Rucete ✏ AP Biology In a Nutshell
8. Cell Communication and Signaling — Practice Questions
This chapter reviews how cells detect, interpret, and respond to signals through various communication pathways, including reception, transduction, and feedback mechanisms.
Need a quick review?
📘 Go to the Concept Summary
(Multiple Choice — Click to Reveal Answer)
1. In which type of signaling does a cell secrete a molecule that affects only itself?
(A) Paracrine signaling
(B) Endocrine signaling
(C) Autocrine signaling
(D) Juxtacrine signaling
Answer
(C) — In autocrine signaling, the cell releases a ligand that binds to its own receptors.
2. What structure allows small molecules to move directly between adjacent plant cells?
(A) Plasmodesmata
(B) Gap junctions
(C) Cell walls
(D) Desmosomes
Answer
(A) — Plasmodesmata are channels between plant cells for direct molecule transfer.
3. Which best describes endocrine signaling?
(A) Signal molecules diffuse across synapses.
(B) Signals travel long distances through the bloodstream.
(C) Signal molecules remain on the cell membrane.
(D) Signals move between adjacent cells via gap junctions.
Answer
(B) — Endocrine signals travel through the blood to distant target cells.
4. What is the immediate effect of ligand binding to a receptor protein on a cell membrane?
(A) DNA replication
(B) Conformational (shape) change in the receptor
(C) Release of enzymes
(D) Fusion of vesicles with the plasma membrane
Answer
(B) — Binding of a ligand causes a receptor to change its shape and activate a response.
5. Which molecule functions as a secondary messenger during signal transduction?
(A) ATP
(B) Glucose
(C) Cyclic AMP (cAMP)
(D) Insulin
Answer
(C) — cAMP acts as a secondary messenger in many signaling pathways.
6. Which of the following types of receptors is located inside the cell rather than on its surface?
(A) Ion channel receptor
(B) G-protein-coupled receptor (GPCR)
(C) Receptor tyrosine kinase
(D) Intracellular receptor
Answer
(D) — Intracellular receptors are found inside the cytoplasm or nucleus and bind lipid-soluble ligands.
7. In G-protein-coupled receptor (GPCR) signaling, which molecule activates the G-protein?
(A) Binding of a ligand to the GPCR
(B) Synthesis of ATP
(C) Release of carbon dioxide
(D) Binding of calcium ions
Answer
(A) — A ligand binding to the GPCR activates the associated G-protein by causing GDP-GTP exchange.
8. What type of receptor is typically associated with phosphorylation cascades in cell signaling?
(A) Ligand-gated ion channel
(B) Receptor tyrosine kinase
(C) Intracellular receptor
(D) GPCR
Answer
(B) — Receptor tyrosine kinases activate phosphorylation cascades that amplify the signal inside the cell.
9. Which ion is commonly involved as a secondary messenger in cell signaling pathways?
(A) Sodium (Na⁺)
(B) Potassium (K⁺)
(C) Calcium (Ca²⁺)
(D) Chloride (Cl⁻)
Answer
(C) — Calcium ions are important secondary messengers involved in many signaling events, such as muscle contraction and neurotransmitter release.
10. What is signal transduction?
(A) The movement of a signal molecule into the nucleus
(B) The conversion of a signal at the cell surface into a specific cellular response
(C) The breakdown of ATP to release energy
(D) The storage of glucose in the liver
Answer
(B) — Signal transduction converts an extracellular signal into a specific intracellular response.
11. Which molecule often acts as a first messenger in cell signaling?
(A) Cyclic AMP
(B) Calcium ions
(C) A hormone or ligand
(D) A protein kinase
Answer
(C) — The first messenger is the signaling molecule (like a hormone) that binds to a receptor to initiate a response.
12. What typically triggers the release of secondary messengers inside a cell?
(A) Active transport of ATP
(B) Activation of membrane receptors
(C) Opening of nuclear pores
(D) Release of water molecules
Answer
(B) — Activation of membrane receptors (like GPCRs) leads to the generation or release of secondary messengers inside the cell.
13. How does a ligand-gated ion channel operate during cell signaling?
(A) It binds GTP directly.
(B) It phosphorylates target proteins.
(C) It opens or closes in response to ligand binding.
(D) It activates second messengers like cAMP.
Answer
(C) — Ligand-gated ion channels open or close when a ligand binds, allowing specific ions to flow across the membrane.
14. Which step immediately follows ligand binding to a receptor in cell communication?
(A) Transduction of the signal
(B) Synthesis of DNA
(C) Degradation of the receptor
(D) Production of ATP
Answer
(A) — After ligand binding, the signal is transduced through a series of intracellular steps.
15. Which molecule helps amplify a cellular response during signal transduction?
(A) Secondary messengers like cAMP
(B) Primary ligands
(C) Enzymes that synthesize DNA
(D) Lipids embedded in the plasma membrane
Answer
(A) — Secondary messengers like cAMP amplify the signal by activating multiple downstream targets inside the cell.
