Concept 7.4: Active transport uses energy to move solutes against their gradients

Flashcards from Concept 7.2 of Pearson's Campbell Biology, Twelfth Edition.

Facilitated diffusion

A passive method of transport that requires no energy due to the molecules only moving down their concentration gradient

Active transport

Transport that requires energy — usually in the form of ATP hydrolysis — to move substances agains their concentration gradient

• Requires carrier proteins specifically

• Allows cells to maintain solute concentrations that differ from their environment

Membrane potential

The voltage across a membrane created by differences in the distribution of positive and negative ions across a membrane

Electrochemical gradient

Two forces that drive the diffusion of ions across the membrane that ions diffuse down:

• Chemical force (the ion’s concentration gradient)

• Electrical force (the effect of the membrane potential on the ion’s movement)

Electrogenic pump

A transport protein that generates voltage across a membrane, storing energy that can be used for cellular work

• Animals have the sodium-potassium pump

• Plants, fungi, and bacteria have the proton pump that transport H⁺ ions out of the cell

Cotransport

Transport that occurs when the active transport of a solute indirectly drives transport of other substances

• Downhill solute movement may couple to uphill transport of another substance against its own concentration gradient

Proton pump

Pump present in plants that generate an H⁺ gradient across the cell membrane

• An H⁺ cotransporter allows sucrose to be coupled to its active transport into the cell, enabling its transport around a plant body

Sodium-potassium pump

Pump present in animals that transport Na⁺ out of the cell to maintain the electrochemical gradient while using ATP in the process

• Sodium in waste is reabsorbed to maintain a constant level in the body

• Drinking concentrated salt and glucose solutions can enable recovery from a rapid, life-threatening loss of sodium too fast for reabsorption