AP Biology Unit 4 Questions

An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism's immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses.

An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism's immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses.

Chemicals that are secreted from antigen-presenting cells then activate helper T cells.

They allow the movement of molecules from one cell to another, enabling communication between cells.

Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells.

cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules

G proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a G protein, the G protein is activated. The G protein then activates an enzyme that produces a second messenger called cAMP.
Which of the following describes a critical role of cAMP during the transduction stage of a G protein signal transduction pathway?

A ligand binds to a receptor.

Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?

Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding.

During a fight-or-flight response, epinephrine is released into the body's circulatory system and transported throughout the body. Some cells exhibit a response to the epinephrine while other cells do not.
Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome.
Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype?

If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development

An experiment showed that a mutation in the ced-9 gene led to excessive cell death in C. elegans.

Researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced-3 and ced-9 . The ced-3 gene was found to promote cell death, and ced-9 to inhibit it. The ced-9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis.
Which of the following statements best justifies the claim that changes in the expression of in C. elegans can affect regulation of apoptosis in the cell?

The irreversible association of FGFR proteins

Fibroblast growth factor receptors are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. The extracellular domains of FGFR proteins bind specifically to signaling molecules called fibroblast growth factors. The intracellular domains of FGFR proteins function as protein kinases, enzymes that transfer phosphate groups from ATP to protein substrates

Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed

Phosphofructokinase is a key enzyme in glycolysis. ATP is one of the two substrates for the reaction catalyzed by PFK. ATP is also an allosteric regulator of PFK. Figure 1 shows the enzyme-substrate interactions of PFK.

More cells are produced per unit of time in the root tips growing in compact sand than in the root tips growing in loose sand.

Researchers grew seedlings of corn, Zea mays, in loose and compact sand. The researchers measured the amount of time required for the cells in the growing root tips of the seedlings to double in number. The mean cell doubling times for the two groups of seedlings are shown in Figure 1

Synthesis of sufficient DNA for two daughter cells occurs in stage 2.

Based on Figure 1, which of the following statements correctly links a stage of the cell cycle with the event occurring at that stage?

18%

Based on the data, the percent of the mitotic cells that were in metaphase is closest to which of the following?

Uncontrolled cell proliferation

The tumor suppressor protein p53 binds to DNA and activates target genes, which results in the synthesis of p21, CD95, and other proteins. The p21 protein promotes cell-cycle arrest, whereas the CD95 protein promotes apoptosis

The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.

A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body

It is a ligand that activates the signal transduction pathway of the activation of AMPK

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMP-activated protein kinase (AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPK in liver cells but cannot cross the plasma membrane. By blocking AMPK with an inhibitor, researchers found that AMPK activation is required for metformin to produce an inhibitory effect on glucose production by liver cells.

The storage of GLUT4 in vesicles inside the cell will increase.

The insulin receptor is a transmembrane protein that plays a role in the regulation of glucose homeostasis. The receptor's extracellular domain binds specifically to the peptide hormone insulin. The receptor's intracellular domain interacts with cellular factors. The binding of insulin to the receptor stimulates a signal transduction pathway that results in the subcellular translocation of GLUT4, a glucose transport protein that is stored in vesicles inside the cell. A simplified model of the insulin receptor-signaling pathway is shown in Figure 1.

The rate of glycogen synthesis in the cell will increase.

The beta-2 adrenergic receptor is a membrane-bound protein that regulates several cellular processes, including the synthesis and breakdown of glycogen. The receptor binds specifically to the hormone epinephrine. The binding of epinephrine to the beta-2 adrenergic receptor triggers a signal transduction cascade that controls glycogen synthesis and breakdown in the cell. A simplified model of the signal transduction cascade is represented in Figure 1.

Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.

A person's blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level.

Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin K is required for the formation of the active form of several of the clotting factors, including Factor X. A simplified model of the blood clotting process is shown in Figure 1.

Factor X will not be activated, which will prevent thrombin from forming

25 percent

Figure 1. Typical life cycle of a eukaryotic cell

Scientists have estimated that it takes yeast cells approximately 20 hours to complete the entire cycle. Table 1 shows the amount of time in each phase of the life cycle for yeast cells

There is a change from 3 to 6 picograms of DNA because DNA is replicated before each round of cell division.

Researchers tracked the amount of DNA (measured in picograms) over time beginning with a single cell and continuing through several rounds of cell division. The researchers observed threadlike chromosomes prior to cell division. The threadlike chromosomes disappeared from view shortly after each division. The amount of DNA in picograms per cell over several rounds of cell division is shown in Figure 1.

Seventy-five percent of the virus-infected cells are found in mitosis. The virus stimulates frequent cell division.

A cell culture commonly used in research was selected to study the effect of a specific virus on the timing of cell cycle phases. Two separate cultures were started, one untreated and one inoculated with the virus. Both cultures were incubated under identical conditions. After a period of time, 200 cells from each culture were observed and classified as shown in Table 1.

Increased cell division will lead to the formation of a tumor.

The epidermal growth factor receptor EGFR is a cell surface receptor. When a growth factor binds to EGFR, the receptor is activated. The activated EGFR triggers a signal transduction pathway, which leads to increased frequency of cell division.
Which of the following best predicts the effect of a mutation that causes EGFR to be active in the absence of a growth factor?

There are not enough nucleotides available to construct new DNA

Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1/S checkpoint?