AP Bio U4: Cell Communication and Cell Cycle

The diagram below shows a developing worm embryo at the four-cell stage. Experiments have shown that when cell 3 divides, the anterior daughter cell gives rise to muscle and gonads and the posterior daughter cell gives rise to the intestine. However, if the cells of the embryo are separated from one another early during the four-cell stage, no intestine will form. Other experiments have shown that if cell 3 and cell 4 are recombined after the initial separation, the posterior daughter cell of cell 3 will once again give rise to normal intestine. Which of the following is the most plausible explanation for these findings? a. A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine. b. The plasma membrane of cell 4 interacts with the plasma membrane of the posterior portion of cell 3, causing invaginations that become microvilli. c. Cell 3 passes an electrical signal to cell 4, which induces differentiation in cell 4. d. Cell 4 transfers genetic material to cell 3, which directs the development of intestinal cells.

a. A cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.

Antidiuretic hormone (ADH) is important in maintaining homeostasis in mammals. ADH is released from the hypothalamus in response to high tissue osmolarity. In response to ADH, the collecting duct and distal tubule in the kidney become more permeable to water, which increases water reabsorption into the capillaries. The amount of hormone released is controlled by a negative feedback loop. Based on the model presented, which of the following statements expresses the proper relationship between osmolarity, ADH release, and urine production? a. As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine. b. As tissue osmolarity rises, less ADH is released, causing less water to be excreted as urine. c. As tissue osmolarity rises, more ADH is released, causing more water to be excreted as urine. d. As tissue osmolarity rises, less ADH is released, causing more water to be excreted as urine.

a. As tissue osmolarity rises, more ADH is released, causing less water to be excreted as urine.

Which of the following is the stage where the cell no longer divides? a. G0 b. G1 c. G2 d. S

a. G0

Anabaena is a simple multicellular photosynthetic cyanobacterium. In the absence of fixed nitrogen, certain newly developing cells along a filament express genes that code for nitrogen-fixing enzymes and become nonphotosynthetic heterocysts. The specialization is advantageous because some nitrogen-fixing enzymes function best in the absence of oxygen. Heterocysts do not carry out photosynthesis but instead provide adjacent cells with fixed nitrogen, in exchange receiving fixed carbon and reduced energy carriers. As shown in the diagram above, when there is low fixed nitrogen in the environment, an increase in the concentration of free calcium ions and 2-oxyglutarate stimulates the expression of genes that produce two transcription factors (NtcA and HetR) that promote the expression of genes responsible for heterocyst development. HetR also causes production of a signal, PatS, that prevents adjacent cells from developing as heterocysts. Based on your understanding of the ways in which signal transmission mediates cell function, which of the following predictions is most consistent with the information given above? a. In an environment with low fixed nitrogen, treating the Anabaena cells with a calcium-binding compound should prevent heterocyst differentiation. b. A strain that overexpresses the patS gene should develop many more heterocysts in a low fixed nitrogen environment. c. In an environment with abundant fixed nitrogen, free calcium levels should be high in all cells so that no heterocysts develop. d. In environments with abundant fixed nitrogen, loss of the hetR gene should induce heterocyst development.

a. In an environment with low fixed nitrogen, treating the Anabaena cells with a calcium-binding compound should prevent heterocyst differentiation.

Insulin is a protein hormone that is secreted in response to elevated blood glucose levels. When insulin binds to its receptors on liver cells, the activated receptors stimulate phosphorylation cascades that cause the translocation of glucose transporters to the plasma membrane. Based on the information provided, which of the following best describes the role of insulin in this liver cell signal transduction pathway? a. It acts as a ligand. b. It acts as a receptor. c. It acts as a secondary messenger. d. It acts as a protein kinase.

a. It acts as a ligand.

Which feedback mechanism involves amplifying responses and processes in biological organisms? a. Positive Feedback b. Negative Feedback

a. Positive Feedback

Platelets are fragments of larger cells and normally circulate in the blood without adhering to blood vessel walls. When the wall of a blood vessel is damaged, collagen fibers in the wall are exposed to the interior of the blood vessel. The exposed fibers and chemicals released from the endothelial cells that line the blood vessel attract platelets, which start to form a plug and release other chemicals (Figure 1). Which of the following best explains the feedback mechanism illustrated in Figure 1? a. This is an example of positive feedback, because the few platelets that initially bind attract more platelets to the damaged area. b. This is an example of positive feedback, because it results from the interactions among collagen, endothelial cells, and platelets. c. This is an example of negative feedback, because a large clump of platelets can block the blood vessel and prevent blood flow through it. d. This is an example of negative feedback, because the accumulation of platelets returns the open blood vessel wall to a closed state.

a. This is an example of positive feedback, because the few platelets that initially bind attract more platelets to the damaged area.

