AP Biology Unit 4 MCQs

(A) G0 is the stage of the cell cycle in which the cell is not actively dividing. Fully differentiated cells are in G0. Interphase consists of G1, S, and G2, so choices (B), (C), and (D) are incorrect.

(D) Tumor suppressor genes detect defects in DNA replication and prevent the replication of cells with those defects. Choice (A) is incorrect because cyclin-dependent kinases are not involved in detecting mutations. Both oncogenes and proto-oncogenes stimulate cell division so choices (B) and (C) are incorrect.

(C) If positive feedback occurs, a stimulus increases the strength of a response and moves the system further from homeostasis, which is the case with oxytocin and uterine contractions. Choices (A), (B), and (D) are incorrect because they describe negative feedback, which brings a system closer to homeostasis.

(B) If the target cell lacks receptors for the signaling molecule, it will not be able to initiate the signal transduction pathway that triggers cell division. Choice (A) is incorrect because the cells will not divide if they lack the appropriate receptor for the ligand; the signaling pathway for cell division will not be triggered. Choice (C) is incorrect because individual cells do not evolve new receptors. If the cell lacks the receptors for the signaling molecule, the cell will not be able to respond to the signal, so choice (D) is incorrect.

(D) Cortisol would stimulate the breakdown of glycogen into glucose. This would provide energy, alleviating one of the symptoms of hunger. Choices (A), (B), and (C) are incorrect because the activation of the immune response, increased storage of calcium in bones, and increased reabsorption of water by the kidneys would not increase the energy available to cells.

(B) Small molecules pass between plant cells through channels called plasmodesmata, an example juxtacrine signaling. Choices (A) and (C) are incorrect because plant cells have a cell wall surrounding the cell membrane. So molecules cannot pass through plant cell membranes unassisted nor can they bind to cell membrane receptors unless they can pass through the cell wall first. Choice (D) is incorrect because not all ligands require active transport.

(C) Growth factors bind to receptors, which triggers a signal transduction process that stimulates cell division. Grouping cells together would not trigger cell division, so choice (A) is incorrect. Removing cyclic AMP from the cytosol would most likely disrupt the signaling process that is required to trigger cell division, so choice (B) is incorrect. Choice (D) is incorrect because growth factors bind to receptor proteins, not to membrane phospholipids.

(B) If an antibody binds to the receptor, the ligand will be prevented from binding to the receptor, and the signaling process will not occur. Choice (A) is incorrect because the result will be decreased, not increased, stimulation of the target cell. The effect of the antibody will be decreased stimulation of the target cell, so choice (C) is also incorrect. Since the antibody is preventing the ligand from binding to the receptor, no stimulation of gene expression could be triggered, making choice (D) incorrect as well.

(C) Both calcium ions and cyclic AMP function as secondary messengers during cell signaling. Ligands bind to the receptor to start the cell signaling process; neither calcium ions not cAMP do this, so choice (A) is incorrect. Receptor proteins and protein kinases are proteins, but neither calcium ions nor cAMP are proteins. So choices (B) and (D) are incorrect.

(C) Protein phosphatases remove phosphate groups from other molecules. Choice (A) is incorrect because cyclic AMP functions as a secondary messenger. Protein kinases add phosphate groups to molecules, so choice (B) is incorrect. Choice (D) is incorrect because adenylyl cyclase is the enzyme that catalyzes the formation of cAMP.

(D) Insulin travels long distances through the circulatory system, so this is an example of endocrine signaling. Choice (A) is incorrect because autocrine signaling involves a cell that produces a ligand, and the ligand then binds to a receptor on the same cell that produced the ligand. Juxtacrine signaling is between cell that are in direct contact, so choice (B) is incorrect. Choice (C) is incorrect because paracrine signaling occurs over short distances.

(C) Signaling over short distances is paracrine signaling. Choice (A) is incorrect because autocrine signaling involves a cell that produces a ligand and the ligand then binds to a receptor on the same cell that produced the ligand. Juxtacrine signaling is between cells that are in direct contact, so choice (B) is incorrect. Endocrine signaling occurs over long distances, so choice (D) is incorrect.