16. Which of the following is an example of paracrine signaling?
(A) A neuron releasing neurotransmitters across a synapse
(B) A hormone traveling through the bloodstream to distant cells
(C) A cell releasing growth factors that affect nearby cells
(D) A signal molecule binding to its own receptor
Answer
(C) — In paracrine signaling, a cell releases a chemical signal that affects nearby cells.
17. What happens to the signal inside the cell after transduction is complete?
(A) The cell divides immediately.
(B) A specific cellular response is triggered.
(C) The DNA is always replicated.
(D) The signal is degraded before it is used.
Answer
(B) — After transduction, the cell activates a specific response, such as gene expression or metabolic change.
18. In a phosphorylation cascade, what typically activates the next kinase in the series?
(A) ATP hydrolysis
(B) Direct ligand binding
(C) A previously activated kinase
(D) DNA synthesis
Answer
(C) — A previously activated kinase phosphorylates and activates the next kinase in the cascade.
19. What is the function of phosphatases in signal transduction pathways?
(A) They add phosphate groups to proteins.
(B) They bind directly to ligands.
(C) They remove phosphate groups and deactivate signaling proteins.
(D) They open ion channels in the membrane.
Answer
(C) — Phosphatases deactivate signaling proteins by removing phosphate groups.
20. Which term refers to the ability of a single signal to trigger multiple responses in different cell types?
(A) Signal degradation
(B) Signal isolation
(C) Signal amplification
(D) Signal specificity
Answer
(D) — Signal specificity means that different cells can interpret the same signal differently based on the receptors and pathways they express.
21. What causes the conformational change in a receptor tyrosine kinase?
(A) Release of a secondary messenger
(B) Binding of a signal molecule (ligand)
(C) Phosphorylation of DNA
(D) Influx of calcium ions
Answer
(B) — Ligand binding to the receptor causes it to change shape and often dimerize, initiating phosphorylation events.
22. What is the outcome of ligand binding in a ligand-gated ion channel?
(A) G-protein activation
(B) Ion flow into or out of the cell
(C) Activation of a transcription factor
(D) Phosphorylation of the receptor
Answer
(B) — Ligand binding opens the ion channel, allowing ions to pass through and change the cell's electrical potential.
23. Which statement best describes signal amplification in a signaling pathway?
(A) One signal molecule activates one response.
(B) One receptor activation leads to multiple downstream activations.
(C) A signal molecule is degraded before reaching the target.
(D) The signal only activates enzymes on the cell surface.
Answer
(B) — Signal amplification allows a single ligand-receptor event to activate many intracellular targets through a cascade.
24. What characteristic distinguishes juxtacrine signaling from other forms?
(A) It occurs through soluble hormones.
(B) It relies on direct cell-to-cell contact.
(C) It involves long-distance signal travel.
(D) It uses cyclic AMP exclusively.
Answer
(B) — Juxtacrine signaling requires direct physical contact between cells.
25. Which type of molecule is most likely to pass through the membrane and bind to an intracellular receptor?
(A) Water-soluble protein
(B) Steroid hormone
(C) Ion like Na⁺
(D) cAMP
Answer
(B) — Steroid hormones are lipid-soluble and can diffuse through the plasma membrane to reach intracellular receptors.
26. Which of the following would most likely occur if a G-protein could no longer hydrolyze GTP to GDP?
(A) Signal transduction would be permanently turned off.
(B) The G-protein would remain continuously active.
(C) Ligand binding would be blocked.
(D) The receptor would degrade immediately.
Answer
(B) — Without GTP hydrolysis, the G-protein remains active, prolonging the signal response.
27. Which of the following best explains why the same ligand can produce different responses in different cell types?
(A) Ligands mutate in different tissues.
(B) Receptors only function in some organs.
(C) Different cells express different intracellular proteins and pathways.
(D) Some cells cannot bind the ligand at all.
Answer
(C) — Signal specificity is determined by the presence of different receptor types and transduction proteins in various cells.
28. What would happen if a phosphatase enzyme in a signaling pathway was nonfunctional?
(A) The signal would be amplified.
(B) The pathway would turn off more quickly.
(C) The signal would remain active longer than normal.
(D) The ligand would degrade immediately.
Answer
(C) — Without phosphatases to deactivate kinases, the signaling remains active longer.
29. In a phosphorylation cascade, what would be the likely result of a mutation that prevents the first kinase from being phosphorylated?
(A) Amplified signal output
(B) Termination of the entire cascade
(C) Overproduction of ATP
(D) Continuous calcium release
Answer
(B) — If the first kinase isn’t activated, the entire cascade cannot proceed.
30. Which situation is most consistent with a cell using a ligand-gated ion channel for signaling?
(A) A neuron triggering rapid sodium influx during synaptic transmission
(B) A liver cell activating a gene expression cascade
(C) An immune cell recognizing a foreign antigen
(D) A hormone traveling through the bloodstream
Answer
(A) — Neurons commonly use ligand-gated ion channels for fast responses like sodium influx during synaptic signaling.