Describe what occurs when the ligand binds to the receptor. a. confirmational change in shape of receptor b. phosphorylation of ligand c. ligand passes through the membrane d. receptor binds additional ligands

a. confirmational change in shape of receptor

Describe the interaction between cyclin and CdK. a. cyclin interacts with CdK to initiate the mitotic phase b. cyclin is the precursor to CdK, when synthesized allow for mitosis proceed c. cyclin acts as an inhibitor to CdK to wait for all DNA to be synthesized d. cyclin binds to CdK to initiate DNA replication

a. cyclin interacts with CdK to initiate the mitotic phase

Which of the following is NOT a role of mitosis? a. gametes b. tissue repair c. growth d. asexual reproduction

a. gametes

What are the three parts of signal transduction pathway? a. reception, transduction, response b. confirmation, transduction, transcription c. reception, amplification, transcription d. confirmation, amplification, response

a. reception, transduction, response

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system? a. During labor, the fetus exerts pressure on the uterine wall, inducing the production of oxytocin, which stimulates uterine wall contraction. The contractions cause the fetus to further push on the wall, increasing the production of oxytocin. b. After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels. c. At high elevation, atmospheric oxygen is more scarce. In response to signals that oxygen is low, the brain decreases an individual's rate of respiration to compensate for the difference. d. A transcription factor binds to the regulatory region of a gene, blocking the binding of another transcription factor required for expression.

b. After a meal, blood glucose levels become elevated, stimulating beta cells of the pancreas to release insulin into the blood. Excess glucose is then converted to glycogen in the liver, reducing blood glucose levels.

The vertebrate forelimb initially develops in the embryo as a solid mass of tissue. As development progresses, the solid mass near the end of the forelimb is remodeled into individual digits. Which of the following best explains the role of apoptosis in remodeling of the forelimb? a. Apoptosis replaces old cells with new ones that are less likely to contain mutations. b. Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells. c. Apoptosis involves the destruction of extra cells in the developing forelimb, which provides nutrients for phagocytic cells. d. Apoptosis in the developing forelimb triggers the differentiation of cells whose fate was not already determined.

b. Apoptosis involves the regulated activation of proteins in specific cells of the developing forelimb that leads to the death of those cells.

Which feedback mechanism involves homeostasis of a particular condition by regulating physiological processes? a. Positive Feedback b. Negative Feedback

b. Negative Feedback

Which of the following describes the order of the steps in mitosis? a. metaphase, telophase, anaphase, prophase b. prophase, metaphase, anaphase, telophase c. telophase, anaphase, metaphase, prophase d. prophase, anaphase, metaphase, telophase

b. prophase, metaphase, anaphase, telophase

Describe the impact of a mutation in any domain of the protein components of the transduction signaling pathway. a. receptor unable to bind to ligand b. no changes in transduction due to initial signal transduction from ligand c. alters response of the cell d. amplification of signaling pathway to bind more ligands

c. alters response of the cell

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 diagram below illustrates feedback control as exerted by the hormone thyroxine. Following surgical removal of the thyroid gland, the level of TSH in the blood will increase. Which of the following best explains this increase? a. Residual blood thyroxine, from prior to thyroid gland removal, will bind to cells in the anterior pituitary, signaling more TSH secretion. b. Thyroxine will remain bound to thyroxine receptors on various body cells, and these body cells will secrete additional hormones that stimulate the anterior pituitary to secrete TSH. c. Thyroxine that was stored in the anterior pituitary prior to thyroid gland removal will signal more TSH secretion. d. A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

d. A decrease in thyroxine levels means a loss of inhibition to the hypothalamus and anterior pituitary, leading to increased TSH secretion.

The figure below shows a model of a ligand precursor being cleaved to produce an active ligand that binds to a specific receptor. Which of the following is most likely to reduce the binding of the active ligand to its receptor? a. A change in the cytoskeletal attachment of transmembrane proteins b. The presence of a large amount of the precursor form of the ligand c. An increase in the ratio of the number of unsaturated to the number of saturated fatty acid tails of the membrane lipids d. A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor

d. A mutation in the receptor gene that causes a substitution of a charged amino acid for a nonpolar amino acid in the ligand binding site of the receptor

Which checkpoint is responsible for ensuring nondisjunction does not take place? a. G1 checkpoint b. S checkpoint c. G2 checkpoint d. M checkpoint

d. M checkpoint

In a classic experiment from the 1970s investigating gene expression, a solution containing equal amounts of rabbit a-hemoglobin mRNA and b-hemoglobin mRNA, which encode subunits of a protein found in red blood cells, was injected into newly fertilized frog eggs. The injected mRNA was not degraded during the course of the experiment. Tadpoles that developed from the injected eggs were dissected into two fragments, one containing predominantly the notochord, muscle tissue, and nerve tissue and the other containing predominantly the other tissue types. Equal amounts of total protein were analyzed after separation by electrophoresis to identify the relative amounts of the different proteins present in each sample. The thickness of the bands indicates the relative amounts of rabbit a-hemoglobin, rabbit b-hemoglobin, and frog tubulin (a cytoskeletal protein that is expressed at relatively constant levels in all tissues) present in each tadpole sample. The experimental protocol and results are summarized in the figure below. Which of the following is the best justification for why the rabbit hemoglobin proteins were found throughout the tadpole? a. Rabbit mRNA is composed of nucleotides that are more stable than those in frog mRNA. b. Rabbit hemoglobin is synthesized more efficiently than frog hemoglobin in frog cells. c. After differentiation, the rabbit hemoglobin proteins move through the circulatory system of the tadpole to every cell. d. The mRNA injected into the newly fertilized frog eggs is distributed in the cytoplasm of every daughter cell during cell division.

d. The mRNA injected into the newly fertilized frog eggs is distributed in the cytoplasm of every daughter cell during cell division.

Which of the following is NOT a response by the cell from a signal transduction pathway? a. cell growth b. gene expression c. secretion of molecules d. all of the above are responses

d. all of the above are responses

Which of the following is NOT a stage of the cell cycle? a. interphase b. cytokinesis c. mitosis d. apoptosis

d. apoptosis

Transduction step traditionally amplifies the signal, which of the following are NOT involved with transduction? a. secondary messengers b. protein modification c. phosphorylation cascade d. ligands

d. ligands