AP Biology: Unit 4 questions

Cancer can result from a variety of different mutational events. Which of the following is LEAST likely to result in the initiation of a cancerous tumor? A receptor mutation results in activation of a cell-division pathway in the absence of the appropriate ligand. A mutation results in the loss of the ability to produce a tumor-suppressor protein. A defect in a cell-cycle checkpoint prevents a cell from entering the S phase. At the anaphase checkpoint, separation of chromatids occurs without all centromeres being attached to kinetochore microtubules from both poles.

A defect in a cell-cycle checkpoint prevents a cell from entering the S phase.

Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describe a positive feedback mechanism? Activated platelets release chemicals that inhibit blood clot formation. Activated platelets release signaling molecules that inhibit cell division in damaged tissue. Activated platelets constrict the blood vessels, stopping blood flow. Activated platelets release chemicals that activate more platelets.

Activated platelets release chemicals that activate more platelets.

Which of the following describe(s) cyclin-dependent kinase (Cdk)? Cdk is inactive, or "turned off," in the presence of cyclin. Cdk is present throughout the cell cycle. Cdk is an enzyme that attaches phosphate groups to other proteins. Cdk is present throughout the cell cycle and is an enzyme that attaches phosphate groups to other proteins.

Cdk is present throughout the cell cycle and is an enzyme that attaches phosphate groups to other proteins.

Ethylene gas is an organic molecule that serves many cell signaling roles in flowering plants. Which of the following best explains how a positive feedback mechanism involving ethylene works? Low water stress causes cells to produce ethylene, which binds to root cells and initiates cell division. Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells. Cells damaged by leaf-eating insects produce ethylene, which is released into the air, and repels insects. Fertilized ovules produce ethylene, which initiates apoptosis in flower petal cells.

Cells of ripening fruit produce ethylene, which activates the ripening response in other fruit cells.

Which of the following most accurately describes a cyclin? It is present in similar concentrations throughout the cell cycle. It is activated to phosphorylate by complexing with a Cdk. It decreases in concentration when MPF activity increases. It activates a Cdk molecule when it is in sufficient concentration

It activates a Cdk molecule when it is in sufficient concentration.

Which of the following describes the events of apoptosis? Its DNA and organelles are fragmented, the cell shrinks and forms blebs, and the cell self-digests. The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled. Its DNA and organelles become fragmented, it dies, and it is phagocytized. The cell dies and the presence of its fragmented contents stimulates nearby cells to divide.

Its DNA and organelles are fragmented, the cell shrinks and forms blebs, and the cell self-digests.

Ethylene causes fruit to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening. Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit? Loss-of-function mutations in ethylene receptors result in changes to the ripening process. Ethylene is a simple gaseous molecule, which makes is easily detected by receptors. Ethylene synthesis is under both positive and negative feedback regulation. Fruit will ripen in closed containers without exposure to air.

Loss-of-function mutations in ethylene receptors result in changes to the ripening process.

Which of the following is the best explanation for the fact that most transduction pathways have multiple steps? Most of the steps were already in place because they are steps in other pathways. Multiple steps in a pathway require the least amount of ATP. Multiple steps provide for greater possible amplification of a signal. Each individual step can remove excess phosphate groups from the cytoplasm.

Multiple steps provide for greater possible amplification of a signal.

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? Homologous chromosomes (each with two sister chromatids) will move toward opposite poles of the cell. Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell. The nuclear envelope will break down, and spindle will begin to form. The chromatin will decondense, and the daughter cell will enter interphase.

Paired chromatids will separate, and the new daughter chromosomes will move toward opposite poles of the cell.

Which of the following statements is true of signal molecules? When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules. In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus. Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling? Cell signaling uses the highest molecular weight molecules found in living cells. Cell signaling has largely been replaced by other cell functions in higher mammals. Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes. Cell signaling functions mainly during early developmental stages.

Similar cell signaling pathways in diverse eukaryotes are evidence of conserved evolutionary processes.

During mammalian labor and delivery, the contraction of uterine muscles is enhanced by oxytocin. This is an example of a negative feedback system. a hormone that acts in an antagonistic way with another hormone. a hormone that is involved in a positive feedback loop. signal transduction immediately changing gene expression in its target cells

a hormone that is involved in a positive feedback loop.

In a positive-feedback system where hormone A alters the amount of protein X an increase in A always produces an increase in X. an increase in X always produces a decrease in A. a decrease in A always produces an increase in X. a decrease in X always causes a decrease in A.

an increase in A always produces an increase in X.

In general, a signal transmitted via phosphorylation of a series of proteins brings a conformational change to each protein. requires binding of a hormone to a cytosol receptor. cannot occur in yeasts because they lack protein phosphatases. requires phosphorylase activity.

brings a conformational change to each protein.

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger. cAMP G-protein GTP adenylyl cyclase

cAMP

The centromere is a region in which chromatids remain attached to one another until anaphase. metaphase chromosomes become aligned at the metaphase plate. chromosomes are grouped during telophase. the nucleus is located prior to mitosis.

chromatids remain attached to one another until anaphase.

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 G-1, with a cell in early M phase would most likely result in the replication of chromosomes only in the G-1 cell. exiting of both cells from the cell cycle and into the G-0 phase. condensation of chromatin in preparation of nuclear division in both cells. transfer of organelles from the G-1 cell to the cell in the M phase

condensation of chromatin in preparation of nuclear division in both cells.

The body's automatic tendency to maintain a constant and optimal internal environment is termed balanced equilibrium. physiological chance. homeostasis. static equilibrium

homeostasis.

Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding? hormonal signaling autocrine signaling paracrine signaling endocrine signaling

paracrine signaling

At which phase are centrioles beginning to move apart in animal cells? telophase anaphase metaphase prophase

prophase

Which of the following does not occur during mitosis? condensation of the chromosomes replication of the DNA separation of sister chromatids spindle formation

replication of the DNA

Positive feedback differs from negative feedback in that positive feedback benefits the organism, whereas negative feedback is detrimental. the positive feedback's effector responses are in the same direction as the initiating stimulus rather than opposite to it. the effector's response increases some parameter (such as body temperature), whereas in negative feedback it can only decrease the parameter. positive feedback systems have only effectors, whereas negative feedback systems have only receptors.

the positive feedback's effector responses are in the same direction as the initiating stimulus rather than opposite to it.

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they are species specific. they always lead to the same cellular response. they amplify the original signal manifold. they counter the harmful effects of phosphatases.

they amplify the original signal manifold.