanism of action of many common medications involves interfering with the normal pathways that cells use to respond to hormone signals. Which of the following best describes a drug interaction that directly interferes with a signal transduction pathway?
A
A medication causes the cell to absorb more of a particular mineral, eventually poisoning the cell.
B
A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.
C
A medication enters the target cell’s nucleus and acts as a mutagen.
D
A medication interrupts the transcription of ribosomal RNA genes.
B
A medication enters the target cell and inhibits an enzyme that normally synthesizes a second messenger.
On average, more ATP can be produced from an NADH molecule than can be produced from a molecule of FADH2. Based on Figure 1, which of the following best explains the difference in ATP production between these two molecules?
A
NADH contributes more electrons to the electron transport chain than FADH2 does and therefore provides more energy to pump protons.
B
The electrons of FADH2 are transferred through three complexes of the electron transport chain whereas those of NADH are transferred through all four complexes.
C
FADH2 contributes more protons to the mitochondrial matrix, which decreases the proton gradient.
D
The protons contributed by FADH2 are combined with �2 to make water and are not pumped across the membrane.
B
The electrons of FADH2 are transferred through three complexes of the electron transport chain whereas those of NADH are transferred through all four complexes.
Which of the following is a valid interpretation of the experimental results that explains how individuals with type 2 diabetes differ from individuals without diabetes?
A
The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals.
B
The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that no functional GLUT4 protein is produced in the muscle cells of those individuals.
C
The absence of activated insulin receptors in individuals with type 2 diabetes indicates that no insulin is secreted by the pancreatic cells of those individuals.
DThe absence of activated IRS-1 in individuals with type 2 diabetes indicates that no functional insulin receptor protein is produced in the muscle cells of those individuals.
A
The relatively low levels of glucose uptake in individuals with type 2 diabetes indicate that mobilization of GLUT4 to the cell surface is reduced in muscle cells of those individuals.
Based on the experimental results, which of the following describes the most likely defect in muscle cells of patients with type 2 diabetes?
A
Insulin receptor proteins do not reach the cell surface.
B
Insulin does not activate its receptor.
C
IRS-1 activation is reduced at high insulin concentrations.
D
GLUT4 blocks glucose from entering cells.
C
IRS-1 activation is reduced at high insulin concentrations.
Based on the information presented, which of the following genetic changes in an individual without diabetes is most likely to result in a disrupted cellular response to insulin signaling similar to that of an individual with type 2 diabetes?
A
A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein
B
Duplication of the gene encoding a PI-3 kinase that results in synthesis of a muscle-specific variant of the enzyme in skin cells as well as in muscle cells
C
A mutation in the gene encoding IRS-1 that causes the protein to be active in muscle cells even in the absence of insulin signaling
DInsertion of a small segment of DNA into the promoter of the Glut4 gene that results in increased synthesis of GLUT4 proteins in muscle cells
A
A deletion in the gene encoding the insulin receptor that removes only the cytoplasmic domain of the protein
Beta cells, a type of cell found in the pancreas, are responsible for producing, storing, and releasing the hormone (chemical signal) insulin. An increase in blood glucose levels stimulates beta cells to produce insulin, which facilitates the uptake of glucose by body cells and reduces the glucose levels in the blood. As the blood glucose levels decrease, beta cells are no longer stimulated and stop producing insulin.
Which of the following best explains the feedback mechanism that regulates blood glucose levels?
A
Regulation of blood glucose levels demonstrates positive feedback, because as the blood glucose levels increase, insulin acts to raise blood glucose levels.
B
Regulation of blood glucose levels demonstrates negative feedback, because as the blood glucose levels increase, insulin acts to lower blood glucose levels.
C
Regulation of blood glucose levels demonstrates positive feedback, because as the production of insulin by beta cells increases, blood glucose levels increase.
D
Regulation of blood glucose levels demonstrates negative feedback, because as the production of insulin by beta cells decreases, blood glucose levels decrease.
B
Regulation of blood glucose levels demonstrates negative feedback, because as the blood glucose levels increase, insulin acts to lower blood glucose levels.
Which of the following best describes the function
of the
coenzymes NAD+ and FAD in eukaryotic
cellular respiration?
A
They participate in hydrolysis reactions by
accepting protons
from water molecules.
B
They participate directly in the
phosphorylation of ADP to ATP.
C
They serve as final electron acceptors in the
electron
transport chain.
D
They aid vitamins such as niacin in the breakdown
of glucose.
E
They accept electrons during oxidation-reduction
reactions.
E. They accept electrons during oxidation-reduction
reactions.
If chemical signals in the cytoplasm control the progression of a cell to the M phase of the cell cycle, then fusion of a cell in G1 with a cell in early M phase would most likely result in the
A
replication of chromosomes only in the G1 cell
B
exiting of both cells from the cell cycle and into the G0 phase
C
condensation of chromatin in preparation of nuclear division in both cells
D
transfer of organelles from the G1 cell to the cell in the M phase
C
condensation of chromatin in preparation of nuclear division in both cells
The drug 5-fluorouracil inhibits thymine production in eukaryotic cells. Which of the following cell cycle stages will be most directly affected by 5-fluorouracil?
