Transport notes AP biology

Hydrophobic (nonpolar) molecules like hydrocarbons can ____

dissolve in the lipid bilayer and pass through the mmebrane rapidly

Polar molecules like sugars ____

do not cross the membrane easily

transport proteins function

allow passage of hydrophilic substances across the membrane

Passive transport

diffusion of a substance across a membrane with no energy

Diffusion

tendency for molecules to spread out evenly into the available space

molecules move from ___ to ___ concentration

high, low

Dynamic equilibrium

many molecules cross the membrane in opposite directions, keeping the gradient even

Substances diffuse down(with) their ____

concentration gradient

concentration gradient

the region along which the density of a chemical substance decreases

Does any work need to be done to move substances down the concentration gradient

no

Why is the diffusion of a substance across a biological membrane passive transport

it requires no energy

Osmosis

diffusion of water across a selectively permeable membrane

Water diffuses across a membrane from the region of ___ solute concentration to the region of ____ solute concentration until it is ____

lower, higher, equal on both sides

Isotonic solution

solute concentration is teh same as the region it is being compared to

water movement in isotonic solution

no net water movement across the membrane

Hypertonic solution

Solute concentration is greater than the region it is being compared to

water movement in hypertonic solution

out of the cell

Hypotonic solution

solute concentration is less than the region it is being compared to

water movement in a hypotonic solution

water moves into the cell

Best environment for animal cell

Isotonic

Best environment for plant cell

Hypotonic

Osmoregulation

the control of solute concentrations and water balance. needed to survive in hyper or hypotonic environments

Paramecium

hypertonic to its pond water environment, has a contractile vacuole that acts as a pump

facilitated diffusion

passive transport aided by proteins

transport proteins function

speed up passive movement of molecules across the plasma membran

channel and carrier protein function

provide help to move a specific molecule or ion across the mmebrane

channel protein examples

aquaporins: facilitated diffusion of water

Ion channels that open or close in response to a stimulus (gated channels)

Active transport

uses energy to move solutes against their gradients

Active transport moves substances ___ their concentration gradients

against

Active transport requires ___ in the form of ____

energy, ATP (adenosine triphosphate)

Who performs active transport

specific proteins embedded in the membranes

Sodium potassium pump

Exchanges ATP so sodium ions can leave the cytoplasm. Potassium ions release a phosphate group to be allowed into the cytoplasm

Proton pump

Maintains voltage across the membrane. 

Hydrogen ions pay ATP to use the proton pump that moves them to the positive area of the extracellular fluid from the cytoplasm

Bulk transport

Movement of large molecules like polysaccharides and proteins across the membrane requiring energy

Exocytosis

transport vesicles migrate to the membrane, fuse with it, and release their contents

endocytosis

the cell takes in macromolecules by forming vesicles from the plasma membrane. Reversal of exocytosis

Three types of endocytosis

phagocytosis, pinocytosis, receptor-mediated endocytosis

Phagocytosis

Cellular eating

• A cell engulfs a particle in a vacuole, which fuses with a lysosome to digest the particle

Pinocytosis

Cellular drinking

• Molecules are taken up when extracellular fluid is “gulped” into tiny vesicles

Receptor-mediated endocytosis

Binding of ligands to receptors triggers vesicle formation.

ligand definition

any molecule that binds specifically to a receptor site of another molecule