AP Biology Unit 2 Study Guide: Cell Structure and Function

### 1. Cell Structure: Subcellular Components

Learning Target: Describe the structure and/or function of subcellular components and organelles.

- Nucleus: Contains DNA; controls cell activities through gene expression.

- Ribosomes: Sites of protein synthesis; free in cytosol or bound to rough ER.

- Endoplasmic Reticulum (ER):

- Rough ER: Has ribosomes; synthesizes and folds proteins.

- Smooth ER: Synthesizes lipids, detoxifies chemicals, stores calcium.

- Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or internal use.

- Lysosomes: Contain digestive enzymes to break down waste and macromolecules.

- Mitochondria: Powerhouse of the cell; site of ATP production via cellular respiration.

- Chloroplasts: Site of photosynthesis in plant cells.

- Vacuoles: Storage organelles; large central vacuole in plant cells for water and nutrient storage.

- Cytoskeleton: Network of fibers (microtubules, microfilaments) providing structure, transport, and support.

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### 2. Cell Structure and Function

Learning Target: Explain how subcellular components and organelles contribute to the function of the cell.

- Organelles work together to carry out essential functions:

- Nucleus: DNA transcription.

- Ribosomes & ER: Protein synthesis.

- Golgi Apparatus: Protein modification and distribution.

- Mitochondria: ATP production for energy.

- Lysosomes: Waste removal.

- Cytoskeleton: Cellular movement and structural integrity.

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### 3. Cell Size

Learning Target: Explain the effect of surface area-to-volume ratios on the exchange of materials between cells and the environment.

- As a cell grows, the surface area-to-volume ratio decreases, reducing efficiency in exchanging materials.

- Cells maintain a high surface area-to-volume ratio to:

- Maximize nutrient uptake.

- Increase waste removal.

- Facilitate diffusion and active transport processes.

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Learning Target: Explain how specialized structures and strategies are used for efficient exchange of molecules with the environment.

- Microvilli in intestinal cells increase surface area for nutrient absorption.

- Root hairs in plants maximize water and nutrient uptake.

- Gills and alveoli in animals increase gas exchange surface area.

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### 4. Plasma Membranes

Learning Target: Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the cell.

- Phospholipids: Form a bilayer that provides a semi-permeable barrier.

- Proteins: Embedded in the membrane; act as transport channels, receptors, and enzymes.

- Cholesterol: Maintains membrane fluidity at different temperatures.

- Carbohydrates: Attached to proteins and lipids for cell recognition and signaling.

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Learning Target: Describe the Fluid Mosaic Model of cell membranes.

- The Fluid Mosaic Model describes the membrane as a dynamic and flexible structure with various proteins and lipids floating in or on the bilayer of phospholipids.

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### 5. Membrane Permeability

Learning Target: Explain how the structure of biological membranes influences selective permeability.

- The phospholipid bilayer is selectively permeable, allowing small, nonpolar molecules (O₂, CO₂) to diffuse freely, while blocking larger or polar molecules (ions, glucose).

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Learning Target: Describe the role of the cell wall in maintaining cell structure and function.

- In plants, cell walls provide support, protection, and regulate water balance (turgor pressure).

- Made primarily of cellulose in plants, chitin in fungi, and peptidoglycan in bacteria.

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### 6. Membrane Transport

Learning Target: Describe the mechanisms that organisms use to maintain solute and water balance.

- Osmoregulation: Control of water balance (ex: contractile vacuoles in protists, kidneys in animals).

- Active transport: Uses ATP to move substances against their concentration gradient (ex: sodium-potassium pump).

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Learning Target: Describe the mechanisms that organisms use to transport large molecules across the plasma membrane.

- Exocytosis: Vesicles fuse with the membrane to release large molecules out of the cell.

- Endocytosis: The cell membrane engulfs large molecules to bring them into the cell.

- Phagocytosis: Engulfing large particles.

- Pinocytosis: Engulfing liquids.

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### 7. Facilitated Diffusion

Learning Target: Explain how the structure of a molecule affects its ability to pass through the plasma membrane.

- Small, nonpolar molecules (e.g., O₂, CO₂) can diffuse directly through the bilayer.

- Polar or large molecules require protein channels or carriers (facilitated diffusion) to cross the membrane (e.g., glucose via GLUT transporters).

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### 8. Tonicity and Osmoregulation

Learning Target: Explain how concentration gradients affect the movement of molecules across membranes.

- Diffusion: Molecules move from high to low concentration.

- Osmosis: Water moves across membranes toward higher solute concentration (lower water potential).

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Learning Target: Explain how osmoregulatory mechanisms contribute to the health and survival of organisms.

- Osmoregulation is vital to maintain internal balance:

- Freshwater organisms actively expel excess water.

- Marine organisms prevent dehydration by retaining water.

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Learning Target: Explain the movement of water by using water potential calculations.

- Water potential (Ψ) = solute potential (Ψs) + pressure potential (Ψp).

- Water moves from high to low water potential.

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### 9. Mechanisms of Transport

Learning Target: Describe the processes that allow ions and other molecules to move across membranes.

- Channel proteins allow ions like Na⁺ and K⁺ to pass through the membrane.

- Carrier proteins undergo a shape change to transport molecules like glucose.

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### 10. Compartmentalization

Learning Target: Describe the membrane-bound structures of the eukaryotic cell.

- Organelles (e.g., mitochondria, ER, Golgi) are surrounded by membranes that isolate them for specific functions (compartmentalization).

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Learning Target: Explain how internal membranes and membrane-bound organelles contribute to compartmentalization of eukaryotic cell functions.

- Compartmentalization allows for different processes to occur in distinct environments (e.g., lysosomes have acidic conditions for digestion).

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### 11. Origins of Cell Compartmentalization

Learning Target: Describe similarities and/or differences in compartmentalization between prokaryotic and eukaryotic cells.

- Prokaryotic cells lack membrane-bound organelles; their functions occur in the cytoplasm.

- Eukaryotic cells have specialized organelles with membranes for different functions.

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Learning Target: Describe the relationship between the functions of endosymbiotic organelles and their free-living ancestral counterparts.

- Endosymbiotic theory: Mitochondria and chloroplasts originated from free-living bacteria that were engulfed by a larger cell.

- Evidence: Both have their own DNA and double membranes.

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This study guide covers all the key concepts from Unit 2. Focus on understanding how each organelle contributes to the overall function and survival of the cell.