7.2 and 7.3 Selective Permeability

The import of nutrients and the export of waste

Traffic of molecules across the plasma membrane in both directions

Selectively permeable

most molecules do not cross the membrane freely

Proteins in the membrane

regulate the transports of molecules across the membrane

Hydrophobic (nonpolar) molecules

can dissolve in the lipid bilayer and are able to cross the membrane freely

hydrophilic (polar)

are not able to cross the membrane freely or rapidly

Small polar molecules like water and certian ions

can slowly leak across the membrane

Aquaporin

is a transport protein that allows for the rapid passage of water

Transport proteins

allows passage of hydrophilic molecules

Channel proteins

are a type of protein that has a hydrophobic channel that specific molecules and ions can use to tunnel through the membrane

Carrier proteins

transport proteins that bind to specific molecules and change shape in order to carry molecules across the membrane

Most transport proteins

are specific for the type of molecule they carry

Thermal energy

the type of energy molecules have because they are constantly in motiond

diffusion

as a result of thermal energy, the movement of molecules so that they spread out evenly into available space

diffusion of a population of molecules

may be directional

Concentration gradient

the region along which the density of a chemical substance increases of decreases

No work needs to be done

to move substances down their gradient (high concentration to low concentration)

Dynamic equilibrium

Just as many molecules cross the membrane in one direction as they cross in the other, not net movement in one direction

passive transport

When a substance diffuses across a biological membrane

In passive transport

No work is required and no energy is expended

What does the concentration gradient represent

potential energy that drives diffusion

Osmosis

the diffusion of water across selectively permeable membrane

what type of diffusion is this

diffusion of one solute

what type of diffusion is this

diffusion of two solutes

water diffuses across a membrane

from a region of lower solute concentration (higher water concentration) to a region of high solute concentration (low water concentration) until the solute concentration is equal on both sides

lower solute concentration

high water concentration

High solute concentration

low water concentration

Old saying

water follows the salt

tonicity

the ability of a solution surrounding a cell to cause the cell to gain or lose water

Isotonic solution

solute concentration surrounding the cell is the same as inside the cell, no water movement

Hypertonic solution

solute concentration of solution surrounding the cell is greater than that of inside the cell, the cell looses water

Hypotonic solution

solute concentration of solution surrounding the cell is less than that inside the cell, the cell gains water

Animal cells

are better in isotonic enviroments

Plant cell

are turgid (firm) and healthiest in hypotonic enviroments

Osmoregulation

the control of solute concentrations and water balance is a necessary adaptation for lie in such enviroments

in a paramecium

has a contractile vacuole that acts as a pump to expel the water that flows into the cell.

cell walls

maintain water balance

a plant cell in a hypertonic

will lose water, and the membrane will pull away from the cell walls, Plasmolysis

Facilitated diffusion

when transport proteins speed the passive movement of specific molecules across the plasma membrane, no energy is required

Ion channels

allow for facilitated diffusion of specific ions and often open or close in response to stimulus, gated channels

Glucose transporter

facilitates diffusion of glucose and only glucose, will also reject fructose