Chapter 5 -Transport Across the Plasma Membrane

Chapter 5 definitions

Selective permeability

Allows some things to diffuse through but not others.

Concentration gradient

The difference in the concentration of a chemical from one place to another, such as from the inside to the outside of the plasma membrane.

Electrical gradient

The difference in electrical charges between two regions.

Membrane potential

Charge difference across the plasma membrane

Electrochemical gradient

The combined influence of the concentration gradient and the electrical gradient on the movement of a particular ion.

Passive processes

Substance moves across the plasma membrane without any energy input from the cell

Active processes

Cellular energy is used to move a substance across the plasma membrane. Cellular energy used is usually in the form of ATP.

Vesicular transport

Type of active process that uses tiny vesicles to move substances across the plasma membrane

Endocytosis

Type of vesicular transport where vesicles detach from the plasma membrane while bringing materials into a cell.

Exocytosis

Type of vesicular transport where merging vesicles with the plasma membrane release materials from the cell.

Passive Transport

Movement of substances across the plasma membrane down their concentration or electrochemical gradients.

Diffusion

Random mixing of particles from one location to another because of the particles kinetic energy.

Solutes

Dissolved substances

Solvent

The liquid that does the dissolving

Fick’s law of diffusion

Mathematical equation that expresses the various factors that determines how quickly a particle diffuses across a membrane from one region to another.

Simple diffusion

Passive process in which solutes move freely through the lipid bilayer of the plasma membrane of cells without the help of membrane transport proteins.

Facilitated diffusion

Integral membrane proteins assists a specific substance across the membrane.

Channel-mediated facilitated diffusion

Solute moves down its concentration or electrochemical gradient across the lipid bilayer through a membrane channel

Ion channels

Integral transmembrane proteins containing pores that allow passage of small, inorganic ions that are too hydrophilic to penetrate the non polar interior of the lipid bilayer.

Carrier-mediated facilitated diffusion

A carrier is used to move a solute down its concentration or electrochemical gradient across the plasma membrane.

Transport maximum

Rate at which a solute is transported by facilitated diffusion.

Osmosis

Type of diffusion in which there is net movement of a solvent through a selectively permeable membrane. It is a passive process

Aquaporins

Integral membrane proteins that function as water channels

Hydrostatic pressure

Pressure exerted by a liquid

Osmotic pressure

The amount of pressure needed to completely stop the osmotic movement of water through a membrane and restoring the starting conditions.

Osmolarity

Measure of the total number of dissolved particles per litre of solution

Osmolality

The number of solute particles per kilogram of water.

Isoosmotic

Two solutions that have the same osmolarity. The solute concentrations are the same so the water concentration is the same.

Hyperosmotic

A solution with a higher osmolarity than another solution. The solute concentration is higher, the water concentration is lower.

Hypoosmotic

A solution with lower osmolarity than another solution. The solute concentration is lower, the water concentration is higher.

Penetrating solutes

Solutes that are able to pass through a membrane

Nonpenetrating solutes

Solutes that are unable to pass through a membrane

Tonicity

The measure of a solutions ability to change the volume of cells by altering their water content.

Isotonic solution

A solution where the cell maintains its normal shape

Hypotonic solution

A solution that has a lower concentration of non penetrating solutes that cytosol inside the cell.

Hemolysis

The rupture of erythrocytes caused by swelling and then bursting.

Lysis

Rupture of other types of cells due to being placed in a hypotonic solution

Hypetonic solution

Higher concentration of non penetrating solutes than the cytosol inside the cell.

Crenation

Shrinkage of the cell due to being placed in a hypertonic solution

Primary active transport

Energy derived from hydrolysis of ATP changes the shape of a carrier protein, which pumps a solute across a plasma membrane against its concentration or electrochemical gradient.

Sodium-potassium pump

Uses primary active transport t expel sodium ions from the cell and brings potassium ions into cells.

Secondary active transport

The energy stored in an ionic electrochemical gradient is used to drive other solutes across the membrane against their own concentration or electrochemical gradients.

Symporters

Carrier proteins that move two solutes in the same direction across the membrane

Antiporters

Carrier proteins that move two solutes in opposite directions across the membrane.

Vesicle

Small membranous sac

Vesicular transport

Vesicles are used to move substances across the plasma membrane

Endocytosis

Process that moves materials into a cell in a vesicle formed from the plasma membrane

Exocytosis

Process that moves materials out of the cell by the fusion with the plasma membrane of vesicles formed from inside the cell.

Receptor-mediated endocytosis

Highly selective type of endocytosis by which cells take up specific ligands.

Phagocytosis

Form of endocytosis in which the cell engulfs large solid particles such as worn out cells, whole bacteria, or viruses.

Phagocytes

Cells that are able to carry out phagocytosis

Pseudopods

Projections of the plasma membrane and cytoplasm

Residual body

Vesicle that holds undigested materials

Bulk-phase endocytosis (pinocytosis)

Form of endocytosis in which tiny droplets of extracellular fluid are taken up.

Secretory vesicle

Membrane-enclosed vesicle that forms inside the cell and fuses with the plasma membrane to release contents outside of the cell.

SNAREs

Proteins that help promote fusion of the secretory vesicle membrane with the plasma membrane.

Transepithelial transport

The movement of solutes across epithelial cells using passive or active transport

Tight junctions

Cell junctions that retard the passage of substances between cells and prevent the contents of these organs from leaking into the blood or surrounding tissues.

Apical membrane

The surface of the epithelial cell that faces the lumen (interior space) of the organ. They can contain microvilli to increase surface area

Basolateral membrane

Surface of epithelial cells that are in contact with interstitial fluid and nearby blood vessels in underlying connective tissue.

Absorption

A solute moves from the lumen of an organ into the bloodstream.

Reabsorption

The epithelial cells lining the tubules of the kidneys transport solutes from the lumen into the bloodstream. It has already been absorbed into the blood stream and then lost by the filtering mechanisms of the kidneys.

Secretion

The movement of a solute from the bloodstream into the lumen of an organ.

Transcytosis

Active process where vesicles undergo endocytosis on one side of a cell, move across the cell, and then undergo exocytosis on the opposite side