31. Why might a mutation in a GPCR cause uncontrolled cell division?
(A) GPCRs never control mitosis.
(B) The receptor could be locked in an "on" state, continuously activating downstream pathways.
(C) The receptor would stop producing secondary messengers.
(D) The G-protein would be unable to bind GTP.
Answer
(B) — A constitutively active GPCR can continuously activate pathways like MAPK, which can promote uncontrolled proliferation.
32. Which of the following best describes how signal amplification benefits a cell?
(A) It ensures that only one protein is activated per signal.
(B) It minimizes the energy required for cell division.
(C) It allows a small number of ligand molecules to produce a large-scale response.
(D) It prevents any unintended cell response.
Answer
(C) — Signal amplification ensures that a small signal can generate a large, rapid response inside the cell.
33. Which component is typically responsible for turning off a signal transduction cascade?
(A) Kinases
(B) Ligands
(C) Phosphatases
(D) GTP
Answer
(C) — Phosphatases deactivate proteins in the pathway by removing phosphate groups.
34. What is a likely consequence of a mutation that increases cyclic AMP phosphodiesterase activity?
(A) cAMP would accumulate excessively, leading to overstimulation.
(B) cAMP levels would drop quickly, reducing signal duration.
(C) The ligand would be unable to bind to its receptor.
(D) Protein kinases would remain active indefinitely.
Answer
(B) — Increased phosphodiesterase activity breaks down cAMP more quickly, shortening the signal.
35. Why is calcium often stored in organelles such as the endoplasmic reticulum during signaling processes?
(A) To keep calcium out of the nucleus
(B) To prevent interference with membrane potential
(C) To maintain low cytosolic calcium concentration and release it rapidly when needed
(D) To provide energy for signal transduction
Answer
(C) — Calcium is stored in organelles so it can be rapidly released as a secondary messenger when needed.
36. Explain how a G-protein becomes activated during cell signaling.
Answer
A G-protein becomes activated when a ligand binds to a GPCR, causing GDP on the G-protein to be exchanged for GTP, which activates the G-protein subunit.
37. Describe the role of phosphorylation cascades in signal transduction.
Answer
Phosphorylation cascades amplify the signal by sequentially activating multiple kinases, which phosphorylate target proteins to produce a cellular response.
38. Why are second messengers like cAMP important in cell signaling?
Answer
Second messengers relay and amplify the signal from a membrane-bound receptor to intracellular targets, enabling a fast and widespread cellular response.
39. What would happen if a cell lacked functional phosphatases?
Answer
Without phosphatases, signaling proteins would remain phosphorylated longer than necessary, leading to prolonged or unregulated cellular responses.
40. How does receptor specificity affect cellular responses to the same signal?
Answer
Different receptors or intracellular signaling components allow cells to respond differently to the same signal molecule depending on the cell type.
41. What is the function of ligand-gated ion channels in signal transduction?
Answer
Ligand-gated ion channels open in response to ligand binding, allowing specific ions to flow across the membrane, triggering electrical or chemical changes in the cell.
42. How can one signal molecule lead to different responses in different cell types?
Answer
Different cells may express different receptors or signal transduction proteins, resulting in varied responses to the same extracellular signal.
43. Why is the ability to rapidly turn off a signal important in cell communication?
Answer
It prevents overstimulation, conserves energy, and allows cells to reset and respond appropriately to new signals.
44. What is the role of calcium ions in cell signaling?
Answer
Calcium acts as a secondary messenger, initiating various responses such as muscle contraction, secretion, and enzyme activation when released into the cytosol.
45. Explain how endocrine signals differ from paracrine and autocrine signals in range.
Answer
Endocrine signals travel long distances via the bloodstream to reach distant target cells, while paracrine and autocrine signals act on nearby or the same cell.
46. Describe one example of signal amplification in a hormone signaling pathway.
Answer
In epinephrine signaling, one hormone-receptor interaction can activate many G-proteins, each triggering cAMP production, which activates multiple protein kinases, amplifying the response.
47. How do intracellular receptors differ from membrane-bound receptors in mechanism?
Answer
Intracellular receptors bind lipid-soluble ligands that pass through the membrane and often act directly on DNA, while membrane-bound receptors trigger signal cascades from the cell surface.
48. Why do cells use second messengers instead of relying solely on the original signal molecule?
Answer
Second messengers diffuse rapidly and amplify the signal inside the cell, enabling a faster and broader response than the original extracellular signal alone could achieve.
49. What is the function of protein kinases in signal transduction?
Answer
Protein kinases transfer phosphate groups to target proteins, activating or modifying them to elicit specific cellular responses.
50. Summarize the three main stages of cell signaling.
Answer
The three main stages are: reception (ligand binds receptor), transduction (relay/amplify signal via molecules like kinases), and response (cell carries out a specific activity).