AP Biology Flashcards: Membrane Permeability
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 11 cards to help you master important concepts.
Can water, a polar molecule, cross the plasma membrane without a transport protein?
Yes, although the membrane's interior is hydrophobic, small polar molecules like water are able to pass through in small amounts.
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Can water, a polar molecule, cross the plasma membrane without a transport protein?
Yes, although the membrane's interior is hydrophobic, small polar molecules like water are able to pass through in small amounts.
What is selective permeability?
Selective permeability is the property of plasma membranes that allows some substances to cross more easily than others, resulting from its hydrophobic interior.
Explain the relationship between the structure of a biological membrane and its selective permeability.
A membrane's structure, specifically its hydrophobic core, directly influences its function of selective permeability by restricting the passage of hydrophilic substances while allowing small, nonpolar molecules to pass freely.
What is the fundamental role of the plasma membrane in relation to the cell's environment?
The plasma membrane separates the cell's internal environment from the external environment, controlling what enters and leaves the cell.
Which groups of organisms possess cell walls for structural support and protection?
Cell walls are found in plants, fungi, bacteria, and archaea.
What are the primary functions of a cell wall?
A cell wall provides a structural boundary and a permeability barrier, offering protection from environmental stress such as osmotic lysis.
What types of molecules can pass freely across the plasma membrane?
Small, nonpolar molecules are able to pass freely across the plasma membrane.
How does a cell wall protect a cell from osmotic lysis?
The cell wall provides a rigid structural boundary that prevents the cell from over-expanding and bursting when it takes on excess water.
What kinds of substances require embedded channels or transport proteins to cross the membrane?
Hydrophilic substances, such as large polar molecules and ions, require embedded channels or transport proteins to move across the membrane.
How do the nonpolar tails of phospholipids affect the passage of polar molecules and ions?
The nonpolar tails of phospholipids create a hydrophobic barrier that prevents most polar molecules and ions from passing through the membrane.
What structural feature of the plasma membrane is primarily responsible for its selective permeability?
The hydrophobic interior, formed by the nonpolar tails of phospholipids, is primarily responsible for the membrane's selective permeability.