Ap Biology Chapter 36 Vocabulary

Front 1

Active transport

Back 1

The movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins.

Front 2

Apoplast

Back 2

In plants, the continuum of cell walls plus the extracellular spaces.

Front 3

Aquaporins

Back 3

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).

Front 4

Bulk flow

Back 4

The movement of water due to a difference in pressure between two locations.

Front 5

Casparian strip

Back 5

A water0impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cells walls.

Front 6

Chemiosmosis

Back 6

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis.

Front 7

Circadian rhythms

Back 7

A physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues.

Front 8

Cotransport

Back 8

The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.

Front 9

Endodermis

Back 9

The innermost layer of the cortex in plant roots; a cylinder one cell think that forms the boundary between the cortex and the vascular cylinder.

Front 10

Flaccid

Back 10

Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter.

Front 11

Guttation

Back 11

The exudation of water droplets, caused by root pressure in certain plants.

Front 12

Megapascals (MPa)

Back 12

A unit of pressure equivalent to 10 atmospheres of pressure.

Front 13

Membrane potential

Back 13

The charge difference between a cell’s cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

Front 14

Mycorrhizae

Back 14

Mutualistic associations of plant roots and fungi.

Front 15

Osmosis

Back 15

The diffusion of water across a selectively permeable membrane.

Front 16

Osmotic potential

Back 16

A component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called solute potential, it can be either zero or negative.

Front 17

Plasmolyze

Back 17

To shrink and pull away from a cell wall, or when a plant cell protoplast pulls away from the cell wall as a result of water loss.

Front 18

Pressure potential (Ψp)

Back 18

A component of water potential that consists of the physical pressure on a solution, which can be positive, zero, or negative.

Front 19

Proton pump

Back 19

An active transport mechanism in cell membranes that uses ATO to force hydrogen ions out of a cell, generating a membrane potential in the process.

Front 20

Root pressure

Back 20

The upward push of xylem sap in the vascular tissue of roots.

Front 21

Solute potential (Ψs)

Back 21

A component of water potential that is proportional to the number of dissolved solute molecules in a solution and measures the effect of solutes on the direction of water movement; also called osmotic potential, it can be either zero or negative.

Front 22

Sugar sink

Back 22

A plant organ that is a net consumer or storer of sugar. Growing roots, shoot tips, stems, and fruits are sugar sinks supplied by phloem.

Front 23

Sugar source

Back 23

A plant organ in which sugar is being produced by either photosynthesis or the breakdown of starch. Mature leaves are the primary sugar sources of plants.

Front 24

Symplast

Back 24

In plants, the continuum of cytoplasm connected by plasmodesmata between cells.

Front 25

Tonoplast

Back 25

A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the vacuolar membrane.

Front 26

Transfer cells

Back 26

A companion cell with numerous ingrowths of its wall, increasing the cell’s surface area and enhancing the transfer of solutes between apoplast and symplast.

Front 27

Transpiration

Back 27

The evaporative loss of water from a plant.

Front 28

Transport proteins

Back 28

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Front 29

Turgid

Back 29

Very firm. A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.

Front 30

Turgor pressure

Back 30

The force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis.

Front 31

Vacuolar membrane

Back 31

A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the tonoplast.

Front 32

Water Potential

Back 32

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

Front 33

Wilting

Back 33

The drooping of leaves and stems as a result of plant cells becoming flaccid.

Front 34

Xerophytes

Back 34

A plant adapted to an arid climate.