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AP Biology 2.3 Plasma Membrane Questions

Practise AP Biology 2.3 questions by connecting phospholipid bilayer structure and protein polarity to membrane organisation and internal cell conditions.

Syllabus
Effective Fall 2025
Course
AP Biology

Exam points

  • orient phospholipid heads and tails from aqueous and nonaqueous environments
  • identify hydrophobic receptor regions interacting with membrane fatty-acid tails
  • justify bilayer organization and transmembrane-protein placement from polar and nonpolar interactions

Covered syllabus points

2.3.A—Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the…2.3.B—Describe the fluid mosaic model of cell membranes

Question 1

[Maximum number: 1]

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.

Many receptors are embedded in the plasma membrane. Describe the polarity of the portion of the receptor that is inside the membrane.

To investigate whether the binding of 20E to its receptor, DopEcR, affects behavior in moths, scientists injected male moths with saline (control solution) or with small interfering RNA molecules (siRNAs) that inhibit the expression of the gene encoding DopEcR. The scientists then exposed the moths to the pheromone and determined the percent of total time observed that the moths engaged in general activity, defined as movement in any direction. The scientists also determined the percent of the general activity time that the moths spent in oriented activity, defined as movement toward an area of high pheromone concentration (Table 1).

Table 1. Average General and Oriented Activity in Male Moths Injected With Saline or siRNA Molecules

Table 1. Average General and Oriented Activity in Male Moths Injected With Saline or siRNA Molecules

DopEcR is a G protein-coupled receptor. When 20E binds to DopEcR, GTP displaces the GDP bound to the G protein, and a signaling pathway is activated. The scientists hypothesize that this leads to the transcription of genes associated with the oriented activity observed in the male moths (Figure 1).

Figure 1. A simplified model of a signaling pathway activated by the binding of 20E to its receptor, DopEcR

Figure 1. A simplified model of a signaling pathway activated by the binding of 20E to its receptor, DopEcR

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