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AP Biology 4.1.A Direct Cell Contact and Juxtacrine Signaling

Practise AP Biology 4.1.A questions by identifying juxtacrine signaling through direct cell contact, including gap junctions and plasmodesmata.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • identify juxtacrine signaling as communication that requires direct contact between cells
  • classify gap junctions and plasmodesmata as structures for direct cell-to-cell signaling

4.1.A—Describe the ways that cells can communicate with one another question 1

A portion of the human immune system response to an invading

pathogen is shown below.

Figure for Question 4.1.A—Describe the ways that cells can communicate with one another question 1 — AP Biology

Macrophages are white blood cells that ingest invading pathogens.

After digesting the pathogen, macrophages present the antigens from

the pathogen to helper T cells in the immune system. These helper T

cells then secrete chemical signals called cytokines. The cytokines can

travel short distances to activate nearby cytotoxic T cells, which will

kill infected cells. Some cytokines will activate the enzyme adenylyl

cyclase in nearby B cells to produce cyclic AMP (cAMP). cAMP will

then activate the production of antibodies in the B cells.

Question (a)

(a)

Part A

Question (i)

(i)
Figure for Question (i) — AP Biology

(i) Describe the characteristics of juxtacrine signaling.

Question (ii)

(ii)
Figure for Question (ii) — AP Biology

(ii) Draw a square around the step (1, 2, 3, or 4) in the figure that

illustrates an example of juxtacrine signaling.

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