AP Biology · Unit 2: Cells
2.4 Membrane Permeability
In short
You must understand how the hydrophobic interior of the plasma membrane dictates selective permeability. You need to know specific examples of molecules that can freely pass (small nonpolar molecules like N2, O2, CO2) versus those that require transport proteins (hydrophilic substances, large polar molecules, and ions).
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What else do you need to know about Membrane Permeability?
You should also recognize that small polar, uncharged molecules like H2O and NH3 can pass in small amounts. Furthermore, you must know the functions of cell walls in Bacteria, Archaea, Fungi, and plants, specifically their roles as structural boundaries, permeability barriers, and protectors against osmotic lysis. No specific exclusion statements are provided for this topic.
Can you do these?
- I can state that plasma membranes separate internal and external environments and that selective permeability is due to the hydrophobic interior.
- I can describe how small nonpolar molecules pass freely, while hydrophilic substances require embedded channels and transport proteins.
- I can explain that nonpolar hydrocarbon tails prevent the movement of ions and polar molecules, but small polar uncharged molecules can pass in small amounts.
- I can explain how cell walls in Bacteria, Archaea, Fungi, and plants provide a structural boundary, permeability barrier, and protection from osmotic lysis.
How is Membrane Permeability tested on the exam?
The topic is assessed using the command words 'Explain' and 'Describe'. Questions may require you to explain the relationship between membrane structure (e.g., phospholipid tails) and its permeability to specific molecules, or to describe the protective and structural roles of the cell wall. The suggested skill for this topic is 'Statistical Tests and Data Analysis' (5.D), meaning you may be asked to use data to evaluate a hypothesis or prediction (including rejecting or failing to reject a null hypothesis) related to membrane permeability or cell wall function.
Free practice questions with full explanations, and instant marking of your free-response answers.
Membrane Permeability: common questions
What do you need to know about Membrane Permeability for AP Biology?
You must understand how the hydrophobic interior of the plasma membrane dictates selective permeability. You need to know specific examples of molecules that can freely pass (small nonpolar molecules like N2, O2, CO2) versus those that require transport proteins (hydrophilic substances, large polar molecules, and ions).
How is Membrane Permeability tested on the AP Biology exam?
The topic is assessed using the command words 'Explain' and 'Describe'. Questions may require you to explain the relationship between membrane structure (e.g., phospholipid tails) and its permeability to specific molecules, or to describe the protective and structural roles of the cell wall.
How do I know I have mastered Membrane Permeability?
Check you can do each of these: state that plasma membranes separate internal and external environments and that selective permeability is due to the hydrophobic interior; describe how small nonpolar molecules pass freely, while hydrophilic substances require embedded channels and transport proteins; explain that nonpolar hydrocarbon tails prevent the movement of ions and polar molecules, but small polar uncharged molecules can pass in small amounts; explain how cell walls in Bacteria, Archaea, Fungi, and plants provide a structural boundary, permeability barrier, and protection from osmotic lysis.
Where does Membrane Permeability fit in AP Biology?
Membrane Permeability is topic 2.4 in Unit 2: Cells of AP Biology.
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