Transport Mechanism (Passive, Active and Bulk) - Vocabulary Flashcards

Definition: movement of molecules across a cell membrane without the need for energy; driven by concentration gradient from high to low.
Types:
- Simple Diffusion: diffusion through the lipid bilayer; small nonpolar molecules like $\mathrm{O<em>2}$ and $\mathrm{CO</em>2}$ ; no energy input.
- Facilitated Diffusion: transport proteins (channels or carriers) help larger or polar molecules cross the membrane; examples include glucose and ions.
- Osmosis: diffusion of water across a selectively permeable membrane; from high water concentration to low.
Daily-life relevance: gas exchange in lungs; nutrient absorption of glucose and amino acids in intestines; osmosis helps regulate tissue fluid; maintains cellular equilibrium.

Definition: tonicity is the ability of a solution to affect water movement in and out of cells; determines how cells respond to their surrounding environment.
Types:
- Hypotonic: lower solute concentration outside the cell; water enters; cells swell; animal cells may lyse; plant cells become turgid.
- Isotonic: solute concentration equal to cell; water enters and leaves at equal rates; cell size remains stable.
- Hypertonic: higher solute concentration outside; water leaves; animal cells crenate; plant cells plasmolyze.
Daily-life notes: IV fluids should be isotonic to avoid red blood cell damage; aquatic organisms adapt to external tonicity; plant vacuoles shrink in hypertonic environments leading to wilting.

Definition: movement of molecules across the membrane against their concentration gradient; requires energy (ATP).
Key features:
- Requires ATP (energy from ATP hydrolysis).
- Against the gradient.
- Involvement of carrier proteins (pumps) that undergo conformational changes.
Example: Sodium-Potassium Pump: pumps $3\,\mathrm{Na^+}$ out and $2\,\mathrm{K^+}$ in using ATP; maintains electrochemical gradients essential for nerve and muscle function.
Importance:
- Acid-base balance: $\mathrm{H^+}$ pumps in stomach and kidneys regulate pH.
- Kidney function and waste removal: reabsorb ions and nutrients; filter wastes.
- Muscle contraction: calcium pumps maintain $\mathrm{Ca^{2+}}$ balance in muscle cells.

Definition: movement of large molecules or particles into or out of a cell via vesicles; requires energy.
Endocytosis: engulfing substances into the cell; subtypes:
- Phagocytosis (cell eating) for large particles.
- Pinocytosis (cell drinking) for extracellular fluids.
- Receptor-mediated endocytosis for specific molecules.
Exocytosis: releasing substances from the cell (hormones, enzymes).
Importance: nutrient uptake; waste removal; hormone secretion.