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cell theory

Biology

QuestionAnswer
Cell Membrane Basics Why can only certain molecules cross the cell membrane easily? The membrane is made of amphipathic phospholipids with hydrophobic interiors, so only small, non‑polar molecules pass easily; large or charged molecules require membrane proteins.
Simple Diffusion What is simple diffusion? Movement of molecules from high concentration to low concentration
Does simple diffusion require ATP? No.
Does simple diffusion require membrane proteins? No
Give examples of molecules that use simple diffusion. O₂, CO₂, N₂, glycerol, short‑chain fatty acids.
Factors Affecting Diffusion Rate How does increasing the concentration gradient affect diffusion rate? Increases it.
How does increasing temperature affect diffusion rate? Increases it.
How does increasing membrane surface area affect diffusion rate? Increases it.
How does increasing diffusion distance affect diffusion rate? Decreases it.
Osmosis What is osmosis? Movement of water from high water concentration to low water concentration; no ATP required.
How can water cross the membrane? It diffuses directly (small size) or through aquaporins.
What is a solute? A substance dissolved in a solvent.
What is a solvent? The liquid that dissolves the solute (e.g., water).
What is the typical osmotic concentration of a cell? ~300 mOsmol.
What is the typical NaCl concentration in cells? 0.9% (normal saline).
Tonicity What is a hypertonic solution? Higher solute concentration than the cell.
What happens to a cell in a hypertonic solution? Water leaves the cell; the cell shrinks.
What is an isotonic solution? Same solute concentration as the cell.
What happens to a cell in an isotonic solution? Water moves equally; the cell stays the same
What is a hypotonic solution? Lower solute concentration than the cell.
What happens to a cell in a hypotonic solution? Water enters the cell; it swells and may burst.
Facilitated Diffusion What does facilitated diffusion require? Membrane proteins
Does facilitated diffusion require ATP? No
Do molecules move down or against their gradient in facilitated diffusion? Down their gradient.
What do channel proteins transport? Ions
What do carrier proteins transport? Nutrients like glucose and amino acids; can also move ions.
Can carrier proteins become saturated? Yes
Where are major ions concentrated? Sodium: higher outside Chloride: higher outside Potassium: higher inside Calcium: higher inside the smooth ER
Primary Active Transport Does primary active transport require ATP? Yes.
Do molecules move down or against their gradient? Against their gradient.
What does the Na⁺/K⁺ pump do? Pumps 3 Na⁺ out and 2 K⁺ into the cell using ATP.
Why is the Na⁺/K⁺ pump important? Maintains electrical gradient (inside more negative) Maintains chemical gradient (high Na⁺ outside for secondary transport)
What does the proton pump do? Pumps protons across membranes (e.g., mitochondria) to create a gradient used to generate ATP via chemiosmosis.
Coupled Transport What is symport? Two substances move in the same direction.
What is antiport? Two substances move in opposite directions.
What is secondary active transport? Uses the sodium gradient (not ATP directly) to pull nutrients like glucose or amino acids into the cell.
Movement of Large Molecules How are bulky substances moved across membranes? Using vesicles.
What is endocytosis? Engulfing substances into the cell via vesicles
What is phagocytosis? Engulfing solids (e.g., immune cells engulfing pathogens).
What is pinocytosis? Engulfing fluids (e.g., human egg taking in nutrient-rich fluid).
What is exocytosis? Releasing substances from vesicles to the outside of the cell.
Created by: oliviavanwort
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