(B) If a cell acks the receptor for ligand, the signal transduction process cannot start. Choice (A) is incorrect because is cAMP was lacking, the cell might still be able to mount an incomplete response if the ligand could bind to a receptor and trigger steps in the signal transduction process that do not depend on the presence of cAMP. Ligands are usually not produced in their target cells, so lacking a gene for the ligand would likely have no effect on the target cell, making choice (C) incorrect. Choice (D) is incorrect because the inability to metabolize a ligand would likely not affect the target cell’s ability to respond to the ligand.

(D) DNA is replicated during the S stage of the cell cycle, so a drug that blocks the replication of DNA would have the greatest effect during the S stage. DNA does not replicate during G0, G1, or G2, so choices (A), (B), and (C) are incorrect.

(A) During G0, the cell is not dividing and has exited the cell cycle, G1, G2, and S are all stages that prepares the cell to divide, so choices (B), (C), and (D) are incorrect.

(C) At the beginning of anaphase, each chromosome consists of two sister chromatids. During anaphase, these chromatids sperate, and at the end of anaphase, each of the chromatids is considered a separate chromosome. Thus, anaphase ands with twice as many chromosomes as it had at its beginning. During prophase, chromosomes condense and become visible, but the number of chromosomes does not change. So choice (A) is incorrect. Choice (B) is incorrect because in metaphase, chromosomes line up along the center of the cell but the number of chromosomes does not change. In telophase, two new nuclei are formed and the number of chromosomes per cell at the end of telophase is less than it was at the beginning of telophase. Thus, choice (D) is also incorrect.

(B) During metaphase, chromosomes line up in the center of the cell on the metaphase plate. Prophase is when chromosomes condense and become visible, so choice (A) is incorrect. Anaphase is when sister chromatids separate and begin to move to opposite ends of the cell, so choice (C) is incorrect. Telophase is when two new nuclei are formed, so choice (D) is also incorrect.

(D) Interphase consists of G1, S, and G2. Therefore, the number of cells in interphase is 73 + 89 + 68 = 230 cells. The total number of cells is 73 + 89 + 68 + 43 = 273. So the percentage of cells in interphase is ²³⁰⁄₂₇₃ ≈ 84%. Choice (A) is incorrect because 16% is the approximate percentage of cells that are in mitosis. Choice (B) is incorrect because 33% is the approximate percentage of cells that are in the S stage. Choice (C) is incorrect because 52% is the approximate percentage of cells in G1 and G2.

(A) Apoptosis is programmed cell death, and it can occur during embryonic development when the soft tissue between the fingers to separate. While choices (B), (C), and (D) also occur during embryonic development, choice (A) is the best answer because it is the most specific to the formation of the fingers during embryonic development.

(D) Cytokinesis is the division of the cytoplasm. Choice (A) is incorrect because apoptosis is programmed cell death. DNA replication occurs during the S stage of the cell cycle, so choice (B) is incorrect. Choice (C) is also incorrect because mitosis is the process of evenly distributing replicated chromosomes between the daughter nuclei.

(B) Many somatic cells in organs and tissues exhibit density-dependent inhibition. Cancer cells do not exhibit anchorage dependence not do they exhibit density-dependent inhibition, so choices (A) and (D) are incorrect. Choice (C) is incorrect because noncancerous cells spend most of their time in interphase, not mitosis.

(D) Mitosis is the distribution of genetic material between the daughter cells. Cytokinesis, not mitosis, is the distribution of cytosol between the daughter cells, so choice (A) is incorrect. Choice (B) is incorrect because the replication of DNA occurs during the S stage, not mitosis. Replication of cell organelles occurs during G1 and G2, not mitosis, so choice (C) is incorrect.

(C) Cytokinesis is the division of the cytoplasm. In animal cytokinesis, a cleavage furrow is formed. In plant cytokinesis, a cell plate is formed. DNA and cellular organelles are replicated during interphase, but the cytoplasm is not yet divided. So choice (A) is incorrect. Choice (B) is incorrect because mitosis is the distribution of genetic material between the daughter cells. G0 is the nondividing phase of the cell cycle, so choice (D) is incorrect.