Biology Unit Four AP Questions.

Which of the following statements best describes how a growth factor stimulates cell division from outside a cell?

The growth factor binds to receptors on the cell surface, initiating a signal transduction pathway that activates specific target genes.

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

condensation of chromatin in preparation of nuclear division in both cells

What is the expected percent change in the DNA content of a typical eukaryotic cell as it progresses through the cell cycle from the start of the G1 phase to the end of the G2 phase?

+100%

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it. The following questions refer to the data in Figures 1 through 4 below, which were collected during a study of the growth of plant seedlings. When the concentration of GAl is highest, the average height of the control seedlings is approximately

10 cm

Directions: Each group of questions below concerns an experimental or laboratory situation or data. In each case, first study the description of the situation or data. Then choose the one best answer to each question following it. The following questions refer to the data in Figures 1 through 4 below, which were collected during a study of the growth of plant seedlings. The concentration of all gibberellins 65 days after planting is approximately

20 ng/gram

Cortisol is a hormone produced in response to stress, including starvation, in humans. Which of the following is most likely an immediate effect of a starvation-induced increase in cortisol secretion?

Increased mobilization of fatty acids from fat cells

Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

It accelerates the production of a second messenger.

Ethylene causes fruits 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.

The relative amount of DNA in a cell at various stages of the cell cycle is shown in Figure 1 . Which of the following best describes how the amount of DNA in the cell changes during M phase?

The amount of DNA does not change while the cell grows.

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

The diagram above 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 cell surface protein on cell 4 signals cell 3 to induce formation of the worm's intestine.

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 describes a positive feedback mechanism?

Activated platelets release chemicals that activate more platelets.

The endocrine system incorporates feedback mechanisms that maintain homeostasis. Which of the following demonstrates negative feedback by the endocrine system?

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 model shown in the figure represents the role of two hormones, calcitonin and parathyroid hormone (PTH), in maintaining normal blood calcium levels in humans. If a dietary change results in an increase in blood calcium concentration above normal levels, which of the following is the most likely effect on calcium homeostasis?

Calcitonin levels will rise, thus promoting the deposit of calcium into bones.

Glycogen synthetase kinase 3 beta is a protein kinase that has been implicated in many types of cancer. Depending on the cell type, the gene for glycogen synthetase kinase 3 beta (GSK3β) can act either as an oncogene or as a tumor suppressor. Which of the following best predicts how GSK3β mutations can lead to the development of cancer?

Cells with inactive GSK3β fail to trigger apoptosis.

Which of the following best describes the role of mitosis in the cell cycle?

Distributing replicated chromosomes to daughter nuclei

Figure 1 shows the number of chromosomes observed in an actively dividing human cell at each stage of cell division. Which of the following presents a correct interpretation of the changes in chromosome number depicted in Figure 1 ?

Chromosomes enter metaphase containing two chromatids attached by a centromere. During anaphase, the chromatids are separated, each becoming a chromosome. Cytokinesis distributes the chromosomes into two separate cells.

Many human cells can be stimulated to divide by hormonelike growth factors that bind to receptor proteins (R) on the plasma membrane and trigger an internal signal-transduction cascade. In many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. Contact inhibition occurs when proteins called cell adhesion molecules (CAMs CAMs are replaced by another protein, called M. Both pathways are depicted in the figures below. Which of the following statements accurately uses the information presented to support the hypothesis that interruption of M function in a single body cell can result in cancer?

Growth-factor signaling can trigger mitosis in cells that are in direct contact with other cells.

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1. Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

In involves enzymes activating other enzymes.

Researchers performed an experiment to determine the effect of certain genetic mutations on mitosis in tropical fruit fly embryos. They determined the percentage of cells in each of four phases of mitosis as shown in Figure 1. Which of the following patterns is shown by the data?

In mutant 3 cells, more time is spent in prophase/prometaphase than in the later stages of mitosis.

Which of the following is a correct conclusion that can be drawn from the data in Figures 1, 2, and 3?

Most of the increase in the concentration of all gibberellins 40 to 45 days after planting is due to an increase in the concentration of GAl.

Cell communication is critical for the function of both unicellular and multicellular eukaryotes. Which of the following is likely true of cell signaling?

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

During mitosis, which of the following normally occurs?

Replicated chromosomes line up on the equatorial plate.

Cancer cells behave differently than normal body cells. For example, they ignore signals that tell them to stop dividing. Which of the following conditions will most likely cause a normal body cell to become a cancer cell?

The environment contains mutagens that induce mutations that affect cell-cycle regulator proteins.

Glucocorticoids are steroid hormones that control cellular responses through several different signaling pathways. One of the signaling pathways involves the glucocorticoid receptor, an intracellular protein that is activated by binding to a glucocorticoid molecule. A simplified model of the glucocorticoid receptor signaling pathway is represented in Figure 1. Which of the following statements best predicts the effect of a mutation that results in a loss of the glucocorticoid receptor's ligand binding function?

The glucocorticoid receptor will remain associated with the accessory proteins.

Researchers studying cell cycle regulation in budding yeast have observed that a mutation in the CDC15 gene causes cell cycle arrest in telophase when the yeast cells are incubated at an elevated temperature. Which of the following statements best predicts the effect of the cell cycle arrest on proliferating yeast cells?

The yeast cells will replicate their chromosomes but will fail to complete cytokinesis.

DNA replication occurs

during the S phase of the cell cycle