UNIT 2: DIFFUSION AND OSMOSIS

Simple Diffusion

random movement of molecules spreading evenly in space

Concentration Gradient

results from unequal distribution of ions

How do molecules move in simple diffusion?

molecules move from high to low concentration to reach equilibrium (diffuses down) and does not use energy

What type of molecules can pass through simple diffusion

small nonpolar molecules like oxygen, carbon dioxide, and water (very slowly)

Passive Transport

movement across a membrane down their concentration gradient

Facilitated Diffusion

molecules moving across a membrane through transport proteins

What types of molecules do facilitated diffusion allow?

ions (Na+, Cl-, Calcium) and polar molecules require protein assistance

Why do ions and polar molecules require facilitated diffusion?

slowed by the hydrophobic core of the membrane

Channel Proteins

provide hydrophilic pathways for certain molecules

Carrier Proteins

change shape to transport specifically, moves larger molecules (glucose)

Transport Proteins

specific to each substance and not allow substance via that route

Active Transport

movement of molecules against their concentration gradient, requiring ATP; cells can maintain solute concentrations different from its environment

Primary Active Transport

uses ATP to pump ions (H+, Ca2+, Na+, K+) against gradient

Proton Pump (H+)

involved in ATP production during cellular respiration

Sodium-Potassium Pump (Na+/K+)

-3 Na+ ions are pumped out and -2 K+ ions are pumped in at once in opposite directions, driving secondary transport

Secondary Active Transport

uses concentration gradient of an ion as its energy source

How does Secondary Active Transport move ions?

moves one ion with its gradient to move another substance AGAINST its gradient (doesn’t use ATP directly)

Electrochemical Gradient

involved in transmitting nervous impulses

COUPLED/Co- Transport

The simultaneous transport of two substances across a biological membrane

Example of Coupled/Co-transport

during secondary transport

Types of Transport

uniport, symport 2, antiport 2

Uniport

moves one substance at a time

Symport 2

moves two substances in the same direction

Antiport 2

moves two substances in opposite directions (Na+/K+ pump)

Exocytosis

cell secretions are released via vesicles

Endocytosis

cell takes in items from outside the cell by creating a vesicle

Phagocytosis v Pinocytosis

Phagocytosis is “cellular eating” (large particles), Pinocytosis is "cellular drinking"

Receptor (Mediated Endocytosis)

targets specific substances through receptor-ligand binding, forming vesicles

Example of Passive Transport

diffusion or osmosis

Osmosis

the diffusion of water through a selectively permeable membrane

How does water move during osmosis

Water moves from areas of lower solute concentration (more water) to areas of higher solute concentration (less water); moves to side with more solute

Aquaporin (Facilitated)

specialized channel protein that transports water through osmosis; water can also diffuse slowly through the lipid bilayer without assistance

Tonicity

ability of a solution to cause a cell to gain or lose water; related to the concentration of solutes that cannot cross membrane

Isotonic

no NET movement of water (at equilibrium)

Hypertonic

region with greater solute concentration (water moves out and cell shrinks)

Hypotonic

region with lower solute concentration, where water enters the cell, causing it to swell and burst (lyse)

Cell Walls

protect against excess water uptake and withstand turgor pressure

Types of water uptake in cell walls

Can be turgid (full of water), flaccid (isotonic), or plasmolyzed (lose water)

Turgor Pressure

pressure of water within central vacuole, keeping cells turgid

Plasmolysis

in hypertonic solution, the membrane pulls away from the cell wall, wilting

Osmoregulation

regulation of water and solute balance to maintain homeostasis

Animal Cells in Osmoregulation

vulnerable to bursting in hypotonic solutions, as they lack cell walls

What is Water Potential?

determines direction of water movement (osmosis), moving from high to low water potential

Water potential (ψ )

the water potential of distilled/pure water in an open container is always 0

Pressure Potential (ψp )

pressure exerted by cell wall, limiting water uptake in plant cells

Solute Potential (ψs)

affected by solute concentration, with pure water having a solute potential of zero

How does adding more solute affect solute potential?

adding solutes makes solute potential more negative, decreasing overall water potential