Water Relations and Transport in Plants

Flashcards covering the physiological processes of osmosis, transpiration, and water/food transport in plant tissues as detailed in the lecture notes.

Osmosis

Diffusion or movement of solvent molecules from a region of high concentration to a region of low concentration across a semi-permeable membrane until equilibrium is attained.

Water-to-Organic Matter Ratio

For every $1\,g$ of organic matter made by the plant, approximately $500\,g$ of water is absorbed, transported, and lost to the atmosphere.

Cytoplasmic membranes

Comprise the tonoplast (vacuolar membrane) and plasmalemma (cell membrane), which are differentially permeable.

Simple Osmometer

An apparatus used to demonstrate osmosis in non-living materials typically using a tube, beaker, concentrated sugar solution, and membranes like toad's bladder or sheep's bladder.

Turgidity

A state of plant cells ensured by osmosis that prevents plasmolysis and supports processes like the opening and closing of stomata.

Fabaceae

The legume family, noted for exhibiting sleep movements controlled by turgor movement.

D.P.D Equation

The interrelationship among osmotic quantities expressed as $D.P.D = O.P. - T.P.$.

Osmotic Pressure ($O.P.$)

The potential maximum pressure that can be developed in a solution as a result of osmosis.

Turgor Pressure ($T.P.$)

The actual pressure that develops in a plant cell or osmometer due to osmosis.

Diffusion Pressure Deficit ($D.P.D$)

The difference in diffusion pressures between a solution and pure solvent when both are subjected to the same atmospheric pressure.

Casparian strips

Waxy strips found in the endodermis that force water to move through the plasma membranes and protoplasts, thereby controlling ions entering the xylem.

Transpiration

The loss of water vapour from the aerial parts of the plant to the atmosphere.

Stomatal transpiration

The loss of water vapour through the stomata, accounting for $80-90\%$ of total transpiration.

Cuticular transpiration

Water vapour loss through the cuticle, which is a wax-like layer of cutin covering leaf surfaces.

Lenticular transpiration

Water vapour loss occurring through the lenticels of stems and fruits.

Ascent of Sap Theories

Physical theories explaining water movement, including root pressure theory, cohesion theory, capillary theory, and imbibition theory.

Tonicity

The strength of a solution in relation to osmosis, determining the direction of water movement.

Isotonic

A solution with an equal percentage of solute (equal $O.P.$) as the cell sap, resulting in no net movement of water.

Hypotonic

A solution with a lower percentage of solute (lower $O.P.$) than the cell sap, causing the cell to gain water and potentially burst.

Hypertonic

A solution with a higher percentage of solute (higher $O.P.$) than the cell sap, causing the cell to lose water and shrink (crenation).

Translocation

The process by which phloem tissue moves products of photosynthesis from mature leaves to areas of growth and storage.

Sources

Exporting organs, typically mature leaves, capable of producing photosynthate in excess of their own needs.

Sinks

Non-photosynthetic organs or those that do not produce enough photosynthate, such as roots, tubers, and developing fruits.

Xylem tissue

Complex permanent tissue consisting of tracheids, vessels (tracheae), wood fibres, and wood parenchyma; conducts water and mineral salts upwards.

Phloem tissue

Complex permanent tissue consisting of sieve tubes, companion cells, phloem parenchyma, and bast fibres; conducts prepared food materials.

Plasmodesmata

Structures through which the movement of substances from one cell to another occurs.