AP Bio- Unit 2 Vocab Notes

1. Surface Area-to-Volume Ratio and Cell Efficiency

• Surface Area-to-Volume Ratio:

  • The ratio between the surface area of a cell (or organism) and its volume. This ratio is critical in determining how efficiently a cell can exchange materials with its environment.

  • Higher ratio: More surface area relative to volume, leading to efficient exchange.

  • Lower ratio: Less surface area relative to volume, reducing the rate of material exchange.

• Adaptations for Efficient Exchange:

  • Microvilli: Small finger-like projections that increase surface area on cells (e.g., in intestines) for absorption.

  • Gills: Thin tissue layers in fish that increase surface area for oxygen absorption.

  • Villi: Finger-like projections in the small intestine that increase the surface area for nutrient absorption.

• Examples of Surface Area-to-Volume Ratio:

  • Larger cells struggle with efficient exchange of gases, nutrients, and waste because the volume grows faster than surface area.

  • Marine Mammals: Larger bodies have smaller surface area-to-volume ratios, helping reduce heat loss in cold environments. Smaller mammals like otters need thick fur to compensate for rapid heat loss.

2. Cell Membrane Structure and Function

• Phospholipid Bilayer:

  • The double-layered structure that forms the foundation of cell membranes.

    • Hydrophilic (water-loving) heads face outward towards water (both intracellular and extracellular).

    • Hydrophobic (water-fearing) tails face inward, creating a water-free interior zone.

  • Vocab:

    • Hydrophilic: Attracted to water.

    • Hydrophobic: Repelled by water.

• Membrane Proteins:

  • Transmembrane proteins: Span across the membrane and help transport molecules.

  • Integral proteins: Embedded within the membrane.

  • Peripheral proteins: Attached to the surface of the membrane, often involved in signaling.

• Fluid Mosaic Model:

  • Describes the cell membrane as a fluid, dynamic structure with a variety of molecules (phospholipids, proteins, cholesterol) that can move laterally within the layer.

    • Fluidity: Refers to the ability of molecules to move within the membrane.

    • Mosaic: Describes the diverse mix of proteins, lipids, and carbohydrates that make up the membrane.

• Membrane Permeability:

  • Selective permeability: The membrane allows certain substances to pass while blocking others.

  • Freely passing molecules: Small nonpolar molecules (e.g., O₂, CO₂) can diffuse through the membrane.

  • Transport proteins: Help large or charged molecules (e.g., glucose, ions) move across the membrane.

3. Transport Across Cell Membranes

• Passive Transport:

  • Movement of molecules from high to low concentration without energy.

    • Simple Diffusion: Movement of molecules (e.g., gases like O₂, CO₂) directly through the phospholipid bilayer.

    • Facilitated Diffusion: Polar molecules or ions pass through channel proteins or carrier proteins without energy.

• Osmosis:

  • The diffusion of water across a selectively permeable membrane from a region of higher water concentration (hypotonic solution) to lower water concentration (hypertonic solution).

    • Hypotonic: Solution with a lower solute concentration.

    • Hypertonic: Solution with a higher solute concentration.

    • Isotonic: Solutions have equal solute and water concentrations, causing no net water movement.

• Active Transport:

  • Movement of molecules against their concentration gradient (low to high concentration), requiring energy in the form of ATP.

    • Na⁺/K⁺ Pump: Actively transports sodium and potassium ions across the membrane, crucial for nerve and muscle function.

• Endocytosis & Exocytosis:

  • Endocytosis: The cell engulfs external substances by folding its membrane inward to form a vesicle.

    • Phagocytosis: "Cell eating"; intake of large particles like bacteria.

    • Pinocytosis: "Cell drinking"; intake of liquid.

  • Exocytosis: The cell expels large molecules by fusing a vesicle with the plasma membrane (e.g., secretion of hormones or neurotransmitters).

4. Osmoregulation and Water Movement

• Water Potential (Ψ):

  • A measure of the potential energy of water in a system, influencing the direction of water movement. Water moves from areas of higher water potential to areas of lower water potential.

    • Solute potential (Ψs): Lowered by adding solutes, reducing water potential.

    • Pressure potential (Ψp): Increased by applying pressure, increasing water potential.

• Osmoregulation:

  • Cells regulate their internal water balance by controlling water movement across the membrane to prevent lysis (bursting) or crenation (shriveling).

