AP Biology - Cell Membrane

Selective Permeability

Allows some substances to cross more easily than others

phospholipid bilayer

a double layer of phospholipids that makes up plasma membranes

Integral Proteins

Proteins that extend through the phospholipid bilayer.

Peripheral Proteins

A protein loosely attached to the surface of a membrane

cholesterol

steroid present in the plasma membranes of animal cells. A large amount of this in a phospholipid bilayer at High Temperatures reduces membrane fluidity, but at Lower Temperature prevents the membrane from solidifying.

Concentration Gradient

a difference in the concentration of a substance across a space

Diffusion

the movement of molecules from an area of higher concentration to an area of lower concentration, so that they spread out evenly reaching equilibrium

Osmosis

The diffusion of water across a selectively permeable membrane

Transport Proteins

proteins that help to transport substances across cell membranes

Aquaporins

Channel proteins that help massive amount of water pass through the membrane; a lot in our kidneys

Passive Transport

movement of materials through a cell membrane without using energy

Isotonic

a solution whose solute concentration equals that inside a cell; the cell will not change

Hypertonic

the solution with the greater concentration of solutes than that inside the cell; the cell will lose water to its environment--> Cell will shrivel up

Hypotonic

the solution with the lower concentration of solutes than that inside the cell; water will enter the cell -> Cell will swell and burst

Osmoregulation

The control of water balance

Turgid

Very firm (healthy state), especially for plant cells

Plasmolysis

As a plant cell shrivels its plasma membrane pulls away from the wall

Facilitated Diffusion

passive transport of ions or polar molecules across a plasma membrane by transport proteins, allows for faster movement of substances that normally move slowly

Active Transport

transport of a substance through a cell membrane against the concentration gradient; requires energy

Sodium-Potassium Pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

Exocytosis

process by which a cell releases large amounts of material by vesicles

Endocytosis

the movement of a substance into a cell by a vesicle

Phagocytosis

a type of endocytosis in which microbes are taken in by immune cells of animals (mainly by macrophages)

Pinocytosis

cellular drinking

Receptor-mediated endocytosis

Taking in large amount of specific substances by binding to receptors, which form vesicles and are then taken in by the cell

osmotic pressure

The force required to resist the movement of water by osmosis. Osmotic pressure is a measure of the concentration of a solution. A solution that is highly concentrated has a strong tendency to draw water into itself, so the pressure required to resist that movement would be high. Thus, highly concentrated solutions are said to have high osmotic pressures.

water potential

The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.

water potential equation

water potential = solute potential + pressure potential

solute potential

This measurement has a maximum value of 0; it decreases as the concentration of a solute increases.

solute potential equation

Ψs = -iCRT

pressure potential

This measurement has a minimum value of 0 (when the solution is open to the environment); it increases as pressure increases.

concentration gradient

difference in the concentration of a substance from one location to another (ex. difference in concentration on the inside of a cell versus the outside)

Concentration

A measurement of how much solute exists within a certain volume of solvent

cotransporter

protein that moves two or more molecules through a cell membrane by secondary active transport

increasing the percentage of unsaturated phospholipids in the membrane

makes cell membranes more fluid

integral proteins

Integral proteins that span the membrane and amphipathic

guard cells

The two cells that flank the stomatal pore and regulate the opening and closing of the pore.

Stomata

Small openings on the underside of a leaf through which oxygen, water, and carbon dioxide can move

Glycoproteins

Membrane carbohydrates that are covalently bonded to proteins. Help with cell to cell recognition

carrier proteins

Proteins that bind to specific solutes and transport them across the plasma membrane

peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

endosymbiotic theory

a theory that states that certain kinds of prokaryotes began living inside of larger cells and evolved into the organelles of modern-day eukaryotes

What kinds of molecules pass through a cell membrane most easily?

small and hydrophobic

hydrolytic enzymes

enzymes that speed up/aid in the breakdown of chemical bonds through the addition of water (hydrolysis), present in lysosomes

fluid mosaic model

model that describes the arrangement and movement of the molecules that make up a cell membrane

surface area to volume ratio

a variable that decreases as cells grow, so that it sets a limit to the size of cells.