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AP Biology 4.3 Signal Transduction Pathways

Practise AP Biology 4.3 questions by linking signal transduction with differentiation, apoptosis, pathway mutations and altered cellular responses.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • identify differentiation and apoptosis as possible cellular outcomes of signaling
  • predict how receptor or pathway mutations alter downstream signaling and phenotype
  • distinguish pathway activation or inhibition by chemicals, ligands and inhibitors
  • use pathway models and quantitative response data to predict changes in downstream molecules or cell behavior

Covered syllabus points

4.3.A—Describe the different types of cellular responses elicited by a signal transduction pathway4.3.B—Explain how a change in the structure of any signaling molecule affects the activity of the signaling pathway

4.3 Signal Transduction Pathways question 1

[Maximum number: 1]
B-cell activation model

B-cell activation model

As represented in the model above, B cells are activated by direct contact with antigens or stimulated helper T cells (TH)\left(\mathrm{T}_{\mathrm{H}}\right). Based on the model, which of the following best describes an outcome of B cell activation?

A

Activated B cells differentiate into plasma cells and memory cells.

B

Activated B cells stimulate TH\mathrm{T}_{\mathrm{H}} cells to secrete antibodies.

C

Both B cells and TH\mathrm{T}_{\mathrm{H}} cells release chemical signals that negatively regulate antigen-presenting cells.

D

Plasma cells produce antibodies that activate additional B cells by a positive feedback mechanism.

4.3 Signal Transduction Pathways question 2

[Maximum number: 2]

Many insects rely on pheromones (chemical signals) that are released by the females to find

mating partners. Scientists hypothesize that, in a certain type of moth, the behavior of male

moths in response to pheromones is regulated by the extracellular signaling molecule 20E.

Question (a)

(a)

C.

[ 1 ]

Question (i)

(i)

The scientists studied some moths with a mutation in the gene encoding the G protein.

The mutation prevents GTP from displacing the GDP bound to the G protein. Based

on Figure 1, predict the effect of this mutation on the oriented activity in male moths

exposed to the pheromone.

Expression of the gene encoding DopEcR is low in the male moths during their first few days

as adults, when they are sexually immature. Gene expression rapidly increases as the moths

reach sexual maturity. The scientists claim that this increase in gene expression increases the

likelihood of males finding females with whom to mate.

[ 1 ]

Question (b)

(b)

D.

[ 1 ]

Question (i)

(i)

Based on Figure 1, explain how an inhibitor of the DopEcR pathway might serve as an

effective chemical to protect crops from moth damage.

[ 1 ]
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