AP BIO UNIT 2 : Cell Transport Foldable & Informational Slides

Diffusion (Simple Diffusion)

• What it is: Direct movement of molecules straight through the lipid bilayer without helper proteins.

• Logic / Core Rule: Only works for small molecules—either nonpolar ($O_2, N_2, CO_2$, benzene) or small polar (glycerol, ethanol, water). No energy or transport proteins needed.

• Easy Memory Hack: Think of slipping through an open crowd—if you're small enough, you slide straight through the middle without needing a door opened for you.

Osmosis Goal & Mechanism (Equilibrium)

• What it is: The process aimed at reaching equilibrium, where solute concentrations become equal on both sides of the membrane.

• Logic / Core Rule: No transport proteins are required. Plus, if multiple solutes are involved, each solute moves down its OWN concentration gradient independently to reach its own equilibrium.

• Easy Memory Hack: Every solute plays its own game—they all move to reach balance without needing any protein doorways!

Facilitated Diffusion

• What it is: Passive transport using helper protein transporters (channel or carrier proteins).

• Logic / Core Rule: Molecules still move down their concentration gradient (high to low), but need proteins because they are too large, charged (ions), or both. Transporters are substance-specific.

• Examples: Glucose, amino acids, nucleotides, ions ($H^+$, $Na^+$, $HCO_3^-$, $K^+$, $Ca^{+2}$, $Cl^-$, $Mg^{2+}$).

• Easy Memory Hack: Think of VIP entry—the molecules are too big or charged to walk through the wall, so they need a specific VIP door (protein channel or carrier) to get inside.

Active Transport

• What it is: Cell membrane transport that requires energy (like ATP).

• Logic / Core Rule: Moves substances against their concentration gradient—from low concentration to high concentration.

• Easy Memory Hack: Think of pushing a boulder up a steep hill—it doesn't happen naturally, so you have to burn energy to force it up!

Concentration Gradient

• What it is: The difference in the concentration (amount) of a substance between two neighboring areas—like inside vs. outside a cell.

• Logic / Core Rule:

  • Going DOWN/WITH the gradient: Moving naturally from high (crowded) to low (empty) concentration $\rightarrow$ Passive (No energy).

  • Going AGAINST the gradient: Forcing movement from low (empty) to high (crowded) concentration $\rightarrow$ Active (Requires energy/ATP).

• Easy Memory Hack: Think of a hill. Going down the gradient is like rolling downhill (zero energy needed). Going against the gradient is like running uphill (takes a lot of energy).

Molecular Active Transport

• What it is: A type of active transport that moves substances against their concentration gradient using a transport protein (like a pump).

• Logic / Core Rule: Requires ATP energy either directly (Primary Active Transport) or indirectly (Secondary Active Transport) to power the protein pump.

• Example: Proton pump pushing $H^+$ ions across the membrane.

• Easy Memory Hack: Think of a motorized sump pump—it constantly burns power to force water out against natural flow!

Primary Active Transport

• What it is: Active transport that involves the direct use of ATP.

• Logic / Core Rule: ATP attaches a phosphate group to the protein pump (phosphorylation), which activates it and changes its shape to move substances against their gradient.

• Classic Example: Sodium/Potassium Pump ($Na^+/K^+$ pump) $\rightarrow$ Pumps 3 $Na^+$ ions out and 2 $K^+$ ions in.

• Easy Memory Hack: Think of paying cash directly—ATP pays the pump with a phosphate to force 3 $Na^+$ OUT and bring 2 $K^+$ IN!

Secondary Active Transport

• What it is: Active transport that uses the indirect energy of ATP.

• Logic / Core Rule: The transport proteins are not phosphorylated by ATP. Instead, they ride the energy wave of a concentration gradient created by primary active transport

• Types of Transporters:

  • Antiporters: Move substances in opposite directions

  • Symporters: Move substances in the same direction

• Easy Memory Hack: Think of piggybacking—one molecule sneaks through while hitching a ride on the energy created by another ion rushing down its gradient!

Membrane Engulfing

The process where the cell membrane wraps its "arms" around outside particles, swallows them, and pinches closed to form a new vesicle.

Vesicle

A tiny, membrane-bound "delivery bag" used to carry large cargo inside the cell.

Bulk Transport (Exocytosis vs. Endocytosis)

• What it is: A form of active transport that moves large quantities of substances into or out of the cell using vesicles.

• Logic / Core Rule:

  • Exocytosis: Vesicles fuse with the cell membrane to move contents OUT to the extracellular environment.

  • Endocytosis: The cell membrane engulfs outside contents and pinches off into a vesicle to bring them IN to the intracellular environment.

• Easy Memory Hack: EXocytosis = EXit the cell; ENdocytosis = ENter the cell!

Endocytosis

Membrane ENGLUFS outside stuff ➔ Pinches off ➔ Becomes a vesicle inside

Exocytosis

Vesicle FUSES with membrane ➔ Dumps contents outside

Phagocytosis

• What it is: "Cell eating"—a type of endocytosis that engulfs large solid particles.

• Logic / Core Rule: The cell extends pseudopodia ("false feet") around solid food/particles to pull them inside a food vacuole.

• Easy Memory Hack: Phagocytosis = Food / Fag (solids)!

Pinocytosis

• What it is: "Cell drinking"—a type of endocytosis that engulfs extracellular liquid.

• Logic / Core Rule: The membrane folds inward to bring in fluid so the cell can absorb dissolved nutrients.

• Easy Memory Hack: Pinocytosis = Piña Colada (liquids)!

Receptor-Mediated Endocytosis

• What it is: A highly specific type of endocytosis that targets exact substances (ligands).

• Logic / Core Rule: Target molecules bind to surface receptors $\rightarrow$ triggers a coated pit to form $\rightarrow$ pinches off into a coated vesicle.

• Easy Memory Hack: VIP endocytosis—only opens the door when the right key binds to the receptor lock!