Introduction to Signal Transduction

Introduction to Signal Transduction is topic 4.2 of AP Biology, inside Cell Communication and Cell Cycle. This page works through three real practice questions on it, with the full reasoning behind each credited answer.

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55 questionsConcept Explanation60% with a figure
Worked examples

Three real introduction to signal transduction questions

From the practice pool, not the mock papers — each with the reasoning that produces the answer.

60% of them come with a figure. Reading the graph or diagram correctly is most of the work here before any content knowledge applies.

Argumentation

A mutation prevents a receptor from changing shape after its ligand binds. Which claim is best supported?

  1. ASignal transduction will increase because receptor shape is irrelevant.
  2. BSignal amplification reduces the number of downstream molecules activated by one receptor.
  3. CImpaired receptor activation can reduce downstream signalingcorrect
  4. DThe receptor will produce glucose without enzymes.
Why C is correct

Ligand binding often changes receptor shape, allowing the signal to be transmitted inside the cell. If the receptor cannot activate, downstream signaling can decrease.

The stem asks students to explain a specific mechanism, not just recall a unit term: "A mutation prevents a receptor from changing shape after its ligand binds. Which claim is best supported". The correct choice is supported by Ligand binding often changes receptor shape, allowing the signal to be transmitted inside the cell. The tempting alternatives such as Signal transduction will increase because receptor shape is irrelevant or Signal amplification reduces the number of downstream molecules... fail because they do not produce the same outcome described in the stem.

Visual Representations · with figure

Based on Figure 1, which statement accurately explains the represented process?

  1. AMarker A: Cascades can amplify a signalcorrect
  2. BMarker B: Protein phosphatases can turn off signaling by removing phosphate groups.
  3. CMarker C: Second messengers can diffuse through the cytosol to relay a signal.
  4. DMarker D: Ligand binding gives receptor specificity at the start of a signaling pathway.
Why A is correct

Figure 1 must be used to determine which marker is supported by the visual model. Marker A: A phosphorylation cascade can amplify a signal by activating multiple downstream proteins. Cascades can amplify signals because one activated molecule can activate multiple downstream molecules.

The evidence in the prompt matters before the topic label: "A signal-transduction model shows one activated kinase activating several copies of another kinase. What advantage...". The supported answer is "It amplifies the signal inside the cell" because Cascades can amplify signals because one activated molecule can activate multiple downstream molecules. Distractors such as It prevents any intracellular response from occurring or Cells lacking the receptor should respond if the signal... either ignore the stated pattern or name a related concept without matching the evidence.

Argumentation

A mutation prevents a receptor tyrosine kinase from dimerizing after its ligand binds. Which outcome is most likely?

  1. AThe receptor will enter the nucleus and bind DNA directly.
  2. BDownstream phosphorylation in the signaling pathway decreases.correct
  3. CThe cell will produce ATP without using enzymes.
  4. DThe ligand will become a second messenger in the cytoplasm.
Why B is correct

Receptor tyrosine kinases typically dimerize and phosphorylate each other to initiate downstream signaling. Preventing dimerization reduces activation of downstream phosphorylation cascades.

The stem asks students to explain a specific mechanism, not just recall a unit term: "A mutation prevents a receptor tyrosine kinase from dimerizing after its ligand binds. Which outcome is most likely". The correct choice is supported by Receptor tyrosine kinases typically dimerize and phosphorylate each other to initiate downstream signaling. The tempting alternatives such as receptor will enter the nucleus and bind DNA directly or cell will produce ATP without using enzymes fail because they do not produce the same outcome described in the stem.

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Last reviewed 2026-08-28. Topic and unit names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
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Work introduction to signal transduction until the reasoning is automatic.

Real AP questions with a full explanation on every answer, and a mistake bank that only clears when you get it right.

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