A
The first growth phase (G1)
B
Synthesis of DNA phase (S)
C
Preparation for mitosis (G2)
D
Cytokinesis
B
Synthesis of DNA phase (S)
Two nutrient solutions are maintained at the same pH. Actively respiring mitochondria are isolated and placed into each of the two solutions. Oxygen gas is bubbled into one solution. The other solution is depleted of available oxygen. Which of the following best explains why ATP production is greater in the tube with oxygen than in the tube without oxygen?
A
The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen.
B
Electron transport is reduced in the absence of a plasma membrane.
C
In the absence of oxygen, oxidative phosphorylation produces more ATP than does fermentation.
D
In the presence of oxygen, glycolysis produces more ATP than in the absence of oxygen.
A
The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen.
A researcher examining a root tip observes a plant cell with condensed sister chromatids, kinetochores with attached microtubules, and individual chromosomes that are aligned at the equatorial plate of the cell. Which of the following best describes what the next process will be in the cell?
A
Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell.
B
Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.
C
The nuclear envelope will break down, and the spindle will begin to form.
D
The chromatin will decondense, and the daughter cell will enter interphase.
B
Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.
Which of the following is true of mitosis?
A
It is also known as cytokinesis.
B
It maintains the same chromosome number in the daughter cells as in the parent cell.
C
It is the last phase of interphase.
D
It regulates the transfer of genetic information from one daughter cell to another.
E
It moves homologous chromosomes to opposite poles.
B
It maintains the same chromosome number in the daughter cells as in the parent cell.
Which of the following best explains the most likely method by which this antitumor drug works?
A
Trabectedin increases the production of cyclin proteins that signal the cancer cells to enter prophase.
B
Trabectedin interferes with the plasma membrane, causing it to break down and expose the DNA to damage.
C
Trabectedin interferes with the duplication of DNA during interphase and thus prevents cancer cells from passing the G2 checkpoint.
D
Trabectedin interferes with the regulations of cyclin proteins, causing their levels to increase and creating errors in DNA.
C
Trabectedin interferes with the duplication of DNA during interphase and thus prevents cancer cells from passing the G2 checkpoint.
Maturation promoting factor, MPF, is a cyclin-CDK complex that catalyzes the phosphorylation of other proteins to start mitosis. The activity level of MPF is dependent on the relative concentrations of the cyclin and CDK components of MPF (Figure 1).
Based on Figure 1, which of the following describes the role of cyclin in the regulation of the cell cycle?
A
During G1 phase, the cyclin level decreases to signal the start of the resting phase of the cell cycle.
B
During M phase, the cyclin level peaks, resulting in an increased binding frequency with CDK.
C
During S phase, the cyclin level remains the same because DNA replication is occurring.
D
During G2 phase, the cyclin level remains low, causing MPF activity to decrease, which leads cells to initiate mitosis.
B
During M phase, the cyclin level peaks, resulting in an increased binding frequency with CDK.
Which of the following is an important difference between light-dependent and light-independent reactions of photosynthesis?
A
The light-dependent reactions occur only during the day; the light-independent reactions occur only during the night.
B
The light-dependent reactions occur in the cytoplasm; the light-independent reactions occur in chloroplasts.
C
The light-dependent reactions utilize CO2 and H2O; the light-independent reactions produce CO2 and H2O.
D
The light-dependent reactions depend on the presence of both photosystems I and II; the light-independent reactions require only photosystem I.
E
The light-dependent reactions produce ATP and NADPH; the light-independent reactions use energy stored in ATP and NADPH.
E
The light-dependent reactions produce ATP and NADPH; the light-independent reactions use energy stored in ATP and NADPH.
One approach to treating patients with pancreatic cancer and other cancers in which the Hedgehog protein is detected is to modify the Hedgehog signaling pathway. Which of the following is the most useful approach?
A
Treating patients with a molecule that is structurally similar to Hedgehog and that will bind to and interact with Ptc in the same fashion as Hedgehog
B
Injecting patients with embryonic cells so that Hedgehog will bind to those cells instead of the cancer cells
C
Treating patients with a membrane-soluble compound that can bind to Smo and block its activity
D
Injecting patients with a preparation of purified membrane-soluble Ci that will enter the nuclei of the cancer cells and induce gene transcription
C
Treating patients with a membrane-soluble compound that can bind to Smo and block its activity
Which of the following best represents a signaling pathway that will lead to multiple responses from the same signaling molecule?
a
b
c
d
e
c (two shapes: wafer and circle)
Figure 1 shows a model of the endocrine signaling pathway that regulates ovulation. Which of the following observations would provide evidence of a positive feedback mechanism in this system?
A
Estrogen from the ovaries inhibits the release of GnRH from the hypothalamus.
B
Progesterone from the ovaries stimulates the thickening of the uterine lining.
C
Progesterone from the ovaries inhibits the release of LH and FSH from the anterior pituitary.
D
Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.
D
Estrogen from the ovaries stimulates the hypothalamus and anterior pituitary to secrete more GnRH, LH, and FSH.