Biology Chapter 7 Flashcards

Plasma Membrane Structure and Composition

• Plasma membranes have distinct lipid and protein compositions on either side, facilitating different functions for the cytoplasmic and exterior surfaces.
• Composed of two layers of phospholipids with proteins embedded or attached to the bilayer, providing structural complexity and functionality.

Membrane Permeability

• Membrane permeability for polar solutes depends on the presence of specific transport proteins, as the lipid bilayer is generally impermeable to polar or charged substances.
• Small nonpolar molecules, e.g., O2 and CO2, can diffuse directly through the bilayer, while ions and larger polar molecules require transport proteins.
• Water molecules can pass through the membrane slowly but efficiently via aquaporins, specialized transport proteins.

Tonicity and Effects on Cells

• Crenation occurs when a red blood cell shrinks in a hypertonic solution (e.g., 3.21% NaCl), while hemolysis is the bursting of a cell in a hypotonic solution (e.g., distilled water).
• Solutions classified as isotonic to red blood cells (e.g., 0.9% NaCl) maintain cell shape.

Mechanisms of Transport

• Simple diffusion is the process by which small, nonpolar molecules pass through the membrane without assistance.
• Facilitated diffusion employs transport proteins to help molecules cross, while active transport requires ATP to move substances against their concentration gradient.
• The sodium-potassium pump is crucial for maintaining Na+ low within cells and K+ high, pumping three Na+ out for every two K+ in.

Energetics of Transport

• Active transport mechanisms use energy (e.g., from ATP hydrolysis) to move substances against their electrochemical gradient, including the cotransport of glucose with sodium ions.
• Osmosis, the diffusion of water, can occur even when solutes cannot cross the membrane, with water moving toward higher solute concentration until equilibrium is reached.

Special Transport Mechanisms

• Endocytosis and exocytosis involve vesicles that transport substances without them crossing the membrane directly.
• Micelles formed by detergents illustrate how amphipathic molecules can encapsulate grease and eliminate it through washing.

Concentration Gradients and Transport

• An electrochemical gradient influences ion movement, with Na+ favoring entry and K+ favoring exit, but inhibited by charge differences.
• The rate of osmotic movement is affected by temperature, pressure, and the concentration gradient of solutes across a selectively permeable membrane.

Osmotic Equilibrium

• At osmotic equilibrium, water molecules remain in dynamic equilibrium, with continuous movement but no net directional flow across the membrane.

Key Transport Proteins

• Specific transporters such as GLUT-1 facilitate glucose diffusion, exemplifying facilitated diffusion, while the sodium-potassium pump exemplifies active transport requiring ATP.

Test your knowledge of the concepts in Chapter 7 of Mastering Biology with these flashcards. Focus on the structure and functions of biological membranes, including the differences in lipid and protein composition. Perfect for reinforcing your understanding of plasma membranes!