AP Bio Unit 2

Q: What is the structure of the phospholipid bilayer?

• A: A glycerol backbone attached to two nonpolar fatty acid tails and one polar phosphate group head. The bilayer is held together by hydrophobic interactions among the tails.

Define the Fluid Mosaic Model.

• A: The plasma membrane as a dynamic structure with proteins floating in a fluid lipid bilayer; nonpolar regions face inward and polar regions face outward.

Q: What are the types and functions of transmembrane proteins?

• Carrier proteins: Actively or passively transport molecules.

• Channel proteins: Allow passive movement through pores.

• Receptor proteins: Receive and transmit signals into the cell.

Q: What is the interior protein network?

A: Structural proteins inside the membrane that support shape and organize membrane proteins for cell function.

Q: What are cell surface markers and their functions?

A: Glycolipids and glycoproteins that act as cell ID tags for cell recognition, tissue sorting, and immune responses.

Q: What are glycolipids vs. glycoproteins?

• Glycolipids: Oligosaccharides covalently bonded to lipids.

• Glycoproteins: Oligosaccharides bonded to proteins; more common.

Q: Which molecules can freely pass through the membrane?

A: Small, nonpolar molecules (N₂, O₂, CO₂).

Q: Which molecules need help to pass through the membrane?

A: Large and/or charged (polar) molecules.

Q: What are cell wall components in different organisms?

• Plants: cellulose

• Fungi: chitin

• Bacteria: peptidoglycan

Q: What is bulk transport and what does it require?

A: Movement of macromolecules using vesicles; requires ATP (active process).

Q: What are the types of endocytosis?

• Phagocytosis: “Cell eating” – intake of solid particles.

• Pinocytosis: “Cell drinking” – intake of liquids.

• Receptor-mediated endocytosis: Intake of specific molecules via receptors.

Q: What happens during exocytosis?

A: Vesicles fuse with the cell membrane to release substances out of the cell.

Q: What defines active transport?

A: Movement of solutes against the concentration gradient (low → high) requiring ATP.

Q: What is the sodium-potassium pump and its function?

A: Uses ATP to pump 3 Na⁺ ions out and 2 K⁺ ions in, maintaining electrochemical gradients and membrane potential.

Q: What is a proton pump?

A: Actively transports H⁺ ions out of the cell to generate voltage and store energy (electrogenic pump).

Q: What is passive transport?

A: Movement of molecules without energy, down the concentration gradient (high → low).

Q: What is facilitated diffusion?

A: Passive movement of polar or charged molecules via specific transport proteins (carrier or channel).

Q: What are carrier proteins?

A: Transmembrane proteins that bind and move specific molecules (e.g., glucose) without ATP use.

Q: What are channel proteins?

A: Proteins forming pores for passive solute movement (e.g., aquaporins for H₂O, ion channels for ions).

Q: What are gated channels and how are they controlled?

A: Channels that open/close in response to stimuli:

• Ligand-gated: Open when a chemical signal binds.

• Voltage-gated: Respond to changes in membrane potential.

Q: What determines water potential (Ψ)?

A: Solute potential (ΨS) and pressure potential (ΨP); Ψ = ΨP + ΨS.

Q: What is the water potential of pure water?

A: 0 MPa at standard conditions.

Q: Why is solute potential (ΨS) always negative?

A: Solutes bind water molecules, reducing free water molecules available to do work.

Q: What is the formula for solute potential?

A: ΨS = -iCRT
(i = ionization constant, C = molarity, R = 0.0831 liter·bar/mole·K, T = Kelvin temperature).

Q: What happens to plant cells in hypertonic, isotonic, and hypotonic solutions?

• Hypertonic: Water exits cell → plasmolysis.

• Isotonic: No net movement → flaccid.

• Hypotonic: Water enters cell → turgid.

Q: What is the difference between ΨP values in plants vs. open systems?

• In open beakers/animal cells: ΨP = 0.

• In plant cells: ΨP is positive due to turgor pressure.

Q: What factors influence diffusion rate?

• Smaller molecules → faster diffusion.

• Higher temperature → faster diffusion.

• Larger concentration gradient → faster diffusion.

Q: What is simple diffusion?

A: Movement of small/nonpolar molecules directly through the lipid bilayer.

Q: Define osmosis.

A: Diffusion of water across a semipermeable membrane toward higher solute concentration.

Q: Define osmotic concentration.

A: Total concentration of all solutes in a solution.

Q: Define hypertonic, isotonic, and hypotonic solutions.

• Hypertonic: Higher solute concentration outside cell (water leaves cell).

• Isotonic: Equal solute concentrations (no net water movement).

• Hypotonic: Lower solute concentration outside cell (water enters cell).

Q: What is osmotic pressure?

A: The pressure required to stop osmosis; proportional to solute concentration.

Q: What is hydrostatic pressure?

A: Pressure of the cytoplasm pushing outward on the cell membrane.

Q: Define plasmolysis, flaccid, and turgid states.

• Plasmolysis: Cell membrane pulls from wall in hypertonic solution.

• Flaccid: Normal for animal cells, wilted for plants (isotonic).

• Turgid: Normal, firm plant cell (hypotonic).

Q: Why is compartmentalization important in eukaryotic cells?

A: It isolates incompatible reactions, increases efficiency, and provides more surface area for reactions.

Q: What is the organelle advantage?

A: Enzymatic reactions are localized, reducing interference and improving speed and control.

Q: Summarize the endosymbiotic theory.

A: Mitochondria and chloroplasts originated from prokaryotic cells engulfed by ancestral eukaryotes.
Evidence: Double membranes, circular DNA, ribosomes, independent replication.