Chapter 36: Resource Acquisition and Transport in Vascular Plants

Vocabulary from Campbell's Biology

Xylem

Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from the roots to the rest of the plant.

Phloem

Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.

Mycorrhizae

A mutualistic association of plant roots and fungus.

Apoplast

Everything external to the plasma membrane of a plant cell, including cell walls, intercellular spaces, and the space within dead structures such as xylem vessels and tracheids.

Symplast

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

Osmosis

The diffusion of free water across a selectively permeable membrane.

Water Potential

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

Megapascal

A unit of pressure equivalent to about 10 atmospheres of pressure.

Solute Potential

A component of water potential proportional to the molarity of a solution; measures the effect of solutes on water movement. Also called osmotic potential, it can be zero or negative.

Pressure Potential

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

Protoplast

The living part of a plant cell, including the plasma membrane.

Turgor Pressure

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

Flaccid

Limp, lacking turgor (stiffness or firmness). Occurs when a plant cell loses water because its water potential is higher than its surroundings.

Plasmolysis

A process in walled cells where the cytoplasm shrivels and the plasma membrane pulls away from the cell wall due to water loss in a hypertonic environment.

Turgid

Swollen or distended. A plant cell becomes turgid if it has a lower water potential than its surroundings, resulting in water entry.

Wilting

The drooping of leaves and stems caused by plant cells becoming flaccid.

Aquaporins

Channel proteins in membranes that specifically facilitate osmosis (the diffusion of free water).

Bulk Flow

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

Endodermis

In plant roots, the innermost layer of the cortex that surrounds the vascular cylinder.

Casparian Strip

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

Xylem Sap

The dilute solution of water and minerals carried through vessels and tracheids.

Transpiration

The evaporative loss of water from a plant.

Root Pressure

Pressure exerted in the roots of plants as the result of osmosis, causing exudation from cut stems and guttation of water from leaves.

Guttation

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

Cohesion-Tension Hypothesis

The leading explanation of the ascent of xylem sap. It states that transpiration exerts pull on xylem sap, putting the sap under negative pressure, or tension, and that the cohesion of water molecules transmits this pull along the entire length of the xylem from shoots to roots.

Circadian Rhythms

A physiological cycle of about 24 hours that persists even in the absence of external cues.

Abscisic Acid (ABA)

A plant hormone that slows growth, often antagonizing the actions of growth hormones. Two of its many effects are to promote seed dormancy and facilitate drought tolerance.

Xerophytes

A plant adapted to an arid climate.

Translocation

The transport of organic nutrients in the phloem of vascular plants.

Phloem Sap

The sugar-rich solution carried through a plant’s sieve tubes.

Sugar Source

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

Sugar Sink

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