AP Biology — Unit 2: Cell Structure and Function

What AP Biology Unit 2 covers

The College Board Course and Exam Description breaks Unit 2 into 10 topics:

1. 2.1 Cell Structure and Function
2. 2.2 Cell Size
3. 2.3 Plasma Membrane
4. 2.4 Membrane Permeability
5. 2.5 Membrane Transport
6. 2.6 Facilitated Diffusion
7. 2.7 Tonicity and Osmoregulation
8. 2.8 Mechanisms of Transport
9. 2.9 Cell Compartmentalization
10. 2.10 Origins of Cell Compartmentalization

AP Biology Unit 2 practice questions

• A drug destroys all ribosomes in a cell. What process shuts down first, and why?

  Protein synthesis stops first — ribosomes run translation. They read mRNA sequences into polypeptides.

• A toxin blocks vesicle formation from the ER. Which organelle is cut off from receiving newly synthesized proteins, and what cellular role is disrupted?

  The Golgi complex is cut off from newly synthesized proteins. It can no longer receive, modify, fold, or package them for trafficking within or out of the cell.

• A mitochondrion's outer membrane is smooth, but its inner membrane is intensely folded. Why does only the inner membrane need that surface area increase?

  ATP synthesis occurs along the inner membrane via the electron transport chain and ATP synthase. More inner membrane surface = more ATP production sites.

• A lysosome's membrane ruptures inside a cell. What happens next, and why is this catastrophic?

  Hydrolytic enzymes spill into the cytoplasm and digest the cell's own macromolecules. That triggers uncontrolled cell death.

• Plant cells have one large central vacuole; animal cells have many small ones. What does the plant's central vacuole do that justifies taking up most of the cell's volume?

  It maintains turgor pressure by storing water and nutrients. That keeps plant cells firm and supports the plant without a rigid skeleton.

• A mutation prevents the Golgi complex from chemically modifying proteins after synthesis. What two downstream consequences are most likely for cell function?

  Proteins are misfolded or misdirected, so they miss their target and signaling or secretion fails. Both failures cripple normal cell function.

• You calculate the SA:V ratio of two cubes — side length 1 cm and side length 3 cm. Which has the higher ratio, and what does that mean for nutrient exchange?

  The 1 cm cube has SA:V = 6:1; the 3 cm cube has SA:V = 2:1. The smaller cube exchanges materials more efficiently relative to its volume.

• As a cell grows larger, its volume increases faster than its surface area. What structural adaptation can compensate, and where is this seen in real biology?

  Membrane folding increases surface area without shrinking the cell. Examples: intestinal microvilli, mitochondrial cristae, and root hair extensions.

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Key terms in Unit 2

These 12 terms show up in the Unit 2 cards. Each one links to its definition in the AP Biology key-term reference.

• Active transport
• Cellular respiration
• Compartmentalization
• Concentration gradient
• Electron transport chain
• Endomembrane system
• Endosymbiotic theory
• Facilitated diffusion
• Fluid mosaic model
• Oxidative phosphorylation
• Passive transport
• Selective permeability