    • Turgor pressure: Pressure exerted by water inside the central vacuole of plant cells, pushing the plasma membrane against the cell wall, helping maintain rigidity.

• Hypotonic, Hypertonic, and Isotonic Solutions:

  • Hypotonic: Cells gain water and may burst (animal cells) or become turgid (plant cells).

  • Hypertonic: Cells lose water, leading to plasmolysis (in plant cells) or crenation (in animal cells).

  • Isotonic: No net movement of water, cells remain stable.

5. Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells:

  • Simpler structure: No membrane-bound organelles, DNA is circular, and located in the nucleoid region.

  • Found in bacteria and archaea.

  • Plasmids: Small circular DNA molecules separate from the main chromosome, often carry antibiotic resistance genes.

• Eukaryotic Cells:

  • Complex structure: Membrane-bound organelles, DNA is linear and enclosed within a nucleus.

  • Found in plants, animals, fungi, and protists.

  • Compartmentalization: Organelles such as the nucleus, mitochondria, ER, and Golgi separate different metabolic reactions, increasing efficiency.

6. Cell Organelles and Their Functions

• Nucleus:

  • Stores genetic information (DNA) and controls cell functions.

  • Nucleolus: Site of ribosome assembly.

• Ribosomes:

  • Free ribosomes: Float in the cytoplasm and synthesize proteins for use inside the cell.

  • Bound ribosomes: Attached to the rough ER, synthesize proteins for secretion or membrane use.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes, synthesizes proteins that will be secreted or used in membranes.

  • Smooth ER: Lacks ribosomes, synthesizes lipids, detoxifies toxins, and stores calcium ions.

• Golgi Apparatus:

  • Modifies, sorts, and packages proteins and lipids into vesicles for delivery to different destinations (e.g., lysosomes, plasma membrane).

• Mitochondria:

  • Powerhouse of the cell: Produces ATP through cellular respiration.

  • Cristae: Folded inner membrane, increasing surface area for ATP production.

• Lysosomes:

  • Contain hydrolytic enzymes for breaking down macromolecules, waste materials, and cellular debris.

  • Play a role in apoptosis (programmed cell death).

• Vacuoles:

  • Large in plant cells, store water, nutrients, and waste products. Help maintain turgor pressure to keep the plant upright.

• Chloroplasts (in plant cells):

  • Perform photosynthesis, converting sunlight into glucose. Have their own DNA and ribosomes, evidence for the endosymbiotic theory.

7. Endosymbiotic Theory

• Theory that explains the origin of mitochondria and chloroplasts in eukaryotic cells:

  • These organelles were once free-living prokaryotic organisms that were engulfed by a host cell through endosymbiosis.

  • Evidence:

    • Mitochondria and chloroplasts have their own circular DNA, like bacteria.

    • Both replicate independently through binary fission.

    • They have double membranes, indicating they were engulfed by the host cell.

    • Their ribosomes resemble prokaryotic ribosomes.

8. Membrane Potential

• Membrane Potential:

  • The voltage difference across a cell membrane due to the differential distribution of ions.

  • Important in nerve and muscle cells, where changes in membrane potential lead to action potentials (electrical signals).

• Sodium-Potassium Pump:

  • Actively transports Na⁺ out of the cell and K⁺ into the cell, helping maintain a negative charge inside the cell and contributing to the resting membrane potential.

9. Key Vocabulary Definitions

• Diffusion: Movement of molecules from high to low concentration (down their concentration gradient) without energy input.

• Facilitated Diffusion: Movement of molecules across a membrane through transport proteins.

• Endocytosis: Cellular process where materials are taken into the cell by engulfing them in a membrane.

• Exocytosis: Process where vesicles fuse with the plasma membrane to release contents outside the cell.

• Osmosis: Diffusion of water through a selectively permeable membrane.

• Turgor Pressure: Pressure exerted by water inside the central vacuole of plant cells that pushes the cell membrane against the cell wall.

• Plasmolysis: Shrinking of the cytoplasm in plant cells when water leaves the cell in a hypertonic environment.

• Crenation: Shriveling of animal cells in a hypertonic solution.

• Hypotonic: A solution with lower solute concentration (more water).

• Hypertonic: A solution with higher solute concentration (less water).

• Isotonic: Solutions with equal solute and water concentrations.

• Water Potential (Ψ): A measure of the potential energy of water in a system, determining the direction of water movement.