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AP®BiologyCollege BoardExam QuestionsUnit 4: Cell Communication & Cell CycleCell Communication

Cell Communication (College Board AP® Biology): Exam Questions

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Cell Communication

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Cells can communicate with other cells using chemical signals.

Which of the following is an example of direct signaling between cells?

  • Neurotransmitters diffusing across a synapse.

  • Ligands diffusing through plasmodesmata that connect adjacent plant cells.

  • Insulin traveling through the bloodstream to the liver.

  • Growth hormone binding to receptors in multiple tissues.

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Cells can communicate with each other over short and long distances within multicellular organisms.

Which of the following correctly compares short- and long-distance signaling?

  • Both short- and long-distance signalling involve hormones.

  • Only long-distance signaling involves ligand-receptor interactions.

  • Short-distance signaling involves local regulator chemicals, while endocrine signaling involves hormones.

  • Long-distance signaling does not involve ligands, only electrical impulses.

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Which of the following correctly describes a signal transduction pathway?

  • Receipt of a cell signal results in a cellular response.

  • An environmental stimulus is detected by a cell.

  • A ligand binds to a specific cell-surface receptor.

  • A phosphorylation cascade occurs.

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Living organisms need to detect and respond to changes in their external and internal environment; this can involve the use of negative feedback systems.

Which of the following correctly describes a negative feedback system?

  • It amplifies a physiological change, pushing the system further from its original state.

  • It reverses changes by restoring a system to its target set point.

  • It prevents any changes from occurring in an organism.

  • It operates at the whole organism level but not at the cellular level.

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The bobtail squid relies on a symbiotic relationship with Vibrio fischeri, a bacterium that produces bioluminescence to help the squid avoid predation. This light production occurs only when the bacterial population reaches a critical density, a process called quorum sensing. During quorum sensing, bacteria release chemical signals into their environment; as these signals accumulate, individual bacteria detect them and regulate their cellular processes based on population density.

Which of the following best explains why quorum sensing is an example of signal transduction?

  • Individual bacteria directly transfer DNA to each other through conjugation tubes.

  • Bacteria use local regulators which bind to receptors on nearby cells and stimulate specific cellular change.

  • The bacteria and the squid are in a relationship that aids the survival of both species.

  • Bacteria communicate through plasmodesmata to coordinate light production.

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Insulin is a protein hormone that plays a role in reducing blood glucose to maintain homeostasis. Figure 1 shows some changes in the blood of an individual after consumption of a meal.

Graph showing blood glucose and insulin levels over time. Solid line rises then falls post-meal; dashed line follows a similar pattern. Key included.
Figure 1. Graph showing how blood glucose and blood insulin concentrations change over time after consuming a meal.

Which of the following best describes the data shown in Figure 1?

  • Blood glucose concentration increases as insulin production increases.

  • Changes in blood insulin levels cause changes in blood glucose levels.

  • Changes in blood insulin levels occur just behind changes in blood glucose levels.

  • Blood insulin and blood glucose levels change at the same time.

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During childbirth the hormone oxytocin plays a vital role in stimulating uterine contractions.

Which of the following best describes how oxytocin facilitates labor through positive feedback?

  • Oxytocin inhibits uterine contractions to prevent premature delivery.

  • Stretch receptors inhibit oxytocin release as contractions increase.

  • Oxytocin triggers contractions, which stimulate more oxytocin release, leading to stronger contractions.

  • Oxytocin maintains a constant level of contraction strength.

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Figure 1 shows an example of a ligand binding to a receptor on a cell surface membrane and initiating a signaling cascade.

Diagram of epinephrine binding to cell membrane receptor, activating adenyl cyclase, converting ATP to cAMP, leading to protein kinase activation, affecting glycogen.
Figure 1. A signaling cascade.

Which of the following best describes the effect of a signaling cascade like this on a cell?

  • Signaling cascades amplify signals from ligands, activating many enzymes inside cells.

  • Signaling cascades result in the release of glucose inside cells.

  • Signaling cascades trigger positive feedback loops inside cells.

  • Signaling cascades activate one enzyme per molecule of ligand that binds to a cell.

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Epinephrine is a hormone involved in the regulation of blood glucose levels through the mechanism shown in Figure 1. A stable blood pH is important for maximizing the efficiency of this signal transduction pathway.

Diagram showing epinephrine binding to a cell membrane receptor, activating adenyl cyclase, converting ATP to cAMP, and promoting glycogen breakdown.
Figure 1. The effect of epinephrine on cells.

Which of the following provides the most likely explanation for the effect of acidic pH on this pathway?

  • A change in blood pH triggers a negative feedback response.

  • A low pH denatures ATP molecules, meaning that they cannot be converted into cAMP.

  • Proteins become denatured, preventing the binding of epinephrine to its receptor.

  • Acidic pH affects membrane permeability, allowing epinephrine to enter cells, and increasing the speed of the transduction pathway.

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A research team investigated the role of protein phosphatases, a class of enzymes that remove phosphate groups from signaling proteins, in the regulation of a signal transduction pathway. They analyzed a cell line in which protein phosphatase enzymes were inactive and observe the following in these cells:

  • signaling proteins remained phosphorylated for extended periods

  • target gene expression remained elevated long after the signaling molecule was removed

  • cellular responses became prolonged and unregulated

Which of the following conclusion is best supported by the data?

  • Without protein phosphatases, kinases are unable to phosphorylate target proteins, preventing signal transduction.

  • Protein phosphatases are essential for terminating signaling events by dephosphorylating target proteins.

  • A lack of functional phosphatase enzymes prevents ligand binding, preventing the initiation of signaling cascades.

  • The mutation increases receptor-mediated endocytosis, leading to enhanced degradation of signaling proteins.

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A study looked at the effects of receptor protein mutations on signal transduction. The table below shows the impact of three different mutations on receptor binding and cAMP production.

Receptor protein

Ligand and receptor binding / %

cAMP production / mmol min-1

Normal (wild-type)

100

2.5

Mutation A

47

1.2

Mutation B

89

2.4

Mutation C

100

0.3

Which of the following is the most likely explanation for the results in the table?

  • Mutation C has a neutral effect on phenotype.

  • Mutation C only affects the intracellular domain of the receptor protein.

  • Mutation A prevents production of the second messenger molecule.

  • Mutation B leads to transcription of a receptor protein that is no longer complementary to its ligand.

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Quorum sensing is a strategy used by bacteria to adjust their cellular processes on the basis of population density. Figure 1 shows part of the quorum sensing mechanism in two different groups of bacteria.

Diagram comparing gram-positive and gram-negative bacteria regulation, showing different interactions between regulator proteins, promoters, and gene expression.
Figure 1. Quorum sensing in gram positive and gram negative bacteria.

Which of the following correctly compares quorum sensing in gram positive and gram negative bacteria?

  • Both types of bacteria use the same type of ligand in quorum sensing.

  • Gram-negative bacteria make use of transcription factors while gram-positive bacteria do not.

  • Both types of bacteria have quorum sensing that involves G protein-coupled receptors.

  • The ligand-binding domain is outside the cell in gram-positive bacteria, and is within the cytoplasm in gram-positive bacteria.

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