Master Cell Structure and Function with AP Biology review games.
This unit covers cell organelles, membrane transport and compartmentalization — essential concepts for AP Biology. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers cell organelles, membrane transport and compartmentalization — essential concepts for AP Biology. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Cell Organelles
Students must know the structure and function of all major eukaryotic organelles and be able to connect organelle function to cell specialization. The AP exam frequently asks students to predict which organelles would be most abundant in a given cell type based on that cell's function. Understanding the endomembrane system as an integrated pathway is essential.
Key Points
- Mitochondria produce ATP via cellular respiration; cells with high energy demands (muscle, liver) have more mitochondria
- Ribosomes on rough ER synthesize proteins destined for secretion or membrane insertion; free ribosomes make cytoplasmic proteins
- The endomembrane system (ER → Golgi → vesicle → membrane/secretion) modifies, packages, and ships proteins
- Chloroplasts (plants only) contain thylakoids for light reactions and stroma for the Calvin cycle; double membrane signals endosymbiotic origin
A researcher examines two cell types: a pancreatic acinar cell that secretes digestive enzymes, and a skeletal muscle cell. Which organelles would you expect to be most abundant in each, and why?
The pancreatic acinar cell secretes large amounts of protein, so it would have abundant rough ER (for protein synthesis), Golgi apparatus (for processing and packaging), and secretory vesicles (for exocytosis). The skeletal muscle cell requires massive ATP for contraction, so it would be densely packed with mitochondria. This question tests the core AP skill of linking organelle function to cell specialization rather than simply recalling definitions.
2 Membrane Transport
Students must distinguish between passive transport (no energy required, moves down concentration gradient) and active transport (requires ATP, moves against gradient), and apply these concepts to specific scenarios involving ions, water, and large molecules. Osmosis is a high-frequency exam topic requiring students to predict cell behavior in hypotonic, hypertonic, and isotonic solutions. The sodium-potassium pump is the canonical active transport example.
Key Points
- Simple diffusion: small, nonpolar molecules (O₂, CO₂, lipids) cross directly through the phospholipid bilayer
- Facilitated diffusion: polar or charged molecules (glucose, ions) require channel or carrier proteins; still passive (no ATP)
- Active transport requires ATP and moves solutes against their concentration gradient (e.g., Na⁺/K⁺ pump: 3 Na⁺ out, 2 K⁺ in)
- Water moves by osmosis from low solute concentration (high water potential) to high solute concentration (low water potential)
A red blood cell is placed in a 0.9% NaCl solution (isotonic), then in a 0.2% NaCl solution (hypotonic). Predict and explain what happens to the cell in each solution.
In the isotonic 0.9% NaCl solution, solute concentration is equal inside and outside the cell, so there is no net movement of water and the cell maintains its normal shape. In the hypotonic 0.2% NaCl solution, solute concentration is lower outside the cell than inside, meaning water potential is higher outside; water moves into the cell by osmosis down its water potential gradient, causing the cell to swell and potentially undergo lysis. This directly mirrors AP free-response questions that require both a prediction and a mechanistic explanation.
3 Compartmentalization
Students must understand why separating cellular processes into membrane-bound compartments increases efficiency and allows incompatible reactions to occur simultaneously within the same cell. The AP exam tests whether students can explain the functional advantage of compartmentalization, not just list compartments. Key examples include the isolation of DNA in the nucleus and the acidic environment of lysosomes.
Key Points
- Compartmentalization allows cells to maintain distinct chemical environments (pH, ion concentration) needed for specific reactions
- Lysosomes maintain an acidic pH (~4.5) optimal for hydrolytic enzymes; if these enzymes were free in the cytoplasm, they would degrade the cell
- The nuclear envelope separates transcription (nucleus) from translation (cytoplasm), allowing additional regulation of gene expression
- Prokaryotes lack membrane-bound organelles, so transcription and translation occur simultaneously in the cytoplasm—a key structural difference from eukaryotes
Explain why it would be harmful if the digestive enzymes normally found in lysosomes were instead released freely into the cytoplasm.
Lysosomal enzymes such as proteases, lipases, and nucleases function optimally at the acidic pH maintained inside the lysosome. If released into the neutral cytoplasm, their activity would be reduced, but even partial activity could degrade essential cytoplasmic proteins, lipids, and nucleic acids, leading to cell death—a process called autolysis. Compartmentalization within the lysosome therefore protects the rest of the cell while still allowing targeted digestion of waste materials and pathogens.
Questions, answered.
What is Cell Structure and Function?
Cell Structure and Function is Unit 2 of AP Biology, covering cell organelles, membrane transport and compartmentalization.
How to study for AP Biology Unit 2?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 30+ review questions across 5 different game modes.